Production of hexanoic acid from D-galactitol by a newly isolated Clostridium sp. BS-1

In a study screening anaerobic microbes utilizing d-galactitol as a fermentable carbon source, four bacterial strains were isolated from an enrichment culture producing H-2, ethanol, butanol, acetic acid, butyric acid, and hexanoic acid. Among these isolates, strain BS-1 produced hexanoic acid as a major metabolic product of anaerobic fermentation with d-galactitol. Strain BS-1 belonged to the genus Clostridium based on phylogenetic analysis using 16S rRNA gene sequences, and the most closely related strain was Clostridium sporosphaeroides DSM 1294(T), with 94.4% 16S rRNA gene similarity. In batch cultures, Clostridium sp. BS-1 produced 550 +/- 31 mL L-1 of H-2, 0.36 +/- 0.01 g L-1 of acetic acid, 0.44 +/- 0.01 g L-1 of butyric acid, and 0.98 +/- 0.03 g L-1 of hexanoic acid in a 4-day cultivation. The production of hexanoic acid increased to 1.22 and 1.73 g L-1 with the addition of 1.5 g L-1 of sodium acetate and 100 mM 2-(N-morpholino)ethanesulfonic acid (MES), respectively. Especially when 1.5 g L-1 of sodium acetate and 100 mM MES were added simultaneously, the production of hexanoic acid increased up to 2.99 g L-1. Without adding sodium acetate, 2.75 g L-1 of hexanoic acid production from d-galactitol was achieved using a coculture of Clostridium sp. BS-1 and one of the isolates, Clostridium sp. BS-7, in the presence of 100 mM MES. In addition, volatile fatty acid (VFA) production by Clostridium sp. BS-1 from d-galactitol and d-glucose was enhanced when a more reduced culture redox potential (CRP) was applied via addition of Na2S center dot 9H(2)O.