Enhanced bacterial cellulose production from spent coffee grounds: a dual-strategy synergy via mannose metabolism and pellicle inoculation

ABSTRACT Mannose constitutes a principal component in numerous biomass hemicelluloses; however, its utilization by the cellulose-producing bacterium Komagataeibacter xylinus is inefficient. Consequently, during biorefinery and the transformation of biomass rich in mannose for the production of the high-value biological product, bacterial cellulose (BC), the biomass components cannot be fully utilized, leading to resource wastage. Moreover, inappropriate discharge of the fermentation effluent may also result in environmental pollution. This study addressed the underutilization of mannose in spent coffee grounds (SCGs) by introducing a fusion vector expressing mannokinase and phosphomannose isomerase into K. xylinus ATCC 23770, thereby enhancing mannose utilization in this strain model. SCG was pretreated with concentrated sulfuric acid to disrupt crystalline structures, followed by enzymatic hydrolysis to extract saccharides. When culturing in SCG hydrolysate, BC pellicle-derived inoculum achieved 1.2-fold higher BC yield than broth inoculum, attributed to BC matrix protection. The engineered strain K. xylinus CGMCC 31806 demonstrated superior mannose assimilation, yielding 1.5-fold more BC than wild type in simulated SCG medium. In authentic SCG medium without extra nitrogen addition, BC production reached 3.80 g/L, a 1.2- to 2.5-fold increase. The obtained BC exhibited enhanced mechanical properties with 40–84% higher tensile strength and 20–75% increased Young’s modulus. This study validates a dual strategy combining agro-waste valorization and targeted strain modification, establishing a collaborative optimization framework linking biomass feedstocks, microbial engineering, and bioprocessing for cost-effective BC production. Future research would utilize existing commercial high-yield strains to replicate the expression strategy of this fusion protein, in order to achieve truly efficient industrial production. IMPORTANCE The inefficient utilization of mannose, a major hemicellulose component prevalent in biomass by Komagataeibacter xylinus represents a significant bottleneck in the sustainable, cost-effective bioproduction of bacterial cellulose (BC). This underutilization would lead to wasted resources and potential environmental pollution from fermentation effluents. The study directly addresses this critical challenge by pioneering a synergistic “Feedstock-Strain-Process” integration strategy in advancing BC industrialization. We demonstrate the significant impact of engineering K. xylinus for enhanced mannose assimilation coupled with optimized biorefinery of agro-industrial waste, taking mannose-rich spent coffee grounds, as the representative raw material. This integrated approach not only valorizes abundant agricultural waste streams significantly boosting BC yields under nutrient-limited conditions but also generates BC with superior mechanical properties. The study establishes an actionable blueprint for advancing BC industrialization through collaborative optimization of biomass feedstocks, targeted microbial engineering, and process innovation, aligning with the goals of the circular bioeconomy and sustainable material production.