Phototrophic Biomass Research Articles

Arctic cyanobacterial mat community diversity decreases with latitude across the Canadian Arctic.

Cyanobacterial mats are commonly reported as hotspots of microbial diversity across polar environments. These thick, multilayered microbial communities provide a refuge from extreme environmental conditions, with many species able to grow and coexist despite the low allochthonous nutrient inputs. The visibly dominant phototrophic biomass is dependent on internal nutrient recycling by heterotrophic organisms within the mats; however, the specific contribution of heterotrophic protists remains little explored. In this study, mat community diversity was examined along a latitudinal gradient (55-83°N), spanning subarctic taiga, tundra, polar desert, and the High Arctic ice shelves. The prokaryotic and eukaryotic communities were targeted, respectively, by V4 16S ribosomal RNA (rRNA) and V9 18S rRNA gene amplicon high-throughput sequencing. Prokaryotic and eukaryotic richness decreased, in tandem with decreasing temperatures and shorter seasons of light availability, from the subarctic to the High Arctic. Taxonomy-based annotation of the protist community revealed diverse phototrophic, mixotrophic, and heterotrophic genera in all mat communities, with fewer parasitic taxa in High Arctic communities. Co-occurrence network analysis identified greater heterogeneity in eukaryotic than prokaryotic community structure among cyanobacterial mats across the Canadian Arctic. Our findings highlight the sensitivity of microbial eukaryotes to environmental gradients across northern high latitudes.

Biological soil crusts on agricultural soils of mesic regions promote microbial cross-kingdom co-occurrences and nutrient retention.

Biological soil crusts (biocrusts) are known as biological hotspots on undisturbed, nutrient-poor bare soil surfaces and until now, are mostly observed in (semi-) arid regions but are currently poorly understood in agricultural systems. This is a crucial knowledge gap because managed sites of mesic regions can quickly cover large areas. Thus, we addressed the questions (i) if biocrusts from agricultural sites of mesic regions also increase nutrients and microbial biomass as their (semi-) arid counterparts, and (ii) how microbial community assemblage in those biocrusts is influenced by disturbances like different fertilization and tillage regimes. We compared phototrophic biomass, nutrient concentrations as well as the abundance, diversity and co-occurrence of Archaea, Bacteria, and Fungi in biocrusts and bare soils at a site with low agricultural soil quality. Biocrusts built up significant quantities of phototrophic and microbial biomass and stored more nutrients compared to bare soils independent of the fertilizer applied and the tillage management. Surprisingly, particularly low abundant Actinobacteria were highly connected in the networks of biocrusts. In contrast, Cyanobacteria were rarely connected, which indicates reduced importance within the microbial community of the biocrusts. However, in bare soil networks, Cyanobacteria were the most connected bacterial group and, hence, might play a role in early biocrust formation due to their ability to, e.g., fix nitrogen and thus induce hotspot-like properties. The microbial community composition differed and network complexity was reduced by conventional tillage. Mineral and organic fertilizers led to networks that are more complex with a higher percentage of positive correlations favoring microbe-microbe interactions. Our study demonstrates that biocrusts represent a microbial hotspot on soil surfaces under agricultural use, which may have important implications for sustainable management of such soils in the future.

Diurnal Methane Dynamics in the Cyanobacterial Community of Soda Lake Bitter 1 (Kulunda Steppe, Altai Krai)

Abstract—The diurnal dynamics of methane content in the near-bottom phototrophic biomass of the shallow soda Lake Bitter 1 (Gorchina 1) with a salinity of 30 g/L during the study period was investigated. The community was dominated by filamentous cyanobacteria, although no layered mat was formed. The maximum value of methane content up to 202.4 nmol CH4/cm3 was revealed in the morning hours, which significantly exceeded the night values (28.9–42.8 nmol CH4/cm3). Comparison of data on the content of methane with the relative abundance of cyanobacteria, methanogenic archaea, and methanotrophic bacteria during the twenty-four hours indicated that active processes of the methane cycle in soda lakes occurred not only in the sediments, but also in the near-bottom cyanobacterial communities. Methane content in the biomass of such a community is the result of a balance between the processes of its release by methanogens, consumption by methanotrophic bacteria, and natural degassing. It is assumed that the morning peak of methane content is associated with the release of hydrogen by diazotrophic cyanobacteria, which stimulates the development and activity of hydrogenotrophic methanogens of the genus Methanocalculus.

