Search

Abstract Background Reciprocal exchanges of metabolites between phytoplankton and bacteria influence the fitness of these microorganisms which ultimately shapes the productivity of marine ecosystems. Recent evidence suggests that plant growth-promoting hormones may be key metabolites within mutualistic phytoplankton-bacteria partnerships, but very little is known about the diversity of plant growth-promoting hormones produced by marine bacteria and their specific effects on phytoplankton growth. Here, we aimed to investigate the capacity of marine bacteria to produce 7 plant growth-promoting hormones and the effects of these hormones on Actinocyclus sp. growth. Results We examined the plant growth-promoting hormone synthesis capabilities of 14 bacterial strains that enhance the growth of the common diatom Actinocyclus. Plant growth-promoting hormone biosynthesis was ubiquitous among the bacteria tested. Indeed all 14 strains displayed the genomic potential to synthesise multiple hormones, and mass-spectrometry confirmed that each strain produced at least 6 out of the 7 tested plant growth-promoting hormones. Some of the plant growth-promoting hormones identified here, such as brassinolide and trans-zeatin, have never been reported in marine microorganisms. Importantly, all strains produced the hormone indole-3 acetic acid (IAA) in high concentrations and released it into their surroundings. Furthermore, indole-3 acetic acid extracellular concentrations were positively correlated with the ability of each strain to promote Actinocyclus growth. When inoculated with axenic Actinocyclus cultures, only indole-3 acetic acid and gibberellic acid enhanced the growth of the diatom, with cultures exposed to indole-3 acetic acid exhibiting a two-fold increase in cell numbers. Conclusion Our results reveal that marine bacteria produce a much broader range of plant growth-promoting hormones than previously suspected and that some of these compounds enhance the growth of a marine diatom. These findings suggest plant growth-promoting hormones play a large role in microbial communication and broaden our knowledge of their fuctions in the marine environment. Video Abstract

Summary: Marine diatoms express genes encoding potential phosphate transporter and alkaline phosphatase (APase) under phosphate‐limited (−P) condition. This indicates that diatoms use high‐affinity phosphate uptake system with organic phosphate hydration. The function of molecules playing roles for Pi uptake was determined in this study.Pi uptake and APase activity of two marine diatoms, Phaeodactylum tricornutum and Thalassiosira pseudonana, were monitored during acclimation to −P condition. The transcript levels of Pi transporter were analyzed, and Pi transporters were localized with GFP tagging in diatom cells. KO mutants of plasma membrane solute carrier proteins (SLC34s) or APase were established, and their phenotype was evaluated.Some Na+/Pi transporter candidates, SLC34s in P. tricornutum and T. pseudonana, increased transcript under −P condition. Whole‐cell Pi transport was specifically stimulated by sodium ion but independent of potassium, lithium, or proton. Genome‐editing KO of PtSLC34‐5 and APase (Pt49678) in P. tricornutum was highly inhibitory for Pi uptake, and KO of TpSLC34‐2 was also highly inhibitory for Pi uptake in T. pseudonana.SLC34s and APase were co‐expressed under −P conditions in marine diatoms. SLC34s play a major role in the initial acclimation stage of diatom cells to −P condition and APase plays an increasing role in the prolonged Pi‐starved condition. [ABSTRACT FROM AUTHOR]

The interaction between marine phyto- and bacterioplankton is regulated by multiple environmental and biological factors. Among them, phages as the major regulators of bacterial mortality are considered to have important impacts on algae-associated bacteria and algae-bacteria relationship. However, little is currently known about the actual impact of phages from this perspective. Here, we revealed that phage infection improved the maximum quantum efficiency of photosystem II of Phaeodactylum tricornutum by regulating the associated bacterial community. Specifically, phage infection weakened bacterial abundance and eliminated their negative effects on the diatom. Unexpectedly, the structure of the bacterial community co-cultured with the diatom was not significantly affected, likely because the shaping effect of the diatom on the bacterial community structure can far outcompete or mask the impact of phage infection. Our results established a link between algae, bacteria, and phages, suggesting that phage infection benefits the diatom by regulating the associated bacterial community. [ABSTRACT FROM AUTHOR]

Carbonic anhydrase (CA) is a crucial component for the operation of CO2-concentrating mechanisms (CCMs) in the majority of aquatic photoautotrophs that maintain the global primary production. In the genome of the centric marine diatom, Thalassiosira pseudonana, there are four putative gene sequences that encode θ-type CA, which was a type of CA recently identified in marine diatoms and green algae. In the present study, specific subcellular locations of four θCAs, TpθCA1, TpθCA2, TpθCA3, and TpθCA4 were determined by expressing GFP-fused proteins of these TpθCAs in T. pseudonana. As a result, C-terminal GFP fusion proteins of TpθCA1, TpθCA2, and TpθCA3 were all localized in the chloroplast; TpθCA2 was at the central chloroplast area, and the other two TpθCAs were throughout the chloroplast. Immunogold-labeling transmission electron microscopy was further performed for the transformants expressing TpθCA1:GFP and TpθCA2:GFP with anti-GFP-monoclonal antibody. TpθCA1:GFP was localized in the free stroma area, including the peripheral pyrenoid area. TpθCA2:GFP was clearly located as a lined distribution at the central part of the pyrenoid structure, which was most likely the pyrenoid-penetrating thylakoid. Considering the presence of the sequence encoding the N-terminal thylakoid-targeting domain in the TpθCA2 gene, this localization was likely the lumen of the pyrenoid-penetrating thylakoid. On the other hand, TpθCA4:GFP was localized in the cytoplasm. Transcript analysis of these TpθCAs revealed that TpθCA2 and TpθCA3 were upregulated in atmospheric CO2 (0.04% CO2, LC) levels, while TpθCA1 and TpθCA4 were highly induced under 1% CO2 (HC) condition. The genome-editing knockout (KO) of TpθCA1, by CRISPR/Cas9 nickase, gave a silent phenotype in T. pseudonana under LC–HC conditions, which was in sharp agreement with the case of the previously reported TpθCA3 KO. In sharp contrast, TpθCA2 KO is so far unsuccessful, suggesting a housekeeping role of TpθCA2. The silent phenotype of KO strains of stromal CAs suggests that TpαCA1, TpθCA1, and TpθCA3 may have functional redundancy, but different transcript regulations in response to CO2 of these stromal CAs suggest in part their independent roles. [ABSTRACT FROM AUTHOR]

