Environmental Microbiology
Detection of plasmids in arsenic (As) resistant bacteria isolated from As-contaminated groundwater
Mahima Rani and Pinaki Sar*
Department of Biotechnology, Indian Institute of Technology, Kharagpur, West Bengal–721302, India mahima06bt11@gmail.com, Ph: +91 8348523016
Abstract
Role of plasmids in conferring resistance to several heavy metals and antibiotics to naturally occurring bacteria is well known. In contaminated environments, presence of metal resistant genes on plasmids often provide the other bacteria within the same niche to acquire the necessary genes at times of severe (metal) stress. Several arsenic (As) resistant bacterial strains were isolated from contaminated groundwater samples collected from Chakdah and Barasat districts of West Bengal and Jorhat district of Assam. All the isolated bacteria were identified by 16S rRNA gene sequencing. The phylogenetic analysis of the strains using 16S rDNA sequence revealed strains to be under the genus Acidovorax, Acinetobacter, Rhizobium, Enterobacter and Rhodococcus. Isolated bacteria were tested for the presence of plasmids using the modified alkaline lysis method. The study revealed that the frequency of the occurrence of plasmids in arsenic resistant bacteria was more than that in the common bacteria. In the present study, fifty seven As resistant bacterial isolates were screened for presence of plasmids within and twenty nine of them were found positive. The size of the plasmid DNAs were between 4 to 11 kb. All the plasmid bearing isolates showed elevated tolerance towards arsenate and arsenite (MTC 400 mM and 20 mM respectively) while tolerance to other heavy metals like Cu2+, Cd2+, Cr2+ and Pb2+ (MTC < 3 mM) was moderate. Plasmid bearing isolates were tested for their resistance against five antibiotics, out of which all except one were found to be resistant against ampicillin. Plasmid curing was successfully carried out with EtBr for few isolates. Compared to wild cured strains showed
Mahima Rani and Pinaki Sar*
Department of Biotechnology, Indian Institute of Technology, Kharagpur, West Bengal–721302, India mahima06bt11@gmail.com, Ph: +91 8348523016
Abstract
Role of plasmids in conferring resistance to several heavy metals and antibiotics to naturally occurring bacteria is well known. In contaminated environments, presence of metal resistant genes on plasmids often provide the other bacteria within the same niche to acquire the necessary genes at times of severe (metal) stress. Several arsenic (As) resistant bacterial strains were isolated from contaminated groundwater samples collected from Chakdah and Barasat districts of West Bengal and Jorhat district of Assam. All the isolated bacteria were identified by 16S rRNA gene sequencing. The phylogenetic analysis of the strains using 16S rDNA sequence revealed strains to be under the genus Acidovorax, Acinetobacter, Rhizobium, Enterobacter and Rhodococcus. Isolated bacteria were tested for the presence of plasmids using the modified alkaline lysis method. The study revealed that the frequency of the occurrence of plasmids in arsenic resistant bacteria was more than that in the common bacteria. In the present study, fifty seven As resistant bacterial isolates were screened for presence of plasmids within and twenty nine of them were found positive. The size of the plasmid DNAs were between 4 to 11 kb. All the plasmid bearing isolates showed elevated tolerance towards arsenate and arsenite (MTC 400 mM and 20 mM respectively) while tolerance to other heavy metals like Cu2+, Cd2+, Cr2+ and Pb2+ (MTC < 3 mM) was moderate. Plasmid bearing isolates were tested for their resistance against five antibiotics, out of which all except one were found to be resistant against ampicillin. Plasmid curing was successfully carried out with EtBr for few isolates. Compared to wild cured strains showed