Biogeochemical Factors of Cs, Sr, U, Pu Immobilization in Bottom Sediments of the Upa River, Located in the Zone of Chernobyl Accident.

Laboratory modeling of Cs, Sr, U, Pu immobilization by phytoplankton of the river Upa, affected after the Chernobyl accident, has been carried out. Certain conditions are selected for strong fixation of radionuclides in bottom sediments due to biogeochemical processes. The process of radionuclide removal from the water phase via precipitation was based on their accumulation by phytoplankton, stimulated by nitrogen and phosphorus sources. After eight days of stimulation, planktonic phototrophic biomass, dominated by cyanobacteria of the genus Planktothrix, appears in the water sample. The effectiveness of U, Pu and Sr purification via their transfer to bottom sediment was observed within one month. The addition of ammonium sulfate and phosphate (Ammophos) led to the activation of sulfate- and iron-reducing bacteria of the genera Desulfobacterota, Desulfotomaculum, Desulfosporomusa, Desulfosporosinus, Thermodesulfobium, Thiomonas, Thiobacillus, Sulfuritallea, Pseudomonas, which form sulphide ferrous precipitates such as pyrite, wurtzite, hydrotroillite, etc., in anaerobic bottom sediments. The biogenic mineral composition of the sediments obtained under laboratory conditions was verified via thermodynamic modeling.

Factors controlling the net ecosystem production of cryoconite on Western Himalayan glaciers

In situ experiments were conducted to determine the net ecosystem production (NEP) in cryoconite holes from the surface of two glaciers (Patsio glacier and Chhota Shigri glacier) in the Western Himalaya during the melt season from August to September 2019. The study aimed to gain an insight into the factors controlling microbial activity on glacier surfaces in this region. A wide range of parameters, including sediment thickness, TOC %, TN %, chlorophyll-a concentration, altitudinal position, and grain size of the cryoconite mineral particles were considered as potential controlling factors. From redundancy analysis, the rate of Respiration observed in cryoconite at Chhota Shigri glacier was predominantly explained by sediment thickness in cryoconite holes (37.1% of the total variance, p < 0.05) with Photosynthesis largely explained by the chlorophyll-a content of the sediment (39.6%, p < 0.05). NEP was explained primarily by the TOC content and sediment thickness in cryoconite holes (35.8% and 22.1% respectively, p < 0.05). The altitudinal position of the cryoconite is strongly correlated with biological activity, suggesting that the stability of cryoconite holes was an important factor driving primary productivity and respiration rate on the surface of Chhota Shigri glacier. We calculated that the number of melt seasons required to accumulate organic carbon in thin sediment layers (< 0.3 cm), based on our measured NEP rates, ranged from 11 to 70 years, indicating that the organic carbon in cryoconite holes largely derives from allochthonous inputs, such as elsewhere on the glacier surface. Phototrophic biomass in the same thin sediment layer of cryoconite was estimated to take atleast 4 months to be produced in situ (with mean estimated time upto 1.7 ± 1.5 years). Organic matter accumulated inside the cryoconite holes both through allochthonous deposition and via biological activity on the glacier surface in these areas may have the potential to export dissolved organic matter and associated nutrients to downstream ecosystems. Given the importance of Himalayan glaciers as a vital water source for millions of people downstream, this study highlights the need for further investigation in aspects of the quantification of in situ produced organic matter and its impact on supraglacial melting in the Himalaya.

