Biosurfactant producing bacteria from the selected soils of Kerala

Abstract

A study on “Biosurfactant producing bacteria from the selected soils of Kerala” was conducted at College of Horticulture, Vellanikkara during the period from 2004-2006. Eight promising BS producing bacteria were selected by screening a total of 92 heterotrophic bacteria isolated from ten different hydrocarbon contaminated soil samples. Based on the morphological and biochemical characters, out of the 8 selected isolates, six cultures were tentatively identified as KCC-2 (Pseudomonas sp.), MCC-2 (Pseudomonas sp.), KFS1 (Pseudomonas sp.), KFN2 (Pseudomonas sp.), DTSC3 (Pseudomonas sp.) and DTSC5 (Pseudomonas sp.). The other two bacterial isolates MCN-3 and PFC-4 were identified through Microbial Type Culture Collections (MTCC), Institute of Microbial Technology (IMTECH), Chandigarh, as Geobacillus kaustophilus and Pseudomonas fluorescens with accession numbers MTCC 8517 and MTCC 8518 respectively. Per cent Biosurfactant producing bacterial population was estimated from the selected heterotrophic bacterial population, based on drop collapse assay and xylene spray method. Mancozeb treated vegetable plot gave maximum per cent BS bacteria (45.4per cent) followed by Eucalyptus plantations, Peechi and forest lands, Wyanad (37.5per cent in both cases). Extraction of BS production indicated that the isolate KFS1 from Eucalyptus plantations, recorded maximum BS production (7.95g/l) followed by MCN-3 (6.45 g/l) and DTSC3 (6.20 g/l). The eight selected BS bacteria recorded good xylene emulsification property. These isolates also lowered the surface tension values of the liquids viz., distilled water, glycerol (10-1 dilution), cyclohexane and methoxy ethanol monomethyl ether. The optimum nutritional and cultural conditions required for maximum BS production and emulsification activity were varied greatly among the bacterial isolates tested. Effect of selected BS bacteria on the degradation of pesticides viz., chlorpyriphos and mancozeb were studied, the isolate KFS1 from Eucalyptus plantations reduced the concentration of chlorpyriphos from 55.84 g /g to 16.03 g/g soil at 40 days after application (DAA) with 71.29 per cent degradation compared to control. And in mancozeb residue analysis studies, the isolate DTSC3 enriched soil sample, reduced the concentration of mancozeb from 0.738g/g to 0.478 g/g soil at 40 DAA and the per cent degradation was 28.44 per cent compared to control. Among the eight BS isolates, most of them showed high per cent inhibition to soil borne pathogens like Pythium aphanidermatum, Phytophthora capsici and Rhizoctonia solani and all of them are compatible to Trichoderma harzianum and T. viride. Among the eight isolates, six were compatible to Pseudomonas fluorescens. Selected BS isolates showed plant growth promoting effect by enhanced seed germination, plumule and radicle length in cowpea and sorghum seeds.