Natural Competence in the Filamentous, Heterocystous Cyanobacterium Chlorogloeopsis fritschii PCC 6912

Extensive Genomic Rearrangement of Catalase-Less Cyanobloom-Forming Microcystis aeruginosa in Freshwater Ecosystems

Many of the world's freshwater ecosystems suffer from cyanobacteria-mediated blooms and their toxins. However, a mechanistic understanding of why and how Microcystis aeruginosa dominates over other freshwater cyanobacteria during warmer summers is lacking. This paper utilizes comparative genomics with other cyanobacteria and literature reviews to predict the gene functions and genomic architectures of M. aeruginosa based on complete genomes. The primary aim is to understand this species' survival and competitive strategies in warmer freshwater environments. M. aeruginosa strains exhibiting a high proportion of insertion sequences (~ 11%) possess genomic structures with low synteny across different strains. This indicates the occurrence of extensive genomic rearrangements and the presence of many possible diverse genotypes that result in greater population heterogeneities than those in other cyanobacteria in order to increase survivability during rapidly changing and threatening environmental challenges. Catalase-less M. aeruginosa strains are even vulnerable to low light intensity in freshwater environments with strong ultraviolet radiation. However, they can continuously grow with the help of various defense genes (e.g., egtBD, cruA, and mysABCD) and associated bacteria. The strong defense strategies against biological threats (e.g., antagonistic bacteria, protozoa, and cyanophages) are attributed to dense exopolysaccharide (EPS)-mediated aggregate formation with efficient buoyancy and the secondary metabolites of M. aeruginosa cells. Our review with extensive genome analysis suggests that the ecological vulnerability of M. aeruginosa cells can be overcome by diverse genotypes, secondary defense metabolites, reinforced EPS, and associated bacteria.

Characterization of Limnospira platensis PCC 9108 R-M and CRISPR-Cas systems

The filamentous cyanobacterium Limnospira platensis, formerly known as Arthrospira platensis or spirulina, is one of the most commercially important species of microalgae. Due to its high nutritional value, pharmacological and industrial applications it is extensively cultivated on a large commercial scale. Despite its widespread use, its precise manipulation is still under development due to the lack of effective genetic protocols. Genetic transformation of Limnospira has been attempted but the methods reported have not been generally reproducible in other laboratories. Knowledge of the transformation defense mechanisms is essential for understanding its physiology and for broadening their applications. With the aim to understand more about the genetic defenses of L. platensis, in this work we have identified the restriction-modification and CRISPR-Cas systems and we have cloned and characterized thirteen methylases. In parallel, we have also characterized the methylome and orphan methyltransferases using genome-wide analysis of DNA methylation patterns and RNA-seq. The identification and characterization of these enzymes will be a valuable resource to know how this strain avoids being genetically manipulated and for further genomics studies.