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Algae-bacteria interaction is one of the main factors underlying the formation of harmful algal blooms (HABs). The aim of this study was to develop a genome-wide high-throughput screening method to identify HAB-influenced specific interactive bacterial metabolites using a comprehensive collection of gene-disrupted E. coli K-12 mutants (Keio collection). The screening revealed that a total of 80 gene knockout mutants in E. coli K-12 resulted in an approximately 1.5-fold increase in algal growth relative to that in wild-type E. coli. Five bacterial genes (lpxL, lpxM, kdsC, kdsD, gmhB) involved in the lipopolysaccharide (LPS) (or lipooligosaccharide, LOS) biosynthesis were identified from the screen. Relatively lower levels of LPS were detected in these bacteria compared to that in the wild-type. Moreover, the concentration-dependent decrease in microalgal growth after synthetic LPS supplementation indicated that LPS inhibits algal growth. LPS supplementation increased the 2,7-dichlorodihydrofluorescein diacetate fluorescence, as well as the levels of lipid peroxidation-mediated malondialdehyde formation, in a concentration-dependent manner, indicating that oxidative stress can result from LPS supplementation. Furthermore, supplementation with LPS also remarkably reduced the growth of diverse bloom-forming dinoflagellates and green algae. Our findings indicate that the Keio collection-based high-throughput in vitro screening is an effective approach for the identification of interactive bacterial metabolites and related genes. [ABSTRACT FROM AUTHOR]

Summary: Phytoplankton communities within the photic zones of the oceans and lakes are characterised by highly complex assemblages of unicellular microalgae and associated bacteria. The interconnected evolutionary history of algae and bacteria allowed the formation of a wide spectrum of associations defined by orchestrated nutrient exchange, mutual support with growth factors, quorum sensing mediation, and episodic killing of the partners to obtain more resources. In this review, we discuss how these cross‐kingdom interactions shape plankton communities that undergo annual, seasonal switching between alternative states with balanced multispecies consortia. We illustrate how these microscopic interactions can have consequences that scale up to influence global element cycling. [ABSTRACT FROM AUTHOR]

Cyanobacteria characterized by exceptional tolerance to environmental stresses often become pioneer settlers in habitats with harsh conditions. There, they can constitute the core of microbial communities. The taxonomic composition of the cyanobacterial component of algal-bacterial consortia dwelling in a habitat with particularly harsh conditions (rock baths at the coast of Kandalaksha Bay of the White Sea) has been elucidated for the first time. Two workflows of the taxonomic analysis of the cyanobacteria were tested including the combinations of two programs and two databases (QIIME+Greengenes and Usearch+NCBI GenBank). Our results obviated the need of the using of a complex approach combining morphological and metagenomic analyses for revealing the taxonomic structure of cyanobacteria in natural habitats. Our results show that the cyanobacterial component of the consortia from the habitats with harsh and highly volatile environmental conditions is enriched with non-diazotrophic and diazotrophic non-branched filamentous cyanobacteria. [ABSTRACT FROM AUTHOR]

Highlights • Microalgae could grow on nutrients in the liquid fraction of agro-digestate. • Microalgae could grow outdoor under sub-optimal climatic conditions for 200 d. • Stable nitrification was established and supported by oxygen from photosynthesis. • Approximately 7 ± 3% of N was assimilated by microalgae while 61 ± 24% was nitrified. • The raceway reactor was slightly more effective than a bubble-column photobioreactor. Abstract This paper addresses the efficiency of a microalgae-based agricultural digestate treatment at pilot-scale in an outdoor raceway pond (880 L, pH-dependent CO 2 dosage) and in a bubble column (74.5 L, air-bubbling). Specifically, nitrogen removal, evolution of the algae-bacteria consortium, and the actual process applicability in the Po Valley climate are discussed. The performance of the two reactors varied seasonally. The average algal productivity in the raceway was 32.4 ± 33.1 mg TSS·L−1·d−1 (8.2 ± 8.5 g TSS·m−2·d−1) while in the PBR it was 25.6 ± 26.8 mg TSS·L−1·d−1; the average nitrogen removal was 20 ± 29% (maximum 78%) and 22 ± 29% (maximum 71%) in the raceway and in the column, respectively. Nevertheless, nitrification had a key role as 61 ± 24% and 52 ± 32% of the nitrogen load was oxidized in the raceway and in the column, respectively. [ABSTRACT FROM AUTHOR]

Abstract Since few studies have investigated the nitrification and assimilation of nitrogens by algal-bacterial consortia, this study aimed to evaluate the effects of supplementary aeration and blue light on nitrogen removal and biomass growth of algal-bacterial consortia in real domestic wastewater. When blue light was weakly irradiated (500 μmol m−2 s−1), it was found that supplementary aeration enhanced ammonia removal from 38.5% to 96.3% and algal growth from 72.5 mg algae L−1 to 345.3 mg algae L−1 by providing oxygen for nitrification and inorganic carbon for photosynthesis of microalgae. It was also observed that ammonia was consumed first and then nitrate produced by nitrification was assimilated, indicating that diauxic growth of consortia on nitrogen sources occurred. Thus, it was expected that nitrogen removal could be enhanced by lowering nitrification and denitrification loads. Moreover, intense blue light was found to accumulate nitrite by selective photoinhibition of nitrite oxidizing bacteria (NOB) of which c-type cytochrome is known to be photo-bleachable at 408 nm. From these results, it was concluded that favorable conditions for growth and nitrogen removal by algal-bacterial consortia in real wastewater could be established by controlling aeration and light intensity. Graphical abstract Image 1 Highlights • In low-light condition, aeration enhanced algal biomass and nitrogen removal. • Diauxic growth of algal cells on nitrogen species was observed. • Blue light inhibited nitrite oxidation to nitrate. [ABSTRACT FROM AUTHOR]

