ANTIFUNGAL PROPERTIES OF CHITINOLYTIC DUNE SOIL BACTERIA

Anti-fungal properties of chitinolytic soil bacteria may enable them t o compete successfully for chitin with fungi. Additionally, the produc tion of chitinase may be part of a lytic system that enables the bacte ria to use living hyphae rather than chitin as the actual growth subst rate, since chitin is an important constituent of most fungal cell wal ls. Lysis of living fungal hyphae by chitinolytic bacteria has been re ported frequently; however, these reports nearly always dear with bact eria that had been selected because of their mycolytic properties. Our main objective was to get a better understanding of the relationship between chitinolytic and anti-fungal properties of bacteria that occur naturally in soils, i.e. without artificial selection. Three inner du ne sites, two of which were lime-poor and one lime-rich, along the Dut ch coast were selected for this study. Bacteria that were able to degr ade colloidal chitin in water-agar comprised 0.2-5.7% of the total amo unt of culturable bacteria of these dune sites. Pseudomonas spp. were the most abundant culturable, chitin-degrading bacteria at the lime-po or sites, whereas Xanthomonas spp. and Cytophaga spp. were important a t the lime-rich site. Chitinolytic actinomycetes were relatively abund ant at all three sites. Chitinolytic and non-chitinolytic bacteria wer e randomly selected and tested for the possession of antagonistic acti vities against Fungal dune strains [Chaetomium globosum, Fusarium culm orum, F. oxysporum, Idriella (Microdochium) bolleyi, Mucor hiemalis, P homa exigua, Ulocladium sp.]. The tests were done using water-agar to Simulate the energy-limiting conditions that bacteria will encounter i n dune soils. The percentage of bacterial isolates that were antagonis tic against these fungi was considerably higher for chitinolytic strai ns than for non-chitinolytic ones. Therefore, the possible involvement of chitinase with respect to the inhibition of fungal growth was stud ied in more detail. It appeared that in many cases the inhibition of f ungal growth was not accompanied by bacterial chitinase production. Th ere was also no clear relationship between the activity of other cell wall degrading enzymes (beta-1, 3-glucanase and protease) and antagoni sm. Chitinolytic bacteria had selective rather than general anti-funga l properties, which were not necessarily related to differences in gen eral susceptibility of the fungi towards antagonism. These results may indicate that antibiotics were involved in the antagonistic activitie s of chitinolytic bacteria against fungi. Only growing fungi were anta gonized by the chitinolytic bacteria; none of the chitinolytic bacteri a were able to lyse existing mycelium of any of the fungi. The relevan ce of the results for the ecology of chitinolytic soil bacteria is dis cussed. (C) 1997 Published by Elsevier Science Ltd. All rights reserve d.