Comparative genomics reveals insights into cyanobacterial evolution and habitat adaptation

Abstract

Cyanobacteria are photosynthetic prokaryotes that inhabit diverse aquatic and terrestrial environments. However, the evolutionary mechanisms involved in the cyanobacterial habitat adaptation remain poorly understood. Here, based on phylogenetic and comparative genomic analyses of 650 cyanobacterial genomes, we investigated the genetic basis of cyanobacterial habitat adaptation (marine, freshwater, and terrestrial). We show: (1) the expansion of gene families is a common strategy whereby terrestrial cyanobacteria cope with fluctuating environments, whereas the genomes of many marine strains have undergone contraction to adapt to nutrient-poor conditions. (2) Hundreds of genes are strongly associated with specific habitats. Genes that are differentially abundant in genomes of marine, freshwater, and terrestrial cyanobacteria were found to be involved in light sensing and absorption, chemotaxis, nutrient transporters, responses to osmotic stress, etc., indicating the importance of these genes in the survival and adaptation of organisms in specific habitats. (3) A substantial fraction of genes that facilitate the adaptation of Cyanobacteria to specific habitats are contributed by horizontal gene transfer, and such genetic exchanges are more frequent in terrestrial cyanobacteria. Collectively, our results further our understandings of the adaptations of Cyanobacteria to different environments, highlighting the importance of ecological constraints imposed by the environment in shaping the evolution of Cyanobacteria.

The <i>Thermosynechococcus</i> Genus: Wide Environmental Distribution, but a Highly Conserved Genomic Core

“… Chen et al (2020) also noted that differences in horizontal gene transfer (HGT) are related to genome size, with smaller genomes showing less HGT and larger genomes having a greater HGT probability. They also found that hot spring cyanobacteria specifically have smaller genome sizes and less HGT into the genome.…”

“…Since all Thermosynechococcus in this study are found in hot springs -which typically have reduced microbial diversity in comparison to other environments such as soils (Ward et al, 1998)-the conserved core and small pangenome of the Thermosynechococcus genus may reflect a more limited opportunity for lateral gene transfer, which in turn could lead to less opportunity for lateral gene transfer and smaller genomes. Chen et al (2020) also noted that differences in horizontal gene transfer (HGT) are related to genome size, with smaller genomes showing less HGT and larger genomes having a greater HGT probability. They also found that hot spring cyanobacteria specifically have smaller genome sizes and less HGT into the genome.…”

Microbial helpers allow cyanobacteria to thrive in ferruginous waters

“…Nostocales; Zamocky et al., 2012). Synechococcus PCC 7002 lacks Mn 2+ ‐catalase, which is widespread in terrestrial cyanobacteria (Ballal et al., 2020; Banerjee et al., 2012; Bihani et al., 2016; Chakravarty et al., 2016; Chen et al., 2020; Table S1) and was likely present in early cyanobacterial lineages (Klotz & Loewen, 2003; Zamocky et al., 2012).…”

Microbial helpers allow cyanobacteria to thrive in ferruginous waters

“…Nostocales; Zamocky et al, 2012). Synechococcus PCC 7002 lacks Mn 2+ -catalase, which is widespread in terrestrial cyanobacteria (Ballal et al, 2020; Banerjee et al, 2012; Bihani et al, 2016; Chakravarty et al, 2016; Chen et al, 2020) (Table S1) and was likely present in early cyanobacterial lineages (Klotz and Loewen, 2003; Zamocky et al, 2012).…”