Our understanding of microbial natural environments combines in situ experimentation with studies of specific interactions in laboratory-based setups. The purpose of this work was to develop, build and demonstrate the use of a microbial culture chamber enabling both in situ and laboratory-based studies. The design uses an enclosed chamber surrounded by two porous membranes that enables the comparison of growth of two separate microbial populations but allowing free exchange of small molecules. Initially, we tested if the presence of the macroalga Fucus vesiculosus inside the chamber affected colonization of the outer membranes by marine bacteria. The alga did indeed enrich the total population of colonizing bacteria by more than a factor of four. These findings lead us to investigate the effect of the presence of the coccolithophoric alga Emiliania huxleyi on attachment and biofilm formation of the marine bacterium Phaeobacter inhibens DSM17395. These organisms co-exist in the marine environment and have a well-characterized interdependence on secondary metabolites. P. inhibens attached in significantly higher numbers when having access to E. huxleyi as compared to when exposed to sterile media. The experiment was carried out using a wild type (wt) strain as well as a TDA-deficient strain of P. inhibens. The ability of the bacterium to produce the antibacterial compound, tropodithietic acid (TDA) influenced its attachment since the P. inhibens DSM17395 wt strain attached in higher numbers to a surface within the first 48 h of incubation with E. huxleyi as compared to a TDA-negative mutant. Whilst the attachment of the bacterium to a surface was facilitated by presence of the alga, however, we cannot conclude if this was directly affected by the algae or whether biofilm formation was dependent on the production of TDA by P. inhibens , which has been implied by previous studies. In the light of these results, other applications of immersed culture chambers are suggested. [ABSTRACT FROM AUTHOR]

In this study, bacterium Pseudomonas sp. strain D was proved to be the main partner assisting Chlamydomonas reinhardtii in improving photolysis-mediated H 2 production and a good partner for promoting H 2 production by the green algae Chlorella and Scenedesmus . In strain D partnered algal-bacterial co-culture, the relative O 2 content in the headspace plus the dissolved oxygen in the culture medium were rapidly consumed by bacterial growth, resulting in a completely anaerobic environment that proved suitable for the activation of algal hydrogenase. Moreover, algal-bacterial cooperation was able to slow the reduction of chlorophyll, enhance starch accumulation, and maintain protein content, which are the potential factors whose control provides an opportunity for improving algal H 2 production. This study systematically analyzed the main pathway responsible for H 2 production by algal-bacterial cooperation and the potential mechanisms for improvement, and proposed an efficient and durable algal-bacterial cooperation system for improving photolysis-mediated H 2 production by green algae. [ABSTRACT FROM AUTHOR]

During the last decade, our concept of chytrid systematics has dramatically changed based on molecular phylogeny and zoospore ultrastructure. In contrast with well-studied saprotrophic chytrids, only a few obligate parasitic chytrids have been investigated with modern methods. Here, we investigate the novel chytrid culture KS93 that is parasitic on the diatom Aulacoseira granulata . Thallus morphology of KS93 was characterized by a spherical, stalked zoosporangium with a single, apical inoperculate discharge pore and zoospore discharge as a mass in a vesicle. A cross-inoculation experiment revealed that the infection of KS93 was specific to A. granulata . Zoospores of KS93 possessed the characters of the Group I type zoospore of the Chytriomycetaceae in the Chytridiales, but does not appear to have a paracrystalline inclusion. Additionally, KS93 also possessed a globule-type KAS (kinetosome-associated structure), first reported here for members of Chytriomycetaceae. In our molecular phylogeny, KS93 was placed in the basal position of the Chytriomycetaceae and was distinguished from any known species in the family. Morphological features of KS93 were distinct from those of any other taxa in the Chytriomycetaceae and from any described chytrids. Based on these results, we describe this chytrid as Pendulichytrium sphaericum gen. et sp. nov. in the family Chytriomycetaceae. [ABSTRACT FROM AUTHOR]

The ability of Chlorella vulgaris-Bacillus licheniformis and Microcystis aeruginosa-Bacillus licheniformis consortiums to eliminate total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and soluble chemical oxygen demand (sCOD) from synthetic wastewater was studied. The highest values of dry cell weight, chlorophyll-a, and chlorophyll metabolism related genes/bacterial rRNA gene copies were obtained in the Chlorella vulgaris - Bacillus licheniformis system at Chlorella vulgaris and Bacillus licheniformis ratio of 1:3. On the 10th day, the Chlorella vulgaris-Bacillus licheniformis system at this ratio removed 86.55%, 80.28% and 88.95% of sCOD, TDP and TDN, respectively. But, the Microcystis aeruginosa-Bacillus licheniformis system at this ratio only removed 65.62%, 70.82%, and 21.56% of sCOD, TDP and TDN, respectively. Chlorella vulgaris and Bacillus licheniformis could coexist as an algae-bacteria consortia and quorum sensing substances (autoinducing peptides and bis (3′-5′) diguanylic acid) concentrations were measured. Finally, the interactions and communication patterns between Chlorella vulgaris and Bacillus licheniformis were depicted. [ABSTRACT FROM AUTHOR]

Data collected from experiments conducted at a flask scale are regularly used as input data for life cycle assessments and techno-economic analyses for predicting the potential productivities of large-scale commercial facilities. This study measures and compares nitrogen removal and biomass growth rates in treatment systems that utilize an algae-bacteria consortium to remediate landfill leachate at three scales: small (0.25 L), medium (100 L), and large (1000 L). The medium- and large-scale vessels were run for 52 consecutive weeks as semibatch reactors under variable environmental conditions. The small-scale experiments were conducted in flasks as batch experiments under controlled environmental conditions. Kolomogov-Smirnov statistical tests, which compare the distributions of entire data sets, were used to determine if the ammonia removal, total nitrogen removal, and biomass growth rates at each scale were statistically different. Results from the Kolmogov-Smirnov comparison indicate that there is a significant difference between all rates determined in the large-scale vessels compared to those in the small-scale vessels. These results suggest that small-scale experiments may not be appropriate as input data in predictive analyses of full scale algal processes. The accumulation of nitrite and nitrate within the reactor, observed midway through the experimental process, is attributed to high relative abundances of ammonia- and nitrite- oxidizing bacteria, identified via metagenomic analysis. [ABSTRACT FROM AUTHOR]