• Isolation of marine diatom, Amphora sp. with high lipid productivity was achieved. • Biomass and lipid production by Amphora grown in municipal wastewater was evaluated. • FTIR, GCMS and 1H NMR were performed to study the fatty acid methyl ester content. • Microalgae cultivation with wastewater helps to improve the economic viability of biofuel. Municipal wastewater contains a high amount of nutrients, which are suitable to cultivate microalgae. This wastewater is considered a potential nutrient source for microalgae cultivation in order to reduce the manufacturing cost for biodiesel production. The present study was focused on the growth and lipid accumulation of newly isolated marine diatom by using municipal wastewater as a culture medium. This diatom was identified as Amphora sp. RRSE1 based on its morphological and molecular characteristics. The optimal medium consists of 80% municipal wastewater mixed with 20% standard De Walne's medium, at pH 8 was supported on the maximum growth and lipid production. It was observed that the peak concentration of biomass was 17.225 mg/L, corresponding to the productivity of 1.46 mg/L/day. The lipid concentration of the biomass was 10.9 mg/L, which shows the maximum productivity of 0.92 mg/L/day. The highest lipid content of 63.12% was achieved on the 14th day of culture. Moreover, Fourier Transform Infrared Spectroscopy (FTIR) was performed for the qualitative and quantitative analysis of organic and inorganic compounds present in the biomass samples. In addition to that, Gas chromatography and mass spectrometry (GCMS) and 1H NMR analyses were also achieved to study the fatty acid methyl ester on the extracted lipids. This study indicates that the microalga Amphora sp. RRSE1 is capable of utilizing nutrients from municipal wastewater and this strain could be a promising feedstock for biofuel production. Furthermore, the use of municipal wastewater as a supplement in nutrient media can greatly reduce the microalgal production costs. [ABSTRACT FROM AUTHOR]

[Display omitted] • PtNRPS1-OE enhances resistance to SA pollution and its removal efficiency. • High binding affinity of rNRPS1 to SA pollutants confirmed. • MS/MS identifies amino acids binding SA pollutants. • Co-localization analysis elucidates pollutant removal mechanism. The accumulation of the emerging pollutant salicylic acid (SA) in the environment has gained much attention. In this study, overexpression of the non-ribosomal peptide synthase (NRPS) gene, PtNRPS1 in the marine diatom Phaeodactylum tricornutum (PtNRPS1-OE) increased resistance to SA pollutants. It was assumed that the enhanced tolerance was due to the high binding affinity between recombinant PtNRPS1 (rNRPS1) and SA pollutants. Moreover, tandem mass spectrometry analysis determined the amino acids that participated in the covalently binding of SA. The removal efficiency of SA pollutants by PtNRPS1-OE cells was found to be markedly elevated. The mechanism underlying the removal of SA and 5-substituted SA (5-sSA) was proposed, following the co-localization analysis of rNRPS1 and SA. The purpose of this study was not about using PtNRPS1 as an enzyme to catalyze the synthesis of metabolite. Rather, it explored the possibility of using PtNRPS1 to remove pollutants, which further improves practical feasibility of microalgae-mediated bioremediation. [ABSTRACT FROM AUTHOR]

Highly efficient, economic feasible and environmentally friendly adsorbents have been a research hotspot for Cd(Ⅱ) sequestration. In this study, various nonliving marine diatom biomass were prepared for Cd(Ⅱ) removal. The Cd(Ⅱ) adsorption properties of the diatom biomass was unveiled by adsorption kinetic, isotherm and thermodynamic analysis, and the adsorption mechanism was revealed using spectrometric identification methods. Results suggested that nonliving marine diatom biomass (Chaetoceros, Nitzschia, and Thalassiosira sp.) could efficiently remove Cd(Ⅱ) from aqueous solution, with nonliving Nitzschia possessing the highest adsorption capacity. The adsorption capacity of nonliving Nitzschia was 289–430 mg g−1 (288–308 K) in the absence of ionic competition and under low turbidity conditions, which was much higher than that of most of adsorbents of great concern. The kinetic, isotherm and thermodynamic analysis suggested the adsorption of Cd(Ⅱ) was a spontaneous, endothermic and chemisorption involved process. Moreover, inorganic salts and turbidity showed negative effects on Cd(Ⅱ) adsorption, whereas humic acid showed a positive effect. Adsorption mechanism analysis demonstrated that amine and pyrrolic nitrogen groups were responsible for Cd(Ⅱ) adsorption. It is also worth noting that organics leaching during adsorption would also affect chemical bonds distribution on the biomass, which should be taken into account when elucidating the heavy metal adsorption mechanism of bio-adsorbents.

The aim of this study was to examine the effect of positively charged (amine-modified) and negatively charged (carboxyl-modified) polystyrene nanoplastics (PS NPs) on the nanostructural, nanomechanical, and antioxidant responses of the marine diatom Cylindrotheca closterium. The results showed that both types of PS NPs, regardless of surface charge, significantly inhibited the growth of C. closterium during short-term exposure (3 and 4 days). However, longer exposure (14 days) to both PS NPs types did not significantly inhibit growth, which might be related to the detoxifying effect of the microalgal extracellular polymers (EPS) and the higher cell abundance per PS NPs concentration. The exposure of C. closterium to both types of PS NPs at concentrations above the corresponding concentrations that resulted in a 50% reduction of growth (EC50) demonstrated phytotoxic effects, mainly due to the excessive production of reactive oxygen species, resulting in increased oxidative damage to lipids and changes to antioxidant enzyme activities. Diatoms exposed to nanoplastics also showed a significant decrease in cell wall rigidity, which could make the cells more vulnerable. Atomic force microscopy images showed that positively charged PS NPs were mainly adsorbed on the cell surface, while both types of PS NPs were incorporated into the EPS that serves to protect the cells. Since microalgal EPS are an important food source for phytoplankton grazers and higher trophic levels, the incorporation of NPs into the EPS and interactions with the cell walls themselves may pose a major threat to marine microalgae and higher trophic levels and, consequently, to the health and stability of the marine ecosystem. [ABSTRACT FROM AUTHOR]

