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Phycobilisomes, the light‐harvesting complexes of cyanobacteria and red algae, are a resource for photosynthetic, photonic and fluorescence labeling elements. They cover an exceptionally broad spectral range, but the complex superstructure and assembly have been an obstacle. By replacing in Synechocystis sp. PCC 6803 the biliverdin reductases, we studied the role of chromophores in the assembly of the phycobilisome core. Introduction of the green‐absorbing phycoerythrobilin instead of the red‐absorbing phycocyanobilin inhibited aggregation. A novel, trimeric allophycocyanin (Dic‐APC) was obtained. In the small (110 kDa) unit, the two chromophores, phycoerythrobilin and phytochromobilin, cover a wide spectral range (550 to 660 nm). Due to efficient energy transfer, it provides an efficient artificial light‐harvesting element. Dic‐APC was generated in vitro by using the contained core‐linker, LC, for template‐assisted purification and assembly. Labeling the linker provides a method for targeting Dic‐APC. [ABSTRACT FROM AUTHOR]

In this hypothesis article, we propose that the timing of the evolution of oxygenic photosynthesis and the diversification of cyanobacteria is firmly tied to the geological evolution of Earth in the Mesoarchean to Neoarchean. Specifically, the diversification of species capable of oxygenic photosynthesis is tied to the growth of subaerial (above sea-level/terrestrial) continental crust, which provided niches for their diversification. Moreover, we suggest that some formerly aerobic bacterial lineages evolved to become anoxygenic photosynthetic as a result of changes in selection following the reintroduction of ferruginous conditions in the oceans at 1.88 GYa. Both conclusions are fully compatible with phylogenetic evidence. The hypothesis carries with it a predictive component—at least for terrestrial organisms—that the development and expansion of photosynthesis species was dependent on the geological evolution of Earth. [ABSTRACT FROM AUTHOR]

Aerobic anoxygenic photoheterotrophic (AAP) bacteria represent a functional group of prokaryotic organisms that harvests light energy using bacteriochlorophyll‐containing photosynthetic reaction centers. They represent an active and rapidly growing component of freshwater bacterioplankton, with the highest numbers observed usually in summer. Species diversity of freshwater AAP bacteria has been studied before in lakes, but its seasonal dynamics remain unknown. In this report, we analysed temporal changes in the composition of the phototrophic community in an oligo‐mesotrophic freshwater lake using amplicon sequencing of the pufM marker gene. The AAP community was dominated by phototrophic Gammaproteobacteria and Alphaproteobacteria, with smaller contribution of phototrophic Chloroflexota and Gemmatimonadota. Phototrophic Eremiobacteriota or members of Myxococcota were not detected. Interestingly, some AAP taxa, such as Limnohabitans, Rhodoferax, Rhodobacterales or Rhizobiales, were permanently present over the sampling period, while others, such as Sphingomonadales, Rhodospirillales or Caulobacterales appeared only transiently. The environmental factors that best explain the seasonal changes in AAP community were temperature, concentrations of oxygen and dissolved organic matter. [ABSTRACT FROM AUTHOR]

Wastewaters are mainly classified as domestic, industrial and agro-industrial based on their production source. Piggery wastewater (PWW) is a livestock wastewater characterized by its high concentrations of organic matter and ammonium, and by its odour nuisance. Traditionally, PWW has been treated in open anaerobic lagoons, anaerobic digesters and activated sludge systems, which exhibit high greenhouse gas emissions, a limited nutrients removal and a high energy consumption, respectively. Photosynthetic microorganisms can support a sustainable wastewater treatment in engineered photobioreactors at low operating costs and with an efficient recovery of carbon, nitrogen and phosphorous. These microorganisms are capable of absorbing solar irradiation through the photosynthesis process to obtain energy, which is used for their growth and associated carbon and nutrients assimilation. Purple phototrophic bacteria (PPB) represent the photosynthetic microorganisms with the most versatile metabolism in nature, whereas microalgae are the most-studied photosynthetic microorganisms in recent years. This review describes the fundamentals, symmetry and asymmetry of wastewater treatment using photosynthetic microorganisms such as PPB and microalgae. The main photobioreactor configurations along with the potential of PPB and microalgae biomass valorisation strategies are also discussed. [ABSTRACT FROM AUTHOR]

Aerobic respiration evolved by bricolage, with modules cobbled together as microbial biochemistry coevolved with Earth's geochemistry. The mitochondrial electron transport chain represents a patchwork of respiratory modules inherited from microbial methanogenesis, iron oxidation, anoxygenic photosynthesis, and denitrification pathways, and preserves a biochemical record of Earth's redox environment over its four-billion-year history. Imprints of the anoxic early Earth are recognizable in Complex I's numerous iron-sulfur cofactors and vestigial binding sites for ferredoxin, nickel-iron, and molybdopterin, whereas the more recent advent of oxygen as a terminal electron acceptor necessitated use of heme and copper cofactors by Complex IV. Bricolage of respiratory complexes resulted in supercomplexes for improved electron transfer efficiency in some bacteria and archaea, and in many eukaryotes. Accessory subunits evolved to wrap mitochondrial supercomplexes for improved assembly and stability. Environmental microbes with 'fossil' proteins that are similar to ancestral forms of the respiratory complexes deserve further scrutiny and may reveal new insights on the evolution of aerobic respiration. The mitochondrial electron transport chain is derived from modular enzyme complexes assembled from microbial pathways, including methanogenesis, iron oxidation, anoxygenic photosynthesis, and denitrification. The vestiges of ancient anaerobic respiratory complexes are especially evident in Complex I, which represents a bricolage of modules, each of which originated with a function different from that which they have today. Ancestral Complex II likely ran in the opposite direction for anaerobic respiration and was later co-opted to provide additional reducing power for aerobic respiration. Complex III likely originated in anaerobic anoxygenic photosynthetic bacteria. Ancestral Complex IV was likely involved in denitrification, and iron-oxidizing bacteria may have contributed to adaptation of Complex IV to higher oxygen levels. [ABSTRACT FROM AUTHOR]

Cyanobacteria capable of oxygenic photosynthesis uses multiple pigments to efficiently convert light radiation energy to chemical energy in the form of ATP (Adenosine Tri-phosphate). A crucial pigment protein from its photosynthetic machinery called phycocyanin has been extensively studied for its immense application in fluorescent probe, food additives, nutraceutical applications, and silver-nanoparticles production. The present review provides a narrative amalgamation of the said applications and technologies to grow, extract, and purify the phycocyanin from various algal cultures. The expression of phycocyanin protein gene at the molecular level has been discussed for its potential to enhance the yield and stability. Furthermore, advantageous methods for the extraction and purification of phycocyanin from possible host cyanobacterial strains (Spirulina platensis, Cyanidium caldarium, Synechococcus vulcanus, Gracilaria chilensis, Polysiphonia urceolata, Thermosynechcoccus vulcanus, and Galdieria sulphuraria) such as physical, chemical and enzymatic methods are also compared to find the most efficient strategy in subsequent scientific applications. The comparative study also expects to ways to achieve sustainable development goal 3 i.e. good health & wellbeing. [ABSTRACT FROM AUTHOR]

