Enhanced Low-Temperature Corn Straw Degradation Using a Synthetic Microbial Mixture

The structural stability of lignocellulosic fibers in crop straw presents a significant challenge to its short-term biodegradation in natural environments, particularly in the cold regions of northern China. To isolate low-temperature straw-degrading bacteria, we selectively enriched microorganisms from straw-amended soils using lignocellulose as the sole carbon source. Three strains were isolated and identified: Stenotrophomonas sp. X24, Flavobacterium sp. X26, and Erwiniaceae bacterium X27. These strains were capable of growth and maize straw degradation within a 4–20 °C range and exhibited key cellulolytic activities (CMCase, FPase, and β-glucosidase). A synthetic three-strain mixture was assembled by combining these isolates in equal proportions. Solid-state fermentation (12 °C, 45 days) was used to assess straw degradation efficacy, while separate enzyme production experiments (12 °C, 3 days) were conducted to evaluate key cellulolytic activities and subsequently optimize culture conditions. The three-strain mixture achieved a net straw degradation rate of 30.93 ± 1.05%. Furthermore, optimization of culture conditions enhanced the carboxymethyl cellulase activity (CMCase) to a maximum of 24.51 ± 0.97 U/mL. The study demonstrates that the three-strain synthetic microbial mixture effectively degrades straw at low temperatures, offering a promising microbial resource to improve straw utilization and soil fertility in cold regions.