In this study, we investigated cell physiological and biochemical responses to copper (Cu) accumulation in the marine diatom Phaeodactylum tricornutum under different nitrogen (N) and phosphorus (P) conditions. Cells with sufficient N and P (+N+P) showed the highest total Cu concentrations and displayed a higher metal-tolerance ability. In the +N+P treatments, 36.5% of dissolved Cu was adsorbed on the frustules (cell walls), 54.9% was occluded in organelles, and 8.6% was in the soluble fraction. In comparison, cells with N and/or P shortages (+N−P, −N+P, and −N−P) adsorbed 10.8–13.1% of the total Cu onto their cell walls, 74.5–80% was occluded in organelles, and 9.2–12.4% was in the soluble fraction. The Cu2+ influx on the +N+P cell wall was faster due to sufficient metal ligands on the cell walls and up-regulated metal-related transporters. A significant increase in protein content occurred under N and/or P shortages, which was accompanied by the inhibition of the antioxidative enzymatic system and cell membrane damage. Our findings indicate that N and P play an important role in both Cu adsorption (cell surface) and uptake (intracellular), and they provide multifaceted evidence of the Cu acquisition mechanism in P. tricornutum under different macronutrient conditions.

The present study was conducted to determine the possible usage of dried Schizochytrium limacinum as a replacement of Arthrospira maxima in a ration of the adult freshwater mussel (Unio crassus). The experimental diets were prepared with the different concentrations of protein-rich green freshwater algae A. maxima and docosahexaenoic acid (DHA)-rich diatom S. limacinum. Combinations were done by replacing A. maxima with 0%, 30%, 70%, and 100% of dried S. limacinum then named AM100, AM70, AM30, and AM0, respectively. These diets were used to feed 180 individuals (15 mussels/tank) of U. crassus in 12 independent glass (4 groups and 3 replicates) tanks. Live weight gain, shell dimensions, biochemical compositions, and fatty acid contents of U. crassus from whole tissue were examined before and after 30 days of feeding trial. The live weight gain was significantly higher in the AM100 (1.66 ± 1.32 g, 5.00 ± 3.95%) and AM70 (1.32 ± 0.83 g, 4.05 ± 2.56%) groups than in the (0.06 ± 1.91 g, 0.31 ± 5.73%) and AM0 (− 0.17 ± 0.61 g, − 0.52 ± 1.84%) groups. We were able to detect increasing levels of DHA in the U. crassus tissues, while the given ratios of S. limacinum were increased in the diet. The results showed that S. limacinum was digested by adult U. crassus to some extent and DHA was retained in the mussel tissue. These results showed that the dependence on live algae can be decreased in the conservation effort of U. crassus by using S. limacinum in a ration. [ABSTRACT FROM AUTHOR]

Marine diatom-infecting DNA/RNA viruses (DI DNA/RNAVs) are of broad interest in basic and applied research on diatoms. However, the mechanisms that underly viral gene expression and its regulation in host diatoms have not been fully elucidated. In silico analysis of DI DNAV genomes revealed the presence of four putative open reading frames (ORFs), including the replication-associated protein (VP3) gene, the structural protein (VP2) gene, and genes of unknown function (the VP1 gene and the VP4 gene). In this study, we analyzed the expression of the viral ORF genes in three combinations of DI DNAVs and host diatoms. RT–PCR analysis was performed to determine the temporal expression pattern of the viral ORF genes in infected host diatoms. Compared with the VP2 and VP3 genes, the VP1 and VP4 genes exhibited increased levels of expression after infection. Furthermore, we characterized the promoter activities of the putative promoter regions in the four ORF genes. The activity of the promoter derived from the VP4 gene might be the highest among these genes. The consensus sequences among the potential promoter regions of the ORF genes were analyzed using consensus motif-finding algorithms and multiple sequence alignment programs. Some consensus sequences were found among the potential promoter regions of the ORF genes. The expression of the VP4 gene induced by strong promoter activity in the early stage of infection may be important for the viral life cycle. These findings may help researchers determine the mechanism of DI DNA/RNAVs gene expression in host diatoms and during viral infection. [Display omitted] • The expression of ORF genes of diatom-infecting viruses within hosts was analyzed. • The VP1 and VP4 genes were expressed immediately after inoculation. • The promoter of the VP4 gene exhibits high-level promoter activity. • VP4 may be important for the viral life cycle. • The promoter of the VP4 gene will do for the metabolic engineering of diatoms. [ABSTRACT FROM AUTHOR]

Although diatoms colonize a vast diversity of immersed hard-surfaced objects and organisms, many diatom species, and sometimes entire genera, show a clear preference towards a particular type of substratum. Studies of animal-associated diatoms indicate that some epizoic forms may require this specific habitat to thrive, and new diatom taxa are expected to be found on as yet unexplored animal hosts. The current study is the first to investigate the diatom flora of sea snakes. Three museum specimens of yellow-bellied sea snakes (Hydrophis platurus) collected over a period of 23 years from the south-eastern coast of South Africa were examined for their diatom flora. Diatoms were abundant on the sea snakes, but communities were composed of only a few species. A previously undescribed species of Nagumoea contributed over 99% of the total diatom assemblage on both the sea snake skin and sea-snake-associated barnacles (Octolasmis sp.). This diatom dominant is described here as Nagumoea hydrophicola sp. nov., based on detailed observations of its frustule ultrastructure using light and scanning electron microscopy. The species is most similar to N. serrata, sharing a similar valvocopula morphology with two rows of pores. However, it can be distinguished from all currently known congeners by its lanceolate central area, short distal raphe endings not reaching the valve mantle, and doubly perforated abvalvar girdle bands. Environmental preferences of the new species are discussed in the context of its host's biology. [ABSTRACT FROM AUTHOR]

