Trichodesmium Erythraeum Research Articles

Marine Colloids Boost Nitrogen Fixation in Trichodesmium erythraeum by Photoelectrophy.

Nitrogen fixation by the diazotrophic cyanobacterium Trichodesmium contributes up to 50% of the bioavailable nitrogen in the ocean. N2 fixation by Trichodesmium is limited by the availability of nutrients, such as iron (Fe) and phosphorus (P). Although colloids are ubiquitous in the ocean, the effects of Fe limitation on nitrogen fixation by marine colloids (MC) and the related mechanisms are largely unexplored. In this study, we found that MC exhibit photoelectrochemical properties that boost nitrogen fixation by photoelectrophy in Trichodesmium erythraeum. MC efficiently promote photosynthesis in T. erythraeum, thus enhancing its growth. Photoexcited electrons from MC are directly transferred to the photosynthetic electron transport chain and contribute to nitrogen fixation and ammonia assimilation. Transcriptomic analysis revealed that MC significantly upregulates genes related to the electron transport chain, photosystem, and photosynthesis, which is consistent with elevated photosynthetic capacities (e.g., Fv/Fm and carboxysomes). As a result, MC increase the N2 fixation rate by 67.5-89.3%. Our findings highlight a proof-of-concept electron transfer pathway by which MC boost nitrogen fixation, broadening our knowledge on the role of ubiquitous colloids in marine nitrogen biogeochemistry.

Influence of environmental heterogeneity on the distribution of micro-zooplankton community along the tropical coastal waters

This study mainly focused on the water quality variability and distribution of micro-zooplankton (MZP) along the coastal waters of Tamil Nadu. Dendrogram analysis using water quality data categorized the study area into three regions: North (Chennai), Central (Puducherry), and South (Karaikal). The MZP consists of 40 ciliates and 8 dinoflagellates, with spirotrichea (52.4 %) significantly dominant, followed by dinophyceae (21.1 %), phyllopharyngea (14.7 %), and others (11.8 %). Paracyrtophoron tropicum, a new report in the coastal waters of India, was identified by comparing its molecular phylogeny (18S rRNA accession no: MT500569) to previously reported species. Statistical analysis revealed a positive correlation between P. tropicum abundance and water temperature, PO4, SiO4, TP, Chl-a, and Trichodesmium erythraeum, suggesting that they might not directly control the growth of P. tropicum but indirectly influence it via food availability, i.e., T. erythraeum. However, to understand these species interactions and ecological pathways, further long-term monitoring studies are required.

Acclimation to medium-level non-lethal iron limitation: Adjustment of electron flow around the PSII and metalloprotein expression in Trichodesmium erythraeum IMS101

The aim of this study was to investigate how acclimation to medium-level, long-term, non-lethal iron limitation changes the electron flux around the Photosystem II of the oceanic diazotroph Trichodesmium erythraeum IMS101. Fe availability of about 5× and 100× lower than a replete level, i.e. conditions common in the natural environment of this cyanobacterium, were applied in chemostats. The response of the cells was studied not only in terms of growth, but also mechanistically, measuring the chlorophyll fluorescence of dark-adapted filaments via imaging fluorescence kinetic microscopy (FKM) with 0.3 ms time resolution. Combining these measurements with those of metal binding to proteins via online coupling of metal-free HPLC (size exclusion chromatography SEC) to sector-field ICP-MS allowed to track the fate of the photosystems, together with other metalloproteins. General increase of fluorescence has been observed, with the consequent decrease in the quantum yields φ of the PSII, while the efficiency ψ of the electron flux between PSII and the PSI remained surprisingly unchanged. This indicates the ability of Trichodesmium to cope with a situation that makes assembling the many iron clusters in Photosystem I a particular challenge, as shown by decreasing ratios of Fe to Mg in these proteins. The negative effect of Fe limitation on PSII may also be due to its fast turnover. A broader view was obtained from metalloproteomics via HPLC-ICP-MS, revealing a differential protein expression pattern under iron limitation with a drastic down-regulation especially of iron-containing proteins and some increase in low MW metal-binding complexes.

