Engineering artificial microbial consortia for efficient lactic acid fermentation from undetoxified hydrolysates: from induced niche succession in a dual Bacillus coagulans consortium to Pseudomonas putida-assisted system reinforcement.

backgroundLignocellulosic biomass represents an ideal feedstock for biochemical production as a sustainable alternative to fossil resources. However, high concentrations of inhibitors inevitably generated during pretreatment-particularly phenolic compounds-severely impede microbial growth and metabolism, representing a major bottleneck in biorefining. In contrast to expensive physicochemical detoxification or single-strain strategies burdened by heavy metabolic loads, microbial co-culture systems employing division of labor offer a highly efficient and cost-effective novel pathway.

resultsThis study developed a novel dual Bacillus coagulans co-culture system consisting of a phenolic acid decarboxylase (PAD)-overexpressing engineered strain, DSM1-25280, and a high-yield L-lactic acid (LA) producer, CC17B-1, capable of directly utilizing highly toxic lignocellulosic hydrolysates for high-titer LA production. Notably, overexpression of PAD in the engineered strain DSM1-25280 not only enhanced tolerance to phenolic acids but also significantly accelerated vanillin degradation. By establishing a sequential inoculation strategy and optimizing both inoculation ratios and intervals, the dual-strain system achieved a LA titer of 124.72 g/L from undetoxified corncob hydrolysates. Multidimensional association analysis suggested a strongly supported model of niche succession process within the system, transitioning from biodetoxification-mediated commensalism to competitive exclusion. Furthermore, we constructed an enhanced three-strain co-culture system by incorporating a sugar-metabolism-deficient engineered Pseudomonas putida KT2440 ZL as a heterologous aromatic scavenger. This system further elevated the LA titer to 146.00 g/L with a yield of 98.9%, ranking among the highest levels reported to date for LA production from undetoxified hydrolysates.

conclusionsThe constructed microbial co-culture system significantly enhances LA fermentation performance using undetoxified lignocellulosic hydrolysates, bypassing the need for physicochemical detoxification. Demonstrating exceptional modularity and robustness, this sequential co-culture strategy effectively overcomes the toxicity bottlenecks inherent in traditional bioconversion processes. Ultimately, this work not only validates the superiority of division of labor in valorizing complex feedstocks but also provides a novel approach for the efficient biomanufacturing of high-value chemicals from low-grade biomass.