Vertical distribution of epibenthic freshwater cyanobacterial Synechococcus spp. strains depends on their ability for photoprotection

Analysis of Fast Fluorescence Kinetics of a Single Cyanobacterium Trapped in an Optical Microcavity

Photosynthesis is one the most important biological processes on earth, producing life-giving oxygen, and is the basis for a large variety of plant products. Measurable properties of photosynthesis provide information about its biophysical state, and in turn, the physiological conditions of a photoautotrophic organism. For instance, the chlorophyll fluorescence intensity of an intact photosystem is not constant as in the case of a single fluorescent dye in solution but shows temporal changes related to the quantum yield of the photosystem. Commercial photosystem analyzers already use the fluorescence kinetics characteristics of photosystems to infer the viability of organisms under investigation. Here, we provide a novel approach based on an optical Fabry-Pérot microcavity that enables the readout of photosynthetic properties and activity for an individual cyanobacterium. This approach offers a completely new dimension of information, which would normally be lost due to averaging in ensemble measurements obtained from a large population of bacteria.

Phylogenetic and Phenogenetic Diversity of Synechococcus along a Yellow Sea Section Reveal Its Environmental Dependent Distribution and Co-Occurrence Microbial Pattern

Synechococcus is a dominant genus of the coastal phytoplankton with an effective contribution to primary productivity. Here, the phylogenetic and phenogenetic composition of Synechococcus in the coastal Yellow Sea was addressed by sequencing marker gene methods. Meanwhile, its co-occurrence pattern with bacterial and eukaryotic microbes was further investigated based on the construction of networks. The result revealed that Synechococcus abundance ranged from 9.8 × 102 cells mL−1 to 1.6 × 105 cells mL−1, which was significantly correlated to sampling depth and nutrient contents of nitrite, ammonia, and dissolved silicon. A total of eight Synechococcus phylogenetic lineages were detected, of which clade III was dominant in most of the samples. Meanwhile, clade I increased along the water column and even reached a maximum value of 76.13% at 20 m of station B. Phenogenetically, Synechococcus PT3 was always the predominant pigment type across the whole study zone. Only salinity was significantly correlated to the phenogenetic constitution. The networks revealed that Synechococcus co-occurred with 159 prokaryotes, as well as 102 eukaryotes including such possible grazers as Gymnodinium clades and Alveolata. Potential function prediction further showed that microbes co-occurring with Synechococcus were associated with diverse element cycles, but the exact mechanism needed further experimentation to verify. This research promotes exploring regularity in the genomic composition and niche position of Synechococcus in the coastal ecosystem and is significant to further discuss its potential participation in materials circulation and bottom-up effects in microbial food webs.

Effects of elevated pressure on Pseudanabaena galeata Böcher in varying light and dark environments

To understand the effect of the hydrostatic pressure on Pseudanabaena galeata Böcher cells in both stratified and frequently mixed lakes, separate laboratory-scale models were developed. The pressure conditions in the stratified and mixed lakes were simulated in those models, and the variations of the cell and chlorophyll-a (Chl-a) concentration were analyzed. It was observed that an increase in pressure and darkness significantly reduced the cell concentration and pigmentation in P. galeata (p < 0.01, n = 3). After 10 days, the cell concentrations of P. galeata that were grown under conditions of a water depth of 30 m were reduced by 7.0%, per day, while the cell concentration rate after 10 days in atmospheric conditions was increased by 2.53% per day. During the experiment, cells were subjected to the prolonged darkness under 0.3 MPa pressure for 10 days and then exposed to the white light under atmospheric pressure for 5 days. Even after running this cycle for 60 days, 19.5% of the initial cells could survive. This rate exceeded the cell concentration-increasing rate in the control. These findings indicate that P. galeata has an adequate tolerance to pressure and fluctuating light irradiance and that the cells are able to propagate after escaping from those stress conditions.

Application of a spectrofluorimetric tool (bbe BenthoTorch) for monitoring potentially toxic benthic cyanobacteria in rivers

Over the last decade reports of animal poisoning following accidental consumption of neurotoxin-producing benthic cyanobacteria (mainly Phormidium spp.) have increased. There is a need for rapid and cost-effective tools to survey benthic cyanobacteria. In this study we assessed the performance of the BenthoTorch, a fluorometric probe that provides in situ estimations of cyanobacteria, diatoms and green algae biomass in biofilms. Biofilms (n = 288) were analysed from two rivers in France and eight in New Zealand. Correlations between chlorophyll-a measured using the BenthoTorch and spectrophotometry were higher for thin (<2 mm) compared to thick (>2 mm) biofilms (r(2) = 0.58 and 0.27 respectively; p < 0.001). When cyanobacteria represented less than 50% of the total biomass (based on biovolumes), microscopic and BenthoTorch compositional estimations were significantly correlated (r(2) = 0.53, p < 0.001). Conversely, there was no correlation when cyanobacteria exceeded 50% of the total biomass. Under this scenario diatoms were overestimated. Our results suggest that the observed biases occur because the BenthoTorch only measures the upper biofilm layer and it underestimates the biomass of phycoerythrin-containing cyanobacteria. To improve the performance of this sensor and render it a useful tool for a rapid evaluation of benthic cyanobacterial biomass in rivers, we propose that: (i) the algorithms based on the LEDs responses currently available on this tool need revision, (ii) new excitation wavelengths should be included that allow the fingerprints of phycoerythrin-containing cyanobacteria to be discriminated, and (iii) a sensor that penetrates the biofilms is needed to obtain more accurate estimates of cyanobacterial biomass.