Environmental pollution caused by wheat bran and domestic effluent are two common problems in many rural areas. This work combines the digestion of wheat bran and the treatment of rural domestic effluent by developing a microbiological system consisting of Chlorella vulgaris and Bacillus sp., which was isolated from wheat bran fermentation and identified by molecular technique. Bacillus sp. converts solid organics of wheat bran into soluble nutrients which are essential to algae growth. The addition of digested wheat bran balances the nutrients profile of rural domestic effluent and increases the biomass yield of algae. After treatment, the rural domestic effluent was converted into farmland irrigation water and valuable algal biomass was produced. In practice, the results of this work may be useful in reconstructing domestic wastewater treatment systems in some rural areas. [ABSTRACT FROM AUTHOR]

Microalga are of high relevance for the global carbon cycling and it is well-known that they are associated with a microbiota. However, it remains unclear, if the associated microbiota, often found in phycosphere biofilms, is specific for the microalga strains and which role individual bacterial taxa play. Here we provide experimental evidence that Chlorella saccharophila, Scenedesmus quadricauda, and Micrasterias crux-melitensis, maintained in strain collections, are associated with unique and specific microbial populations. Deep metagenome sequencing, binning approaches, secretome analyses in combination with RNA-Seq data implied fundamental differences in the gene expression profiles of the microbiota associated with the different microalga. Our metatranscriptome analyses indicates that the transcriptionally most active bacteria with respect to key genes commonly involved in plant--microbe interactions in the Chlorella (Trebouxiophyceae) and Scenedesmus (Chlorophyceae) strains belong to the phylum of the α-Proteobacteria. In contrast, in the Micrasterias (Zygnematophyceae) phycosphere biofilm bacteria affiliated with the phylum of the Bacteroidetes showed the highest gene expression rates. We furthermore show that effect or molecules known from plant--microbe interactions as inducers for the innate immunity are already of relevance at this evolutionary early plant-microbiome level. [ABSTRACT FROM AUTHOR]

The use of algal-bacterial symbiotic association establishes a sustainable and cost-effective strategy in wastewater treatment. Using municipal wastewater, the removal performances of inorganic nutrients (nitrogen and phosphorus) and organic pollutants were investigated by the co-culture system having different inoculum ratios (R) of suspended activated sludge to alginate-immobilized microalgae Chlorella vulgaris . The co-culture reactors with lower R ratios obtained more removal of nitrogen than in pure culture of C. vulgaris . The reactor with R = 0.5 (sludge/microalgae) showed the highest performance representing 66% removal after 24 h and 95% removal after 84 h. Phosphorus was completely eliminated (100%) in the co-culture system with inoculum ratios of 0.5 and 1.0 after 24 h and in the pure C. vulgaris culture after 36 h. The COD level was greatly reduced in the activated sludge reactor, while, it was increasing in pure C. vulgaris culture after 24 h of incubation. However, COD was almost stabilized after 24 h in the reactors with high R ratios such as 2.0, 5.0, and 10 due to the higher concentration of activated sludge. The growth of C. vulgaris was promoted from 0.03 g/L/d to 0.05 g/L/d in the co-culture of low inoculum ratios such as R = 0.5, implying that there exist an optimum inoculum ratio in the co-culture system in order to achieve efficient removal of nutrients. [ABSTRACT FROM AUTHOR]

The bioconversion of biogas to biomethane coupled to centrate treatment was evaluated in an outdoors pilot scale high rate algal pond interconnected to an external CO 2 -H 2 S absorption column (AC) via settled broth recirculation. CO 2 -removal efficiencies ranged from 50 to 95% depending on the alkalinity of the cultivation broth and environmental conditions, while a complete H 2 S removal was achieved regardless of the operational conditions. A maximum CH 4 concentration of 94% with a limited O 2 and N 2 stripping was recorded in the upgraded biogas at recycling liquid/biogas ratios in the AC of 1 and 2. Process operation at a constant biomass productivity of 15 g m −2 d −1 and the minimization of effluent generation supported high carbon and nutrient recoveries in the harvested biomass (C = 66 ± 8%, N = 54 ± 18%, P ≈ 100% and S = 16 ± 3%). Finally, a low diversity in the structure of the microalgae population was promoted by the environmental and operational conditions imposed. [ABSTRACT FROM AUTHOR]

A shortcut nitrogen removal process was investigated for treatment of high ammonium strength wastewater using an algal-bacterial consortium in photo-sequencing batch reactors (PSBRs). In this process, algae provide oxygen for nitritation during the light period, while denitritation takes place during the dark (anoxic) period, reducing overall energy and chemical requirements. Two PSBRs were operated at different solids retention times (SRTs) and fed with a high ammonium concentration wastewater (264 mg NH4+ N L-1), with a '12 hour on, 12 hour off' light cycle, and an average surface light intensity of 84 µmol m-2 s-1. High total inorganic nitrogen removal efficiencies (~95%) and good biomass settleability (sludge volume index 53-58 mL g-1) were observed in both PSBRs. Higher biomass density was observed at higher SRT, resulting in greater light attenuation and less oxygen production. A mathematical model was developed to describe the algal-bacterial interactions, which was based on Activated Sludge Model No. 3, modified to include algal processes. Model predictions fit the experimental data well. This research also proposes an innovative holistic approach to water and energy recovery. Wastewater can be effectively treated in an anaerobic digester, generating energy from biogas, and later post-treated using an algal-bacterial PSBR, which produces biomass for additional biogas production by co-digestion. [ABSTRACT FROM AUTHOR]

A novel anthraquinone-2,6-disulfonate/MnO x -doped polypyrrole film (AQDS/Mn/PPy) electrode was prepared by one-step electropolymerization method and was used to improve performance of a reversible photo-bioelectrochemical cell (RPBEC). The RPBEC was operated in polarity reversion depended on dark/light reaction of alga Chlorella vulgaris by which sequential decolorization of azo dye and mineralization of decolorization products coupled with bioelectricity generation can be achieved. The results showed that formation of uniform AQDS/Mn/PPy film significantly enhanced electroactive surface area and electrocatalytic activity of carbon electrode. The RPBEC with AQDS/Mn/PPy electrodes demonstrated 77% increases in maximum power and 73% increases in Congo red decolorization rate before polarity reversion, and 198% increases in maximum power and 138% increases in decolorization products mineralization rate after polarity reversion, respectively, compared to the RPBEC with bare electrode. This was resulted from simultaneous dynamics improvement in half-reaction rate of anode and photo-biocathode due to enhanced electron transfer and algal-bacterial biofilm formation. [ABSTRACT FROM AUTHOR]