In the World Cultural Heritage of Leshan Giant Buddha and the West Lake area, the statues and monuments have been affected by the colonizing organisms. In the past three years, we used next-generation sequencing technology to analyze the biofilm of 14 sites in two places. The result showed that microbiomes were different on monuments, especially in terms of microbial composition, diversity, and potential functions. More phototrophic organisms and bacteria involved in the nitrogen-sulfur cycle were found in the West Lake area (WLA), while heterotrophs were discovered in the Leshan Giant Buddha area (LGBA). The biofilms on sandstone in LGBA possessed a higher alpha diversity of bacteria and fungi community than that on limestone in WLA. Biofilms in LGBA showed higher gene expression in metabolisms, such as the metabolism of carbohydrates, lipids, xenobiotics, and terpenoids. While biofilms in WLA exhibited higher levels of genetic information processing genes, which are associated with coping with harsh environments. Combine with XRD and SEM-EDS analysis, petrographic properties were considered the main factors that affect biological colonization. Environmental conditions (temperature, humidity, and precipitation) were similar in the two regions, which are suitable for the growth of organisms. Microbiome dissimilarities (beta diversity) indicated that the microbial compositions of biofilms were associated with the geographic features of the sampling sites. The stones in the two regions have their own petrographic properties that greatly influence microbiome colonization, such as microstructure, porosity, water permeability, and minerals composition. [ABSTRACT FROM AUTHOR]

Cyanobacteria are photosynthetic microorganisms capable of using solar energy to convert CO2 and H2O into O2 and energy-rich organic compounds, thus enabling sustainable production of a wide range of bio-products. More and more strains of cyanobacteria are identified that show great promise as cell platforms for the generation of bioproducts. However, strain development is still required to optimize their biosynthesis and increase titers for industrial applications. This review describes the most well-known, newest and most promising strains available to the community and gives an overview of current cyanobacterial biotechnology and the latest innovative strategies used for engineering cyanobacteria. We summarize advanced synthetic biology tools for modulating gene expression and their use in metabolic pathway engineering to increase the production of value-added compounds, such as terpenoids, fatty acids and sugars, to provide a go-to source for scientists starting research in cyanobacterial metabolic engineering. [ABSTRACT FROM AUTHOR]

Carotenoids are well-known isoprenoid pigments naturally produced by plants, algae, photosynthetic bacteria as well as by several heterotrophic microorganisms. In plants, they are synthesized in plastids where they play essential roles in lightharvesting and in protecting the photosynthetic apparatus from reactive oxygen species (ROS). Carotenoids are also precursors of bioactive metabolites called apocarotenoids, including vitamin A and the phytohormones abscisic acid (ABA) and strigolactones (SLs). Genetic engineering of carotenogenesis made possible the enhancement of the nutritional value of many crops. New metabolic engineering approaches have recently been developed to modulate carotenoid content, including the employment of CRISPR technologies for single-base editing and the integration of exogenous genes into specific "safe harbors" in the genome. In addition, recent studies revealed the option of synthetic conversion of leaf chloroplasts into chromoplasts, thus increasing carotenoid storage capacity and boosting the nutritional value of green plant tissues. Moreover, transient gene expression through viral vectors allowed the accumulation of carotenoids outside the plastid. Furthermore, the utilization of engineered microorganisms allowed efficient mass production of carotenoids, making it convenient for industrial practices. Interestingly, manipulation of carotenoid biosynthesis can also influence plant architecture, and positively impact growth and yield, making it an important target for crop improvements beyond biofortification. Here, we briefly describe carotenoid biosynthesis and highlight the latest advances and discoveries related to synthetic carotenoid metabolism in plants and microorganisms. [ABSTRACT FROM AUTHOR]

The use of biostimulants and/or biofertilizers has acquired considerable importance and can contribute to the sustainable management agriculture, reducing the use of chemical fertilizers, pesticides, and water. This study aims to assess the effects of Effective Microorganisms (EM) and Olive Mill Wastewater (OMW) on the growth, photosynthetic performance and polyphenols content of the medicinal plant Tanacetum balsamita. The EM and OMW were used at two dilution rates. The EM was added to 5% v/v and 10% v/v, while OMW was added to 2.5% v/v and 5% v/v in plants at the early growth stage. After 75 days of treatment, all the treated plants had a leaf number and leaf area almost 2-fold higher than in the Control plants. Moreover, the treatments, at all the concentrations applied had a positive effect on the photosynthetic activity, with an improvement both in terms of the quantum yield of photosynthesis and electrons transport efficiency. The best photosynthetic and growth performances in the treated plants coincided with the higher production of phenolic compounds; indeed, after 75 days, the content of chlorogenic acid, caffeic acid, and isochlorogenic acid was even 2-fold of the Control plants. Also, rutin content was 1.28–1.50-fold respect to the Control extracts. The highest phenolic compound content was reflected by the highest antiradical activity, found in the extracts of the treated plants. The effectiveness of EM to increase the growth and quality of plants and in particular, the potential use of OMW on the cultivated crop was confirmed to this study. [ABSTRACT FROM AUTHOR]

The photosynthetic reaction center complex (RCC) of green sulfur bacteria (GSB) consists of the membrane‐imbedded RC core and the peripheric energy transmitting proteins called Fenna–Matthews–Olson (FMO). Functionally, FMO transfers the absorbed energy from a huge peripheral light‐harvesting antenna named chlorosome to the RC core where charge separation occurs. In vivo, one RC was found to bind two FMOs, however, the intact structure of RCC as well as the energy transfer mechanism within RCC remain to be clarified. Here we report a structure of intact RCC which contains a RC core and two FMO trimers from a thermophilic green sulfur bacterium Chlorobaculum tepidum at 2.9 Å resolution by cryo‐electron microscopy. The second FMO trimer is attached at the cytoplasmic side asymmetrically relative to the first FMO trimer reported previously. We also observed two new subunits (PscE and PscF) and the N‐terminal transmembrane domain of a cytochrome‐containing subunit (PscC) in the structure. These two novel subunits possibly function to facilitate the binding of FMOs to RC core and to stabilize the whole complex. A new bacteriochlorophyll (numbered as 816) was identified at the interspace between PscF and PscA‐1, causing an asymmetrical energy transfer from the two FMO trimers to RC core. Based on the structure, we propose an energy transfer network within this photosynthetic apparatus. [ABSTRACT FROM AUTHOR]

The response of phytoplankton and its satellite bacteria to various concentrations (0.01%–10% v/v) of ethanol is studied. To elucidate the effect of ethanol, single-strains of phytoplankton (SSP) culture, pure strains of satellite bacteria isolated from nonaxenic SSP cultures, and Escherichia coli were screened. Results indicate that ethanol could promote the growth and photosynthetic efficiency (Fv/Fm) of SSP at 0.01% and the growth of satellite bacteria at 0.01%–1%. Nevertheless, ethanol inhibited the growth and Fv/Fm of SSP at 0.1%–1%, and killed bacteria and SSP at 10% concentration. Further investigation on a satellite bacterium (Mameliella alba) revealed that ethanol promotes growth by serving as a growth stimulant rather than a metabolic carbon source. The 16S rRNA gene amplicon indicated that all nonaxenic SSP cultures harbor distinct satellite bacteria communities where the SSP culture of Skeletonema costatum, Phaeodactylum tricornutum, and Dunaliella bardawil were dominated by bacteria genera of Marivita (∼80%), Dinoroseobacter (∼47%), and Halomonas (∼87%), respectively, indicating that every SSP cultures have their own distinct satellite bacterial community. The bacteria family Rhodobacteraceae was dominant in the two marine diatoms, whereas Halomonadaceae was dominant in the saline green microalga. Compared to their respective controls, the supply of 0.5% ethanol to SSP cultures promoted the growth of the satellite bacteria but did not cause a significant difference in species composition of satellite bacteria. Therefore, a low concentration of ethanol can promote the growth of bacteria in a non-selective way. This study enriched our knowledge about the effect of ethanol on aquatic microbes and provided a baseline for basic and applied biotechnological research in the aquatic environment in the future. [ABSTRACT FROM AUTHOR]

