Thermophilic and Thermotolerant Fungi Isolated from Mangrove Swamps

Abstract

The ability of fungi to populate natural and man-made self-heated habitats has been reported by several workers, among them Cooney and Emerson (1964), Tansey (1971) and Tansey and Brock (1978). In addition, thermophilic fungi have been isolated from mesic habitats (Subrahamanyam, 1978; Ellis, 1980). Mangrove regions, because of their particular ecological conditions, viz., high salinity, moisture level, organic matter and pH, poor aeration, dense evergreen vegetation, and absence of elevated temperature, afford an interesting habitat for exploring comparatively the occurrence of thermophilic and thermotolerant fungi. Mud and wood samples were collected aseptically from Sunderban mangrove areas of West Bengal, India. Thermophilic fungi were isolated by a modified direct plate and a dilution plate method (Warcup, 1950, 1955). Three serial dilutions were used each with eight replicate plates. The fungi were isolated on Emerson's YpSs agar, Czapek-Dox agar supplemented with 1% cellulose, and malt extract agar with dicrysticin (0.2%), and incubated at 45 and 50 C in moist chambers. The thermophilic or thermotolerant nature of the species was determined by measuring their radial growth and dry mycelial weight on solid and liquid YpSs medium, respectively, at 20 and 50 C. Twenty-five species (Zygomycotina, Ascomycotina, and Deuteromycotina) were isolated including Aspergillus carbonarius, A. niger, A. niveus, and A. terreus var. africanus, recorded for the first time from India. Aspergillus carneus, A. fumigatus, A. niger, A. terreus, Chaetomium thermophile, Mucor pusillus, Sporotrichum sp., and Thermomyces lanuginosus were dominant and first to appear on agar plates, while Acrophialophorafusispora, Humicola insolans, Malbranchea sulfurea, and Paecilomyces variotii were rather rare. Per cent frequency of the species is given in TABLE I. The presence of thermophilic fungi in the mangrove swamp is of interest since the temperature is not elevated but there are extreme ecological conditions in other parameters. In spite of high salinity, pH, poor aeration, and dense vegetative cover, the presence of high organic matter and elevated moisture level in the swamp provides a suitable substrate for the growth of many fungi including thermophiles. Elliott (1930), who gave the first account of fungi inhabiting salt marsh sediments, concluded that organic matter is mainly responsible for the activity of fungi in such a unique habitat. The average annual rainfall and surface temperature in the study area are 192.04 cm and 20 to 33.7 C, respectively. These situations provide a suitable environment for the decomposition of organic matter thus favoring the conditions for the growth and occurrence of thermophilic fungi but at the same time other abnormal ecological conditions mentioned above limit this possibility. Although there is no evidence that these fungi are actively growing in the mangrove, the observations do show that propagules of thermophilic fungi exist in the mangrove swamps. There are three possible explanations. (1) Thermophilous fungi have a wide range of temperature tolerance so can grow within the range found in a mangrove habitat. (2) These fungi may be part of the microflora of the indigenous biota and may exist in soil and woods only as spores. (3) These fungi actually may be growing in warm microenvironments associated with de