Pseudo-nitzschia is a cosmopolitan marine diatom which can cause the poisoning of humans, marine mammals, and birds through the production of the neurotoxin domoic acid and subsequent contamination of the marine food web. Severe poisoning events are induced when environmental conditions allow: (1) the rapid proliferation ('bloom') of resident toxic species of Pseudo-nitzschia, and/or (2) their enhanced toxin production, and (3) the conveyance of the toxin into prey items. The introduction of domoic acid into the food web was recognized as a public health concern along the coast of California following a Pseudo-nitzschia bloom and seabird mortality event in the Monterey Bay area in 1991, and blooms of Pseudo-nitzschia have since been observed in the region with regularity. Since the recognition of the public health concern posed by these recurrent harmful algal bloom (HAB) events, the California Department of Public Health (CDPH) has been charged with protecting the public from domoic acid intoxication through the Preharvest Shellfish Protection and Marine Biotoxin Monitoring Program. This regulatory program (1) conducts, surveys, classifies and monitors commercial shellfish growing areas, and (2) monitors numerous points along the California coastline for marine biotoxins in shellfish and toxigenic phytoplankton in the waters. While these regulatory efforts have successfully prevented significant injury to public health since they began, they remain relatively inefficient in terms of time, energy, and cost.This thesis begins with an investigation of the environmental factors that contribute to Pseudo-nitzschia bloom formation in Monterey Bay (Chapter 1). The identification of nitrate and river discharge as seasonal bloom factors motivated an explicit evaluation and contextualization of river nitrate loading within the 'upwelling-dominated' region of Monterey Bay (Chapter 2). Finally, a new monitoring technology, Solid Phase Adsorption Toxin Tracking (SPATT), is presented, developed primarily for use by public health managers for more effective and efficient monitoring of domoic acid, the toxin produced by Pseudo-nitzschia and the ultimate cause for concern (Chapter 3, with addendum).

Carbonic anhydrases (CAs) are ubiquitous metalloenzymes, which started to be investigated in detail in pathogenic, as well as non-pathogenic species since their pivotal role is to accelerate the physiological CO2 hydration/dehydration reaction significantly. Here, we propose the marine unicellular diatom Phaeodactylum tricornutum as a model organism for testing the membrane penetrability of CA inhibitors (CAIs). Seven inhibitors belonging to the sulphonamide type and possessing a diverse scaffold have been explored for their in vitro inhibition of the whole diatom CAs and the in vivo inhibitory effect on the growth of P. tricornutum. Interesting, inhibition of growth was observed, in vivo, demonstrating that this diatom is a good model for testing the cell wall penetrability of this class of pharmacological agents. Considering that many pathogens are difficult and dangerous to grow in the laboratory, the growth inhibition of P. tricornutum with different such CAIs may be subsequently used to design inhibition studies of CAs from pathogenic organisms.

The impact of the heavy metal cadmium on the lightly silicified marine diatom Cylindrotheca closterium was studied with regard to growth dynamics, organic matter production and morphological characteristics. C. closterium cultures were able to sustain positive growth in the tested range of 0–1000 μg Cd l–1 with a significant decrease in specific growth rate in the exponential growth phase at the highest tested Cd concentration. The concentrations of both dissolved (DOCcell) and particulate organic carbon per cell (POCcell) in C. closterium cultures exposed to 500 and 1000 µg l–1 Cd more than doubled compared with the control culture. Enhanced organic matter production as a feedback response to Cd exposure may thus contribute to cell detoxification, supported by the electrochemical data showing that Cd was not significantly accumulated by or associated with diatom cells except for the culture exposed to 1000 μg Cd l–1. In order to gain more insight into the effects of cadmium on diatom morphological features, the cell surface of C. closterium was characterized at the nanoscale on a single cell level using atomic force microscopy (AFM). Changes induced by Cd were observed as irregular patterns of silica spheres on more silicified parts of the cell, girdle band and around the raphe. These changes clearly show that beside the physiological response, C. closterium also showed a morphological response which is probably due to the interference of Cd with the diatom biosilification process. This study overall contributes to better understanding of the effects of cadmium on diatoms and shows that morphological characteristics assessed by AFM may be a valuable indicator for metal contamination. [ABSTRACT FROM AUTHOR]

Minidiscus Hasle is a genus of small sized diatoms comprising about eight nanoplanktonic marine species. Renewed interest in this genus has arisen since recent investigations recorded a fairly high contribution of some species to the phytoplankton biomass on a global scale. In Brazil, very few studies have been performed, and only two species of Minidiscus have been reported over the 8500 Km coastline. In this paper, we report five species found in Southeast and South Brazilian waters: Minidiscus alphacrucis sp. nov., M. chilensis, M comicus, M. trioculatus, and M. variabilis (also the variety inornata). One of the tiniest diatom ever described, the new species M. alphacrucis has poroidal areolae, which are organized in radial striae with two rows of poroids, conspicuously limited by the interstriae. Minidiscus alphacrucis is compared with other morphologically similar species. In addition, the world distribution of the extant Minidiscus species is reviewed and discussed. [ABSTRACT FROM AUTHOR]