In this historical perspective, we focus on selected discoveries that Albert Frenkel (1919–2015) made all by himself – single-handedly – which is the discovery of photophosphorylation and NAD reduction in anoxygenic photosynthetic bacteria. Then, we present various aspects of his research life through his unpublished letters with some key scientists in his research field. To give a glimpse of his personal life, we have also provided some photographs. [ABSTRACT FROM AUTHOR]

Microbial communities play critical roles in fixing carbon from the atmosphere and fixing it in the soils. However, the large‐scale variations and drivers of these microbial communities remain poorly understood. Here, we conducted a large‐scale survey across China and found that soil autotrophic organisms are critical for explaining CO2 fluxes from the atmosphere to soils. In particular, we showed that large‐scale variations in CO2 fixation rates are highly correlated to those in autotrophic bacteria and phototrophic protists. Paddy soils, supporting a larger proportion of obligate bacterial and protist autotrophs, display four‐fold of CO2 fixation rates over upland and forest soils. Precipitation and pH, together with key ecological clusters of autotrophic microbes, also played important roles in controlling CO2 fixation. Our work provides a novel quantification on the contribution of terrestrial autotrophic microbes to soil CO2 fixation processes at a large scale, with implications for global carbon regulation under climate change. [ABSTRACT FROM AUTHOR]

Dimensions of particulate matter found in the water column of marine and freshwater environments (the pelagic realm) range from nanometers to tens of meters. Included in this enormous size range are miniature bacteria, phytoplankton (photosynthetic microalgae), mixoplankton (mixotrophic microorganisms), micro- to meter sized drifting animals (zooplankton), plastic particles, detrital aggregates and fecal pellets, fish, whales and many others. These particles and organisms are involved in many different processes and perform a multitude of services, such as in oceanic biogeochemistry (carbon fixation, oxygen production, carbon export and others) or human nourishment (fisheries). Digital optical tools used in pelagic imaging approaches now allow to bridge this enormous size span and to image micro- to meter-sized objects in situ or on discrete samples. Monitoring plankton, nekton, and particle dynamics at spatial and temporal scales that enable effective management of marine and freshwater environments poses a collective challenge for society. We here argue that a global, distributed and operational network for pelagic imaging is needed and within reach, and we provide recommendations how it can be attained via the voluntary activities of the pelagic imaging community and strategic support from funding agencies and other stakeholders. [ABSTRACT FROM AUTHOR]

Soils have the most diversified microbial communities of any environment on the planet. Bacteria, fungi, algae, and protozoa are all found in abundance in soil. Maintaining a healthy environment for crops requires a strong link between plants and soil microorganisms that are essential for good crop development. Soil bacteria are key regulators of the nutrient cycle. Mineralization, legume nitrogen fixation, and ammonia conversion to plant-available nitrate would all be impossible without bacteria. Effective microorganisms have the ability to boost crop growth and yield. When used in conjunction with organic amendments, these bacteria performs better than to the sole application. It also contributes to soil health and provides a variety of ecological services. They also help in the cleaning of the environment, landfill disinfection, and the development and implementation of sustainable, closed-cycle organic waste treatment processes across the globe. The whole study remarks a conclusion that the application or presence of effective microbes to soil not only enhance the nutritional capacity, fertility and productivity of soils but also helps to remediate soil problems cost effectively.

Abstract Background As an antioxidant, hydrogen (H2) can selectively react with the highly toxic hydroxyl radical (·OH) in tumor cells to break the balance of reactive oxygen species (ROS) and cause oxidative stress. However, due to the high diffusibility and storage difficulty of hydrogen, it is impossible to achieve long-term release at the tumor site, which highly limited their therapeutic effect. Results Photosynthetic bacteria (PSB) release a large amount of hydrogen to break the balance of oxidative stress. In addition, as a nontoxic bacterium, PSB could stimulate the immune response and increase the infiltration of CD4+ and CD8+ T cells. More interestingly, we found that hydrogen therapy induced by our live PSB did not lead to the up-regulation of PD-L1 after stimulating the immune response, which could avoid the tumor immune escape. Conclusion Hydrogen-immunotherapy significantly kills tumor cells. We believe that our live microbial hydrogen production system provides a new strategy for cancer hydrogen treatment combining with enhanced immunotherapy without up-regulating PD-L1. Graphical Abstract

The article discusses the discovery of a new photosystem I (PSI) assembly factor called Ycf51 in cyanobacteria. The authors conducted experiments on cyanobacteria strains with mutated ycf51 genes and found that these strains showed reduced capacity for photosynthesis and severe growth retardation. Further investigation revealed that Ycf51 interacts with other PSI assembly factors, PsaC and Ycf3, and plays a crucial role in the assembly of PSI. The authors suggest that Ycf51 may have played a role in the evolution of photosynthetic complexes during the transition from anoxic to oxic environments. [Extracted from the article]

Purple phototrophic bacteria use a 'photosystem' consisting of light harvesting complex 1 (LH1) surrounding the reaction centre (RC) that absorbs far-red-near-infrared light and converts it to chemical energy. Blastochloris species, which harvest light >1000 nm, use bacteriochlorophyll b rather than the more common bacteriochlorophyll a as their major photopigment, and assemble LH1 with an additional polypeptide subunit, LH1γ, encoded by multiple genes. To assign a role to γ, we deleted the four encoding genes in the model Blastochloris viridis. Interestingly, growth under halogen bulbs routinely used for cultivation yielded cells displaying an absorption maximum of 825 nm, similar to that of the RC only, but growth under white light yielded cells with an absorption maximum at 972 nm. HPLC analysis of pigment composition and sucrose gradient fractionation demonstrate that the white light-grown mutant assembles RC-LH1, albeit with an absorption maximum blue-shifted by 46 nm. Wavelengths between 900-1000 nm transmit poorly through the atmosphere due to absorption by water, so our results provide an evolutionary rationale for incorporation of γ; this polypeptide red-shifts absorption of RC-LH1 to a spectral range in which photons are of lower energy but are more abundant. Finally, we transformed the mutant with plasmids encoding natural LH1γ variants and demonstrate that the polypeptide found in the wild type complex red-shifts absorption back to 1018 nm, but incorporation of a distantly related variant results in only a moderate shift. This result suggests that tuning the absorption of RC-LH1 is possible and may permit photosynthesis past its current low-energy limit. [ABSTRACT FROM AUTHOR]

