Whole genome sequencing of mesorhizobia isolated from northern Canada

• Published in: Canadian Journal of Microbiology
• Main Authors: Duan, Yi Fan, Grogan, Paul, Walker, Virginia K, diCenzo, George C
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2022
• Subjects: Genetics; Molecular Biology; Applied Microbiology and Biotechnology; General Medicine; Immunology; Microbiology; Arctic; Tundra
• Online Access: http://dx.doi.org/10.1139/cjm-2022-0102; https://cdnsciencepub.com/doi/full-xml/10.1139/cjm-2022-0102; https://cdnsciencepub.com/doi/pdf/10.1139/cjm-2022-0102

Rhizobia are soil-dwelling bacteria that can form N 2 -fixing symbioses with legume plant species (Fabaceae). These bacteria are globally distributed; however, few studies have examined the genomics of rhizobia that live in cold environments. Here, we isolated and characterized three rhizobial strains from legume nodules collected at a pair of distant low Arctic tundra and boreal forest sites in northern Canada. Phylogenetic and average nucleotide identity measurements suggested that the three strains are members of the genus Mesorhizobium, and that each strain represents a novel genospecies. Intriguingly, whereas most mesorhizobia contain the classical determinants of nodulation and nitrogen fixation on their chromosome, whole genome sequencing revealed that all three strains carry these genes on large symbiotic megaplasmids of ∼750 to ∼1000 kb. Phylogenetic and sequence analyses of the common nodulation genes revealed highly conserved alleles amongst these northern mesorhizobia, leading us to propose that they belong to a novel symbiovar that we termed symbiovar oxytropis. Interestingly, these nod gene alleles are uncommon in mesorhizobia isolated from similar plant hosts in other climatic regions, suggesting potential functional adaptive differences.