Effects of phylogeny and environment on genomic properties of extremophiles

Abstract

Only a handful of microorganisms have successfully adapted to extreme conditions. It raises a question: which of two factors, phylogeny relation or environmental condition, has had stronger influence on the genomic properties of extremophiles. We expected that answers to the question would be different among different types of extremophiles. We conducted a small-scale comparative analysis on the overall genomic properties- the numbers of ribosomal RNA operons (the rrn operon numbers), the genome sizes, and the GC contents of 193 genera in 9 taxonomic groups: Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Clostridia, Deinococci, Bacteroidetes, Thermotogae, Euryarchaeota, and Spirochaetes. The results from two Kruskal wallis (KW) tests, one for assessing equality among orders (phylo group) in a taxonomic group and the other among genera that contained extremophiles and those that contained none (extremo group), indicated that both groups, phylo group and extremo group, were statistically significantly different in all three variables except the GC contents of the phylo group in Deinococci, the genome sizes of the extremo group in Spirochaetes, and the rrn operon numbers of the extremo group in Bacteroidetes (Chi-square statistics P value < 0.05). Equality tests applied to P values from the KW tests applied to species groups in a genus showed that the P values of the rrn operon numbers were relatively mores. We expected that answers to the question would be different among different types of extremophiles. We conducted a small-scale comparative analysis on the overall genomic properties- the numbers of ribosomal RNA operons (the rrn operon numbers), the genome sizes, and the GC contents of 193 genera in 9 taxonomic groups: Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Clostridia, Deinococci, Bacteroidetes, Thermotogae, Euryarchaeota, and Spirochaetes. The results from two Kruskal wallis (KW) tests, one for assessing equality among orders (phylo group) in a taxonomic group and the other among genera that contained extremophiles and those that contained none (extremo group), indicated that both groups, phylo group and extremo group, were statistically significantly different in all three variables except the GC contents of the phylo group in Deinococci, the genome sizes of the extremo group in Spirochaetes, and the rrn operon numbers of the extremo group in Bacteroidetes (Chi-square statistics P value < 0.05). Equality tests applied to P values from the KW tests applied to species groups in a genus showed that the P values of the rrn operon numbers were relatively mor