Benthic O2 uptake by coral gardens at the Condor seamount (Azores)

Using the non-invasive aquatic eddy covariance technique, we provide the first oxygen (O2) uptake rates from within coral gardens at the Condor seamount (Azores). To explore some of the key drivers of the benthic O2 demand, we obtained benthic images, quantified local hydrodynamics, and estimated phototrophic biomass and deposition dynamics with a long-term moored sediment trap. The coral gardens were dominated by the octocorals Viminella flagellum and Dentomuricea aff. meteor. Daily rates of O2 uptake within 3 targeted coral garden sites (203 to 206 m depth) ranged from 10.0 ± 0.88 to 18.8 ± 2.0 mmol m-2 d-1 (mean ± SE) and were up to 10 times higher than 2 local sandy reference sites within the seamount summit area. The overall mean O2 uptake rate for the garden (13.4 mmol m-2 d-1) was twice the global mean for sedimentary habitats at comparable depths. Combined with parallel ex situ incubations, the results suggest that the octocorals might contribute just ~5% of the observed O2 uptake rates. Deposition of particulate organic matter (POM) assessed by the sediment trap accounted for less than 10% of the O2 demand of the coral garden, implying a substantial POM supply circumventing the deployed traps. Our results expand the database for carbon turnover rates in cold-water coral habitats by including the first estimates from these largely understudied coral gardens.

Shedding light on phototrophic biomass production of Chlorella variabilis: The importance of dissolved CO2, light intensity and duty cycle.

Chlorella variabilis NC64A has recently gathered significant scientific attention due to its unique relationship with the PBCV-1 virus which can potentially simplify downstream processing and reduce associated costs for the bio-production of ethanol or hyaluronan. However, photoautotrophic process optimisation is far from trivial due to the unique characteristics of incident light as a critical process parameter (CPP) and its complex interactions with other CPPs. In the present work, a formalised statistical Design of Experiments (DoE) approach is employed for the multiparametric optimisation of phototrophic growth of C. variabilis in closed, controlled and artificially illuminated batch cultures. Initially, the process design space comprising six CPPs, three related to the quality of incident light and three related to the culture environment, was explored using a fractional factorial screening design. Subsequently, a higher resolution face-centred central composite design involving the three most influential parameters identified from the screening round was used for process optimisation. The optimal growth conditions obtained in the present study (light intensity: 600 µE, spectral composition: white LED, duty cycle: 60%, temperature: 28 °C, pH: 7.1, dissolved inorganic carbon [DIC]: 16.3 mM) resulted in a biomass concentration of 0.749 g/L which represents a 70% increase compared to previously reported efforts.

Solids Residence Time Impacts Carbon Dynamics and Bioenergy Feedstock Potential in Phototrophic Wastewater Treatment Systems.

The use of wastewater-grown microalgae has the potential to reduce the cost of algae-derived biofuels while simultaneously advancing nutrient recovery at water resource recovery facilities (WRRFs). However, a significant barrier has been the low yield and high protein content of phototrophic biomass. Here, we examine the use of solids residence time (SRT) as a selective pressure in driving biochemical composition, yield, biofuel production, and WRRF nutrient management cost. We cultivated mixed phototrophic communities in controlled, laboratory-scale photobioreactors on the local WRRF secondary effluent to link SRT with biochemical composition and techno-economic analysis to yield insights into biomass composition and downstream processing effects on minimum fuel selling price. SRT significantly impacted biochemical composition, with total and dynamic carbohydrates the highest at low SRT (total carbohydrates being 0.60 and 0.32 mg-carbohydrate·mg-protein-1 at SRT 5 and 15 days, respectively). However, there were distinct differences between extant, steady-state performance and intrinsic potential, and longer SRT communities were able to accumulate significant fractions (51% on an ash-free dry weight basis, AFDW %) of carbohydrate reserves under nutrient starvation. Overall, hydrothermal liquefaction (HTL) was found to be more suitable than lipid extraction for hydrotreating (LEH) and combined algal processing (CAP) for conversion of biomass to fuels, but LEH and CAP became more competitive when intrinsic carbon storage potential was realized. The results suggest that the use of algae for nutrient recovery could reduce the nutrient management cost at WRRFs through revenue from algal biofuels, with HTL resulting in a net revenue.

