Fermentative biohydrogen production by a new chemoheterotrophic bacterium Citrobacter sp. Y19

摘要

A newly isolated Citrobacter sp. Y19 for CO-dependent H_2 production was studied for its capability of fermentative H_2 production in batch cultivation. When glucose was used as carbon source, the pH of the culture medium significantly decreased as fermentation proceeded and H_2 production was seriously inhibited. The use of fortified phosphate at 60-180 mM alleviated this inhibition. By increasing culture temperatures (25-36℃), faster cell growth and higher initial H_2 production rates were observed but final H_2 production and yield were almost constant irrespective of temperature. Optimal specific H_2 production activity was observed at 36℃ and pH 6-7. The increase of glucose concentration (1-20 g/l) in the culture medium resulted in higher H_2 production, but the yield of H_2 production (mol H_2/mol glucose) gradually decreased with increasing glucose concentration. Carbon mass balance showed that, in addition to cell mass, ethanol, acetate and CO_2 were the major fermentation products and comprised more than 70% of the carbon consumed. The maximal H_2 yield and H_2 production rate were estimated to be 2.49 mol H_2/mol glucose and 32.3 mmol H_2/g cell h, respectively. The overall performance of Y19 in fermentative H_2 production is quite similar to that of most H_2-producing bacteria previously studied, especially to that of Rhodopseudomonas palustris P4, and this indicates that the attempt to find an outstanding bacterial strain for fermentative H_2 production might be very difficult if not impossible.