The potential of an algal-bacterial system consisting of a high rate algal pond (HRAP) interconnected to an absorption column (AC) via recirculation of the cultivation broth for the upgrading of biogas and digestate was investigated. The influence of the gas-liquid flow configuration in the AC on the photosynthetic biogas upgrading process was assessed. AC operation in a co-current configuration enabled to maintain a biomass productivity of 15 g m −2 d −1 , while during counter-current operation biomass productivity decreased to 8.7 ± 0.5 g m −2 d −1 as a result of trace metal limitation. A bio-methane composition complying with most international regulatory limits for injection into natural gas grids was obtained regardless of the gas-liquid flow configuration. Furthermore, the influence of the recycling liquid to biogas flowrate (L/G) ratio on bio-methane quality was assessed under both operational configurations obtaining the best composition at an L/G ratio of 0.5 and co-current flow operation. [ABSTRACT FROM AUTHOR]

Emiliania huxleyi is a model coccolithophore micro-alga that generates vast blooms in the ocean. Bacteria are not considered among the major factors influencing coccolithophore physiology. Here we show through a laboratory model system that the bacterium Phaeobacter inhibens, a well-studied member of the Roseobacter group, intimately interacts with E. huxleyi. While attached to the algal cell, bacteria initially promote algal growth but ultimately kill their algal host. Both algal growth enhancement and algal death are driven by the bacterially-produced phytohormone indole-3-acetic acid. Bacterial production of indole-3-acetic acid and attachment to algae are significantly increased by tryptophan, which is exuded from the algal cell. Algal death triggered by bacteria involves activation of pathways unique to oxidative stress response and programmed cell death. Our observations suggest that bacteria greatly influence the physiology and metabolism of E. huxleyi. Coccolithophore-bacteria interactions should be further studied in the environment to determine whether they impact micro-algal population dynamics on a global scale. [ABSTRACT FROM AUTHOR]

Experiments to re-synthesise lichens so far focused on co-cultures of fungal and algal partners. However, recent studies have revealed that bacterial communities colonise lichens in a stable and host-specific manner. We were therefore interested in testing how lichenised fungi and algae interact with selected bacteria in an experimental setup. We selected the symbiotic system of Schizoxylon albescens and the algal genera Coccomyxa and Trebouxia as a suitable model. We isolated bacterial strains from the naturally occurring bacterial fraction of freshly collected specimens and established tripartite associations under mixed culture experiments. The bacteria belong to Actinobacteria, Firmicutes and Proteobacteria and corresponded to groups already found associated with fungi including lichens. In mixed cultures with Coccomyxa, the fungus formed a characteristic filamentous matrix and tightly contacted the algae; the bacteria distributed in small patches between the algal cells and attached to the cell walls. In mixed cultures with Trebouxia, the fungus did not develop the filamentous matrix, but bacterial cells were observed to be tightly adhering to the fungal hyphae. Our experiments show that this tripartite fungal-algal-bacterial model system can be maintained in culture and can offer multiple opportunities for functional studies based on experiments under controlled conditions in the laboratory. [ABSTRACT FROM AUTHOR]

Microalgal–bacterial interactions are commonly found in marine environments and are well known in diatom cultures maintained in laboratory. These interactions also exert strong effects on bacterial and algal diversity in the oceans. Small green eukaryote algae of the class Mamiellophyceae (Chlorophyta) are ubiquitous and some species, such as Ostreococcus spp., are particularly important in Mediterranean coastal lagoons, and are observed as dominant species during phytoplankton blooms in open sea. Despite this, little is known about the diversity of bacteria that might facilitate or hinder O. tauri growth. We show, using rDNA 16S sequences, that the bacterial community found in O. tauri RCC4221 laboratory cultures is dominated by g-proteobacteria from the Marinobacter genus, regardless of the growth phase of O. tauri RCC4221, the photoperiod used, or the nutrient conditions (limited in nitrogen or phosphorous) tested. Several strains of Marinobacter algicola were detected, all closely related to strains found in association with taxonomically distinct organisms, particularly with dinoflagellates and coccolithophorids. These sequences were more distantly related to M. adhaerens, M. aquaeoli and bacteria usually associated to euglenoids. This is the first time, to our knowledge, that distinct Marinobacter strains have been found to be associated with a green alga in culture. [ABSTRACT FROM AUTHOR]

Bacteria and phages have traditionally been viewed as ‘antagonists’. However, temperate phages can transfer genes, which can broaden their bacterial hosts’ metabolic repertoire, confer or enhance virulence, or eliminate competing organisms, and so enhance bacterial fitness. Recent evidence shows that phages can also promote biofilm formation leading to population-level benefits for their bacterial hosts. Here, we provide a perspective on the ecological and evolutionary consequences for the bacteria interacting with phages, when phage and host interests are aligned. Furthermore, we examine the question whether bacterial hosts can lower immune barriers to phage infection, thereby facilitating infection by beneficial phages. Taking recent evidence together, we suggest that in many cases temperate phages are to be considered as being mutualistic as well as parasitic, at the same time. [ABSTRACT FROM AUTHOR]

The effect of the inoculation of a microalgae-bacteria system on the removal of nutrients and organic matter using municipal, piggery and digestate wastewaters was evaluated. Three conditions for each substrate were evaluated: (1) inoculation with activated sludge and illumination, (2) inoculation with activated sludge without illumination, and (3) inoculation with activated sludge plus a native microalgae consortium under illumination. The illuminated reactors that were inoculated only with activated sludge developed microalgae after 12 operation days. In these reactors, the formation of flocs was observed affecting the sedimentation of the biomass positively. The removal of chemical oxygen demand, ammonium and phosphorous reached 84%, 65% and 77%, respectively. [ABSTRACT FROM AUTHOR]

