Meta-fermentation system with a mixed culture for the production of optically pure l-lactic acid can be reconstructed using the minimum isolates with a simplified pH control strategy

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

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 and 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.

Global trends and future prospects of lactic acid production from lignocellulosic biomass

Lignocellulosic biomass (LCB) stands as a substantial and sustainable resource capable of addressing energy and environmental challenges. This study employs bibliometric analysis to investigate research trends in lactic acid (LA) production from LCB spanning the years 1991 to 2022. The analysis reveals a consistent growth trajectory with minor fluctuations in LA production from LCB. Notably, there's a significant upswing in publications since 2009. Bioresource Technology and Applied Microbiology and Biotechnology emerge as the top two journals with extensive contributions in the realm of LA production from LCB. China takes a prominent position in this research domain, boasting the highest total publication count (736), betweenness centrality value (0.30), and the number of collaborating countries (42), surpassing the USA and Japan by a considerable margin. The author keywords analysis provides valuable insights into the core themes in LA production from LCB. Furthermore, co-citation reference analysis delineates four principal domains related to LA production from LCB, with three associated with microbial conversion and one focused on chemical catalytic conversion. Additionally, this study examines commonly used LCB, microbial LA producers, and compares microbial fermentation to chemical catalytic conversion for LCB-based LA production, providing comprehensive insights into the current state of this field and suggesting future research directions.

Noninvasive fecal metabolic profiling for the evaluation of characteristics of thermostable lactic acid bacteria, Weizmannia coagulans SANK70258, for broiler chickens

Weizmannia coagulans SANK70258 is a spore-forming thermostable lactic acid bacterium and an effective probiotic for the growth of livestock animals, but its growth-promoting mechanism remains unclear. Here, the composition of fecal metabolites in broilers continuously administered with W. coagulans SANK70258 was assessed under a regular program with antibiotics, which was transiently given for 6 days after birth. Oral administration of W. coagulans to broiler chicks tended to increase the average daily gain of body weights thereafter. The composition of fecal metabolites in the early chick stage (Day 10 after birth) was dramatically altered by the continuous exposure. The levels of short-chain fatty acids (SCFAs) propionate and butyrate markedly increased, while those of acetate, one of the SCFAs, and lactate were reduced. Simultaneously, arabitol, fructose, mannitol, and erythritol, which are carbohydrates as substrates for gut microbes to produce SCFAs, also increased along with altered correlation. Correlation network analyses classified the modularity clusters (|r| > 0.7) among carbohydrates, SCFAs, lactate, amino acids, and the other metabolites under the two conditions. The characteristic diversities by the exposure were visualized beyond the perspective associated with differences in metabolite concentrations. Further, enrichment pathway analyses showed that metabolic composition related to biosynthesis and/or metabolism for SCFAs, amino acids, and energy were activated. Thus, these observations suggest that W. coagulans SANK70258 dramatically modulates the gut metabolism of the broiler chicks, and the metabolomics profiles during the early chick stages may be associated with growth promotion.