Chitinolytic activity of Pseudomonas fluorescens isolates from barley and sugar beet rhizosphere

Twelve isolates of Pseudomonas fluorescens, isolated from barley and sugar beet rhizosphere as antagonists towards the plant pathogenic microfungi Rhi zoctonia solani and Pythium ultimum, showed chitinolytic activity in batch cultures when grown in media without exogenous chitin. Enzyme tests in cult ures demonstrated a complete array of chitinolytic enzymes. Endochitinase a nd chitobiosidase activities seemed to be tightly coupled in the isolates, while there was no relationship to N-acetyl-glucosaminidase activity. Endoc hitinase activity, showing hydrolysis of chitin polymers, was found to be e xtracellular in all isolates, although the most active isolates also retain ed a cell-bound fraction. Isoelectric focusing gel electrophoresis of super natants containing extracellular enzyme activity showed that all isolates p roduced one native endochitinase in logarithmic phase. This enzyme was subs equently modified into several isozymes by extracellular processing as the cultures aged in stationary phase. The 12 isolates could be grouped into se ven isozymic patterns. Detailed studies of three selected isolates showed t hat extracellular release of endochitinase activity also took place in stat ionary phase. The results, however, indicated that in stationary phase regu lation of both the overall production of native enzyme and the subsequent f ormation of isozymes were different among the P. fluorescens isolates. (C) 1999 Federation of European Microbiological Societies. Published by Elsevie r Science B.V. All rights reserved.