A remediation system for the removal of nitrogen from landfill leachate by a mixed algae-bacteria culture was investigated. This system was designed to treat leachate with minimal inputs and maintenance requirements, andwas operated as an open semi-batch reactor in an urban greenhouse. The results of this study showed a maximumnitrogen removal rate of 9.18 mg N/(L·day) and maximum biomass density of 480 mg biomass/L. The ammonia removal rates of this culture increased with increasing initial ammonia concentration; maximum nitrogen removal occurred at an ammonia concentration of 80mg N-NH3/L. At starting ammonia concentrations above 80 mg N-NH3/L a reduction in nitrogen removal was seen; this inhibition is hypothesized to be caused by ammonia toxicity. This inhibiting concentration is considerably higher than that of many other published studies. [ABSTRACT FROM AUTHOR]

Algae and bacteria have coexisted ever since the early stages of evolution. This coevolution has revolutionized life on earth in many aspects. Algae and bacteria together influence ecosystems as varied as deep seas to lichens and represent all conceivable modes of interactions — from mutualism to parasitism. Several studies have shown that algae and bacteria synergistically affect each other's physiology and metabolism, a classic case being algae–roseobacter interaction. These interactions are ubiquitous and define the primary productivity in most ecosystems. In recent years, algae have received much attention for industrial exploitation but their interaction with bacteria is often considered a contamination during commercialization. A few recent studies have shown that bacteria not only enhance algal growth but also help in flocculation, both essential processes in algal biotechnology. Hence, there is a need to understand these interactions from an evolutionary and ecological standpoint, and integrate this understanding for industrial use. Here we reflect on the diversity of such relationships and their associated mechanisms, as well as the habitats that they mutually influence. This review also outlines the role of these interactions in key evolutionary events such as endosymbiosis, besides their ecological role in biogeochemical cycles. Finally, we focus on extending such studies on algal–bacterial interactions to various environmental and bio-technological applications. [ABSTRACT FROM AUTHOR]

Despite their potential impact on phytoplankton dynamics and biogeochemical cycles, biological associations between algae and bacteria are still poorly understood. The aim of the present work was to characterize the influence of bacteria on the growth and function of the dinoflagellate Alexandrium tamarense . Axenic microalgal cultures were inoculated with a microbial community and the resulting cultures were monitored over a 15-month period, in order to allow for the establishment of specific algal–bacterial associations. Algal cells maintained in these new mixed cultures first experienced a period of growth inhibition. After several months, algal growth and cell volume increased, and indicators of photosynthetic function also improved. Our results suggest that community assembly processes facilitated the development of mutualistic relationships between A. tamarense cells and bacteria. These interactions had beneficial effects on the alga that may be only partly explained by mixotrophy of A. tamarense cells. The potential role of organic exudates in the establishment of these algal–bacterial associations is discussed. The present results do not support a role for algal–bacterial interactions in dinoflagellate toxin synthesis. However, variations observed in the toxin profile of A. tamarense cells during culture experiments give new clues for the understanding of biosynthetic pathways of saxitoxin, a potent phycotoxin. [ABSTRACT FROM AUTHOR]

In most high-latitude wetlands, carbon accumulation as peat represents a balance between plant net primary productivity and heterotrophic decomposition. We hypothesized that this assessment of ecosystem metabolism is incomplete as it does not include information on energy inputs from microalgae, which form complex biofilms with heterotrophic micro-organisms on the peat surface., To investigate the potential for algae (and associated exudates) to support heterotrophic metabolism under ambient and elevated nutrient levels, we conducted a factorial enrichment of nutrients (nitrogen and phosphorus) and carbon (glucose) in mesocosms with and without the presence of algae (using light-transparent and dark treatments, respectively) in an Alaskan fen. We measured respiration rates and changes in bacterial biomass to characterize the response of heterotrophic bacteria to our experimental treatments., During incubation assays, algae released up to 38% of their net productivity as exudates and there was a positive relationship between algal production and concentrations of dissolved organic carbon inside mesocosms., Elevated algal productivity in the presence of nutrient enrichment stimulated heterotrophic bacterial respiration and biomass. These responses did not occur with nutrient enrichment in the dark (without algae). The response of bacteria to algae was similar in magnitude to bacterial responses to glucose enrichment., Synthesis. We conclude that bacteria in this boreal fen were primarily limited by labile carbon, and this constraint was alleviated in the presence of elevated algal production. Consequently, algae may facilitate hotspots of microbial activity in northern peatlands, especially in conditions of greater nutrient availability associated with more variable hydrology expected for this region with ongoing climate change. [ABSTRACT FROM AUTHOR]

In planktonic ecosystems, algae and bacteria exhibit complex interrelationships, as algae provide an important organic matter source for microbial growth while microbial metabolism recycles limiting nutrients for algae in a loose commensalism. However, algae and bacteria can also compete for available nutrients if supplies of organic matter are sufficient to satisfy bacterial demand. We developed a stoichiometrically explicit model of bacteria–algae interactions that incorporated realistic assumptions about algal light and nutrient utilization, algal exudation of organic matter, and bacterial processing of organic matter and nutrients. The model makes specific predictions about how the relative balance of algae and bacteria should change in response to varied nutrient and light availability seen in lakes and oceans. The model successfully reproduces published empirical data and indicates that, under moderate nutrient supply, the bacterial percentage of total respiration should be maximal at intermediate light intensity. [ABSTRACT FROM AUTHOR]

Microalgae undertake a wide range of mutualistic interactions with bacteria. Here we consider how transcriptomic, metagenomic and metabolomic approaches have been combined with microbiological and biochemical analyses to expand our understanding of algal–bacterial interactions. Identification of the major bacterial species associated with algae indicates that specific bacterial groups, particularly the alpha-Proteobacteria, are found more frequently, suggesting that these may have the means to initiate and maintain symbiotic relationships. Nutrient exchange is frequently the basis of algal–bacterial mutualism, and as the compounds involved are characterised, evidence is accumulating that these are complex and specific molecules, offering opportunities for signalling processes and regulation rather than merely passive diffusion. At the same time, it is clear that the interactions are not static, but can be initiated and broken in response to environmental and developmental cues. [ABSTRACT FROM AUTHOR]