Mapping the in situ microspatial distribution of ice algal biomass through hyperspectral imaging of sea-ice cores

Ice-associated microalgae make a significant seasonal contribution to primary production and biogeochemical cycling in polar regions. However, the distribution of algal cells is driven by strong physicochemical gradients which lead to a degree of microspatial variability in the microbial biomass that is significant, but difficult to quantify. We address this methodological gap by employing a field-deployable hyperspectral scanning and photogrammetric approach to study sea-ice cores. The optical set-up facilitated unsupervised mapping of the vertical and horizontal distribution of phototrophic biomass in sea-ice cores at mm-scale resolution (using chlorophyll a [Chl a] as proxy), and enabled the development of novel spectral indices to be tested against extracted Chl a (R2 ≤ 0.84). The modelled bio-optical relationships were applied to hyperspectral imagery captured both in situ (using an under-ice sliding platform) and ex situ (on the extracted cores) to quantitatively map Chl a in mg m−2 at high-resolution (≤ 2.4 mm). The optical quantification of Chl a on a per-pixel basis represents a step-change in characterising microspatial variation in the distribution of ice-associated algae. This study highlights the need to increase the resolution at which we monitor under-ice biophysical systems, and the emerging capability of hyperspectral imaging technologies to deliver on this research goal.

Enhanced Phototrophic Biomass Productivity through Supply of Hydrogen Gas.

Industrial production of phototrophic microorganisms is often hindered by low productivity due to limited light availability and therefore requires large land areas. This letter demonstrates that supply of hydrogen gas (H2) increases in phototrophic biomass productivity compared to a culture growing on light only. Experiments were performed growing Synechocystis sp. in batch bottles, with and without H2 in the headspace, which were exposed to light intensities of 70 and 100 μmol/m2/s. At 70 μmol/m2/s with H2, the average increase in biomass was 96 mg DW/L/d, whereas at 100 μmol/m2/s without H2, the average increase in biomass was 27 mg DW/L/d. Even at lower light intensity, the addition of H2 tripled the biomass yield compared to growth under light only. Photoreduction and photosynthesis occurred simultaneously, as both H2 consumption and O2 production were measured during biomass growth. Photoreduction used 1.85 mmol of H2 to produce 1.0 mmol of biomass, while photosynthesis produced 1.95 mmol of biomass. After transferring the culture to the dark, growth ceased, also in the presence of H2, showing that both light and H2 were needed for growth. A renewable H2 supply for higher biomass productivity is attractive since the combined efficiency of photovoltaics and electrolysis exceeds the photosynthetic efficiency.

A Novel System for Real-Time, In Situ Monitoring of CO2 Sequestration in Photoautotrophic Biofilms.

Climate change brought about by anthropogenic CO2 emissions has created a critical need for effective CO2 management solutions. Microalgae are well suited to contribute to efforts aimed at addressing this challenge, given their ability to rapidly sequester CO2 coupled with the commercial value of their biomass. Recently, microalgal biofilms have garnered significant attention over the more conventional suspended algal growth systems, since they allow for easier and cheaper biomass harvesting, among other key benefits. However, the path to cost-effectiveness and scaling up is hindered by a need for new tools and methodologies which can help evaluate, and in turn optimize, algal biofilm growth. Presented here is a novel system which facilitates the real-time in situ monitoring of algal biofilm CO2 sequestration. Utilizing a CO2-permeable membrane and a tube-within-a-tube design, the CO2 sequestration monitoring system (CSMS) was able to reliably detect slight changes in algal biofilm CO2 uptake brought about by light–dark cycling, light intensity shifts, and varying amounts of phototrophic biomass. This work presents an approach to advance our understanding of carbon flux in algal biofilms, and a base for potentially useful innovations to optimize, and eventually realize, algae biofilm-based CO2 sequestration.

