Background  Hydraulic fracturing serves as a stimulation technique extensively used in the commercial development of coalbed methane (CBM), in which guar gum is commonly used as a fracturing fluid thickener. However, under the low-temperature conditions of coal reservoirs, conventional chemical gel-breaking methods often suffer from incomplete gel breaking and high residue content, resulting in formation damage and a decrease in the production efficiency of CBM wells.

Methods  Using indigenous bacteria in coal seams as functional strains, this study conducted microbial gel-breaking experiments. It systematically investigated the characteristics of guar gum biodegradation by these bacteria and determined the dominant microbial taxa responsible for guar gum degradation.

Results and Conclusions  Indigenous bacteria in coal seams achieved the complete degradation of guar gum, meeting the gel-breaking requirement of fracturing fluids (viscosity≤5 mPa·s). Concurrently, they also reduced both the content and particle size of residues, effectively alleviating the potential formation damage induced by insoluble residues during the gel breaking of guar gum fracturing fluids. Guar gum was primarily hydrolyzed by indigenous bacteria into soluble polysaccharides, thereby reducing viscosity and achieving gel breaking. Analysis of microbial community structures revealed that Bacteroidota and Spirochaetota were the dominant functional phyla involved in guar gum degradation. Functional prediction using PICRUSt2 (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States 2) indicated that the guar gum degradation was primarily attributed to the synergistic activities of α-galactosidase (EC 3.2.1.22), β-mannosidase (EC 3.2.1.25), and β-mannanase (EC 3.2.1.78). Among these, β-mannanase exhibited the most pronounced increase in gene abundance, suggesting its central role in gel-breaking of guar gum. Furthermore, environmental factors directly influenced gel-breaking efficiency of guar gum, with the highest degradation efficiency occurring at 45 ℃ and pH 6.0. Despite the inhibitory effect of high salinity on guar gum degradation, the indigenous bacteria retained gel-breaking capability even at a salinity of 40 g/L. This study elucidates the degradation mechanism of guar gum by indigenous bacteria in coal seams and identifies the impact patterns of environmental factors on microbial gel-breaking performance. These findings provide a theoretical basis for the application of indigenous bacteria-based biological gel-breaking technology in CBM extraction.