Dilution rates and their transition modes influence organic acid productivity and bacterial community structure on continuous meta-fermentation using complex microorganisms

• Published in: Journal of bioscience and bioengineering 2023-11, Vol.136 (5), p.391-399
• Main Authors: Koga, Tomonori, Ishizu, Mitsuoki, Watanabe, Kota, Miyamoto, Hirokuni, Oshiro, Mugihito, Sakai, Kenji, Tashiro, Yukihiro
• Format: Article
• Language: English
• Subjects: bacteria; bacterial communities; butyric acid; Caldibacillus; Clostridium cochlearium; community structure; lactic acid; species
• ISSN: 1389-1723; 1347-4421
• DOI: 10.1016/j.jbiosc.2023.08.004

We investigated the effect of dilution rates (D) (0.05, 0.15, and 0.4 h⁻¹) and its transition mode strategies (constant, up, and down modes) on organic acid productivity and bacterial community structure on continuous meta-fermentation using complex microorganisms. The number of bacterial species decreased with increasing D in the constant mode while up and down modes maintained high and low values, respectively, regardless of the changing D values. Caldibacillus hisashii was the predominant species in all modes at all D values, while other bacterial species, including Anaerosalibacter bizertensis and Clostridium cochlearium were predominant in only certain modes and D values. The highest total organic acid productivity of 3.16 g L⁻¹ h⁻¹ was obtained with 82.2% lactic acid selectivity at D = 0.4 h⁻¹ in constant mode. Heterofermentation occurred in the up mode, while the down mode exhibited the maximum butyric acid productivity of 0.348 g L⁻¹ h⁻¹ with 43.8% selectivity at D = 0.05 h⁻¹. The constant, up, and down modes showed the distinct main products of lactic, acetic, formic, and butyric acids, respectively. In this study, we proposed a new parameter of species-specific productivity (SSP) to estimate which species and how much a bacterium quantitatively contributes to the targeted organic acid productivity in continuous meta-fermentation. SSP was determined based on the abundance of functional genes encoding key enzymes from the results of 16S amplicon analysis. In conclusion, D values and their transition modes affect productivity by changing the bacterial community structure, and are a significant factor in establishing a highly productive process in continuous meta-fermentation.