Aluminum-induced changes in the net carbon fixation and carbon decomposition of a nitrogen-fixing cyanobacterium Trichodesmium erythraeum

Aluminum-induced changes in the net carbon fixation and carbon decomposition of a nitrogen-fixing cyanobacterium Trichodesmium erythraeum

Co‐acquisition of mineral‐bound iron and phosphorus by natural Trichodesmium colonies

AbstractLow iron (Fe) and phosphorus (P) ocean regions are often home to the globally important N2‐fixing cyanobacterium Trichodesmium spp., which are physiologically adapted to Fe/P co‐limitation. Given Trichodesmium's eminent ability to capture particles and the common associations between Fe and P in sediments and aerosols, we hypothesized that mineral bio‐dissolution by Trichodesmium spp. may enable them to co‐acquire Fe and P. We present a new sensitive assay to determine P uptake from particles, utilizing 33P‐labeled ferrihydrite. To validate the method, we examined single natural Trichodesmium thiebautii colonies in a high‐resolution radiotracer ß‐imager, identifying strong colony‐mineral interactions, efficient removal of external 33P‐labeled ferrihydrite, and elevated 33P uptake in the colony core. Next, we determined bulk P uptake rates, comparing natural Red Sea colonies and P‐limited Trichodesmium erythraeum cultures. Uptake rates by natural and cultured Trichodesmium were similar to P release rates from the mineral, suggesting tight coupling between dissolution and uptake. Finally, synthesizing P‐ferrihydrite labeled with either 33P or 55Fe, we probed for Fe/P co‐extraction by common microbial mineral solubilization pathways. Dissolution rates of ferrihydrite were accelerated by exogenous superoxide and strong Fe‐chelator and subsequently enhanced 33P release and uptake by Trichodesmium. Our method and findings can facilitate further Fe/P co‐acquisition studies and highlight the importance of biological mechanisms and microenvironments in controlling bioavailability and nutrient fluxes from particles.

Deoxygenation enhances photosynthetic performance and increases N2 fixation in the marine cyanobacterium Trichodesmium under elevated pCO2.

Effects of changed levels of dissolved O2 and CO2 on marine primary producers are of general concern with respect to ecological effects of ongoing ocean deoxygenation and acidification as well as upwelled seawaters. We investigated the response of the diazotroph Trichodesmium erythraeum IMS 101 after it had acclimated to lowered pO2 (~60 μM O2) and/or elevated pCO2 levels (HC, ~32 μM CO2) for about 20 generations. Our results showed that reduced O2 levels decreased dark respiration significantly, and increased the net photosynthetic rate by 66 and 89% under the ambient (AC, ~13 μM CO2) and the HC, respectively. The reduced pO2 enhanced the N2 fixation rate by ~139% under AC and only by 44% under HC, respectively. The N2 fixation quotient, the ratio of N2 fixed per O2 evolved, increased by 143% when pO2 decreased by 75% under the elevated pCO2. Meanwhile, particulate organic carbon and nitrogen quota increased simultaneously under reduced O2 levels, regardless of the pCO2 treatments. Nevertheless, changed levels of O2 and CO2 did not bring about significant changes in the specific growth rate of the diazotroph. Such inconsistency was attributed to the daytime positive and nighttime negative effects of both lowered pO2 and elevated pCO2 on the energy supply for growth. Our results suggest that Trichodesmium decrease its dark respiration by 5% and increase its N2-fixation by 49% and N2-fixation quotient by 30% under future ocean deoxygenation and acidification with 16% decline of pO2 and 138% rise of pCO2 by the end of this century.

