Physiological growth parameters and enzyme production in tropical freshwater fungi

Physiological growth parameters and enzymatic activities were investigated in wood decay fungi to understand their ecological roles. Ascomycetes and h yphomycetes were isolated from submerged wood collected in tropical and sub -tropical freshwater. The radial growth rates of these isolates at various temperatures and on selected medium were measured every two days. The optim um temperatures for growth of most tropical and subtropical freshwater fung i are 20 degrees C and 25 degrees C, which is similar to the results, repor ted in temperate species. The radial growth rates of most fungi tested were greater than 2 mm per day with the exception of Lophiosphaeria rivulicola and Massarina thalassiensis. Tropical freshwater fungi do not grow well, at low temperatures and so are absent in temperate regions. Although temperat e species grow best at 25 degrees C, they are not able to grow as rapidly a s tropical species and this probably accounts for their absence in tropical streams. Enzyme tests on agar plates showed that most isolates were able t o produce a variety of enzymes including amylase, polyphenol oxidase, endog lucanase and laccase. Ophioceras dolichostomum II and Annulatascus cateract ispora which are commonly recorded fast extending fungi, produced negative results in phenol oxidase and laccase, but had a high amylase activity. It is possible that these are early successional species which utilize soluble sugar and starch only, and have no lignin degradation ability.