Cyanotoxins and Other Bioactive Compounds from the Pasteur Cultures of Cyanobacteria (PCC)

Insight on the heterocyte patterning and the proheterocyte division in the toxic cyanobacterium Kaarinaea lacus gen. nov., sp. nov., and its genomic potential for natural products

Nostoc sp. 152 (= PCC 9237T), a toxic cyanobacterium, isolated from mixed cyanobacterial bloom in a Finnish freshwater lake was reassessed using phylogenetic, morphological and genomic analyses. Multilocus and 16S rRNA gene phylogenetic analyses confirmed that this strain represents a novel Nostocalean genus for which we propose the name Kaarinaea lacus gen. nov., sp. nov., in accordance with the International Code of Nomenclature of Prokaryotes. The most intriguing morphological feature exhibited by PCC 9237T is the occasional division of proheterocytes. Based on our observations, we propose a hypothesis for the sequence of events taking place leading to this phenomenon. The other interesting feature includes the unusual heterocyte patterning resulting in the development of heterocytes in series in the old culture followed by its fragmentation at this site. Among the genes involved in heterocyte differentiation and patterning, patC and three homologs of hetP were not found from the genome of PCC 9237T. Furthermore, genomic investigations revealed a variant of heterocyte glycolipid gene cluster with a reduced hglB, but having additional gene coding for a protein with TubCN terminal docking domain. Finally, the presence of a pks2-like gene cluster, whose product may interfere with the cellular differentiation, and an anachelin-like gene cluster demands further investigations.

The genus Limnospira contains only two species, both unable to produce microcystins: L. maxima and L. platensis

Spirulina is the commercial name for edible cyanobacteria of the genus Limnospira. The taxonomy of this genus is confusing with four species distributed in two lineages. Furthermore, the species Limnospira fusiformis has been cited as toxic by potentially producing microcystins. Taxonomic ambiguity combined with suspected health concerns constitute a major issue for spirulina producers. In a collection of six cultivars and one ecotype, we identified strains of the two lineages through metagenetic and morphological analyses. We demonstrated that the genus Limnospira only comprises two distinct species according to genomic comparisons of three genomes obtained in this study and 19 reference genomes. We showed that the V3-V4 region of the 16S rRNA gene is sufficient to identify the genus Limnospira and to distinguish the two species. Toxinogenesis investigations on eleven genomes from each Limnospira species revealed no genes involved in cyanotoxin synthesis, reflecting the inability of this genus to produce microcystins.

The secondary outbreak risk and mechanisms of Microcystis aeruginosa after H2O2 treatment

The secondary outbreak of cyanobacteria after algicide treatment has been a serious problem to water ecosystems. Hydrogen peroxide (H2O2) is an algaecide widely used in practice, but similar re-bloom problems are inevitably encountered. Our work found that Microcystis aeruginosa (M. aeruginosa) temporarily hibernates after H2O2 treatment, but there is still a risk of secondary outbreaks. Interestingly, the dormant period was as long as 20 and 28 days in 5 mg L-1 and 20 mg L-1 H2O2 treatment groups, respectively, but the photosynthetic activity was both restored much earlier (within 14 days). Subsequently, a quantitative imaging flow cytometry-based method was constructed and confirmed that the re-bloom had undergone two stages including first recovery and then re-division. The expression of ftsZ and fabZ genes showed that M. aeruginosa had active transcription processes related to cell division protein and fatty acid synthesis during the dormancy stat. Furthermore, metabolomics suggested that the recovery of M. aeruginosa was mainly by activating folate and salicylic acid synthesis pathways, which promoted environmental stress resistance, DNA synthesis, and cell membrane repair. This study reported the comprehensive mechanisms of secondary outbreak of M. aeruginosa after H2O2 treatment. The findings suggest that optimizing the dosage and frequency of H2O2, as well as exploring the potential use of salicylic acid and folic acid inhibitors, could be promising directions for future algal control strategies.