Mechanistic understanding of diazotroph aggregation and sinking: “A rolling tank approach”

AbstractDiazotrophs are ubiquitous in the surface (sub)tropical ocean, where they sustain most new primary production. Several recent studies also report the presence of diverse cyanobacterial diazotrophs in the mesopelagic and bathypelagic ocean, suggesting that they gravitationally sink, potentially supporting organic matter export and the biological carbon pump. Yet, the mechanisms leading to their export are not elucidated. Here, we simulated the sinking of diazotrophs in the water column by using rolling tanks, and measured the aggregation capacity and sinking velocities of four globally distributed strains having different sizes, shapes, and abilities to produce transparent exopolymer particles (TEP): two filamentous diazotrophs (Trichodesmium erythraeum, Calothrix sp.) and two unicellular cyanobacterial diazotrophs (UCYN‐B, Crocosphaera watsonii) and (UCYN‐C, Cyanothece sp.). All diazotrophs tested, regardless their size and shape, were capable of forming aggregates and sunk, albeit at different velocities depending on the aggregation capacity. Overall, UCYN formed aggregates as large as those formed by the filamentous diazotrophs (7000–32,014 μm ESD, equivalent spherical diameter), and sunk at 100–400 m d−1, i.e., at the same velocity as filamentous diazotrophs (92–400 m d−1). Although TEP are generally considered as enhancers of aggregation, TEP did not clearly influence aggregation rates nor sinking velocities during our study. We conclude that diazotrophs may be important contributors to carbon export in the ocean and need to be considered in future studies to improve the accuracy of current regional and global estimates of export.

Winter Bloom of Marine Cyanobacterium, Trichodesmium erythraeum and Its Relation to Environmental Factors

A winter bloom event of Trichodesmium erythraeum was monitored for the first time in the southeastern coastal parts of Bangladesh along the Bay of Bengal. This study presents the brownish to light pinkish bloom that appeared in mid-winter and disappeared abruptly during spring. Heavy blooms of T. erythraeum revealed the highest concentration of 91.47 ± 52.94 × 103 colonies/L in the Bakkhali River Estuary, and 66.93 ± 12.95 × 103 colonies/L in the Maheshkhali Channel of the Bay of Bengal. Three distinct morphological shapes, namely puffs, tufts and asymmetrical colonies, were depicted as major types. Several environmental factors, such as water temperature, salinity, pH, dissolved oxygen, NO3–N and PO4–P, were analyzed to determine their relationship with the occurrence, abundance and bloom formation of T. erythraeum. The abundance of the species showed a positive correlation with salinity and pH while exhibiting a negative correlation with temperature and DO. A cluster analysis revealed a clear indication of T. erythraeum bloom during winter. Thus, the prevalence of the highest density of the bloom in the present study area strongly suggests increased monitoring and research efforts in order to effectively manage or impede harmful algal blooms.

Trichodesmium erythraeum produces a higher photocurrent than other cyanobacterial species in bio-photo electrochemical cells

The increase in world energy consumption, and the worries from potential future disasters that may derive from climate change have stimulated the development of renewable energy technologies. One promising method is the utilization of whole photosynthetic cyanobacterial cells to produce photocurrent in a bio-photo electrochemical cell (BPEC). The photocurrent can be derived from either the respiratory or photosynthetic pathways, via the redox couple NADP+/NADPH mediating cyclic electron transport between photosystem I inside the cells, and the anode. In the past, most studies have utilized the fresh-water cyanobacterium Synechocystis sp. PCC 6803 (Syn). Here, we show that the globally important marine cyanobacterium Trichodesmium erythraeum flourishing in the subtropical oceans can provide improved currents as compared to Syn. We applied 2D-fluorescence measurements to detect the secretion of NADPH and show that the resulting photocurrent production is enhanced by increasing the electrolyte salinity, Further enhancement of the photocurrent can be obtained by the addition of electron mediators such as NAD+, NADP+, cytochrome C, vitamin B1, or potassium ferricyanide. Finally, we produce photocurrent from additional cyanobacterial species: Synechocystis sp. PCC6803, Synechococcus elongatus PCC7942, Acaryochloris marina MBIC 11017, and Spirulina, using their cultivation media as electrolytes for the BPEC.

