Bioactive Potential of Two Marine Picocyanobacteria Belonging to Cyanobium and Synechococcus Genera

Snapshot of cyanobacterial toxins in Pakistani freshwater bodies

Cyanobacteria are known to produce diverse secondary metabolites that are toxic to aquatic ecosystems and human health. However, data about the cyanotoxins occurrence and cyanobacterial diversity in Pakistan's drinking water reservoirs is scarce. In this study, we first investigated the presence of microcystin, saxitoxin, and anatoxin in 12 water bodies using an enzyme-linked immunosorbent assay (ELISA). The observed cyanotoxin values for the risk quotient (RQ) determined by ELISA indicated a potential risk for aquatic life and human health. Based on this result, we made a more in-depth investigation with a subset of water bodies (served as major public water sources) to analyze the cyanotoxins dynamics and identify potential producers. We therefore quantified the distribution of 17 cyanotoxins, including 12 microcystin congeners using a high-performance liquid chromatography-high-resolution tandem mass spectrometry/mass spectrometry (HPLC-HRMS/MS). Our results revealed for the first time the co-occurrence of multiple cyanotoxins and the presence of cylindrospermopsin in an artificial reservoir (Rawal Lake) and a semi-saline lake (Kallar Kahar). We also quantified several microcystin congeners in a river (Panjnad) with MC-LR and MC-RR being the most prevalent and abundant. To identify potential cyanotoxin producers, the composition of the cyanobacterial community was characterized by shotgun metagenomics sequencing. Despite the noticeable presence of cyanotoxins, Cyanobacteria were not abundant. Synechococcus was the most abundant cyanobacterial genus found followed by a small amount of Anabaena, Cyanobium, Microcystis, and Dolichospermum. Moreover, when we looked at the cyanotoxins genes coverage, we never found a complete microcystin mcy operon. To our knowledge, this is the first snapshot sampling of water bodies in Pakistan. Our results would not only help to understand the geographical spread of cyanotoxin in Pakistan but would also help to improve cyanotoxin risk assessment strategies by screening a variety of cyanobacterial toxins and confirming that cyanotoxin quantification is not necessarily related to producer abundance.

Concentration of total microcystins associates with nitrate and nitrite, and may disrupt the nitrogen cycle, in warm-monomictic lakes of the southcentral United States

Cyanobacterial blooms and the toxins they produce pose a growing threat worldwide. Mitigation of such events has primarily focused on phosphorus management and has largely neglected the role of nitrogen. Previous bloom research and proposed management strategies have primarily focused on temperate, dimictic lakes, and less on warm-monomictic systems like those at subtropical latitudes. The in-lake conditions, concentration of total microcystins, and microbial functioning of twenty warm-monomictic lakes in the southcentral United States were explored in the spring and summer of 2021. Our data revealed widespread microcystins in lakes across this region, some of which exceeded regulatory limits. Microcystins were higher in the spring compared to the summer, indicating that warm-monomictic lakes, even across a large range of precipitation, do not follow the trends of temperate dimictic lakes. Microcystins were found in surface waters and bottom waters well below the photic zone, reflecting the persistence of these toxins in the environment. Principal components analyses showed a strong association between microcystins, nitrate + nitrite, and Planktothrix relative abundance and transcriptional activity. Many systems exhibited stronger denitrification in the spring, perhaps contributing to the decreased toxin concentrations in the summer. Counter to most sampled lakes, one lake with the highest concentration of total microcystins indicated nitrogen cycle disruption, including inhibited denitrification. These findings are relevant to mitigating cyanobacterial blooms and toxin production in warm-monomictic systems, and suggests a need to consider nitrogen, and not solely phosphorus, in nutrient management discussions.

Microcystins and Cyanobacterial Contaminants in the French Small-Scale Productions of Spirulina (Limnospira sp.)

Spirulina is consumed worldwide, in the form of food or dietary supplements, for its nutritional value and health potential. However, these products may contain cyanotoxins, including hepatotoxic microcystins (MCs), produced by cyanobacterial contaminants. The French spirulina market has the particularity of being supplied half-locally by approximately 180 small-scale spirulina production farms. Data about this particular production and possible contaminations with other cyanobacteria and MCs are scarce. Thus, we collected the results of MC analyses and total cyanobacteria counts, carried out between 2013 and 2021, from 95 French spirulina producers who agreed to share their data. These data consisted of MC concentrations determined with an enzyme-linked immunosorbent assay (ELISA) using 623 dry spirulina samples and 105 samples of spirulina cultures. In addition, potentially unsafe samples of dry spirulina were further investigated through mass spectrometry, as duplicate analysis. We confirmed that the situation of the French spirulina production stayed within the safe regulatory level in terms of MC levels. On the other hand, the inventory of cyanobacterial contaminants, based on 539 count results, included 14 taxa. We present their prevalence, interannual evolution and geographical distribution. We also suggested improvements in cultivation practices to limit their propagation.

Prokaryotic and eukaryotic microbial communities associated with coral species have high host specificity in the South China Sea

Reef-building corals are well known for their obligate association with Symbiodiniaceae, and an array of other microbes, including bacteria, fungi, and symbiotic algae (i.e., total microbiome), which together form the coral holobiont. The total microbiome plays an intricate part in maintaining the homeostasis of the coral holobiont and is closely associated with host health. However, the composition of the coral associated microbiome and interaction between its different members remains elusive because few analyses have bridged taxonomically disparate groups. This research gaps have prevented a holistic understanding of the total microbiome. Thus, to simultaneously characterize the bacterial, fungal and symbiotic algal communities associated with different coral species, and explore the relationship between these symbionts and coral health, healthy and bleached tissues from four coral species, Acropora muricata, Galaxea fascicularis, Platygyra daedalea, and Pavona explanulata, were collected from the Xisha Islands of the South China Sea. Using high throughput sequencing, a high degree of host-specificity was observed among bacterial, fungal, and algal groups across coral species. There were no obvious changes in the microbial community structure of apparently healthy and bleached corals, but host bleaching allowed colonization of the holobionts by diverse opportunistic microbes, resulting in a significant elevation in the α-diversity of microbial communities. In addition, co-occurrence analysis of the coral microbiota also identified more complex microbial interactions in bleached corals than in healthy ones. In summary, this study characterized the structure of coral-associated microbiomes across four coral species, and systematically studied microbiome differences between healthy and bleached corals. The findings improve our understanding of the heterogeneity of symbiotic microorganisms and the impact of coral's physiological status on its associated microbial communities composition.