Production of extracellular enzymes participating in the degradation of biopolymers was studied in 29 strains of nonbasidiomycetous microfungi isolated from Quercus petraea forest soil based on the frequency of occurrence. Most of the isolates were ascomycetes and belonged to the genera Acremonium, Alternaria, Cladosporium, Geomyces, Hypocrea, Myrothecium, Ochrocladosporium, and Penicillium (18 isolates), and two isolates were zygomycetes. Only six isolates showed phenol oxidation activity which was low and none of the strains were able to degrade humic acids. Approximately half of the strains were able to degrade cellulose and all but six degraded chitin. Most strains produced significant amounts of the cellulolytic enzymes cellobiohydrolase and β-glucosidase and the chitinolytic enzymes chitinase, chitobiosidase, and N-acetylglucosaminidase. The highest cellulase activities were found in Penicillium strains, and the highest activity of chitinolytic enzymes was found in Acremonium sp. The production of the hemicellulose-degrading enzymes α-galactosidase, β-galactosidase, and α-mannosidase was mostly low.The microfungal strains were able to produce significant growth on a range of 41-87, out of 95 simple Ccontaining substrates tested in a Biolog™ assay, monosaccharides being for all strains the most rapidly metabolized C-sources. Comparison with saprotrophic basidiomycetes from the same environment showed that microfungi have similar cellulolytic capabilities and higher chitinase activities which testifies for their active role in the decomposition of both lignocellulose and dead fungal biomass, important pools of soil carbon.

No abstract

No abstract

Selected flavonoids that are known as inducers and a suppressor of nodulation (nod) genes of the symbiotic bacterium Rhizobium leguminosarum bv. viciae were tested for their effect on symbiosis formation with garden pea as the host. A solid substrate was omitted from the hydroponic growing system in order to prevent losses of flavonoids due to adsorption and degradation. The presumed interaction of the tested flavonoids with nod genes has been verified for the genetic background of strain 128C30. A stimulatory effect of a nod gene inducer naringenin on symbiotic nodule number formed per plant 14 d after inoculation was detected at concentrations of 0.1 and 1 micro g ml(-1) nutrient solution. At 10 micro g ml(-1), the highest concentration tested, naringenin was already inhibitory. By contrast, nodulation was negatively affected by a nod gene suppressor, quercetin, at concentrations above 1 micro g ml(-1), as well as by another tested nod gene inducer, hesperetin. The deleterious effect of hesperetin might be due to its toxicity or to the toxicity of its degradation product(s) as indicated by the inhibition of root growth. Both the stimulatory effect of naringenin and the inhibitory effect of quercetin on nodule number were more pronounced at earlier stages of nodule development as revealed with specific staining of initial nodules. The lessening of the flavonoid impact during nodule development was ascribed to the plant autoregulatory mechanisms. Feedback regulation of nodule metabolism might also be responsible for the fact that the naringenin-conditioned increase in nodule number was not accompanied by any increase in nitrogenase activity. By contrast, the inhibitory action of quercetin and hesperetin on nodule number was associated with decreases in total nitrogenase activity. Naringenin also stimulated root hair curling (RHC) as one of the earliest nodulation responses at concentrations of 1 and 10 microg ml(-1), however, the same effect was exerted by the nod gene suppressor, quercetin, suggesting that feedback regulatory mechanisms control RHC in the range of nodulation-inhibiting high flavonoid concentrations. The comparison of the effect of the tested flavonoids in planta with nod gene activity response showed a two orders of magnitude shift to higher concentrations. This shift is explained by the absorption and degradation of flavonoids by both the symbionts during 3 d intervals between hydroponic solution changes. The losses were 99, 96.4, and 90% of the initial concentration of 10 micro g ml(-1) for naringenin, hesperetin, and quercetin, respectively.

No abstract