The influence of TiO 2 nanoparticles (TiO 2 -NPs) (10–50 mg/L) on aerobic granulation of algal–bacterial symbiosis system was investigated by using two identical sequencing batch reactors (SBRs). Although little adverse effect was observed on their nitritation efficiency (98–100% in both reactors), algal–bacterial granules in the control SBR ( R c ) gradually lost stability mainly brought about by algae growth. TiO 2 -NPs addition to R T was found to enhance the granulation process achieving stable and compact algal–bacterial granules with remarkably improved nitratation thus little nitrite accumulation in R T when influent TiO 2 -NPs ⩾ 30 mg/L. Despite almost similar organics and phosphorus removals obtained in both reactors, the stably high nitratation efficiency in addition to much stable granular structure in R T suggests that TiO 2 -NPs addition might be a promising remedy for the long-term operation of algal–bacterial granular system, most probably attributable to the stimulated excretion of extracellular polymeric substances and less filamentous TM7. [ABSTRACT FROM AUTHOR]

In this study, the biodegradation of total acid-extractable organics (TAOs), commonly called naphthenic acids (NAs), was investigated. An indigenous microbial culture containing algae and bacteria was taken from the surface of a tailings pond and incubated over the course of 120 days. The influence of light, oxygen and the presence of indigenous algae and bacteria, and a diatom ( Navicula pelliculosa ) on the TAO removal rate were elucidated. The highest biodegradation rate was observed with bacteria growth only (without light exposure) with a half-life ( t 1/2 ) of 203 days. The algae–bacteria consortium enhanced the detoxification process, however, bacterial biomass played the main role in toxicity reduction. Principal component analysis (PCA) conducted on FT-IR spectra, identified functional groups and bonds (representing potential markers for biotransformation of TAOs) as follows: hydroxyl, carboxyl and amide groups along with C H, aryl H, aryl OH and N H bonds. [ABSTRACT FROM AUTHOR]

Background: The growing concern regarding the use of agricultural land for the production of biomass for food/feed or energy is dictating the search for alternative biomass sources. Photosynthetic microorganisms grown on marginal or deserted land present a promising alternative to the cultivation of energy plants and thereby may dampen the 'food or fuel' dispute. Microalgae offer diverse utilization routes. Results: A two-stage energetic utilization, using a natural mixed population of algae (Chlamydomonas sp. and Scenedesmus sp.) and mutualistic bacteria (primarily Rhizobium sp.), was tested for coupled biohydrogen and biogas production. The microalgal-bacterial biomass generated hydrogen without sulfur deprivation. Algal hydrogen production in the mixed population started earlier but lasted for a shorter period relative to the benchmark approach. The residual biomass after hydrogen production was used for biogas generation and was compared with the biogas production from maize silage. The gas evolved from the microbial biomass was enriched in methane, but the specific gas production was lower than that of maize silage. Sustainable biogas production from the microbial biomass proceeded without noticeable difficulties in continuously stirred fed-batch laboratory-size reactors for an extended period of time. Co-fermentation of the microbial biomass and maize silage improved the biogas production: The metagenomic results indicated that pronounced changes took place in the domain Bacteria, primarily due to the introduction of a considerable bacterial biomass into the system with the substrate; this effect was partially compensated in the case of co-fermentation. The bacteria living in syntrophy with the algae apparently persisted in the anaerobic reactor and predominated in the bacterial population. The Archaea community remained virtually unaffected by the changes in the substrate biomass composition. Conclusion: Through elimination of cost- and labor-demanding sulfur deprivation, sustainable biohydrogen production can be carried out by using microalgae and their mutualistic bacterial partners. The beneficial effect of the mutualistic mixed bacteria in O2 quenching is that the spent algal-bacterial biomass can be further exploited for biogas production. Anaerobic fermentation of the microbial biomass depends on the composition of the biogas-producing microbial community. Co-fermentation of the mixed microbial biomass with maize silage improved the biogas productivity. [ABSTRACT FROM AUTHOR]

Lack of knowledge about how the various drivers of global climate change will interact with multiple stressors already affecting ecosystems is the basis for great uncertainty in projections of future biological change. Despite concerns about the impacts of changes in land use, eutrophication and climate warming in running waters, the interactive effects of these stressors on stream periphyton are largely unknown. We manipulated nutrients (simulating agricultural runoff), deposited fine sediment (simulating agricultural erosion) (two levels each) and water temperature (eight levels, 0-6 °C above ambient) simultaneously in 128 streamside mesocosms. Our aim was to determine the individual and combined effects of the three stressors on the algal and bacterial constituents of the periphyton. All three stressors had pervasive individual effects, but in combination frequently produced synergisms at the population level and antagonisms at the community level. Depending on sediment and nutrient conditions, the effect of raised temperature frequently produced contrasting response patterns, with stronger or opposing effects when one or both stressors were augmented. Thus, warming tended to interact negatively with nutrients or sediment by weakening or reversing positive temperature effects or strengthening negative ones. Five classes of algal growth morphology were all affected in complex ways by raised temperature, suggesting that these measures may prove unreliable in biomonitoring programs in a warming climate. The evenness and diversity of the most abundant bacterial taxa increased with temperature at ambient but not with enriched nutrient levels, indicating that warming coupled with nutrient limitation may lead to a more evenly distributed bacterial community as temperatures rise. Freshwater management decisions that seek to avoid or mitigate the negative effects of agricultural land use on stream periphyton should be informed by knowledge of the interactive effects of multiple stressors in a warming climate. [ABSTRACT FROM AUTHOR]

Highlights: [•] Large gas–liquid interfacial area and instant transfer of reactive species to water. [•] Effective decomposition of taste-and-odor compounds and cyanobacteria algae. [•] Good correlation of the decomposition efficiency to the specific energy input. [Copyright &y& Elsevier]

Highlights: [•] Degrading the thiocyanate and producing lipids were achieved by algal–bacterial culture. [•] Two-mode was sequentially employed: a photoauto- and photoheterotrophic mode. [•] Significant increase of lipids was observed under photoheterotrophic condition. [•] Statistical methodology was used to evaluate the effects of organic substrates on lipid. [Copyright &y& Elsevier]

Highlights: [•] Modified current assay to investigate internalization of C. jejuni by A. castellanii. [•] C. jejuni survives assay independently of A. castellanii. [•] C. jejuni not consistently internalized or protected by A. castellanii. [Copyright &y& Elsevier]

