The Succession of the Cellulolytic Microbial Community from the Soil during Oat Straw Decomposition

The decomposition of straw is a dynamic process, which is reflected in the decomposing microbial consortia, however, this process is poorly understood. Here we performed an experiment on the gradual colonization of oat straw by the soil microbial community. The results showed that soil respiration and bacterial diversity were negatively correlated – while the first decreased, the latter increased. In accordance with the dynamics of diversity and respiration, succession was divided into early, middle, and late decomposition phases. Analysis of 16S rRNA and ITS2 amplicon sequencing data revealed three jointly changing groups of phylotypes, corresponding with distinguished phases of decomposition. The presence of cellulolytic members of Proteobacteria, Bacteroidota, Firmicutes, and Actinobacteriota for bacteria and Ascomycota for fungi had been detected since the early phase, but most of the initial phylotypes were gone by the end of the phase. The second phase marked the functional core with a constant set of other phylotypes from these phyla, persisting in the community. Full metagenome sequencing of the microbial community from the end of the middle phase confirmed that major members of this consortium had GH genes, connected to cellulose and chitin degradation. The appearance of non-cellulolytic members from Bdellovibrio, Myxococcota, Chloroflexi, and Crenarchaeota characterized the last phase of the mature community.