Biochemistry and genetics of taste- and odor-producing cyanobacteria

Cyanobacteria are one of the principal sources of volatile organic compounds (VOCs) which cause offensive taste and odor (T&O) in drinking and recreational water, fish, shellfish and other seafood. Although non-toxic to humans, these T&O compounds severely undermine public trust in these commodities, resulting in substantial costs in treatment, and lost revenue to drinking water, aquaculture, food and beverage and tourist/hospitality industries. Mitigation and control have been hindered by the complexity of the communities and processes which produce and modify T&O events, making it difficult to source-track the major producer(s) and the factors governing VOC production and fate. Over the past decade, however, advances in bioinformatics, enzymology, and applied detection technologies have greatly enhanced our understanding of the pathways, the enzymes and the genetic coding for some of the most problematic VOCs produced by cyanobacteria. This has led to the development of tools for rapid and sensitive detection and monitoring for the VOC production at source, and provided the basis for further diagnostics of endogenous and exogenous controls. This review provides an overview of current knowledge of the major cyanobacterial VOCs, the producers, the biochemistry and the genetics and highlight the current applications and further research needs in this area.

Altered levels of LIL3 isoforms in Arabidopsis lead to disturbed pigment-protein assembly and chlorophyll synthesis, chlorotic phenotype and impaired photosynthetic performance

Light-harvesting complex (LHC)-like (LIL) proteins contain two transmembrane helices of which the first bears a chlorophyll (Chl)-binding motif. They are widespread in photosynthetic organisms, but almost nothing is known about their expression and physiological functions. We show that two LIL3 paralogues (LIL3:1 and LIL3:2) in Arabidopsis thaliana are expressed in photosynthetically active tissues and their expression is differentially influenced by light stress. Localization studies demonstrate that both isoforms are associated with subcomplexes of LHC antenna of photosystem II. Transgenic plants with reduced amounts of LIL3:1 exhibited a slightly impaired growth and have reduced Chl and carotenoid contents as compared to wild-type plants. Ectopic overexpression of either paralogue led to a developmentally regulated switch to co-suppression of both LIL3 isoforms, resulting in a circular chlorosis of the leaf rosettes. Chlorotic sectors show severely diminished levels of LIL3 isoforms and other proteins, and thylakoid morphology was changed. Additionally, the levels of enzymes involved in Chl biosynthesis are altered in lil3 mutant plants. Our data support a role of LIL3 paralogues in the regulation of Chl biosynthesis under light stress and under standard growth conditions as well as in a coordinated ligation of newly synthesized and/or rescued Chl molecules to their target apoproteins.

Distribution and ecology of cyanobacteria in the rocky littoral of an english lake district water body, devoke water

Cyanobacteria were sampled along two vertical and two horizontal transects in the littoral of Devoke Water, English Lake District. Profiles of cyanobacterium diversity and abundance showed that both attained a maximum close to the water line, but declined rapidly 20–40 cm above it. The distribution of individual species with height together with species and site ordinations showed that several taxa occurred in well-defined zones. A narrow “black zone” in the supralittoral was colonised mainly by species of Calothrix, Dichothrix and Gloeocapsa with pigmented sheaths. There was no evidence of lateral variation of species around the lake, but the height of the black zone correlated positively with wind exposure. The flora of Devoke Water is that of a base-poor mountain lake with some elements of a lowland, more alkaline water-body.

