Isolation of a Stenotrophomonas strain and identification of methyltransferase genes conferring the high arsenic volatilizing ability.

Abstract

Microbial arsenic (As) volatilization plays a significant role in the global As biogeochemical cycle and presents a promising approach for bioremediation. In this study, an autotrophic strain of Stenotrophomonas maltophilia was isolated from sewage water containing 75 ppb of arsenic, exhibiting a high arsenic metabolism and volatilization rate. This strain tolerated arsenic concentrations ranging from 10 to 500 ppm. Volatilization tests were conducted at an environmental median of 200 ppb (0.2 ppm) As. The strain eliminated 50% of the total arsenic within 48 h, and 0.1 ppm (101 ppb) of arsenic was reported to be trapped in the headspace of the culture tube, confirming its volatilization. After genome isolation, sequencing, and assembly, the existence of the As metabolizing operon (arsRABC), as well as other As-resistance conferring genes (arsM, arsI, aioA, aoxB, and arxA), was identified using different annotation methodologies. The genes conferring resistance against different heavy metals and multiple drugs used as antimicrobials were also identified in the genome assembly of the isolate. Based on the gene expression measured using real-time polymerase chain reaction, complete gene sequences of four arsM genes were mined, cloned, and expressed in Escherichia coli BL21(DE3) cells. The cells harboring recombinant plasmid of each construct could volatilize As up to 86 ppb after 48 h incubation in arsenic-enriched media. The isolated strain of Stenotrophomonas and its heterologously expressed methyltransferase genes could be a potent tool for permanently removing arsenic from water samples by volatilization.IMPORTANCEArsenic contamination in water, soil, and air poses significant health and environmental risks, as inorganic arsenic compounds are highly toxic and carcinogenic. Microorganisms capable of transforming arsenic into volatile forms play a pivotal role in the biogeochemical cycling of this metalloid, reducing its bioavailability and toxicity in contaminated environments. In this work, a strain of Stenotrophomonas sp. was isolated from the sewage water and tested for its ability to survive in minimal arsenic media. The strain was found to be highly resistant to arsenic and volatilized more than 50% of the arsenic from the growth media. The putative methyltransferase genes from the isolated strain, when heterologously expressed in Escherichia coli, conferred an ability to volatilize arsenic in the recombinant host, too. Therefore, the isolated microorganism offers a natural, eco-friendly alternative to conventional chemical methods, making it an important tool for addressing arsenic biosafety issues in the environment.