Insight into hydrogen production through halotolerant and cellulose-degrading Clostridium thermopalmium

High salinity waste, such as food waste, is difficult for microbial utilization as high salt increases cellular osmosis. In this study, a novel cellulolytic halotolerant (<150 g/L salinity) strain Clostridium thermopalmarium HCD (halotolerant and cellulose-degrading strain) was screened from paper sludge, which obtained 108.47 and 42.53 mM hydrogen from cellobiose under 30 and 80 g/L NaCl respectively. HCD could improve 25.14 % hydrogen production of MT (a mixed thermophilic Clostridiales) consortium from co-substrates of pretreated sugarcane bagasse and food waste as bio-enhancer. Microbial community analysis showed that the inoculation of HCD profoundly changed the original community structure and dominant species of MT with the prolongation of fermentation time, leading to increase utilization of co-substrates and higher hydrogen production. In response to high salinity, HCD regulated the cell shape from a slender rod to a stubby one, balancing the high osmotic pressure. Furthermore, HCD could secrete and transport betaine as the main response to high salinity. Betaine could mediate the Na/K pump-like transport system, especially Na+/H+ antiporter to balance the intracellular osmotic pressure. Betaine could also relieve cell membrane damage, improving the transportation of extracellular P ions to the intracellular. Moreover, betaine could increase the levels of extracellular polymers and intracellular ATP. This study provided a halotolerant hydrogen-producing strain and its halotolerant mechanism, which paid a solid foundation for the utilization of high-salt waste biomass.