Seasonal assessment of the trophic status in the coastal waters adjoining Tuticorin harbor in relation to water quality and plankton community in the Gulf of Mannar, India

Seasonal variations in hydrography, trophic status, and plankton community structure were studied along the Tuticorin coastal waters (TCWs) in the Gulf of Mannar (GoM). Samples were collected in 2015 and 2016 to analyze physico-chemical (temperature, pH, salinity, suspended particulate matter (SPM), dissolved oxygen (DO), nutrients, etc.) and biological parameters (chlorophyll-a, phytoplankton, and zooplankton). The trophic index (TRIX) and eutrophication index (EI) were calculated to describe the eutrophication status of TCWs. Temperature, pH, salinity, DO, and SPM showed seasonality due to the impact of the northeast monsoon. A massive bloom of Trichodesmium erythraeum was observed, with a visible impact on water quality and the plankton community. The cluster and principal component analysis indicated the bloom event as a distinct phenomenon. ANOVA results showed significant seasonal variations rather than spatial variations. According to the trophic indices, the area had a low trophic level in 2015 and a high trophic level in 2016. The Tuticorin inshore waters had the highest TRIX and EI values during the dominance of cyanobacteria bloom in the post-monsoon 2016. The trophic indices had a positive relationship with phytoplankton abundance but showed an inverse relation with zooplankton abundance. The overall range of the TRIX index (3.18–5.96) indicated that the environment was oligotrophic to eutrophic, and EI values (0.72–21.61) indicated that the state of coastal waters was moderate to poor. This study states that periodic monsoonal flow and frequent algal bloom events have a significant impact on the GoM coastal waters.

Çanakkale Boğazı'ndan Toplanan Müsilajda Siyanobakteri Toplulukları: Metagenomik Yaklaşım

In this study, cyanobacterial communities in mucilage samples collected from three stations in the Dardanelles Strait were analyzed with a metagenomic approach. Mucilage samples were collected at the beginning of June 2021 from three points of the Dardanelles (Station 1: 40°6'42.78"N, 26°23'57.00"E; Station 2: 40°9'8.09"N, 26°24'16.19"E; Station 3: 40°6 '21.62"N, 26°22'41.25"E). The dominant cyanobacteria were Prochlorococcus marinus (39.17%), Synechococcus sp. (20.85%), Lyngbya sp. (12.00%), Trichodesmium erythraeum (7.33%), Aphanocapsa sp. (4.33%) and Leptolyngbya sp. (3.33%), which constituted 87.00 % of the total number of sequences. In this study, cyanobacteria species that can cause harmful algal blooms and have toxic effects on the mucilage structure have been determined. The Marmara Sea and the Dardanelles Strait, which have been affected by serious disturbances, including industrial activities, anthropogenic impacts, tourism and artificial lighting, will never be fully restored to their former ecological state. In addition, cyanobacteria species in the mucilage may cause harmful algal blooms and have toxic effects that threaten the future well-being of coastal populations and ecosystem stability. Thus, the government and local authorities should pay more attention to combating the mucilage.

Metagenomes of Red Sea Subpopulations Challenge the Use of Marker Genes and Morphology to Assess Trichodesmium Diversity.

Trichodesmium are filamentous cyanobacteria of key interest due to their ability to fix carbon and nitrogen within an oligotrophic marine environment. Their blooms consist of a dynamic assemblage of subpopulations and colony morphologies that are hypothesized to occupy unique niches. Here, we assessed the poorly studied diversity of Trichodesmium in the Red Sea, based on metagenome-assembled genomes (MAGs) and hetR gene-based phylotyping. We assembled four non-redundant MAGs from morphologically distinct Trichodesmium colonies (tufts, dense and thin puffs). Trichodesmium thiebautii (puffs) and Trichodesmium erythraeum (tufts) were the dominant species within these morphotypes. While subspecies diversity is present for both T. thiebautii and T. erythraeum, a single T. thiebautii genotype comprised both thin and dense puff morphotypes, and we hypothesize that this phenotypic variation is likely attributed to gene regulation. Additionally, we found the rare non-diazotrophic clade IV and V genotypes, related to Trichodesmium nobis and Trichodesmium miru, respectively that likely occurred as single filaments. The hetR gene phylogeny further indicated that the genotype in clade IV could represent the species Trichodesmium contortum. Importantly, we show the presence of hetR paralogs in Trichodesmium, where two copies of the hetR gene were present within T. thiebautii genomes. This may lead to the overestimation of Trichodesmium diversity as one of the copies misidentified T. thiebautii as Trichodesmium aureum. Taken together, our results highlight the importance of re-assessing Trichodesmium taxonomy while showing the ability of genomics to capture the complex diversity and distribution of Trichodesmium populations.

