Characteristics and Propionate Production of Propionibacterium Isolated from a Methane fermentation Digester

Abstract

Characteristics and propionate production of propionate-producing becteria in an anaerobic digester were examined.Strains VA-1, MC-1 and KA-2 isolated from sludge were nonmotile, nonspore forming, gram-positive and pleomorphic rods.They fermented lactate to propionate and acetate both with a complex medium and with a mineral medium.The molar ratio of propionate to acetate was 2/1.They utilized glucose, lactate, fumarate, malate, pyruvate and serine for growth, but could not use starch and inulin.From these results the propionate-producing bacteria are considered to be classified into the genus Propionibacterium according to Bergey’s manual of determinative bacteriology.Propionibacterium in methane fermentation sludges may utilize low molecular compounds such as monosaccharides, organic acids and amino acids to produce propionate and acetate.PCR amplification using genus-specific primers supported this identification as Propionibacterium.Lactate was converted to propionate and acetate in the dual culture with Propionibacterium sp.strain VA-1 and Desulfovibrio vulgaris strain F-1 in the presence of sulfate.In the triculture with strain VA-1 and strain F-1 in syntrophic association with Methanobacterium formicicum strain HM-1 in the absence of sulfate, lactate was fermented to propionate, acetate and methane.The molar ratio of propionate to acetate in both mixed cultures decreased by about 1/8 as compared with that of the single culture of strain VA-1.The ratio, however, increased 2/1 in the case of the triculture at pH 5.0.Although the population of Propionibacterium in the dual culture and the triculture at pH 7.0 was large, the amount of propionate produced was not.Because of the slow growth rate of Propionibacterium, the propionate production may increase slowly.Under acidic conditions, propionate produced by Propionibacterium is considered to be accumulated in an anaerobic digester as sulfate reducers and methanogens are not able to grow under the conditions.