Increasing evidence exists that bacterial communities interact with and shape the biology of algae and that their evolutionary histories are connected. Despite these findings, physiological studies were and still are generally carried out with axenic or at least antibiotic-treated cultures. Here, we argue that considering interactions between algae and associated bacteria is key to understanding their biology and evolution. To deal with the complexity of the resulting 'holobiont' system, a metabolism-centred approach that uses combined metabolic models for algae and associated bacteria is proposed. We believe that these models will be valuable tools both to study algal-bacterial interactions and to elucidate processes important for the acclimation of the holobiont to environmental changes. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new algae-bacteria combined system is investigated for nutrient removal. [•] and P are more efficiently removed by the combined system than by the singles. [•] Bacillus licheniformis is a growth-promoting bacterium for Chlorella vulgaris. [•] pH control is crucial in the removal process by the combined system. [•] Algae-bacteria combined system has potential in wastewater treatment. [Copyright &y& Elsevier]

The macroalga Fucus vesiculosus carries a specific community of surface bacteria. To identify chemical compounds that possibly mediate abundance and community composition of algae-associated bacteria, we tested the effect of surface-available algal compounds on bacterial settlement and community composition under field conditions. Compounds on algal thalli were separated from the surface by extraction with organic solvents and investigated on growth inhibition and settlement of bacterial isolates. Based on in vitro data, partially purified extract fractions were then exposed to bacterial colonizers in vivo followed by bacterial enumeration and community analysis. The polar fraction of the algal surface extract revealed a significant profouling effect for Vibrionales, whereas the nonpolar fraction - containing the xanthophyll pigment fucoxanthin and other unidentified nonpolar surface compounds - revealed a significant 80% reduction of surface colonizing bacteria. The analysis of bacterial surface communities by 454 pyrosequencing demonstrated that the antifouling activity of nonpolar algal surface compounds was targeting the abundance of natural bacterial colonizers rather than the relative composition of bacterial members within the community. Moreover, the bacterial community composition on F. vesiculosus was markedly different from artificial control substrates and chemically manipulated experimental treatments, suggesting that other, nonextractable surface features and/or physical properties render algal-specific epiphytic bacterial communities. [ABSTRACT FROM AUTHOR]

Diversity and functional association of bacteria with Eutreptiella sp. was investigated. 16S rDNA analysis of ectobiotic bacteria revealed various lineages of Alphaproteobacteria and abundant Gammaproteobacteria, specifically Marinobacter. Antibiotic treatment yielded axenic cultures, and experiments based on them indicated that ectobiotic bacteria likely provide vitamin B12 and other growth-enhancing factors for the alga. Further, DAPI staining and transmission electron microscopy revealed endobiotic bacteria in the cytoplasm of algal cells. 16S rDNA analysis showed that the bacteria belonged to one species that was most closely related to Rickettsiales endosymbionts of other organisms and phylogenetically affiliated with a new group of aquatic Rickettsiales. Observations from a diel experiment indicated that the endobiotic bacteria reproduced asynchronously with Eutreptiella sp. and had no adverse effects on lipid production (bioenergetics) or growth of the host alga. Our study reveals a diverse microbiome associated with this euglenoid alga, offering a system for studying the roles of algae-bacteria associations. [ABSTRACT FROM AUTHOR]

Alga-bacterium interactions are crucial for aggregate formation and carbon cycling in aquatic systems. To understand the initiation of these interactions, we investigated bacterial Chemotaxis within a bilateral model system. Marinobacter adhaerens HP 15 has been demonstrated to attach to the diatom Thalassiosira weissflogii and induce transparent exopolymeric particle and aggregate formation. M. adhaerens possesses one polar flagellum and is highly motile. Bacterial cells were attracted to diatom cells, as demonstrated by addition of diatom cell homogenate or diatom culture supernatant to soft agar, suggesting that Chemotaxis might be important for the interaction of M. adhaerens with diatoms. Three distinct che-motaxis-associated gene clusters were identified in the genome sequence of M. adhaerens, with the clusters showing significant sequence similarities to those of Pseudomonas aeruginosa PAOl. Mutations in the genes cheA, cheB, chpA, and chpB, which encode histidine kinases and methylesterases and which are putatively involved in either flagellum-associated Chemotaxis or pilus-mediated twitching motility, were generated and mutants with the mutations were phenotypically analyzed. δcheA and δcheB mutants were found to be swimming deficient, and all four mutants were impaired in biofilm formation on abiotic surfaces. Comparison of the HP 15 wild type and its Chemotaxis mutants in cocultures with the diatom revealed that the fraction of bacteria attaching to the diatom decreased significantly for mutants in comparison to that for the wild type. Our results highlight the importance of M. adhaerens Chemotaxis in initiation of its interaction with the diatom. In-depth knowledge of these basic processes in interspecies interactions is pivotal to obtain a systematic understanding of organic matter flux and nutrient cycling in marine ecosystems [ABSTRACT FROM AUTHOR]

Wild populations of brown marine algae (Phaeophyta) provide extensive surfaces to bacteria and epiphytic eukaryotes for colonization. On one hand, various strategies allow kelps prevent frond surface fouling which would retard growth by reducing photosynthesis and increasing pathogenesis. On the other hand, production and release of organic exudates of high energy value, sometimes in association with more or less selective control of settlement of epiphytic strains, allow bacteria to establish surface consortia not leading to macrofouling. Here, we present the analysis of adhesion and biofilm formation of bacterial isolates from the kelp Laminaria digitata and of characterized and referenced marine isolates. When they were grown in flow cell under standard nutrient regimes, all used bacteria, except one, were able to adhere on glass and then develop as biofilms, with different architecture. Then, we evaluated the effect of extracts from undisturbed young Laminaria thalli and from young thalli subjected to oxidative stress elicitation; this latter condition induced the production of defense molecules. We observed increasing or decreasing adhesion depending on the referenced strains, but no effects were observed against strains isolated from L. digitata. Such effects were less observed on biofilms. Our results suggested that L. digitata is able to modulate its bacterial colonization. Finally, mannitol, a regular surface active component of Laminaria exudates was tested individually, and it showed a pronounced increased on one biofilm strain. Results of these experiments are original and can be usefully linked to what we already know on the oxidative halogen metabolism peculiar to Laminaria. Hopefully, we will be able to understand more about the unique relationship that bacteria have been sharing with Laminaria for an estimated one billion years. [ABSTRACT FROM AUTHOR]