The biohydrogen production is promising for the alternative green hydrogen. The two-stage of the dark and photo-fermentation system increases the hydrogen production yield. In this study, the experiments carried out the cell immobilizations on dark and photo bacteria; and liquid suspended photo bacteria for those two-stage batch systems. The optimized parameters obtained, such as materials for immobilized cells, different substrates, and the substrate concentrations for hydrogen fermentation. The experiment results showed pure substrate glucose could produce a higher amount of hydrogen in the photo immobilized cells, the hydrogen concentration was up to about 40%, the utilization rate of glucose was as high as 99.41%, the accumulated hydrogen volume was 169.13 mL, and the hydrogen yield, HY, was 0.63 mol H 2 /mol glucose. In addition, the activated immobilized cells are used for two-stage fermentation to generate hydrogen, HY 1.75 mol H 2 /mol substrate. The two-stage batch fermentations for producing hydrogen, used the Gompertz equation model to obtain the cumulative hydrogen volume and hydrogen production rate (HPR). When the ratio of dark immobilized cells (DIMC) to photo suspended liquids (PSL) is 1.0:5.0, the hydrogen production shows well performance. Moreover, an advanced molecular biological technique, next-generation sequencing (NGS) with ultra-high-throughput DNA output, was applied to perform microbial communities in a different stage of hydrogen fermentation. The NGS help to understand the detailed microbial community change in such fermentation processes and provide better biological efficacy via clarifying the role of microorganisms and their interactions. After the experiments, the Clostridia increased to 28%, and the Enterobacter also increased to 15%, therefore the Rhodobacter and Bosea were reduced from 55% to 17%. Understand the detailed composition of microbial populations in stages of such bio-system will provide the useful information via clarify the biological role of microorganisms and its interactions. [Display omitted] • The study successfully made the immobilized cells of photosynthetic bacteria in batch reactors. • Photo-immobilized cells obtained the best hydrogen production of 169.13 mL H 2 /100 mL. • The microbial community of photo-immobilized cells changed significantly before and after the experiments. • The next-generation sequencing technique provides the relations of microbial and H 2 production. • Immobilized cells applied to two-stage of dark/photo H 2 productions obtained good outcomes. [ABSTRACT FROM AUTHOR]

In this study, three metagenome-assembled genomes of a sediment sample were constructed. A Bin1 (JB001) genome was identified as a photo-litho-auto/heterotroph (purple sulfur bacteria) bacterium with the ability to fix nitrogen, tolerate salt, and to produce bacteriochlorophyll a. It has a genome length of 4.1 Mb and a G + C content of 64.9%. Phylogenetic studies based on concatenated 92 core genes and photosynthetic genes (pufLM and bchY) showed that Bin JB001 is related to Thiococcus pfennigii, "Thioflavicoccus mobilis" and to the Lamprocystis purpurea lineage. Bin JB001 and its closely related members were subjected to the genome-based study of phenotypic and phylogenomic analysis. Genomic similarity indices (dDDH and ANI) showed that Bin JB001 could be defined as a novel species. The average amino acid identity (AAI) and percentage of conserved proteins (POCP) values were below 60 and 50%, respectively. The pan-genome analysis indicated that the pan-genome was an open type wherein Bin JB001 had 855 core genes. This study shows that the binned genome, Bin JB001 could represent a novel species of a new genus under the family Chromatiaceae, for which the name "Candidatus Thioaporhodococcus sediminis" gen. nov. sp. nov. is proposed. [ABSTRACT FROM AUTHOR]

The phenomenon of photosynthetic adaptation of cyanobacteria to far-red light (FRL; 700−750 nm) is closely related to such basic themes as: phototrophy, microbial ecology, and diversity of bacteria. In applied terms, this bioenergetic strategy is essential for biotechnology, with a perspective to possess additional photosynthetic energy. The majority of cyanobacteria is known to use 400−700 nm light, excited state being channeled from light-harvesting complex to reaction centers of two photosystems containing chlorophyll (Chl) a showing red maxima at ~700 nm. After the isolation of first strains producing Chls d and f it became clear that cyanobacteria can also use FRL. Large amount of data has been obtained on cyanobacteria which constitutively produce Chl d as well as on those strains which produce Chl f or Chl f/Chl d during FRL photoacclimation (FaRLiP). Inclusion of these pigments in photosynthetic apparatus, particularly using FaRLiP mechanisms, augments the adaptive potential of cyanobacteria and expands their distribution range. The review provides evidence on such aspects as: photosynthetic apparatus containing Chl d or Chld/Chl f; the FaRLiP gene cluster; phylogeny of cyanobacteria which constitutively or inducibly produce red-shifted chlorophylls; the use of chlorophylls in chemotaxonomy of cyanobacteria, and application of this character in nomenclature. [ABSTRACT FROM AUTHOR]

Key organisms in the environment, such as oxygenic photosynthetic primary producers (photosynthetic eukaryotes and cyanobacteria), are responsible for fixing most of the carbon globally. However, they are affected by environmental conditions, such as temperature, which in turn affect their distribution. Globally, the cyanobacterium Fischerella thermalis is one of the main primary producers in terrestrial hot springs with thermal gradients up to 60 °C, but the mechanisms by which F. thermalis maintains its photosynthetic activity at these high temperatures are not known. In this study, we used molecular approaches and bioinformatics, in addition to photophysiological analyses, to determine the genetic activity associated with the energy metabolism of F. thermalis both in situ and in high-temperature (40 °C to 65 °C) cultures. Our results show that photosynthesis of F. thermalis decays with temperature, while increased transcriptional activity of genes encoding photosystem II reaction center proteins, such as PsbA (D1), could help overcome thermal damage at up to 60 °C. We observed that F. thermalis tends to lose copies of the standard G4 D1 isoform while maintaining the recently described D1INT isoform, suggesting a preference for photoresistant isoforms in response to the thermal gradient. The transcriptional activity and metabolic characteristics of F. thermalis, as measured by metatranscriptomics, further suggest that carbon metabolism occurs in parallel with photosynthesis, thereby assisting in energy acquisition under high temperatures at which other photosynthetic organisms cannot survive. This study reveals that, to cope with the harsh conditions of hot springs, F. thermalis has several compensatory adaptations, and provides emerging evidence for mixotrophic metabolism as being potentially relevant to the thermotolerance of this species. Ultimately, this work increases our knowledge about thermal adaptation strategies of cyanobacteria. [ABSTRACT FROM AUTHOR]

In recent years, extensive efforts have been made to develop clean energy technologies to replace fossil fuels to assist the struggle against climate change. One approach is to exploit the ability of bacteria and photosynthetic organisms to conduct external electron transport for electricity production in bio-electrochemical cells. In this work, we first show that the sea anemones Nematostella vectensis and eggs of Artemia (brine shrimp) secrete redox-active molecules that can reduce the electron acceptor Cytochrome C. We applied 2D fluorescence spectroscopy and identified NADH or NADPH as secreted species. Finally, we broaden the scope of living organisms that can be integrated with a bio-electrochemical cell to the sea anemones group, showing for the first time that Nematostella and eggs of Artemia can produce electrical current when integrated into a bio-electrochemical cell. [ABSTRACT FROM AUTHOR]

Aquaponics is considered a new industrialized food production approach to meet the increasing needs of expanding urbanization. In this system, nutrient recovery from aquaculture sludge can achieve zero solid waste discharge and supplement nutrients to hydroponics system, which yield environmental and economic benefits. Anaerobic and aerobic mineralization are common approaches for the nutrient conversion of aquaculture sludge, but they are challenged by low-value products, nutrient loss, and large amounts of biomass by-products produced during the process. In this review paper, phototrophic bioconversion of aquaculture sludge by anoxygenic phototrophic bacteria (APB) is proposed to minimize carbon and nutrient dissipation, through which the resulting mineral nutrients can be taken up by plants and the assimilated protein-rich biomass can be utilized by aquaculture animals as food. Pre-treatment to solubilize aquaculture sludge is essential to obtain bioavailable substrates, because aquaculture sludge cannot be utilized by APB in the organic solid form. The characteristics of anaerobic and aerobic solubilization processes are discussed, and the performance of phototrophic bioconversion by APB under anaerobic and aerobic conditions is compared. A multi-loop aquaponic system with four ecological coupling models was developed for the recovery of APB-based nutrients. The symbiotic mechanism between the solubilization and phototrophic bioconversion process should be focused in the future. [ABSTRACT FROM AUTHOR]