Fucoxanthin is a specific marine carotenoid with extensive bioactivities. Diatom is considered a potential industrial resource due to its rich fucoxanthin. The focus of commercialization is to establish high-yield strains and related extraction and culture accumulation conditions, but there is still lack of intensive understandings. This study selected the strain of Chaetoceros muelleri from 16 strains of marine diatom culture stock by comparing fucoxanthin content (ranged from 0.03 mg/g to 5.02 mg/g) and extraction efficiency (ranged from 1% to 89.78%). The experiment showed that, first, fucoxanthin changed strongly under different light intensities [low: 50 µmol/(m²⋅s); medium: 100 µmol/ (m²⋅s); high: 200 µmol/(m²⋅s)], the highest content was obtained under low light intensity. Second, fucoxanthin content was higher in red light than in the blue light. Third, the change of fucoxanthin content is closely related with chlorophyll a and β-carotene. Under monochromatic light condition, the content of these photosynthetic pigments increased at late growth stage. These results indicated that strain and light selection can greatly increase the yield of fucoxanthin in the diatom. [ABSTRACT FROM AUTHOR]

Inoculation of axenic diatom monocultures with individual bacterial strains has been used effectively to examine the relationship between bacteria and a diatom host. Both beneficial and harmful effects on diatom fitness have been observed. Yet, diatoms commonly host a consortium of bacteria that could influence their response to perturbation by bacterial inoculations. In this study, diatom cultures with an existing microbiome were inoculated with individual bacterial strains. Strains of two genera of bacteria commonly found associated with diatoms (Alteromonas and Marinobacter) were isolated from a culture of the diatom Chaetoceros sp. KBDT20. To evaluate whether bacterial inoculations can impact the growth, peak abundance, or decline of diatoms with an intact microbiome, individual bacterial strains were inoculated into batch cultures of the original host as well as two non-origin diatom hosts (Chaetoceros sp. KBDT32 and Amphiprora sp. KBDT35). Inoculations were repeated under vitamin-replete and vitamin-deficient conditions to assess whether vitamin concentration modulates the impact of bacterial inoculations on the host. The origin Chaetoceros culture was largely unperturbed by bacterial inoculations. In contrast, non-origin hosts experienced long-term impacts on their growth trajectory, and those impacts were found to be dependent on the concentration of vitamins in the growth medium. For the non-origin Chaetoceros, all positive impacts were observed in vitamin-replete conditions and all negative impacts were observed in vitamin-deficient conditions. Amphiprora was only impacted by inoculation with Marinobacter strains in vitamin-deficient conditions, and the effect was negative. Neither individual bacterial strains nor genera resulted in exclusively beneficial nor detrimental impacts, and the magnitude of effect varied among bacterial strains. This study demonstrates that bacterial inoculations can have long-lasting impacts on the growth trajectory of diatoms with an existing microbiome, that this impact can differ even between congeneric diatoms, and that the impact can be significantly modulated by vitamin concentration.

The marine diatom Gyrosigma sp. was cultured in a medium comprised of inorganic nutrients dissolved in palm oil mill effluent (POME) wastewater. The production of lipids in the biomass was optimized using a statistical design of experiments in combination with the response surface method. The experimental factors were incident light level and initial concentrations of nitrate, phosphate, and silicate in the medium in batch culture. At 25 ± 2 °C, the maximum lipid content in the biomass harvested at the end of a 12-day batch culture was 70.7 ± 6.0% by dry weight for the following values of the experimental factors: an incident light level of 131 μmol photons m−2 s−1, a nitrate concentration of 1.8 mg L−1 (29.0 μM), a phosphate concentration of 6.8 mg L−1 (71.6 μM), and a silicate concentration of 10.1 mg L−1 (132.7 μM). Under the optimized conditions, the maximum dry mass concentration of the diatom was 560 mg L−1 on day 8 of a batch culture, declining to ~409 mg L−1 on day 12. For the 12-day batch operation, the final average productivities of the biomass and the lipids were 34.1 ± 5.5 mg L−1 day−1 and 24.1 ± 0.2 mg L−1 day−1, respectively. The fatty acids in the algal lipids were found to be as follows (%, w/w of total lipids): palmitic acid (48.6%), eicosapentaenoic acid (10.6%), myristic acid (8.1%), stearic acid (8.0%), linoleic acid (7.5%), oleic acid (6.4%), and linolenic acid (5.8%). The response surface model predicted the lipid content in the biomass with a high degree of confidence. [ABSTRACT FROM AUTHOR]

Inoculation of axenic diatom monocultures with individual bacterial strains has been used effectively to examine the relationship between bacteria and a diatom host. Both beneficial and harmful effects on diatom fitness have been observed. Yet, diatoms commonly host a consortium of bacteria that could influence their response to perturbation by bacterial inoculations. In this study, diatom cultures with an existing microbiome were inoculated with individual bacterial strains. Strains of two genera of bacteria commonly found associated with diatoms (Alteromonas and Marinobacter) were isolated from a culture of the diatom Chaetoceros sp. KBDT20. To evaluate whether bacterial inoculations can impact the growth, peak abundance, or decline of diatoms with an intact microbiome, individual bacterial strains were inoculated into batch cultures of the original host as well as two non-origin diatom hosts (Chaetoceros sp. KBDT32 and Amphiprora sp. KBDT35). Inoculations were repeated under vitamin-replete and vitamin-deficient conditions to assess whether vitamin concentration modulates the impact of bacterial inoculations on the host. The origin Chaetoceros culture was largely unperturbed by bacterial inoculations. In contrast, non-origin hosts experienced long-term impacts on their growth trajectory, and those impacts were found to be dependent on the concentration of vitamins in the growth medium. For the non-origin Chaetoceros, all positive impacts were observed in vitamin-replete conditions and all negative impacts were observed in vitamindeficient conditions. Amphiprora was only impacted by inoculation with Marinobacter strains in vitamin-deficient conditions, and the effect was negative. Neither individual bacterial strains nor genera resulted in exclusively beneficial nor detrimental impacts, and the magnitude of effect varied among bacterial strains. This study demonstrates that bacterial inoculations can have long-lasting impacts on the growth trajectory of diatoms with an existing microbiome, that this impact can differ even between congeneric diatoms, and that the impact can be significantly modulated by vitamin concentration. [ABSTRACT FROM AUTHOR]

