Seasonal variation and distribution of total and active microbial community of β-glucosidase encoding genes in coniferous forest soil

Abstract

Cellulose is the most abundant polysaccharide in the dead plant biomass, and its degradation is an important part of global carbon cycle. β-Glucosidases complete the final step of cellulose hydrolysis by converting cellobiose to glucose. Genetic potential and expression of β-glucosidase genes were studied in the topsoil of a Picea abies forest in two contrasting seasons. These seasons were the summer, representing the peak of plant photosynthetic activity, and late winter, after an extended period with no photosynthate input. Fungal and bacterial β-glucosidase genes belonging to glycoside hydrolase families GH1 and GH3 amplified from DNA and RNA and amplicon pools were analyzed. Transcript pool were largely corresponded to gene pools, although some abundant transcripts were not found in the gene pool. The major reservoirs of β-glucosidase genes were the fungal phylum Ascomycota and Basidiomycota and the bacterial phyla Firmicutes, Actinobacteria, Proteobacteria Acidobacteria and Deinococcus-Thermus. This indicates that a diverse microbial community utilized cellobiose. Seasonality influenced both genetic diversity of β-glucosidase genes and their expression. The results indicate that a complex community of bacteria and fungi expresses β-glucosidases in forest soils. Even β-glucosidase genes showing low abundance in DNA may be functionally important as revealed by their high expression especially in basidiomycota. The functional diversity in the studied ecosystem clearly exhibited a seasonal pattern.