Development and Diversity of Bacterial Biofilms in Response to Internal Tides, a Case Study off the Coast of Kuwait

Information pertaining to changes in abundance and composition of microbial communities on offshore platforms in relation to changes in environmental conditions due to internal tides are scarce. In this study, artificial substrata were deployed at two locations on a gently sloping seabed off the coast of Kuwait. The abiotic factors at the two sites were recorded spatially and temporally using time-series measurements and continuous turbulence profiling for 13 days. Results showed variations in water density between the upper and deeper waters with the pycnocline undulating between 6 and 15 m depth at both locations. In the water layer beneath the pycnocline, significant current shear due to the internal tides led to higher turbidity coupled with lower dissolved oxygen (DO) and chlorophyll a concentration. The microbiological data showed a significant decrease in the biofilm total biomass, bacterial counts and phototrophic biomass with increase in depth at both locations. The 16S rRNA amplicon sequence non-metric multidimensional (NMDS) scaling analysis revealed that biofouling bacterial communities affected by depth with Alphaproteobacteriaand Bacteroidetes members dominated upper and deeper water at both locations. The based-ordination analysis revealed that biofouling bacterial communities at 3 m were different than at 15 m, with a percentage of shared Operational taxonomic units (OTUs) ≤64% between locations and between depths. Despite the limitations of the study, the power of the employed system is demonstrated in the results that shed light on the significance of prevailing environmental conditions associated with internal tides in shaping the biofilm community in subtropical offshore water systems.

Direct capture and conversion of CO2 from air by growing a cyanobacterial consortium at pH up to 11.2.

Bioenergy with carbon capture and storage (BECCS) is recognized as a potential negative emission technology, needed to keep global warming within safe limits. With current technologies, large‐scale implementation of BECCS would compromise food production. Bioenergy derived from phototrophic microorganisms, with direct capture of CO2 from air, could overcome this challenge and become a sustainable way to realize BECCS.Here we present an alkaline capture and conversion system that combines high atmospheric CO2 transfer rates with high and robust phototrophic biomass productivity (15.2 ± 1.0 g/m 2/d). The system is based on a cyanobacterial consortium, that grows at high alkalinity (0.5 mol/L) and a pH swing between 10.4 and 11.2 during growth and harvest cycles.

The conversion of carbon dioxide from biogas into phototrophic microalgal biomass

This study examines the conversion of CO2 from biogas into microalgal biomass during photosynthetic biogas upgrading. In this process, CO2 is separated from biogas by microalgae, which use the CO2 for photosynthesis. However, the conversion of biogas C into biomass of individual microalgal species is still not fully understood. Therefore, Chlorella vulgaris, Chloroparva pannonica, Synechococcus cedrorum, Synechocystis minuscula and Spirulina laxissima were screened for growth in C-limited media. Secondly, algal biomass was produced in C-limited media at bench-scale. Subsequently, two of these cultures were treated with biogas and the biogas CO2 fixation rates as well as several growth parameters were determined. C. vulgaris and C. pannonica grew well during the screening. During the following biomass production, the cultures grew at rates of 0.42 and 0.48 day−1, respectively. After biogas treatment, the increases in cell growth, biomass and organic carbon of C. vulgaris were significantly higher than in the controls. In contrast, the growth of biogas-treated C. pannonica cultures did not differ from their controls. Thus, the accumulation of biogas C in microalgae is species-specific. The measurements of carbon in biomass of individual algal species proved to be inevitable to determine exact CO2 fixation rates. The CO2 fixation of 1.0 g per formed g C. vulgaris was lower compared to other biogas upgrading studies with photosynthetic microalgae. Ultimately, the introduced species-specific approach helps to prevent the misinterpretation of CO2 fixation rates during photosynthetic biogas upgrading as well as the enhanced biological carbon fixation with phototrophic microalgae.

