Directional screening for straw-degrading microorganisms tolerant to saline-alkali soil

To address the technical bottleneck of isolating low-abundance straw-degrading functional microorganisms in the soda saline-alkali soil of the Songnen Plain, this study adopted a "enrichment followed by screening" strategy. By simulating the dual selection pressure of salt-alkali stress and straw carbon source limitation, it broke through the limitation of the capture efficiency of salt-alkali-tolerant straw-degrading bacteria in traditional methods and screened salt-alkali-tolerant straw-degrading microorganisms. The study enriched the straw-degrading bacterial communities from the typical saline-alkali soil of the Songnen Plain, namely the Da'an rice field (DA) and the Taobei rice field (TB), and the target bacterial communities DA-12W and TB-12W after 12 rounds of serial dilution and amplification were obtained. The bacterial community structure and function were systematically analyzed through amplicon sequencing, and the dominant strains were screened by the aniline blue plate coloration method. The strains were then identified through morphological, physiological and biochemical, and molecular biological methods. A total of 165 initial screening strains were isolated from the DA and TB soils. Among them, three highly efficient strains maintain high growth activity under pH 9 - 11 with advantages in laccase, xylanase and cellulase activities. The degradation rate of rice straw by these three strains is 11.8% - 16.2%. The initial relative abundance of strain TB324A in TB soil is 0.49%; and after 12 generations of continuous enrichment, its proportion in the TB-12 community significantly increases to 2.19%, with an enrichment factor of 4.47 times. Strain 524A in DA exhibits stronger enrichment potential. Its original proportion is only 0.02%; and after the same number of generations of cultivation, its proportion in the DA-12W community increases sharply to 0.28%, achieving a 14-fold increase. Strain HY01 achieves a 1.5-fold increase (0.02% → 0.03%) under the same culture conditions. The "enrichment followed by screening" strategy can efficiently mine microbial resources with both salt-alkali tolerance and straw degradation functions. The screened strains have good adaptability to salt-alkali environments and degradation capabilities, providing a technical paradigm for the exploration of microbial resources in saline-alkali soils.