Assessment and characterization of heavy metal resistance in Palk Bay sediment bacteria

The present study aimed at characterizing the heavy metal resistance and assessing the resistance pattern to multiple heavy metals (300 mmol L−1) by Palk Bay sediment bacteria. From 46 isolates, 24 isolates showed resistance to more than eight heavy metals. Among the 24 isolates S8-06 (Bacillus arsenicus), S8-10 (Bacillus pumilus), S8-14 (B. arsenicus), S6-01 (Bacillus indicus), S6-04 (Bacillus clausii), SS-06 (Planococcus maritimus) and SS-08 (Staphylococcus pasteuri) exhibited high resistance against arsenic, mercury, cobalt, cadmium, lead and selenium. Plasmid curing confirmed that the heavy metal resistance in S8-10 is chromosomal borne. Upon treatment with the heavy metals, the strain S8-10 showed many morphological and physiological changes as shown by SEM, FTIR and AAS analysis. S8-10 removed 47% of cadmium and 96% of lead from the growth medium. The study suggests that sediment bacteria can be biological indicators of heavy metal contamination.

► Forty six isolates were screened for heavy metal resistance and 24 isolates showed resistance to more than eight heavy metals.
► Among the 24 isolates S8-06 (Bacillus arsenicus), S8-10 (Bacillus pumilus), S8-14 (B. arsenicus), S6-01 (Bacillus indiucs), S6-04 (Bacillus clausii), SS-06 (Planococcus maritimus) and SS-08 (Staphylococcus pasteuri) exhibited high resistance to elevated concentration of arsenic, mercury, cobalt, cadmium, lead and selenium.
► Among the seven strains the heavy metal resistance in S8-10 is chromosomal borne rather than by plasmids.
► Characterization by SEM, FTIR and AAS revealed the morphological changes, variation in macromolecules secretion and accumulation of heavy metals in S8-10 cells. S8-10 removed 47% of cadmium and 96% of lead from growth medium that had initial metal concentrations of 200 ppm.
► The present study is an indicator of the heavy metal pollution in the Palk Bay region and alarms the necessity to monitor the heavy metal load in this region.