The duo Clostridium and Lactobacillus linked to hydrogen production from a lignocellulosic substrate

Abstract

The study aimed to identify interspecies interactions within a native microbial community present in a hydrogen-producing bioreactor fed with two wheat straw cultivars. The relationships between the microbial community members were studied building a canonical correspondence analysis and corroborated through in vitro assays. The results showed that the bioreactor reached a stable hydrogen production of ca. 86 mL/kg·d in which the cultivar change did not affect the average performance. Lactobacillus and Clostridium dominated throughout the whole operation period where butyric acid was the main metabolite. A canonical correspondence analysis correlated positively Lactobacillus with hydrogen productivity and hydrogen-producing bacteria like Clostridium and Ruminococaceae. Agar diffusion testing of isolated strains confirmed that Lactobacillus inhibited the growth of Enterococcus, but not of Clostridium. We suggest that the positive interaction between Lactobacillus and Clostridium is generated by a division of labor for degrading the lignocellulosic substrate in which Lactobacillus produces lactic acid from the sugar fermentation while Clostridium quickly uses this lactic acid to produce hydrogen and butyric acid. The significance of this work lies in the fact that different methodological approaches confirm a positive association in the duo Lactobacillus–Clostridium in a bioreactor with stable hydrogen production from a complex substrate. HIGHLIGHTS Native microbiota of wheat straw reached a stable hydrogen production.; Microbial structure was stable dominated by Lactobacillus and Clostridium.; Statistical analysis and in vitro assays demonstrated positive interactions.; Division of labor in lignocellulose consumption could promote positive interactions.;

Keywords

• agar diffusion method
• antibacterial activity
• bioenergy
• complex substrate
• microbial interactions