Assesment of the Biological Activity of Marine Microbes

Abstract

Diverse marine bacteria dwell in the oceans under competitive biological environment with extreme conditions of salinity, pressure, nutrition, temperature and complex relations among their different counterparts. Under iron-depleted conditions, bacteria produce iron chelators called siderophores that scavenge iron and make it available to bacteria. Most of the reports till date on siderophore producing organisms have been restricted to terrestrial and fresh water organisms only. Hence the present study was needed to investigate the siderophore producing ability of marine bacteria. Around 150 morphologically distinct isolates that were studied and screened, only 9 isolates exhibited significant biological activity. The isolate S31, a potent siderophore producer was selected for detailed study. The siderophore producing ability of this isolate was confirmed using the cell free supernatant (CFS) with Chrome azurol S (CAS) assay. The isolate S31 was identified as Pseudomonas aeruginosa MGPB 31 (GenBank Accession No. MF511820) based on morphological, biochemical and molecular identification. S31 was further characterized for the effect of different media and its components were studied on siderophore production. The results revealed that modified M9 broth (MM9) exhibited highest siderophore production at room temperature in 72 hours. This media was further optimized by applying a two stage statistical approach namely Plackett Burman (PB) design and Response Surface Methodology (RSM). During validation of these experiments, S31 showed a significant increase in siderophore production. The siderophore in the CFS were extracted using 8-hydroxyquinoline, purified using column chromatography and characterized using LC-MS and FTIR. Application studies indicate the use of P. aeruginosa MGPB31 as an excellent plant growth promoter (PGPR) for plants in saline sodic areas. Apart from the isolate as PGPR, the CFS of the isolate also exhibited significant antibacterial and antioxidant activity.