Butyric acid production from red algae, Gelidium amansii, hydrolysate by a newly isolated Clostridium sp. S1

Abstract

Because of the depletion of petroleum oil and increasing concern for global warming, there have been considerable efforts and progress in developing renewable energy. Biomass is regarded as a key resource because it can be used as a feed stock for microbial production of biofuels and biochemicals. Seaweed (macroalgae) is attractive as biomass feedstock because it does not encounter foodstuff and can grow in vast tracts of sea. Especially, red algae such as Gelidium amansii contain high level of carbohydrates (77.2 %), feasible for using as a feed stock for microbial fermentation. Galactose is a main carbohydrate in G. amansii. Here, we report a newly isolated bacterium, designated as Clostridium sp. S1, which is capable of producing butyric acid from galactose as a sole carbon source and the hydrolysate of G. amansii. In batch cultures, the strain S1 produced 7.0 g/L of butyric acid from 13.1 g/L of galactose in 48 hours. Interestingly, Clostridium sp. S1 simultaneously utilized glucose and galactose without catabolite repression. When G. amansii was hydrolyzed through dilute acid hydrolysis, 12.5 g/L of sugar was obtained from 40 g/L of G. amansii and Clostridium sp. S1 successfully produced 5.0 g/L of butyric acid as the only product using the hydrolysate of G. amansii. Since Clostridium sp. S1 was not inhibited by inhibitors generated during G. amansii hydrolysis process, additional detoxification step was not needed. To our knowledge, this study is the first report of butyric acid production using galactose and the hydrolysate of G. amansii with a high yield and selectivity.