Coculture with hemicellulose-fermenting microbes reverses inhibition of corn fiber solubilization by Clostridium thermocellum at elevated solids loadings

Abstract Background The cellulolytic thermophile Clostridium thermocellum is an important biocatalyst due to its ability solubilize lignocellulosic feedstocks without the need for pretreatment or exogenous enzyme addition. At low concentrations of substrate, C. can corn fiber > 95% in 5 days, but solubilization declines markedly at substrate higher than 20 g/L. This differs model cellulose like Avicel, on which maximum rate increases proportion concentration. goal this study was examine fermentation increasing and investigate possible reasons declining performance. Results growth fiber, inferred from CipA scaffoldin levels measured by LC–MS/MS, showed very little increase with solids loading. To test inhibition, we evaluated effects spent broth cellulase activity. liquids remaining after were found be strongly inhibitory cellobiose, a that does not require hydrolysis. Additionally, hydrolytic activity also reduced less-than half adding broth. Noting 15 g/L hemicellulose oligosaccharides accumulated 40 fermentation, tested effect various carbohydrates cellobiose Avicel. Some compounds xylooligosaccharides caused decline reduction However, there no relevant could replicate strong inhibition cellobiose. Cocultures hemicellulose-consuming partners— Herbinix spp. strain LL1355 Thermoanaerobacterium thermosaccharolyticum —exhibited lower unfermented hydrolysis products, doubling rate, final increased 67 93%. Conclusions documents concentration demonstrates xylooligosaccharides, further work needed understand why inhibited Our results support importance hemicellulose-utilizing coculture partners augment high