Large-scale production of single-cell protein (SCP) has the potential not only to solve some of the food insecurity and water scarcity crises that plague a significant portion of our world today but also holds the promise to reduce the cost associated with the treatment of industrial and agricultural wastewater. Resource recovery of SCP from organic waste by microbes like yeast and microalgae is commonly documented. However, recently, a class of phototrophic bacteria, purple non-sulphur bacteria (PNSB), has emerged as a favourable option in terms of both wastewater treatment and resource recovery. PNSB are metabolically versatile and tolerant to a wide range of conditions, hence their ability to thrive in diverse waste streams. Besides its rich protein content, PNSB contains other nutritionally valuable bioproducts like carotenoids, coenzyme Q10, 5-aminolevulinic acid, and pantothenic acid. Recent evidence also indicates that PNSB-based aquafeed enhances growth and boosts immunity in certain aquaculture trials. It does not possess the same toxicity as most gram-negative bacteria due to its comparatively less potent lipopolysaccharide composition. With diverse promising prospects of PNSB-based SCP, it is critical to extensively examine the landscape from a holistic standpoint, highlighting the potential challenges large-scale SCP production may pose. Thus, this review explores the comparative advantages of utilizing PNSB for SCP production, essential components of PNSB-based SCP processing, and possible environmental and economic gains associated with the process. Current challenges with PNSB-based SCP production and future outlooks are also examined. [ABSTRACT FROM AUTHOR]

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A phototrophic purple bacterium Allochromatium sp. strain GSKRLMBKU–01 was used in this study for the reduction of hexavalent chromium. This phototrophic bacterium was isolated from samples collected from the coastal area of Visakhapatnam, India. Both the cells (free (FC) and alginate entrapped immobilized (IC)) are used for the reduction of chromate. Among them, chromate reduction was increased using immobilized cells. Immobilized cells entrapped in sodium alginate reduced the chromate up to 33 ± 3.0 μM on the 8th day of incubation by Allochromatium sp., incubated in presence of light (2000 lx) under the strictly anaerobic conditions, while a chromate reduction up to 26 ± 0.20 µM was recorded by FC of Allochromatium sp. Chromate reduction can be recorded even up to the 20th day by both FC and IC. An incubation period of 8 days was found to be optimum for its growth and chromate reduction. The maximum growth in terms of dry cell weight (DCW) of FC is recorded up to 1.7 ± 0.20 g.L-1 and IC is 2.0 ± 0.30 g.L-1. The growth was recorded even on complete chromate reduction. The final pH of the FC was recorded at pH 8.5 ± 0.10, while the final pH of 8.6 ± 0.20 was recorded for the IC of Allochromatium sp. in the growth medium. The obtained results were mentioned in terms of mean and standard deviation which are statistically significant at P ≤ 0.001 level. The detoxification of chromium in the large-scale systems by employing a purple phototrophic bacteria Allochromatium sp., is proposed. [ABSTRACT FROM AUTHOR]

Cyanobacteria are blue-green Gram-negative and photosynthetic bacteria which are seen as one of the most morphologically numerous groups of prokaryotes. Because of their ability to fix gaseous nitrogen and carbon dioxide to organic materials, they are known to play important roles in the universal nutrient cycle. Cyanobacteria has emerged as one of the promising resources to combat the issues of global warming, disease outbreaks, nutrition insecurity, energy crises as well as persistent daily human population increases. Cyanobacteria possess significant levels of macro and micronutrient substances which facilitate the versatile popularity to be utilized as human food and protein supplements in many countries such as Asia. Cyanobacteria has been employed as a complementary dietary constituent of feed for poultry and as vitamin and protein supplement in aquatic lives. They are effectively used to deal with numerous tasks in various fields of biotechnology, such as agricultural (including aquaculture), industrial (food and dairy products), environmental (pollution control), biofuel (bioenergy) and pharmaceutical biotechnology (such as antimicrobial, anti-inflammatory, immunosuppressant, anticoagulant and antitumor); recently, the growing interest of applying them as biocatalysts has been observed as well. Cyanobacteria are known to generate a numerous variety of bioactive compounds. However, the versatile potential applications of cyanobacteria in biotechnology could be their significant growth rate and survival in severe environmental conditions due to their distinct and unique metabolic pathways as well as active defensive mechanisms. In this review, we elaborated on the versatile cyanobacteria applications in different areas of biotechnology. We also emphasized the factors that could impede the implementation to cyanobacteria applications in biotechnology and the execution of strategies to enhance their effective applications. [ABSTRACT FROM AUTHOR]

Sharing structural and mechanistic properties with the dinitrogen‐fixing enzyme nitrogenase, dark‐operative protochlorophyllide oxidoreductase (DPOR) participates in the biosynthesis of bacteriochlorophyll, subsequently enabling photosynthesis by photosynthetic bacteria. In contrast to the light‐dependent POR, electron transfer in DPOR is coupled to the hydrolysis of adenosine triphosphate for the two‐electron stereoselective reduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide), a coupling also employed by nitrogenases for the multielectron reduction of dinitrogen to ammonia. The importance of adenosine triphosphate hydrolysis is not fully understood for these enzymes, and electrochemistry is a valuable technique to regulate and/or monitor electron delivery to these enzymes. Here, we report three alternative electron donors that support protochlorophyllide reduction in the DPOR system, which could also enable electroenzymatic studies of DPOR. We demonstrate the turnover of DPOR within a spectroelectrochemical configuration, permitting the formation of Chlide to be followed and coupled to electron utilization by DPOR. [ABSTRACT FROM AUTHOR]

Cyanobacteria are the only oxygenic photosynthetic organisms that can fix nitrogen. In diazotrophic cyanobacteria, the regulation of photosynthesis during the diurnal cycle is hypothesized to be linked with nitrogen fixation and involve the D1 protein isoform PsbA4. The amount of bioavailable nitrogen has a major impact on productivity in aqueous environments. In contrast to low- or nitrogen-fixing (−N) conditions, little data on photosynthetic regulation under nitrogen-replete (+ N) conditions are available. We compared the regulation of photosynthesis under −N and + N conditions during the diurnal cycle in wild type and a psbA4 deletion strain of the unicellular diazotrophic cyanobacterium Cyanothece sp. ATCC 51142. We observed common changes to light harvesting and photosynthetic electron transport during the dark in + N and −N conditions and found that these modifications occur in both diazotrophic and non-diazotrophic cyanobacteria. Nitrogen availability increased PSII titer when cells transitioned from dark to light and promoted growth. Under −N conditions, deletion of PsbA4 modified charge recombination in dark and regulation of PSII titer during dark to light transition. We conclude that darkness impacts the acceptor-side modifications to PSII and photosynthetic electron transport in cyanobacteria independently of the nitrogen-fixing status and the presence of PsbA4. [ABSTRACT FROM AUTHOR]