Carbonic anhydrases (CAs) are ubiquitous metalloenzymes, which started to be investigated in detail in pathogenic, as well as non-pathogenic species since their pivotal role is to accelerate the physiological CO2 hydration/dehydration reaction significantly. Here, we propose the marine unicellular diatom Phaeodactylum tricornutum as a model organism for testing the membrane penetrability of CA inhibitors (CAIs). Seven inhibitors belonging to the sulphonamide type and possessing a diverse scaffold have been explored for their in vitro inhibition of the whole diatom CAs and the in vivo inhibitory effect on the growth of P. tricornutum. Interesting, inhibition of growth was observed, in vivo, demonstrating that this diatom is a good model for testing the cell wall penetrability of this class of pharmacological agents. Considering that many pathogens are difficult and dangerous to grow in the laboratory, the growth inhibition of P. tricornutum with different such CAIs may be subsequently used to design inhibition studies of CAs from pathogenic organisms. [ABSTRACT FROM AUTHOR]

The diatom genus Proschkinia is a common element of biofilms covering diverse substrata in saline inland or shallow coastal environments. It can be distinguished from other naviculoid taxa by its lanceolate valves with a fistula located within the central area and numerous open girdle bands with a U-shaped cross-section and a single row of perforations on the internal side of the fold. Despite this distinct morphology, frustules of Proschkinia are typically weakly silicified and often overlooked when cleaned diatom material is analysed. The current paper describes six new species of Proschkinia: P. browderiana sp. nov., P. lacrimula sp. nov., P. maluszekiana sp. nov., P. sulcata sp. nov., P. torquata sp. nov. and P. vergostriata sp. nov., found in numerous samples of marine organisms, such as sea turtles (including sea turtle museum specimens), sea turtle-associated barnacles and seagrass from across the three oceans. Some of the newly described taxa were found on multiple individuals belonging to different sea turtle species, whereas others were in samples collected from different continents. Molecular phylogenetic analysis indicated that examined Proschkinia strains formed a monophyletic clade, sister to Fistulifera. [ABSTRACT FROM AUTHOR]

Potential production of fucoxanthin from a marine diatom (Chaetoceros sp.) isolated from the Pranburi River mouth, Gulf of Thailand was investigated. Results showed that Chaetoceros sp. had a high growth rate. Specific growth rate (µ) was approximately 0.59 day-1, while doubling time was approximately 1.18 days under irradiance of 70 µmol photons·m-2·s-1. Specific growth rate increased with increasing irradiance (µ=1.04 at 140 µmol photons·m-2·s-1). The doubling time of this Chaetoceros sp. was only 0.67 days under irradiance of 140 µmol photons·m-2·s-1. Results from HPLC analysis demonstrated that Chaetoceros sp. gave maximum fucoxanthin production at 7.68 mg·g-1 dry weight or 5.87 pgcell-1 under irradiance of 140 µmol photons·m-2·s-1. Findings implied that the selected Chaetoceros sp. showed higher potential for commercial-scale fucoxanthin production than other seaweeds and diatoms. [ABSTRACT FROM AUTHOR]

Abstract Aluminum (Al) is widespread in the environment including the ocean. The effects of Al on marine organisms have attracted more and more attention in recent years. However, the mechanisms of uptake of Al by marine organisms and the subcellular distribution of Al once assimilated are unknown. Here we report the uptake and subcellular distribution of Al in a marine diatom Thalassiosira weissflogii. Short-term (< 120 min) uptake experiments showed that the Al uptake rate by the diatom was 0.033 ± 0.013 fmol-1 cell-1 min-1 (internalization flux normalized to the exposure Al concentration of 2 µM = 0.034 ± 0.013 nmol m−2 min−1 nM−1). Subcellular fractionation experiments showed that the internalized Al was partitioned to subcellular components in the following order: granules (69 ± 5%) > debris (17 ± 4%) > organelles (12 ± 2%) > heat-stable peptides (HSP) (~2%) > heat-denaturable proteins (HDP) (< 1%), indicating that the majority of intracellular Al was detoxified and stored in inorganic forms. The subcellular distribution of Al in the diatom is different from that of Al in freshwater green algae, in which most of the internalized Al is partitioned to organelles. We also evaluated an artificial seawater-based EDTA rinse solution to remove Al adsorbed on the diatom cell surface. Overall, our study provides new information to understand the mechanisms of uptake of Al by marine diatoms, and the mechanisms responsible for the biological effects (both toxic and beneficial) of Al on the growth of marine phytoplankton, especially diatoms. Graphic Abstract fx1 Highlights • Little is known about the uptake of Al by marine algae and its intracellular fate. • Aluminum can cross the plasmalemma of a marine diatom and accumulate within the alga. • Internalized Al is bound largely as insoluble granules (~ 70%) followed by debris (17%) and organelles (12%). • A seawater-based EDTA rinse solution was tested for removal of Al adsorbed on the algal cell surface. [ABSTRACT FROM AUTHOR]

Minidiscus comicus is a marine centric diatom that has cells with diameters as small as 1.9 μm, which brings it close to the lower limit of diatom cell size and also near to the lower limit of photosynthetic eukaryote cells. One of the questions that this raises is whether the cycle of size decline and size restoration used by most diatoms to time their life cycle can operate in such small cells. In samples collected from the western Mediterranean during 2009, M. comicus cells were found with diameters ranging from 1.9 to 6.0 μm. The larger cells were initial cells after size restoration, and these still had the valves of their parent cells attached, making it possible to determine the diameter of the threshold below which size restoration could be induced (3.1 μm). During size decline, M. comicus cell shape changed from discoid to spherical. This adaptation helped to reduce and even halt the rate of cell volume decrease, allowing cells to continue to use diameter decline as a clocking mechanism. The results show how adaptable the diatom cell wall can be, in spite of its rigid appearance.

