To better understand how microbes adapt to As/Sb environment, arsenic and antimony resistant bacteria were isolated from the Xikuangshan antimony mine, Hunan Province. An arsenite-oxidizing bacteria Achromobacter sp. As-55 was screened and further studied. A spontaneous mutant strain SMAs-55 of As-55 with enhanced antimony resistance was obtained under stress caused by Sb(III) exposure, suggesting strong plasticity of the genome of Achromobacter sp. As-55. To identify crucial gene products essential for survival of strain As-55 in high Sb environment, strain As-55 being used as the ancestral strain was continuously cultured for one year in a medium containing increasing concentrations of Sb(III). The As/Sb resistance of the Sb-evolved populations did increase, and the number of mutations (26-254) of Sb-evolved populations was much higher than control (13-14). The mutations in the Sb-evolved populations mainly occurred in genes encoding functions encompassing transcriptional regulators (iscR, gntR), inorganic ion transport and metabolism (arsD, arsO, heavy metal P-type ATPase, fur), energy production and conversion (FoF1 type ATP synthase) and post-translational modification, protein turnover and chaperones (clpA, clpB). This indicated that the Sb-evolved populations mainly adapted to the high concentrations of an Sb environment by mutating genes encoding global transcriptional regulators thereby affecting the transcription of the genes they regulate, and increasing the ability of ion transport, ATP synthesis and protein repair.
This study use an effective approach, long term laboratory evolution under Sb(III) stress, to identify unexpected alteration genetic changes in a number of genes required for survival under Sb(III) exposure.
 

Achromobacter, arsenic/antimony resistant bacteria, adaptative mechanism, laboratory adaptive evolution