Spatio-temporal variations of phytoplankton assemblage in coastal waters of Maharashtra, north-eastern Arabian Sea

Seasonal variations in phytoplankton species and abundance along the coast of Maharashtra from two different locations (Mumbai and Ratnagiri) and depths were investigated during August 2014-May 2017. A total of 84 species of phytoplankton were recorded from the region out of which 67 were diatoms, 16 dinoflagellates and one blue green alga. Seventy-five and 60 species of phytoplankton were recorded from Ratnagiri and Mumbai respectively. Diatoms dominated the phytoplankton community (81.7-93.3%) followed by dinoflagellates (4.7-7.2%) and blue green algae in both locations. Maximum phytoplankton density was recorded during post-monsoon season followed by pre-monsoon and monsoon seasons at Mumbai and Ratnagiri. Highest average phytoplankton cell density recorded was 9.09 x 104 cells l-1 and 4.06 x 104 cells l-1 during post-monsoon season at Ratnagiri and Mumbai respectively. Maximum cell density was observed at 20 m depth from Mumbai and Ratnagiri. Thalassiosira subtilis, Trieres mobiliensis, Skeletonema costatum, Coscinodiscus centralis and Ditylum brightwelli were the most abundant phytoplankton species recorded at Mumbai, whereas Chaetoceros curvisetus, S. costatum, Trichodesmium erythraeum, Chaetoceros lorenzianus and Ditylum brightwelli were abundant in Ratnagiri waters. The blue green alga, T. erythraeum was abundantly recorded during pre-monsoon season. Species diversity index (H’) ranged from 4.72 to 5.52 and was higher during post-monsoon season compared to pre-monsoon and monsoon. Highest phytoplankton diversity was observed at 20 m depth compared to 40 m depth.Keywords: Arabian Sea, Diversity, Mumbai, Phytoplankton, Ratnagiri

Observed denitrification in the northeast Arabian Sea during the winter-spring transition of 2009

The central and northeast Arabian Sea (AS) has an intense and thick oxygen minimum zone (OMZ) and denitrification zone. It is comparable with the strongest OMZ of the north-equatorial Pacific Ocean. Denitrification in the AS is revisited using a set of cruise observations collected during February–March of 2009 by the Centre for Marine Living Resources, India. The region possesses one of the most robust N* depleted water reaching as low as -20 μmol l −1 at depths (~600 m). In AS, the oxygen depletion is mainly due to sluggish circulation, weak lateral and vertical ventilation. The biological respiration in oxygen deficit condition depletes nitrate and further modifies the Redfield ratio at intermediate depths (200-600 m) from 16N:1P to 8N:1P. Further, analysis of phytoplankton groups present at the surface identifies the presence of Trichodesmium erythraeum , a nitrogen fixing species. The denitrification rate is estimated as 25.3 ± 7.0 Tg N yr −1 . It is consistent with past estimates, and no dramatic change in denitrification in the AS was noticed. The study also highlights the potential for further research on N 2 production from the Arabian Sea Oxygen Minimum Zones in a changing climate. Nitrate is an essential compound for phytoplankton photosynthesis. In most ocean waters, the ratio between N and P is a constant (16:1), called the Redfield ratio. Various processes can modify the Redfield ratio in the ocean, such as denitrification, nitrification, and anammox. Denitrification is a process through which the microbial processes remove the fixed nitrogen in the absence of enough dissolved oxygen in the water column (oxygen minimum zone; OMZ). In the Arabian Sea, a vast region of OMZ formed due to the combined effects of biological respiration, sluggish circulations in the intermediate depths, and strong thermocline, which prohibits the supply of oxygen from deep waters. Our study revisits the denitrification in the Arabian Sea OMZ region during the winter to spring transition season in 2009 using a set of onboard measurements. Due to this denitrification, an intense modification in the Redfield ratio in the northeast Arabian Sea region's intermediate depths is noted as 8N:1P. • Low N* in the intermediate depths in the Arabian Sea indicates denitrification. • Denitrification modifies the Redfield Ratio from 16 N:1P to 8 N:1P. • The study estimates a rate of denitrification as 25.3 ± 7.0 Tg N yr -1. • Study confirms no drastic change in denitrification for the Arabian Sea.