Rhodopila globiformis is the most acidophilic of anaerobic purple phototrophs, growing optimally in culture at pH 5. Here we present a cryo-EM structure of the light-harvesting 1–reaction center (LH1–RC) complex from Rhodopila globiformis at 2.24 Å resolution. All purple bacterial cytochrome (Cyt, encoded by the gene pufC) subunit-associated RCs with known structures have their N-termini truncated. By contrast, the Rhodopila globiformis RC contains a full-length tetra-heme Cyt with its N-terminus embedded in the membrane forming an α-helix as the membrane anchor. Comparison of the N-terminal regions of the Cyt with PufX polypeptides widely distributed in Rhodobacter species reveals significant structural similarities, supporting a longstanding hypothesis that PufX is phylogenetically related to the N-terminus of the RC-bound Cyt subunit and that a common ancestor of phototrophic Proteobacteria contained a full-length tetra-heme Cyt subunit that evolved independently through partial deletions of its pufC gene. Eleven copies of a novel γ-like polypeptide were also identified in the bacteriochlorophyll a-containing Rhodopila globiformis LH1 complex; γ-polypeptides have previously been found only in the LH1 of bacteriochlorophyll b-containing species. These features are discussed in relation to their predicted functions of stabilizing the LH1 structure and regulating quinone transport under the warm acidic conditions. The cryo-EM structure of the unusual light-harvesting 1–reaction center (LH1–RC) complex from Rpi. globiformis, the most acidophilic anaerobic purple bacteria, is presented, characterized and compared to other photosynthetic bacteria. [ABSTRACT FROM AUTHOR]

Control phenomena in biology usually refer to changes in gene expression and protein translation and modification. In this paper, another mode of regulation is highlighted; we propose that photosynthetic organisms can harness the interplay between localization and delocalization of energy transfer by utilizing small conformational changes in the structure of light‐harvesting complexes. We examine the mechanism of energy transfer in photosynthetic pigment‐protein complexes, first through the scope of theoretical work and then by in vitro studies of these complexes. Next, the biological relevance to evolutionary fitness of this localization‐delocalization switch is explored by in vivo experiments on desert crust and marine cyanobacteria, which are both exposed to rapidly changing environmental conditions. These examples demonstrate the flexibility and low energy cost of this mechanism, making it a competitive survival strategy. [ABSTRACT FROM AUTHOR]

The vision to replace coal with hydrogen goes back to Jules Verne in 1874. However, sustainable hydrogen production remains challenging. The most elegant approach is to utilize photosynthesis for water splitting and to subsequently save solar energy as hydrogen. Cyanobacteria and green algae are unicellular photosynthetic organisms that contain hydrogenases and thereby possess the enzymatic equipment for photosynthetic hydrogen production. These features of cyanobacteria and algae have inspired artificial and semi-artificial in vitro techniques, that connect photoexcited materials or enzymes with hydrogenases or mimics of these for hydrogen production. These in vitro methods have on their part been models for the fusion of cyanobacterial and algal hydrogenases to photosynthetic photosystem I (PSI) in vivo , which recently succeeded as proofs of principle. Biotechnological solar hydrogen production has the aim to utilize electrons from the light reactions of photosynthesis. Recently, cyanobacterial and algal H 2 ases, the enzymes that catalyze production of H 2 , were successfully fused to PSI. They intercept electrons from the photosynthetic electron transport chain. Both engineered strains produce photosynthetic hydrogen for prolonged periods. They maintained their ability to grow photoautotrophically. The processes do not exclusively rely upon water oxidation as desired, which is mostly due to the fact that the H 2 ases are sensitive to oxygen. [ABSTRACT FROM AUTHOR]

An efficient and rapid energy transfer (ET) mechanism is theoretically proposed only by mimicking the circular structure of natural photosynthetic light‐harvesting (LH) antennae, without spatial and energetic disorders as in natural photosynthetic systems. Two B850 LH complexes of photosynthetic bacterium are adopted, and it is shown that for close LH antennae the ET rate can be optimized by functionally separating ET from photon absorption within exciton energy levels by an adjustment of the distance between the LH antennae at room temperature. As a result, for close LHs, the two processes of photon absorption and ET can be energetically and functionally divided within the same exciton energy level. From the analysis of the temperature dependence of transfer rate, it is also shown that the two energetically separated processes are connected by thermal pumping of the exciton population and an optimized ET rate can be achieved at room temperature when the energy difference between optically allowed and forbidden states is comparable with the thermal energy of the environment. [ABSTRACT FROM AUTHOR]

Purple non‐sulphur bacteria (PNSB) are an emerging group of microbes attractive for applied microbiology applications such as wastewater treatment, plant biostimulants, microbial protein, polyhydroxyalkanoates and H2 production. These photoorganoheterotrophic microbes have the unique ability to grow selectively on organic carbon in anaerobic photobioreactors. This so‐called selectivity implies that the microbial community will have a low diversity and a high abundance of a particular PNSB species. Recently, it has been shown that certain PNSB strains can produce antimicrobials, yet it remains unclear whether these contribute to competitive inhibition. This research aimed to understand which type of antimicrobial PNSB produce and identify whether these compounds contribute to their selective growth. Mining 166 publicly‐available PNSB genomes using the computational tool BAGEL showed that 59% contained antimicrobial encoding regions, more specifically biosynthetic clusters of bacteriocins and non‐ribosomal peptide synthetases. Inter‐ and intra‐species inhibition was observed in agar spot assays for Rhodobacter blasticus EBR2 and Rhodopseudomonas palustris EBE1 with inhibition zones of, respectively, 5.1 and 1.5–5.7 mm. Peptidomic analysis detected a peptide fragment in the supernatant (SVLQLLR) that had a 100% percentage identity match with a known non‐ribosomal peptide synthetase with antimicrobial activity. [ABSTRACT FROM AUTHOR]

The study of microbial mats in extreme environments is of high scientific interest from geological, ecological, and geomicrobiological aspects. These mats represent multilayer bio-structures where each taxonomic group dominates a specific vertical layering distribution resulting from its growth and metabolic activity. In the present study, microbial mats in a hot spring environment from Aedipsos (Euboea Island, Greece) resulting in the creation of thermogenic travertine, were studied through an interdisciplinary approach. The mineralogical composition was determined by optical microscopy, XRD, and SEM-EDS microanalysis, and the identification of Cyanobacteria was made primarily on morphological characteristics. The main mineral phase in the studied samples is calcite and, to a less extent, aragonite, with several trace elements in the mineral-chemistry composition, i.e., up to 1.93 wt. % MgO, up to 0.52 wt. % SrO, up to 0.44 wt. % Na2O, up to 0.17 wt. % K2O, and up to 3.99 wt. % SO3. The dominant facies are lamination and shrubs, which are the most common among the facies of thermogenic travertines of the area. Several layers were identified, (i) a top mainly abiotic layer consisting of calcium carbonate micritic crystals, (ii) a second biotic layer–the Cyanobacteria layer, dominated by the species Leptolyngbya perforans, (iii) a third biotic layer where Leptolyngbya perforans, Chloroflexus and other bacteria occur, and (iv) a deeper abiotic part with several layers where no photosynthetic microorganisms occur. In the upper layers, nineteen (19) species of Cyanobacteria were identified, classified in the orders Chroococcales (37%), Synechococcales (31%), Oscillatoriales (16%), and Spirulinales (6%). Among the identified Cyanobacteria, there are typical thermophilic and limestone substrate species. These Cyanobacteria are found to participate in the biomineralization and biologically-influenced processes, i.e., (i) filamentous Cyanobacteria are trapping calcium carbonate crystals, and diatoms, (ii) extracellular polymeric substances (EPS) create crystal retention lattice contributing to the biomineralization process, and (iii) filamentous sheaths of Cyanobacteria are calcified, resulting in the creation of calcium carbonate tubes. [ABSTRACT FROM AUTHOR]

