Metagenomic insights into the development of microbial communities of straw and leaf composts.

The microbial communities formed on two types of contrasting lignocellulosic biomass were used as the objects of investigation. As the basis we conducted a long-term experiment on the decomposition of oat straw and leaf litter using soil as a microbial inoculum. We studied enzymatic activity, taxonomic, CAZy (Carbohydrate-Active enzymes) and PULs (Polysaccharide Utilization Loci) composition of microbial communities at different stages of decomposition between substrates using a combination of 16S rRNA gene amplicon and long-read nanopore sequencing. The microbial community during straw degradation demonstrated higher amylase, protease, catalase, and cellulase activities, while leaf litter - peroxidase, invertase, and polyphenoloxidase. In accordance with this, the metagenome analysis showed that the microbiome of the straw compost was enriched in the genes from the metabolic pathways of simpler compounds, while leaf litter was more abundant in genes from pathways of aromatic compounds degradation. We revealed 8 MAGs (Metagenome-assembled genomes) as the most promising procaryotic decomposers due to the abnormally high quantity of PULs for their genome sizes, which were verified by 16S rRNA gene amplicon sequencing to be a major part of the community at all stages of decomposition. The MAGs belonging to Bacteroidota (Chitinophaga, Ohtaekwangia), Actinomycetota (Streptomyces) were found in both substrates, while ones from Bacillota (Pristimantibacillus) were specific for leaf litter. The most frequent PULs were specialized on xylans and pectins, but not cellulose, suggesting that PUL databases may be lacking PULs for complex substrates.