Phytoplankton Community Patterns in the Northeastern South China Sea: Implications of Intensified Kuroshio Intrusion During the 2015/16 El Niño

AbstractKuroshio intrusion into the South China Sea (SCS) varies seasonally and interannually under different climatic conditions. To characterize the intensity of the climate‐driven Kuroshio intrusion and its impact on the phytoplankton community in the northeastern South China Sea (NESCS), two cruises were conducted during the 2015/16 El Niño event. In situ observations and remote sensing data showed that the Kuroshio strongly intruded into the SCS in both summer and winter. The summer phytoplankton community was dominated by cyanobacteria (Trichodesmium erythraeum), associated with high surface temperature, shallower mixed layer depth, and low nutrient concentrations. The winter phytoplankton community was mainly dominated by cosmopolitan diatoms (Thalassiosira diporocyclus, Thalassionema nitzschioides, and Chaetoceros socialis), associated with low surface temperature, deeper mixed layers, and relatively higher nutrient concentrations. Meanwhile, the elevated abundance of T. erythraeum coupled well with the Kuroshio intrusion index during the El Niño summer. The phytoplankton network was unstable in summer but not in winter, induced by the Kuroshio intrusion. Our findings show that intensified Kuroshio intrusion during the El Niño event was a vital driving force for reshaping phytoplankton community dynamics of the NESCS through lateral advection and affecting temperature, mixed layer depth, and nutrient supply.

Spatial variability in the community structure of microphytoplankton along the southeastern Arabian sea during an unusually warm winter monsoon season

The microphytoplankton community structure and composition were investigated along the South Eastern Arabian Sea (SEAS) during the late winter monsoon season (January 2020). A total of 186 species of phytoplankton were identified, with cyanobacteria Trichodesmium erythraeum (72%) being the most dominant, followed by diatoms (11%) and dinoflagellates (2.7%). Major blooms of T. erythraeum were observed towards the southern region of SEAS characterised by high SST (28.75 ± 0.7 °C), high surface salinity (34.6 ± 1.2 psu) and low wind speed (∼3.6 m s−1). The T. erythraeum bloom areas generally observed high nitrate and low silicate and phosphate concentrations with high chlorophyll a concentration (8.96 ± 2.92 mg m−3). In non-bloom regions, centric diatoms like Chaetoceros spp., Bacteriastrum spp. and Leptocylindrus sp. dominated. The abundance of diatoms observed a decreasing trend towards the southern extend of SEAS. The remote sensing data derived for the area observed sea surface temperatures are about 1.0 °C higher than the climatological mean of January. The higher temperatures (29 °C–32 °C) are clearly visible in the Indian coastal region from Kanyakumari to the Gujarat coast, suggesting unusual warming in the eastern coast of the Arabian Sea in January 2020. This warming which was more prominent towards the southern extend of SEAS, might have augmented the proliferation of T. erythraeum along the surface waters of SEAS.

Production of Two Highly Abundant 2-Methyl-Branched Fatty Acids by Blooms of the Globally Significant Marine Cyanobacteria Trichodesmium erythraeum.

