Antibiotic producing and antagonistic microorganisms in the forest soils of Kerala

Abstract

The antibiotic producing and antagonistic fungi, actinomycetes and bacteria in the evergreen forest soils of Ladysmith forest of Thariyode in Wynad, and Cheriyakanom forest of Thekkadi in Idukki districts of Kerala State were studied. The phanerogamic flore around the sites of soil sample collection in both localities were identified. The total microbial population was studied in relation to the depth of soil. The microbial population was maximum in the top layer and decreased with increase in depth of soil. The total microbial population was higher in Idukki and in both districts, population of bacteria was maximum followed by actinomycetes and fungi. A diversified group of fungi consisting, Mucor, Syncephalastrum, Trichoderma, Microascus, Cunningphamella, Absidia, Aspergillus, Penicillium, Talaromyces, Paecelomyces and Fusarium was present. Three types of actinomycetes viz. Streptomyces sp. with straight sporophores, flexuous sporophores and fascicled sporophores were present while four types of bacteria viz., B. subtilis. Bacillus sp. identical to B. subtilis, Bacillus sp. with small cell and fast growth in NA and Bacillus sp. with small cell and slow growth in NA were present. Antagonistic properties of the isolated were studied with the test organisms Pythium myriotylum, Phytophthora palmivora and Rhizoctonia soleni. Mucor sp. and Cunninchamella elegans showed intermingling and overgrowth with all the test organisms while Absidia corymbefera, Syncephalastrum racemosum, Aspergillus meleus, A. tarreus, Microascus cinereus and Fusarium oxysporum showed this character with P. myriotylum and P. palmivora. Intermingling and overgrowth character was observed in Paecelomyces lilacinus with P. palmivora and R. solani whereas A. versicolor and three species of streptomyces showed this character only with P. palmivora. Mutual inhibition on contact was exhibited by Talaromyces wortmannii with all the three test organisms, while A. versicolor and Streptomyces spp. with flexuous sporophores and fascicled sporophores showed this character with P. myriotylum and R. solani. This character was observed in case of A. corymbefera, S. racemosum, A. meleus, M. cinereus, F. oxysporum and Streptomyces sp. with straigtht sporophores, with R. solani while P. lilacinus showed this with P. myrootylum. Mutual inhibition at a distance was shown by Penicillium citrinum, P. simplicissimum, B. subtilis and the other three Bacillus spp. when tested with P. palmivora and R. solani, but A. terreus showed this reaction only with R. solani. Inhibition at a distance and disintegration of test organism was shown by A. niger with P. myriotylum and R. solani while P. citrinum and P. simplicissimum showed this character only with P. myriotylum. All the three spp. of Trichoderma showed die – back and disintegration of all the three test organisms, while A. niger showed this character only with P. palmivora and A. sydowii showed this character with R. solani only. streptomyces sp. with straight sporophores, B. subtilis and the other three Bacillus spp. showed this character with P. myriotylum alone. Inhibitory properties of antagonists using cell free culture filtrates were estimated and found that A. niger inhibited 100 per cent growth of all the three test organisms while P. citrinum, P. simpliciccimum and B. subtilis showed 100 per cent inhibition of P. myriotylum and a range of 67-87 per cent in case of P. palmovora and R. solani. A. terreus did not inhibit P. myriotylum and P. palmivora, but inhibites 78 per cent of R. solani. All the three Trichoderma spp. moderately inhibited all the three test organisms (13-26 per cent) while A. sydowii showed 20 per cent inhibition of R. solani only. Antibiotic property of the antagonists was determined and P. citrinum exhibited maximum, equivalent to 325 ppm tetracycline followed by Streptomyces with straight sporophores having 250 ppm. T. longibracheatum, P. simplicissimum and A. versicolor recovered antibiotic property equivalent to 150 ppm tetracycline hydrochloride while the other isolates had < 100 ppm equivalence of tetracycline hydrochloride.