Light-dependent kinetic model for microalgae experiencing photoacclimation, photodamage, and photodamage repair

Microalgae naturally are exposed to changing light conditions. While a higher light intensity can promote a faster growth rate, it also can cause photodamage that leads to a temporary or semi-permanent decline in growth rate. We developed a model of photosynthetic growth including photoacclimation, reversible photodamage to photosystem II (PSII), and more severe photodamage to photosystem I (PSI). Phototrophic biomass optimizes its photosynthetic machinery to the light intensity it is experiencing; this is captured in the model by photoacclimation, in which photodamage to PSII caused by absorbed light is balanced by repair. However, repair of PSII photodamage can be overwhelmed by increases of light outside the photoacclimated condition, and this leads to severe PSII photodamage that slows the cells' specific growth rate. Furthermore, very large increases in light intensity can lead to photodamage to PSI, which is semi-permanent in that it can take days to weeks to repair. Our model captures all these phenomena. Example model outputs demonstrate the importance of each phenomenon for increases and decreases in light intensity from the photoacclimated state.

Solids Retention Time Dependent Phototrophic Growth and Population Changes in Chemostat Cultivation Using Wastewater

There has been renewed interest in using algae for wastewater polishing and treatment in recent years. Because solids retention time (SRT) is a key design and operating parameter in bioreactor operation, this research determined the effect of SRT on phototrophic growth and microbial population dynamics in continuous-flow chemostat systems. There was a unique feature of phototrophic growth that differed from chemotrophic growth in chemostat. It was found that the phototrophic biomass concentration increased proportionally as SRT increased from 3 to 9 days. Regardless of the change in SRT, a step function model was successfully applied with the predicted phototrophic production rate of 4.5 ± 0.9 g/m(2)·d at the light intensity of 68.5 μmol/m(2)·s. Even though the continuous-flow systems were initially seeded with a 1:1 mixture of green algae and cyanobacteria, Chlorella vulgaris always dominated (98%) in the continuous-flow chemostat systems under steady-state conditions.

Carbon dynamics in highly heterotrophic subarctic thaw ponds

Abstract. Global warming has accelerated the formation of permafrost thaw ponds in several subarctic and arctic regions. These ponds are net heterotrophic as evidenced by their greenhouse gas (GHG) supersaturation levels (CO2 and CH4), and generally receive large terrestrial carbon inputs from the thawing and eroding permafrost. We measured seasonal and vertical variations in the concentration and type of dissolved organic matter (DOM) in five subarctic thaw (thermokarst) ponds in northern Quebec, and explored how environmental gradients influenced heterotrophic and phototrophic biomass and productivity. Late winter DOM had low aromaticity indicating reduced inputs of terrestrial carbon, while the high concentration of dissolved organic carbon (DOC) suggests that some production of non-chromophoric dissolved compounds by the microbial food web took place under the ice cover. Summer DOM had a strong terrestrial signature, but was also characterized with significant inputs of algal-derived carbon, especially at the pond surface. During late winter, bacterial production was low (maximum of 0.8 mg C m−3 d−1) and was largely based on free-living bacterioplankton (58 %). Bacterial production in summer was high (up to 58 mg C m−3 d−1), dominated by particle-attached bacteria (67 %), and strongly correlated with the amount of terrestrial carbon. Primary production was restricted to summer surface waters due to strong light limitation deeper in the water column or in winter. The phototrophic biomass was equal to the heterotrophic biomass, but as the algae were mostly composed of mixotrophic species, most probably they used bacteria rather than solar energy in such shaded ponds. Our results point to a strong heterotrophic energy pathway in these thaw pond ecosystems, where bacterioplankton dominates the production of new carbon biomass in both summer and winter.

Depth-Related Effects on a Meiofaunal Community Dwelling in the Periphyton of a Mesotrophic Lake.

