Abstract
Background: Cyanobacteria are of special concern because they proliferate in eutrophic water bodies worldwide and affect water quality. As an ancient photosynthetic microorganism, cyanobacteria can survive in ecologically diverse habitats because of their capacity to rapidly respond to environmental changes through a web of complex signaling networks, including using second messengers to regulate physiology or metabolism. A ubiquitous second messenger, bis-(3′,5′)-cyclic-dimeric-guanosine monophosphate (c-di-GMP), has been found to regulate essential behaviors in a few cyanobacteria but not Microcystis, which are the most dominant species in cyanobacterial blooms. In this study, comparative genomics analysis was performed to explore the genomic basis of c-di-GMP signaling in Microcystis aeruginosa.
Results: General characterization along with a pan-genome analysis showed that M. aeruginosa have a medium size genome (4.99 Mb in average), a conserved core genome, and an expansive pan-genome. Phylogenetic analysis showed good overall congruence between the two types of phylogenetic trees based on 31 highly conserved protein-coding genes and pan-genome matrix. Furthermore, phylogenetic analysis revealed no correlation between geographic distribution and phylogenetic relationships of the M. aeruginosa strains isolated from different regions. Moreover, proteins involved in c-di-GMP metabolism and regulation, such as diguanylate cyclases, phosphodiesterases, and PilZ-containing proteins, were encoded in M. aeruginosa genomes. It was revealed that the numbers of genes that encode diguanylate cyclases, phosphodiesterases, and hybrid proteins with GGDEF-EAL domains in M. aeruginosa might result from environment-specific adaptation. Bioinformatics and structure analysis of c-di-GMP signal-related GGDEF, EAL and GGDEF-EAL domains revealed that they all possess essential conserved amino acid residues that bind the substrate. In addition, it was also found that all selected M. aeruginosa genomes encode PilZ domain containing proteins.
Conclusions: Comparative genomics analysis of c-di-GMP metabolism and regulation in M. aeruginosa strains helped elucidate the genetic basis of c-di-GMP signaling pathways in M. aeruginosa. Knowledge of c-di-GMP metabolism and relevant signal regulatory processes in cyanobacteria can enhance our understanding of their adaptability to various environments and bloom-forming mechanism.
Keywords: Microcystis aeruginosa, Comparative genomics, c-di-GMP, Phylogenetic analysis, GGDEF, EAL, PilZ
A HindIII BAC library construction of Mesobuthus martensii Karsch (Scorpiones:Buthidae): An important genetic resource for comparative genomics and phylogenetic analysis