Since their discovery, at least 15 diatom viruses have been isolated and characterised using a culture method with two cycles of extinction dilution. However, the method is time consuming and laborious, and it isolates only the most dominant virus in a water sample. Recent studies have suggested inter-species host specificity of diatom viruses. Here, we describe a new protocol to estimate previously unrecognised host-virus relationships. Host cell cultures after inoculation of natural sediment pore water samples were obtained before complete lysis. The proliferated viral genomes in the host cells were amplified using degenerate primer pairs targeting protein replication regions of single-stranded RNA (ssRNA) and single-stranded DNA (ssDNA) viruses, and then sequenced. Diverse ssRNA virus types within known diatom virus group were detected from inoculated Chaetoceros tenuissimus and C. setoensis cells. A previously unknown ssDNA virus type was detected in inoculated C. tenuissimus cells, but not in C. setoensis cells. Despite the possible protocol biases, for example non-specific adsorptions of virions onto the host cells, the present method helps to estimate the viruses infectious to a single host species. Further improvements to this protocol targeting the proliferated viral genomes might reveal unexpected diatom–virus ecological relationships.

Macronutrients such as nitrogen (N), phosphorus (P), and silicon (Si) are essential for the productivity and distribution of diatoms in the ocean. Responses of diatoms to a particular macronutrient deficiency have been investigated, however, we know little about their common or specific responses to different macronutrients. Here, we investigated the physiology and quantitative proteomics of a diatom Thalassiosira pseudonana grown in nutrient-replete, N-, P-, and Si-deficient conditions. Cell growth was ceased in all macronutrient deficient conditions while cell volume and cellular C content under P- and Si-deficiencies increased. Contents of chlorophyll a, protein and cellular N decreased in both N- and P-deficient cells but chlorophyll a and cellular N increased in the Si-deficient cells. Cellular P content increased under N- and Si-deficiencies. Proteins involved in carbon fixation and photorespiration were down-regulated under all macronutrient deficiencies while neutral lipid synthesis and carbohydrate accumulation were enhanced. Photosynthesis, chlorophyll biosynthesis, and protein biosynthesis were down-regulated in both N- and P-deficient cells, while Si transporters, light-harvesting complex proteins, chloroplastic ATP synthase, plastid transcription and protein synthesis were up-regulated in the Si-deficient cells. Our results provided insights into the common and specific responses of T. pseudonana to different macronutrient deficiencies and identified specific proteins potentially indicating a particular macronutrient deficiency.

Diatoms are a keystone algal group, with diverse cell morphology and a global distribution. The biogeography of morphological, functional, and life-history traits of marine diatoms were investigated in Arctic and Atlantic waters of the Labrador Sea during the spring bloom (2013-2014). In this study, trait-based analysis using community-weighted means showed that low temperatures (< 0°C) in Arctic waters correlated positively with diatom species that have traits such as low temperature optimum growth and the ability to produced ice-binding proteins, highlighting their sea ice origin. High silicate concentrations in Arctic waters, as well as sea ice cover and shallow bathymetry, favoured diatom species that were heavily silicified, colonial and capable of producing resting spores, suggesting that these are important traits for this community. In Atlantic waters, diatom species with large surface area to volume ratios were dominant in deep mixed layers, whilst low silicate to nitrate ratios correlated positively with weakly silicified species. Sharp cell projections, such as processes or spines, were positively correlated with water-column stratification, indicating that these traits promote positive buoyancy for diatom cells. Our trait-based analysis directly links cell morphology and physiology with diatom species distribution, allowing new insights on how this method can potentially be applied to explain ecophysiology and shifting biogeographical distributions in a warming climate.

Carotenoids exert beneficial effects on human health through their excellent antioxidant activity. To increase carotenoid productivity in the marine Pennales Phaeodactylum tricornutum, we genetically engineered the phytoene synthase gene (psy) to improve expression because RNA-sequencing analysis has suggested that the expression level of psy is lower than other enzyme-encoding genes that are involved in the carotenoid biosynthetic pathway. We isolated psy from P. tricornutum, and this gene was fused with the enhanced green fluorescent protein gene to detect psy expression. After transformation using the microparticle bombardment technique, we obtained several P. tricornutum transformants and confirmed psy expression in their plastids. We investigated the amounts of PSY mRNA and carotenoids, such as fucoxanthin and β-carotene, at different growth phases. The introduction of psy increased the fucoxanthin content of a transformants by approximately 1.45-fold relative to the levels in the wild-type diatom. However, some transformants failed to show a significant increase in the carotenoid content relative to that of the wild-type diatom. We also found that the amount of PSY mRNA at log phase might contribute to the increase in carotenoids in the transformants at stationary phase.

Abstract The interactions between metal and phytoplankton are affected by salinity in estuarine environments. While water chemistry is an important factor regulating the metal bioavailability in phytoplankton, the physiological adaptation of the algae cells may also change their intrinsic response to metals. In this work, we tried to interpret the salinity-dependent Cd toxicity in a pennate diatom Nitzchia closterium from a biological side. As with many studies, we observed Cd toxicity to the diatom increased with decreasing salinity. However, changing free Cd ion concentrations may be partly responsible for the enhanced Cd toxicity. Multiple evidences showed that diatom cells acclimated at low salinity had stronger intrinsic Cd adsorption capacity. Salinity significantly affected not only the nanostructures but also the biochemical composition in the cell surface of the diatom. Diatom cells grown at lower salinity had a lower surface potential, higher specific surface area, and more sulfur-containing groups in the cell wall, leading to stronger Cd binding capacity in the cells. Meanwhile, more Si was present as poly-silicic acid when the salinity decreased. The change of Si content and speciation in the cell wall are also considered a major reason for the variations of Cd surface binding. Our study provided new clues for the salinity-dependent metal toxicity in marine diatoms. Highlights • Lower salinity increased Cd toxicity in marine diatom Nitzschia closterium. • Diatoms grown at lower salinity had more negatively charged cell surface and thus had higher Cd adsorption capacity. • The nanostructures, mechanical properties, and chemical composition of the diatom cell surface were affected by salinity. • Lowering the salinity increased the Si content and influenced Si speciation on the diatom cell surface. [ABSTRACT FROM AUTHOR]

