Fermentative hydrogen production from different sugars by Citrobacter sp. CMC-1 in batch culture

In this study, production of hydrogen (H2) from glucose, xylose, galactose, mannose, arabinose and rhamnose by a strain isolated from activated sludge was investigated. The strain, named as Citrobacter sp. CMC-1, was enriched in cellobiose amended minimal media. Based on 16S rRNA sequence, the CMC-1 strain is a close relative of Citrobacter amalonaticus strain SA01 (99%). Optimal cultivation parameters for H2 production and growth such as pH and temperature were investigated. H2 yields from glucose at optimal conditions (pH 6.0 and 34 °C) were 1.82 ± 0.02 mol-H2/mol-glucose. Strain CMC-1 fermented galactose, mannose, xylose, arabinose and rhamnose. After 48 h incubation, the strain CMC-1 completely fermented all sugars tested, except arabinose. Increase in fermentation period lowered residual formate level in the media and improved H2 production for galactose, mannose and xylose (1.68 ± 0.24, 1.93 ± 0.14 and 1.63 ± 0.07 mol-H2/mol-substrate respectively).

► An efficient hydrogen producing strain, CMC-1 affiliated with Citrobacter sp., was isolated from activated sludge. ► The isolate produced H2 at all pH and temperature ranges tested. ► H2 yield at optimal conditions were 1.82 ± 0.02. ► CMC-1 fermented monomeric hemicellulose sugar moieties producing H2. ► Prolonged fermentation resulted in residual formate breakdown and improved H2 production from xylose, galactose and mannose.