Aims: Isolation and characterization of heavy metal tolerant microorganism from sea shore soil of Andaman Islands (India).
(a) Sample collection and isolation of multimetal resistant bacteria.
(b) Relative growth of bacterial isolates in presence of heavy metal.
(c) Characterization of bacterial isolates and antibiotic sensitivity profile.
(d) Capability of the production of extracellular enzyme(s).
Place and Duration of Study: Sea shore soils were collected from Ross I, Ross II, Port Blair and Havelock of Andaman Islands (India) with seasonal variation.
Methodology: Soil samples were analyzed for physico-chemical and microbiological characteristics. Bacteria isolated from sea shore soil were tested for their ability to tolerate cadmium, chromium, zinc, nickel, copper, cobalt, manganese, mercury, lead and arsenic in their growth medium and their relative growth in the presence of heavy metals determined. Antibiotic susceptibility test was done for different antibiotics with different concentrations. Biochemical tests were done to observe the diversity of the isolates. Degree of NaCl tolerance and extracellular enzyme production of selected isolates were done.
Results: The abundance of heavy metals in the sea shore soil are Pb>Zn>Cd>Cu>Mn>Ni=Co>Cr. The relative growth of the bacterial isolates were different for each strain, but the general order of resistance to the metals supplemented media was found to be as Pb> As> Mn> Zn > Cu > Cd> Ni and toxic effects of these metals increased with increasing concentration; however most of the isolates were sensitive to Hg, Cr and Co. Antibiotic susceptibility test showed varying results. Additionally, it was found that the strains were sensitive to four of the antibiotics tested. Biochemical characterization was indicative of the diverse microbial flora having multimetal resistance on one hand; on the other hand, they are potent producers of many useful enzymes like amylase, protease, lipase, catalase, urease, phosphatase etc., and are moderately halophilic.
Conclusion: The bacterial isolates from saline soil are of interest as they exhibit profound heavy metal tolerance and hence may be promising for bioremediation purpose and their molecular mechanisms for resistance to multiple metals needs further speculation.