As hypoxic tumors show resistance to several clinical treatments, photosynthetic microorganisms have been recently suggested as a promising safe alternative for oxygenating the tumor microenvironment. The relationship between organisms and the effect microalgae have on tumors is still largely unknown, evidencing the need for a simple yet representative model for studying photosynthetic tumor oxygenation in a reproducible manner. Here, we present a 3D photosynthetic tumor model composed of human melanoma cells and the microalgae Chlamydomonas reinhardtii, both seeded into a collagen scaffold, which allows for the simultaneous study of both cell types. This work focuses on the biocompatibility and cellular interactions of the two cell types, as well as the study of photosynthetic oxygenation of the tumor cells. It is shown that both cell types are biocompatible with one another at cell culture conditions and that a 10:1 ratio of microalgae to cells meets the metabolic requirement of the tumor cells, producing over twice the required amount of oxygen. This 3D tumor model provides an easy-to-use in vitro resource for analyzing the effects of photosynthetically produced oxygen on a tumor microenvironment, thus opening various potential research avenues. [ABSTRACT FROM AUTHOR]

Aerobic anoxygenic photosynthetic bacteria (AAPB) are a kind of heterotrophic prokaryote that can use bacteriochlorophyll (BChl) for photosynthesis without oxygen production and they are widely distributed in aquatic environments, including oceans, lakes, and rivers. A novel aerobic anoxygenic photosynthetic bacterium strain XJSPT was isolated during a study of water microbial diversity in Sayram Lake, Xinjiang Province, China. Strain XJSPT was found to grow optimally at 33 °C, pH 7.5 with 1.0% (w/v) NaCl, and to produce bacteriochlorophyll a and carotenoids. Phylogenetic analysis based on 16S rRNA gene sequence and concatenated alignment sequences of 120 ubiquitous single-copy proteins both supported that strain XJSPT belonged to the genus Pseudotabrizicola. Both average nucleotide identity (ANI) and DNA–DNA hybridization (DDH) values were below the species delineation threshold. The primary polar lipids were phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, one unknown lipid, and one unidentified phospholipid. Based on the results of polyphasic analyses performed in this study, strain XJSPT represents a new member of the genus Pseudotabrizicola, for which the name Pseudotabrizicola formosa sp. nov. is proposed. The type strain is XJSPT (= KCTC 52636T = MCCC 1H00184T = SDUM 107003T). Comparative genomic analysis showed that four species of the genus Pseudotabrizicola shared 2570 core genes and possessed a complete anoxygenic photosystem II. [ABSTRACT FROM AUTHOR]

In bacterial photosynthesis, the excitation energy transfer (EET) from carotenoids to bacteriochlorophyll a has a significant impact on the overall efficiency of the primary photosynthetic process. This efficiency can be enhanced when the involved carotenoid has intramolecular charge-transfer (ICT) character, as found in light-harvesting systems of marine alga and diatoms. Here, we provide insights into the significance of ICT excited states following the incorporation of a higher plant carotenoid, β-apo-8′-carotenal, into the carotenoidless light-harvesting 1 (LH1) complex of the purple photosynthetic bacterium Rhodospirillum rubrum strain G9+. β-apo-8′-carotenal generates the ICT excited state in the reconstituted LH1 complex, achieving an efficiency of EET of up to 79%, which exceeds that found in the wild-type LH1 complex. Studying the excitation energy transfer from carotenoids to bacteriochlorophyll a in purple photosynthetic bacteria could provide insights on how to optimize photosynthetic light-harvesting. Here, the authors study a carotenoid reconstituted core light-harvesting 1 complex from Rhodospirillum rubrum and find that the involvement of the intramolecular charge-transfer excited state of β-apo-8′-carotenal plays a key role in achieving an excitation energy transfer efficiency of ~77%. [ABSTRACT FROM AUTHOR]

The genomes of some purple photosynthetic bacteria contain a multigene puc family encoding a series of a- and ß-polypeptides that together form a heterogeneous antenna of light-harvesting 2 (LH2) complexes. To unravel this complexity, we generated four sets of puc deletion mutants in Rhodopseudomonas palustris, each encoding a single type of pucBA gene pair and enabling the purification of complexes designated as PucA-LH2, PucB-LH2, PucD-LH2, and PucE-LH2. The structures of all four purified LH2 complexes were determined by cryogenic electron microscopy (cryo-EM) at resolutions ranging from 2.7 to 3.6 Å. Uniquely, each of these complexes contains a hitherto unknown polypeptide, γ, that forms an extended undulating ribbon that lies in the plane of the membrane and that encloses six of the nine LH2 αβ-subunits. The γ-subunit, which is located near to the cytoplasmic side of the complex, breaks the C9 symmetry of the LH2 complex and binds six extra bacteriochlorophylls (BChls) that enhance the 800-nm absorption of each complex. The structures show that all four complexes have two complete rings of BChls, conferring absorption bands centered at 800 and 850 nm on the PucA-LH2, PucB-LH2, and PucE-LH2 complexes, but, unusually, the PucD-LH2 antenna has only a single strong near-infared (NIR) absorption peak at 803 nm. Comparison of the cryo-EM structures of these LH2 complexes reveals altered patterns of hydrogen bonds between LH2 aß-side chains and the bacteriochlorin rings, further emphasizing the major role that H bonds play in spectral tuning of bacterial antenna complexes. [ABSTRACT FROM AUTHOR]

Purple bacteria (PPB), anoxygenic photoorganoheterotrophic organisms with a hyper-versatile metabolism and high biomass yields over substrate, are promising candidates for the recovery of nutrient resources from wastewater. Infrared light is a pivotal parameter to control and design PPB-based resource recovery. However, the effects of light intensities on the physiology and selection of PPB in mixed cultures have not been studied to date. Here, we examined the effect of infrared irradiance on PPB physiology, enrichment, and growth over a large range of irradiance (0 to 350 W m-2) in an anaerobic mixed-culture sequencing batch photobioreactor. We developed an empirical mathematical model that suggests higher PPB growth rates as response to higher irradiance. Moreover, PPB adapted to light intensity by modulating the abundances of their phototrophic complexes. The obtained results provide an in-depth phylogenetic and metabolic insight the impact of irradiance on PPB. Our findings deliver the fundamental information for guiding the design of light-driven, anaerobic mixed-culture PPB processes for wastewater treatment and bioproduct valorization. [ABSTRACT FROM AUTHOR]

The geological record of microbial metabolisms and ecologies primarily consists of stable isotope fractionations and the diagenetic products of biogenic lipids. Carotenoid lipid biomarkers are particularly useful proxies for reconstructing this record, providing information on microbial phototroph primary productivity, redox couples, and oxygenation. The biomarkers okenane, chlorobactane, and isorenieratene are generally considered to be evidence of anoxygenic phototrophs, and provide a record that extends to 1.64 Ga. The utility of the carotenoid biomarker record may be enhanced by examining the carbon isotopic ratios in these products, which are diagnostic for specific pathways of biological carbon fixation found today within different microbial groups. However, this joint inference assumes that microbes have conserved these pathways across the duration of the preserved biomarker record. Testing this hypothesis, we performed phylogenetic analyses of the enzymes constituting the reductive tricarboxylic acid (rTCA) cycle in Chlorobiales, the group of anoxygenic phototrophic bacteria usually implicated in the deposition of chlorobactane and isorenieretane. We find phylogenetically incongruent patterns of inheritance across all enzymes, indicative of horizontal gene transfers to both stem and crown Chlorobiales from multiple potential donor lineages. This indicates that a complete rTCA cycle was independently acquired at least twice within Chlorobiales and was not present in the last common ancestor. When combined with recent molecular clock analyses, these results predict that the Mesoproterzoic lipid biomarker record diagnostic for Chlorobiales should not preserve isotopic fractionations indicative of a full rTCA cycle. Furthermore, we conclude that coupling isotopic and biomarker records is insufficient for reliably reconstructing microbial paleoecologies in the absence of a complementary and consistent phylogenomic narrative. [ABSTRACT FROM AUTHOR]