Periphyton is a complex assemblage of micro- and meiofauna embedded in the organic matrix that coats most submerged substrate in the littoral of lakes. The aim of this study was to better understand the consequences of depth-level fluctuation on a periphytic community. The effects of light and wave disturbance on the development of littoral periphyton were evaluated in Lake Erken (Sweden) using an experimental design that combined in situ shading with periphyton depth transfers. Free-living nematodes were a major contributor to the meiofaunal community. Their species composition was therefore used as a proxy to distinguish the contributions of light- and wave-related effects. The periphyton layer was much thicker at a depth of 30 cm than at 200 cm, as indicated by differences in the amounts of organic and phototrophic biomass and meiofaunal and nematode densities. A reduction of the depth-level of periphyton via a transfer from a deep to a shallow location induced rapid positive responses by its algal, meiofaunal, and nematode communities. The slower and weaker negative responses to the reverse transfer were attributed to the potentially higher resilience of periphytic communities to increases in the water level. In the shallow littoral of the lake, shading magnified the effects of phototrophic biomass erosion by waves, as the increased exposure to wave shear stress was not compensated for by an increase in photosynthesis. This finding suggests that benthic primary production will be strongly impeded in the shallow littoral zones of lakes artificially shaded by construction or embankments. However, regardless of the light constraints, an increased exposure to wave action had a generally positive short-term effect on meiofaunal density, by favoring the predominance of species able to anchor themselves to the substrate, especially the Chromadorid nematode Punctodora ratzeburgensis.

Dominance of picophytoplankton in the newly open surface water of the central Arctic Ocean

Picophytoplankton are the main primary producers in oligotrophic oceans. They account for more than 90 % of the phototrophic biomass. Investigations of picophytoplankton in the central Arctic Ocean region are rare because these waters used to be completely covered with sea ice. Large, newly exposed water areas, however, appeared in the sea ice zone during the summer of 2010. This provided the first opportunity to study the Arctic picophytoplankton community in these newly open surface waters. This study focuses on the picophytoplankton in the areas near the Alpha-Mendeleev Ridge and Makarov Basin. Here, HPLC pigment analysis with CHEMTAX was used to study community populations, and 454 pyrosequencing with bioinformatics analysis was used to identify the dominant genera (species). Both Pearson correlation analysis and canonical correlation analysis were used to study the relationships between the community and environmental factors. We found chlorophyll a concentrations were low (0.05–0.39 μg l−1), and picophytoplankton dominated these areas. The abundances of picophytoplankton were 1.58 × 106–9.47 × 106 cells l−1 and made up 44–80 % of the total chlorophyll a. Prasinophytes made up 0–88 % of the picoplanktonic chlorophyll a with the following distributions: diatoms (2–80 %), cyanobacteria (0–20 %), haptophytes (4–14 %), and dinoflagellates (2–11 %). The dominant genera (species) in the picoeukaryotes were Pyramimonas (Pyramimonas gelidicola), Micromonas (Micromonas pusilla), and Phaeocystis. Salinity and latitude were the primary factors controlling the community structure of the picophytoplankton.

Oxygen suppresses light-driven anodic current generation by a mixed phototrophic culture.

This paper describes the detrimental effect of photosynthetically evolved oxygen on anodic current generation in the presence of riboflavin upon illumination of a mixed phototrophic culture enriched from a freshwater pond at +0.6 V vs standard hydrogen electrode. In the presence of riboflavin, the phototrophic biomass in the anodic compartment produced an electrical current in response to light/dark cycles (12 h/12 h) over 12 months of operation, generating a maximum current density of 17.5 mA x m(-2) during the dark phase, whereas a much lower current of approximately 2 mA x m(-2) was generated during illumination. We found that the low current generation under light exposure was caused by high rates of reoxidation of reduced riboflavin by oxygen produced during photosynthesis. Quantification of biomass by fluorescence in situ hybridization images suggested that green algae were predominant in both the anode-based biofilm (55.1%) and the anolyte suspension (87.9%) with the remaining biovolume accounted for by bacteria. Genus-level sequencing analysis revealed that bacteria were dominated by cyanobacterium Leptolyngbia (∼35%), while the prevailing algae were Dictyosphaerium, Coelastrum, and Auxenochlorella. This study offers a key comprehension of mediator sensitivity to reoxidation by dissolved oxygen for improvement of microbial solar cell performance.