Characterization and whole-genome sequencing of an extreme arsenic-tolerant Citrobacter freundii SRS1 strain isolated from Savar area in Bangladesh

Abstract

Citrobacter freundii SRS1, Gram-negative bacteria, were isolated from Savar, Bangladesh. The strain could tolerate up to 80 mM sodium arsenite, 400 mM sodium arsenate, 5 mM manganese sulfate, 3 mM lead nitrate, 2.5 mM cobalt chloride, 2.5 mM cadmium acetate, and 2.5 mM chromium chloride. The whole-genome sequencing revealed that the genome size of C. freundii SRS1 is estimated to be 5.4 Mbp long, and the G+C content is 51.7%. The genome of C. freundii SRS1 contains arsA. arsB, arsC, arsD, arsH, arsR and acr3 genes for arsenic resistance; czcA, czcD, cbiN, and cbiM genes for cobalt; chrA, and chrB genes for chromium; mntH, sitA, sitB, sitC, and sitD genes for manganese; and zntA genes for lead and cadmium resistance. This novel acr3 gene has never previously been reported in any C. freundii strain except SRS1. A set of 130 completely sequenced strains of C. freundii were selected for phylogenomic analysis. The phylogenetic tree showed that the SRS1 strain is closely related to the C. freundii 62 strain. Further analyses of the genes involved in metal and metalloid resistance might facilitate identifying the mechanisms and pathways involved in high metal resistance in the C. freundii SRS1 strain.