Isolation of heterotrophic bacteria from Palk Bay sediments showing heavy metal tolerance and antibiotic production.

Analysis of culturable and unculturable bacteria and their potential bioactive compounds from Palk Bay is yet to be explored. The present study for the first time characterizes the culturable bacteria from Palk Bay sediment using 16S rRNA gene sequencing. The characterized bacteria were also screened for antibacterial activity against human and aquaculture pathogens. In the 16S rRNA gene sequence analysis characterized that most of the bacteria were affiliated to members of Firmicutes and less with Gammaproteobacteria, Actinobacteria and Alphaproteobacteria. A high portion of (39%) of the bacteria showed antibacterial activity against both Gram positive and Gram negative test strains. The antibiotics from the strain S6-05 were partially purified using solvent extraction followed by TLC and silica column and further characterized by IR analysis. Two active principles A and B showed difference in the activity against Gram positive and Gram negative pathogens. But in the synergistic application they showed excellent activity against all the test pathogens. This study provides the first evidence on the existence of certain Bacillus species in the marine environment, namely Bacillus arsenicus, Bacillus indicus, Bacillus boroniphilus, Bacillus cibi and Bacillus niabensis which also had antibacterial activity. Several of the isolates exhibited tolerance to arsenic and boron to a new level of 25 and 100 mM, respectively. The current study reveals the fact that a great deal remains in the bacterial diversity of Palk Bay region.