The bloom-forming cyanobacteria Trichodesmium contribute up to 30% to the total fixed nitrogen in the global oceans and thereby drive substantial productivity. On an expedition in the Gulf of Mexico, we observed and sampled surface slicks, some of which included dense blooms of Trichodesmium erythraeum. These bloom samples contained abundant and atypical free fatty acids, identified here as 2-methyldecanoic acid and 2-methyldodecanoic acid. The high abundance and unusual branching pattern of these compounds suggest that they may play a specific role in this globally important organism.

Massive Blooms of Cyanobacteria Trichodesmium erythraeum and Synechococcus sp. in Mandapam Group of Islands, Southeast Coast of India, Tamil Nadu

Massive Blooms of Cyanobacteria Trichodesmium erythraeum and Synechococcus sp. in Mandapam Group of Islands, Southeast Coast of India, Tamil Nadu

Structure, morphogenesis of calyptra and nomenclatural identity of Trichodesmium erythraeum Ehr. (Cyanobacteria) newly recorded off the Southwest coast of Bangladesh

Trichodesmium erythraeum Ehrenberg 1830 (Cyanobacteria) has been described and newly recorded from three km off the west coast of the St. Martin’s Island (SMI), Cox’s Bazar, Bangladesh. The Red Sea algal bloom was narrowly elliptical raft-like loose aggregates 20-40 cm long, 4-8 cm wide and 2-3 cm thick. Volume of small and large Sea sawdust were 160×10-6 to 960×10-6 m3 consisting of 25-153 millions flat tuft or spindlelike colonies measured 830-1500 μm long and 155-260 μm wide with 13-16 filaments laterally in the median region. Sheath was present around each trichome even covering the tip cell wall the feature has so far not been reported for the Trichodesmium spp. Because of most likely sticky nature of the sheath 300-600 μm long filaments of 195-450 formed compact colonies without colonial sheath around. In interior filaments cells were rectangular 7-10 μm long and 6.3-10 μm wide with abundant gas vacuoles, bluish-green red, no diazocytes developed and without calyptrae. Cells of peripheral filaments were without gas vacuoles, cytoplasm disorganized, appearing necrotic with glycogen granules, and produced convex to sickle-shaped four-layered calyptra consisting of outermost sheath followed by outer extra thick wall, tip cell wall and inner extra thick wall on the tip cell. Calyptra was also produced on tip cells of tapered filaments. Presence of sheath around each trichome binding all filaments into a colony without colonial sheath described here, and presence of nitrogenase containing diazocytes in interior filaments, both temporal and spatial segregation of N2 fixation and photosynthesis within the photoperiod described and discussed in literature made the authors to consider T. erythraeum Ehr. a distinct taxon under family Microcoleacece.
 Bangladesh J. Plant Taxon. 27(2): 273-282, 2020 (December)

A Rise in ROS and EPS Production: New Insights into the Trichodesmium erythraeum Response to Ocean Acidification.

The diazotrophic cyanobacterium Trichodesmium is thought to be a major contributor to the new N in parts of the oligotrophic, subtropical, and tropical oceans. In this study, physiological and biochemical methods and transcriptome sequencing were used to investigate the influences of ocean acidification (OA) on Trichodesmium erythraeum (T. erythraeum). We presented evidence that OA caused by CO2 slowed the growth rate and physiological activity of T. erythraeum. OA led to reduced development of proportion of the vegetative cells into diazocytes which included up-regulated genes of nitrogen fixation. Reactive oxygen species (ROS) accumulation was increased due to the disruption of photosynthetic electron transport and decrease in antioxidant enzyme activities under acidified conditions. This study showed that OA increased the amounts of (exopolysaccharides) EPS in T. erythraeum, and the key genes of ribose-5-phosphate (R5P) and glycosyltransferases (Tery_3818) were up-regulated. These results provide new insight into how ROS and EPS of T. erythraeum increase in an acidified future ocean to cope with OA-imposed stress.