The engineering of complex communities can be a successful path to understand the ecology of microbial systems and improve biotechnological processes. Here, we developed a strategy to assemble a minimal and effective lignocellulolytic microbial consortium (MELMC) using a sequential combination of dilution-to-stimulation and dilution-to-extinction approaches. The consortium was retrieved from Andean forest soil and selected through incubation in liquid media with a mixture of three types of agricultural plant residues. After the dilution-to-stimulation phase, approximately 50 bacterial sequence types, mostly belonging to the Sphingobacteriaceae, Enterobacteriaceae, Pseudomonadaceae and Paenibacillaceae, were significantly enriched. The dilution-to-extinction method demonstrated that only eight of the bacterial sequence types were necessary to maintain microbial growth and plant biomass consumption. After a subsequent stabilization, only two bacterial species (Pseudomonas sp. and Paenibacillus sp.) became highly abundant (> 99%) within the MELMC, indicating that these are the key players of degradation. Differences in the composition of bacterial communities between biological replicates indicated that selection, sampling and/or priority effects could shape the consortium structure. The MELMC can degrade up to ∼13% of corn stover, consuming mostly its (hemi)cellulosic fraction. Tests with chromogenic substrates showed that the MELMC secrete an array of endo-enzymes able to degrade xylan, arabinoxylan, carboxymethyl cellulose and wheat straw. Additionally, the metagenomic profile inferred from the phylogenetic composition next to an analysis of carbohydrate-active enzymes of twenty bacterial genomes supports the potential of the MELMC to deconstruct plant polysaccharides. This capacity was mainly attributed to the presence of Paenibacillus sp.
IMPORTANCE The significance of our study mainly lies on the development of a combined top-down enrichment strategy (i.e. dilution-to-stimulation coupled to dilution-to-extinction) to build a minimal and versatile lignocellulolytic microbial consortium. We demonstrated that mainly two selectively enriched bacterial species (Pseudomonas sp. and Paenibacillus sp.) are required to drive an effective degradation of plant polymers. Our findings can guide the design of a synthetic bacterial consortium that could improve saccharification (i.e. release of sugars from agricultural plant residues) processes in biorefineries. In addition, they can help to expand our ecological understanding of plant biomass degradation in enriched bacterial systems.