Background: The robust model cyanobacterium Synechocystis PCC 6803 is increasingly explored for its potential to use solar energy, water and atmospheric CO2 for the carbon-neutral production of terpenes, the high-value chemicals that can be used for the production of drugs, favors, fragrances and biofuels. However, as terpenes are chemically diverse, it is extremely difcult to predict whether Synechocystis is a suitable chassis for the photosynthetic production of various terpenes or only a few of them. Results: We have performed the frst-time engineering and comparative analysis of the best-studied cyanobacterium Synechocystis PCC 6803 for the photosynthetic production of fve chemically diverse high-value terpenes: two monoterpenes (C10H16) limonene (cyclic molecule) and pinene (bicyclic), and three sesquiterpenes (C15H24) bisabolene (cyclic), farnesene (linear) and santalene (cyclic). All terpene producers appeared to grow well and to be genetically stable, as shown by the absence of changes in their production levels during the 5--9-month periods of their sub-cultivation under photoautotrophic conditions). We also found that Synechocystis PCC 6803 can efciently and stably produce farnesene and santalene, which had never been produced before by this model organism or any other cyanobacteria, respectively. Similar production levels were observed for cells growing on nitrate (the standard nitrogen source for cyanobacteria) or urea (cheaper than nitrate). Furthermore, higher levels of farnesene were produced by cloning the heterologous farnesene synthase gene in a RSF1010-derived replicating plasmid as compared to the well-used slr0168 neutral cloning site of the chromosome. Conclusions: Altogether, the present results indicate that Synechocystis PCC 6803 is better suited to produce sesquiterpenes (particularly farnesene, the most highly produced terpene of this study) than monoterpenes (especially pinene). [ABSTRACT FROM AUTHOR]

Background: Studies suggest that sulfur may react with plants or monocellular organisms, such as fungi, to produce toxic agents. It has been theorized that sulfur enters cells and affects their respiration. This study reports on a phototroph development that leads to the diminution and/or production of sulfur and release of hydrogen sulfide from public ponds. Methods: This study was conducted in anoxic stabilization ponds at a dimension of 1×0.25×1 (m), with a hydraulic retention time of 6 days. The ponds' water was tested during the dark and light cycles. The experiments were carried out by factorial design and measured three variables: volumetric organic loading, sulphate concentrations and temperature. Results: Cyanobacteria and Rhodobacter species were the most abundant phototroph cellular organisms. The mean value of total sulfur and un-ionized hydrogen sulfide concentration were 74 mg/L and 21 mg/L, respectively, at the volumetric organic loading of 100 g BOD5/m3 per day. The efficiencies of biochemical and chemical oxygen removal were 71.9% and 59.1%, respectively. The mean proliferation rate of photosynthetic sulfur bacteria was 3.4×106 cells/ml. Conclusion: photosynthetic sulfur bacteria significantly reduced the sulfur concentration generated in the ponds. The illumination of bright light enhanced the sulfur reduction by the photosynthetic sulfur bacteria in the wastewater of the anoxic stabilization ponds. [ABSTRACT FROM AUTHOR]

It was established that in a heterogeneous model system, which consisted of two types of complexes: reaction center or core complex of photosystem 2 of higher plants and LH2 complex of the sulfur bacterium Alc. vinosum, BChl850 oxidation of the LH2 complex could be observed under illumination by the light at a wavelength of 662 nm, which is the red absorption band of Chl. It has been shown that this process induces release of singlet oxygen, which is generated in photosystem II complexes and then partially diffuses into LH2 complex, where it oxidizes BChl850. It was established by HPLC that this results in formation of a product of BChl oxidation, 3-acetylchlorophyll. The process of BChl850 oxidation is inhibited by singlet oxygen quenchers (Trolox and Na ascorbate). It is suggested that the LH2 complex from the sulfur bacterium Alc. vinosum could be used to detect generation of singlet oxygen by the chlorophyll containing samples. [ABSTRACT FROM AUTHOR]

The mechanism of bacteriochlorophyll photooxidation in light-harvesting complexes of a number of purple photosynthetic bacteria when the complexes are excited into the carotenoid absorption bands remains unclear for many years. Here, using narrow-band laser illumination we measured action spectrum of this process for the spectral ranges of carotenoid and bacteriochlorophyll. It is shown that bacteriochlorophyll excitation results in almost no photooxidation of these molecules, while carotenoid excitation leads to oxidation with quantum yield of about 0,0003. Low value of the yield enabled an assumption that the studied process is initiated by the triplet states of the main carotenoids of the complexes with the number of conjugated double-bond chain length of N = 11. Interaction of these states with oxygen facilitates formation, though with low efficiency, of the excited singlet oxygen, which oxidizes bacteriochlorophylls. The carotenoid triplet states are formed in the process of the earlier studied singlet-triplet fission. The obtained results point at the necessity of reconsidering the functions of carotenoids in the light-harvesting complexes of purple bacteria. [ABSTRACT FROM AUTHOR]

To elucidate the mechanism of site-selective chemical replacement of chromophores in the reaction centers (RCs) of photosynthetic bacteria by external pigments, we investigated how the efficiency of incorporation of plant pheophytin a (Pheo) into the binding sites for bacteriopheophytin a molecules (BPheo) in the isolated Rhodobacter sphaeroides R-26 RCs depended on the incubation medium temperature, Pheo aggregation state, and the presence of organic solvent (acetone). When Pheo was in a form of monomers in free detergent micelles in a water–detergent incubation medium, the degree of selective replacement of photochemically inactive BPheo HB molecules upon incubation of the RC/Pheo mixture at 5°C was ~15%. The exchange efficiency increased to 40% upon incubation at 25°C and reached 100% at the same temperature when 10% acetone was added to the incubation medium. At both 5 and 25°C, the degree of pigment exchange increased approximately twice, when a mixture of Pheo monomers and dimers in the presence of 10% acetone was used as the incubation medium. The removal of acetone from this medium with the preservation of pigment forms led to a significant decrease in the efficiency of Pheo incorporation. The effect of acetone on the pigment exchange was also observed at an elevated incubation temperature (43.5°C), when functionally active BPheo HA molecules were partially replaced. The results are discussed in terms of the mechanism according to which (i) the temperature-dependent internal movements of the RC protein facilitate the release of the BPheo molecule from the binding site with simultaneous insertion of the Pheo molecule into the same site in a coupled process, (ii) the role of temperature largely depends on the steric accessibility of binding pockets in the RC protein, (iii) the incorporation of Pheo occurs from a pool of monomeric molecules included in the RC-detergent micelles, and (iv) the presence of acetone in the incubation medium facilitates the exchange of Pheo monomers between micelles in the solution and the detergent belt of the RC complex. [ABSTRACT FROM AUTHOR]