The article presents the research into the taxonomic diversity of cyanobacteria and algae, as well as the relationships between these organisms and the habitat conditions of certain water ecosystems varying in origin and location (both rural and urban reservoirs in the Lower Silesia region - Poland). Another issue addressed in the paper is the influence of ecological conditions and the origins of the reservoirs on the structure of phytoplankton. The RDA enabled to identify the most important biological parameters (the biodiversity of cyanobacteria and algae described using the Shannon-Weaver Index) and the physicochemical properties of the studied basins. The results distinguished four groups of basins (I - artificial basins within urban areas; II - old river-beds within urban areas; III - ponds in rural areas; IV - an old river-bed in forest areas). This distinction shows major relevance of the reservoirs' origins and their presence in the landscape. Additional PCA and RDA analyses of the studied basins have shown that the biological parameters are more efficient in diversifying the basins in respect of their origins than the physicochemical parameters. [ABSTRACT FROM AUTHOR]

Many algae are auxotrophs for vitamin B12 (cobalamin), which they need as a cofactor for B12-dependent methionine synthase (METH). Because only prokaryotes can synthesize the cobalamin, they must be the ultimate source of the vitamin. In the laboratory, a direct interaction between algae and heterotrophic bacteria has been shown, with bacteria supplying cobalamin in exchange for fixed carbon. Here we establish a system to study this interaction at the molecular level. In a culture of a B12-dependent green alga Chlamydomonas nivalis, we found a contaminating bacterium, identified by 16S rRNA analysis as Mesorhizobium sp. Using the sequenced strain of M. loti (MAFF303099), we found that it was able to support the growth of B12-dependent Lobomonas rostrata, another green alga, in return for fixed carbon. The two organisms form a stable equilibrium in terms of population numbers, which is maintained over many generations in semi-continuous culture, indicating a degree of regulation. However, addition of either vitamin B12 or a carbon source for the bacteria perturbs the equilibrium, demonstrating that the symbiosis is mutualistic and facultative. Chlamydomonas reinhardtii does not require B12 for growth because it encodes a B12-independent methionine synthase, METE, the gene for which is suppressed by addition of exogenous B12. Co-culturing C. reinhardtii with M. loti also results in reduction of METE expression, demonstrating that the bacterium can deliver the vitamin to this B12-independent alga. We discuss the implications of this for the widespread distribution of cobalamin auxotrophy in the algal kingdom. [ABSTRACT FROM AUTHOR]

Abstract: The impacts of different nutrient additions (N+P, N+P+C, 4N+P, 4N+P+C, N+2P) on the growth of algae and bacteria were studied in a microcosm experiment. Since alkaline phosphatase activity (APA) provides an indication of phosphorus deficiency, the higher value for algal APA in the treatments with excess nitrogen and for bacterial APA in the treatments with excess carbon suggested that, algal and bacterial phosphorus-limited status were induced by abundant nitrogen and carbon input, respectively. Bacterial phosphorus-limited status was weakened due to higher bacterial competition for phosphorus, compared to algae. In comparison with the bacterial and specific bacterial APA, higher values of algal and specific algal APA were found, which showed a gradual increase that coincided with the increase of chlorophyll a concentration. This fact indicated not only a stronger phosphorus demand by algae than by bacteria, but also a complementary relationship for phosphorus demand between algae and bacteria. However, this commensalism could be interfered by glucose input resulting in the decline of chlorophyll a concentration. Furthermore, the correlation between bacterial numbers and chlorophyll a concentration was positive in treatments without carbon and blurry in treatments with carbon. These observations validate a hypothesis that carbon addition can stimulate bacterial growth justifying bacterial nutrient demand, which decreases the availability of nutrients to algae and affects nutrient relationship between algae and bacteria. However, this interference would terminate after algal and bacterial adaption to carbon input. [Copyright &y& Elsevier]

Abstract: The paper deals with microalgae–bacteria interrelationships in the “autotroph–heterotroph” aquatic biotic cycle. Explanations of why and how algal–bacterial ecosystems are formed still remain controversial. The paper presents results of experimental and theoretical investigations of the functioning of the algal–bacterial cenosis (the microalga Chlorella vulgaris and concomitant microflora). The Chlorella microbial community is dominated by representatives of the genus Pseudomonas. Experiments with non-sterile batch cultures of Chlorella on Tamiya medium showed that the biomass of microorganisms increases simultaneously with the increase in microalgal biomass. The microflora of Chlorella can grow on organic substances released by photosynthesizing Chlorella. Microorganisms can also use dying Chlorella cells, i.e. form a “producer–reducer” biocycle. To get a better insight into the cenosis-forming role of microalgae, a mathematical model of the “autotroph–heterotroph” aquatic biotic cycle has been constructed, taking into account the utilization of Chlorella photosynthates and dead cells by microorganisms and the contribution of the components to the nitrogen cycle. A theoretical study showed that the biomass of concomitant bacteria grown on glucose and detritus is larger than the biomass of bacteria utilizing only microalgal photosynthates, which agrees well with the experimental data. [Copyright &y& Elsevier]

This study investigated the symbiotic structure relationship between mixed algae and activated sludge while treating high-load printing and dyeing wastewater under natural light. The effects of hydraulic retention time (HRT) (12 h, 16 h and 20 h) and aeration rate (0.1–0.15, 0.4–0.5 and 0.7–0.8 L/min) on algal–bacterial symbiosis (ABS) and conventional activated sludge (CAS) systems. Experimental results showed that the ABS system exhibited the best removal performance for chemical oxygen demand (COD), ammonia nitrogen (NH4+-N) and total phosphorus (TP), which was increased by 12.5%, 23.1% and 10.5%, respectively, and reduced colour 80 times compared with the printing and dyeing wastewater treatment plant. Algae growth could be promoted under lower dissolved oxygen (DO), and the addition of algae could provide more DO to the ABS system. The particle size distribution of sludge in the ABS system was stable, which guaranteed a stable treatment effect. In addition, the COD and colour could be further degraded under the conditions of no external carbon source and longer HRT. It is expected that the present study will provide a foundation for the practical application of the ABS system, and new insights for the treatment of printing and dyeing wastewater. [ABSTRACT FROM AUTHOR]