The aim of the present study was to investigate biosurfactant-producing culturable bacteria inhabiting the coast of the Arabian Sea at Karachi. Overall, 15 seawater samples were collected from the Arabian Sea coast of Karachi. Isolation, characterization, and screening for 89 biosurfactant-producing bacterial strains were conducted through 8 conventional screening tests. Through GSP agar plate method 22 strains were found to be Pseudomonas aeruginosa and Gram reaction revealed 70% of the isolates to be gramnegative. Furthermore, 24% of the isolates showed hemolytic activity, 44% exhibited positive results for oil-spreading test, 54% showed emulsification to at least 1 of the 3 hydrocarbons tested, BATH assay results indicated maximum adhesion for hexane, 52.8% produced positive results for CTAB agar plate assay, drop-collapse activity was found in 84% of the isolates, and emulsification assay revealed highest emulsification for xylene. Findings revealed none of the isolates to be negative for every screening test conducted, while only one gram-negative isolate, DGHE65, identified as Pseudomonas aeruginosa, was positive for all the tests for biosurfactant production. Results indicate that these isolates have potential for future environmental friendly applications such as bioremediation and industrial biotechnology.

The horizontal gene transfer of plasmid-determined stress tolerance was achieved under lab conditions. Bacterial isolates, Enterobacter cloacae (DGE50) and Escherichia coli (DGE57) were used throughout the study. Samples were collected from contaminated marine water and soil to isolate bacterial strains having tolerance against heavy metals and antimicrobial agents. We have demonstrated plasmid transfer, from Amp(+)Cu(+)Zn(-) strain (DGE50) to Amp(-)Cu(-)Zn(+) strain (DGE57), producing Amp(+)Cu(+)Zn(+) transconjugants (DGE(TC50→57)) and Amp(+)Cu(-)Zn(+) transformants (DGE(TF50→57)). DGE57 did not carry any plasmid, therefore, it can be speculated that zinc tolerance gene in DGE57 is located on chromosome. DGE50 was found to carry three plasmids, out of which two were transferred through conjugation into DGE57, and only one was transferred through transformation. Plasmid transferred through transformation was one out of the two transferred through conjugation. Through the results of transformation it was revealed that the genes of copper and ampicillin tolerance in DGE50 were located on separate plasmids, since only ampicillin tolerance genes were transferred through transformation as a result of one plasmid transfer. By showing transfer of plasmids under lab conditions and monitoring retention of respective phenotype via conjugation and transformation, it is very well demonstrated how multiple stress tolerant strains are generated in nature.