Low and high doses of UV-B differentially modulate chlorpyrifos-induced alterations in nitrogen metabolism of cyanobacteria

The present study assessed the comparative responses on the specific growth rate, nitrogen metabolism and enzymes associated with nitrogen metabolism in two nitrogen fixing cyanobacteria-Nostoc muscorum and Phormidium foveolarum exposed to two UV-B doses (low; UV-BL: 0.5472kJm(-2) and high; UV-BH: 5.472kJm(-2)) and two doses of the insecticide chlorpyrifos (O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate; low i.e. CPL, 1µgml(-1) and high i.e. CPH, 2µgml(-1)) singly and in combination. The specific growth rate, NO3(-) and NO2(-) uptake, nitrate assimilating enzymes - nitrate reductase and nitrite reductase and ammonium assimilating enzymes - glutamine synthetase and glutamate synthase were severely affected when treated either with CPH or/and UV-BH while glutamate dehydrogenase exhibited a stimulatory response. CPL also reduced all the measured parameters (except GDH activity) after 24h, however, a stimulatory effect was observed after 72h due to an increase in nitrogen metabolism (and other antioxidant) enzymes during this period. UV-BL did not cause significant alteration in the studied parameters while in combination with CP doses, it either alleviated the inhibitory effects or further enhanced the CPL induced activities of these enzymes (except GDH). Overall results indicate the resistant nature of P. foveolarum against the inhibitory doses of UV-B and chlorpyrifos in comparison to N. muscorum.

Tolerance of soil algae and cyanobacteria to drought stress

Tolerance to drought stress in soil crust microorganisms is essential for exploiting suitable organisms for restoring soil. In this study, the responses to drought stress of two drought-tolerant species, a green alga and a cyanobacterium, were compared with those of two non-tolerant green algae. In response to drought stress, induced by treatment with polyethylene glycol, the intracellular proline levels increased and were associated with increases in malondialdehye, pigment contents, and enzyme activities such as superoxide dismutase (SOD) and peroxidase (POD). Our results suggest that tolerance to drought stress could be indicated by the intracellular levels of proline, SOD, and carotenoids. This study provides insights into the drought physiology of the photosynthetic microorganisms and suggests that Leptolyngbya boryana and Chlorella vulgaris are suitable pioneer organisms for soil restoration.

Differential effect of UV-B radiation on growth, oxidative stress and ascorbate-glutathione cycle in two cyanobacteria under copper toxicity

Effects of low (UV-B(L); 0.1 μmol m(-2) s(-1)) and high (UV-B(H); 1.0 μmol m(-2) s(-1)) fluence rates of UV-B radiation on growth, oxidative stress and ascorbate-glutathione cycle (AsA-GSH cycle) were investigated in two cyanobacteria viz. Phormidium foveolarum and Nostoc muscorum under copper (2 and 5 μM) toxicity after 24 and 72 h of experiments. Cu at 2 and 5 μM and UV-B(H) irradiation decreased growth in both the organisms and the effect was more pronounced in N. muscorum. Superoxide radical (SOR) and hydrogen peroxide (H(2)O(2)) productions were significantly enhanced by Cu and UV-B(H) which was accompanied by accelerated lipid peroxidation (malondialdehyde; MDA) and protein oxidation (reactive carbonyl groups; RCG). The components of AsA-GSH cycle, i.e. ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascobate reductase (MDHAR) and dehydroascorbate reductase (DHAR) activities as well as total ascorbate and glutathione contents and their reduced/oxidized ratios were decreased considerably by Cu and UV-B(H). Further, combined treatments of Cu and UV-B(H) exacerbated damaging effects in both the cyanobacteria. Unlike UV-B(H), UV-B(L) irradiation rather than damaging cyanobacteria caused alleviation in Cu-induced toxicity by down-regulating the levels of SOR, H(2)O(2), MDA and RCG due to enhanced activity of APX, GR, MDHAR and DHAR, and contents of ascorbate and glutathione. Results revealed that UV-B radiation at low fluence rate (UV-B(L)) stimulated protective responses in both the organisms under Cu toxicity while UV-B(H) irradiation caused damage alone as well as together with Cu, and the components of AsA-GSH cycle play significant role in these responses.

Compatibility of ascorbate-glutathione cycle enzymes in cyanobacteria against low and high UV-B exposures, simultaneously exposed to low and high doses of chlorpyrifos

This study deals with the comparative responses of the two cyanobacteria viz. Nostoc muscorum and Phormidium foveolarum against single and combined doses of low (UV-B(L,) 0.1 μmol m(-2) s(-1)) and high (UV-B(H), 1.0 μmol m(-2) s(-1)) fluence rates of ultraviolet-B radiation with low (CP(L), 1 μg ml(-1)) and high (CP(H), 2 μg ml(-1)) doses of the insecticide chlorpyrifos by measuring changes in growth, ascorbate-glutathione cycle enzymes and related metabolites. CP(L) and UV-B(L) both caused lesser increase in ROS but significantly stimulated AsA-GSH cycle enzymes. On the other hand, CP(H) and UV-B(H) posed inhibitory effects by enhancing ROS and inhibiting AsA-GSH cycle enzymes. Inhibitions in CP(H) or UV-B(H) treated samples were significantly prevented when they were supplemented with UV-B(L) and CP(L) (after 72 h), respectively by lowering down ROS and enhancing AsA-GSH enzymes and related metabolites which manifested in terms of improved biomass accumulation.