Macronutrients such as nitrogen (N), phosphorus (P), and silicon (Si) are essential for the productivity and distribution of diatoms in the ocean. Responses of diatoms to a particular macronutrient deficiency have been investigated, however, we know little about their common or specific responses to different macronutrients. Here, we investigated the physiology and quantitative proteomics of a diatom Thalassiosira pseudonana grown in nutrient-replete, N-, P-, and Si-deficient conditions. Cell growth was ceased in all macronutrient deficient conditions while cell volume and cellular C content under P- and Si-deficiencies increased. Contents of chlorophyll a, protein and cellular N decreased in both N- and P-deficient cells but chlorophyll a and cellular N increased in the Si-deficient cells. Cellular P content increased under N- and Si-deficiencies. Proteins involved in carbon fixation and photorespiration were down-regulated under all macronutrient deficiencies while neutral lipid synthesis and carbohydrate accumulation were enhanced. Photosynthesis, chlorophyll biosynthesis, and protein biosynthesis were down-regulated in both N- and P-deficient cells, while Si transporters, light-harvesting complex proteins, chloroplastic ATP synthase, plastid transcription and protein synthesis were up-regulated in the Si-deficient cells. Our results provided insights into the common and specific responses of T. pseudonana to different macronutrient deficiencies and identified specific proteins potentially indicating a particular macronutrient deficiency. [ABSTRACT FROM AUTHOR]

A new marine benthic diatom, Pleurosira nanjiensis sp. nov., is described from the rocky intertidal zone of the Xiaochaiyu Island of the Nanji Islands in China. Its morphology was examined with light and scanning electron microscopy. Molecular phylogeny was reconstructed based on SSU rRNA and rbcL gene sequences. Pleurosira nanjiensis differs from congeners in possession of a combination of morphological features including the domed valve with broadly lanceolate, elliptical or circular valve outline, two elevated marginal ocelli, two (rarely three) rimportulae, and radiate striae. [ABSTRACT FROM AUTHOR]

The nitrogen (N) and phosphorus (P) loadings in coastal waters have greatly increased due to anthropogenic input. However, the silicate levels have remained stable in the past decades, leading to nutrient status alternating from N limitation to Si limitation. Few studies have examined the effects of such nutrient imbalance on Cd accumulation in marine diatoms. In the present study, we provide multiple lines of evidence that Si limitation reduced the Cd binding capability in the marine diatom Nitzschia closterium . Diatom cells adapted to lower Si exposure had weaker mechanical strength and less negatively charged surfaces. Close examination of the cell surface revealed that Si shortage changed the biochemical composition of the cell surface and decreased the diatom’s silicification ability. The lower density of the silanol groups in the cell wall is the most likely reason for the weaker Cd adsorption ability observed in the Si limited diatom cells. This study demonstrates the significance of Si in controlling the metal accumulation in marine diatoms. [ABSTRACT FROM AUTHOR]

Several populations of a new Craspedostauros species were observed on museum specimens of juvenile green turtle and Kemp’s ridleys collected from Long Island Beach, New York, USA. The new taxon, Craspedostauros alatus Majewska & Ashworth sp. nov., exhibits a distinctive set of morphological features typical of the genus, including cribrate areolae, a stauros narrower than the fascia, multiple doubly perforated girdle bands, and two fore and aft chloroplasts, but clearly differs from all known Craspedostauros species in possessing partially fused proximal helictoglossae forming an internal thickening with a shallow central cavity, distinctive external wing-like silica flaps near the apices, and a combination of valve dimensions and stria density not observed in other taxa. The same taxon was identified in the NCMA culture collection (strain CCMP120), isolated in 1967 from a sample collected from the equatorial upwelling zone in the Pacific Ocean. Nine samples from three sea turtle species were collected from the same location (Long Island Beach). Statistical analyses suggested that the epizoic diatom flora composition was not affected by the collection season but differed among sea turtle species. The most significant difference was observed between the samples with and without C. alatus. Samples with C. alatus were always dominated by Achnanthes elongata and Berkeleya cf. rutilans, while those lacking the new taxon were characterized by remarkably higher contributions of epizoic Poulinea species. This observation suggests that the microhabitat provided by each sea turtle differs among specimens, which may be related to the different stages of biofilm development on the host sea turtle. Additionally, the value of zoological museum collections for epizoic diatom surveys is briefly discussed. [ABSTRACT FROM AUTHOR]

Incorporated aluminum (Al) in diatom biogenic silicon (BSi) by biological behaviors shows a dissolution-inhibition effect for BSi, thus affecting the organic carbon export driven by diatoms. Ocean iron fertilization (OIF) aims to reduce the amount of atmospheric CO 2 by promoting diatom blooms to enhanced the biological pump. However, BSi dissolved in a short time, leading to low efficacy of the carbon export. Considering the key role of incorporated Al in BSi dissolution, it is necessary to investigate the influence of increasing iron concentrations during OIF on Al incorporation of BSi. A lab simulation experiment, whereby Thalassiosira weissflogii was selected as a model marine diatom, was performed to reveal the effects of increasing iron concentrations on Al incorporation to BSi. Microanalyses including focused ion beams (FIB), high-resolution transmission electron microscopy (HRTEM), and high-resolution energy dispersive X-ray spectrometry (EDS) were used to identify the incorporated Al in BSi and evaluate its content. Results showed that increasing the iron concentration in the culture medium increased the cell yields but decreased the relative content of incorporated Al in BSi. The Al decrease resulted in the reduction of its effects in dissolution-habitation of BSi, which most likely also occurred during OIF. Therefore, the coupled Si Al biogeochemical cycle and the export of organic carbon from the surface ocean driven by diatoms would be influenced by the addition of iron during OIF. • Incorporated aluminum (Al) shows a dissolution-inhibition effect in diatom biogenic silica (BSi). • The increased iron (Fe) concentration limited the Al incorporation in BSi. • Increasing Fe concentration decreases the Al/Si ratio of BSi, enhancing the BSi dissolution. [ABSTRACT FROM AUTHOR]