Dynamics of Dark Fermentation Microbial Communities in the Light of Lactate and Butyrate Production

Abstract

Background: This study focuses on the processes occurring during acidogenic step of anaerobic digestion, especially resulting from nutritional interactions between dark fermentation (DF) bacteria and lactic acid bacteria (LAB). Previously, we have confirmed that DF microbial communities fed on molasses are able to convert lactate and acetate to butyrate in batch experiments. The aims of the study were: (i) to recognize biodiversity of DF microbial communities able and unable to convert lactate and acetate to butyrate and (ii) to define the conditions for the transformation in static batch experiments.Results: Sucrose stimulated bacterial growth, especially LAB. In the samples where the microbial communities fermented media containing carbohydrates the two main tendencies were observed: (i) a low pH (pH≤4), lactate and ethanol as the main fermentation products, microbial communities dominated with Lactobacillus, Bifidobacterium, Leuconostoc and Fructobacillus was characterised by a low biodiversity; (ii) pH in the range 5.0-6.0, butyrate dominated among the fermentation products, the microbial communities composed mailny of Clostridium (especially Clostridium sensu stricto 12), Lactobacillus, Bifidobacterium and Prevotella. The biodiversity increased with the ability to convert acetate and lactate to butyrate. The microbial communities processing exclusively lactate and acetate showed the highest biodiversity and was dominated by Clostridium (especially Clostridium sensu stricto 12). LAB were reduced, other genera such as Terrisporobacter, Lachnoclostridium, Paraclostridium or Sutterella were found. Butyrate was the main metabolite and pH was 7. WGS analysis of the selected butyrate-producing microbial communities independently on the substrate, revealed C. tyrobutyricum as a dominant Clostridium species. Conclusions: The batch tests revealed dynamics of metabolic activity and composition of DF microbial communities dependent on fermentation conditions. The results expand our knowledge on lactate to butyrate conversion by DF microbial communities. The relevant factor for conversion of lactate and acetate to butyrate in the presence of carbohydrates is pH in the range 5-6 and the balance between LAB (especially Lactobacillus), lactate and acetate producers (Bifidobacterium) and butyrate producers (mainly Clostridium) as well Prevotella. The pH below 4 and ethanol concentration might be the signalling factors responsible for metabolic shift of the dark fermentation microbial communities towards lactate fermentation.

Dynamics and Complexity of Dark Fermentation Microbial Communities Producing Hydrogen From Sugar Beet Molasses in Continuously Operating Packed Bed Reactors

“…It is illustrated by PBR3 (34 g COD of molasses/L), where the development of all groups of bacteria and a large variety of non-gaseous fermentation products were observed. On the other hand, a decrease of substrate concentration to 8.5 g COD of molasses/L inhibited the development of LAB in the microbial community (PBR2) that supports our current (PBR4) and previous (Detman et al, 2020) observations that sucrose stimulates LAB in DF consortia. Other factors preventing biomass accumulation and overproduction of SCFAs or alcohols are the HRT and the working volume that, together with the proper substrate concentration, ensure effective substrate utilization and gas release (Castelló et al, 2020).…”

“…Recently, we have reported that the balance between LAB and butyrate-producing clostridia, and the pH conditions are the most relevant factors for the process of conversion of lactate and acetate to butyrate. Furthermore, the structure of the microbial communities most efficiently producing hydrogen presented here is comparable to the structure of consortia capable of conversion of lactate and acetate to butyrate (Detman et al, 2020). This supports the significance of the lactate and acetate conversion pathways in hydrogen-producing microbial communities postulated by other authors (Hung et al, 2007;Matsumoto and Nishimura, 2007;Yang et al, 2007;Jo et al, 2008;Juang et al, 2011;Wu et al, 2012;García-Depraect et al, 2017, 2019aGarcía-Depraect and León-Becerril, 2018;Palomo-Briones et al, 2018;Fuess et al, 2019).…”

“…Then we have recognized the biodiversity and dynamics of DF microbial communities able and unable to convert lactate and acetate to butyrate, and the conditions for conversion. The relevant factors for transformation of lactate and acetate to butyrate in the presence of carbohydrates are pH in the range 5–6 and the balance between LAB (especially Lactobacillus ), acetate producers ( Bifidobacterium) and butyrate producers (mainly Clostridium ) as well as Prevotella ( Detman et al, 2020 ).…”

Mixed Acid Fermentation of Carbohydrate-Rich Dairy Manure Hydrolysate

“…However, Liu et al proposed Clostridium sensu stricto 12 to be able to perform such a co-utilization (Liu et al, 2020). Furthermore, an experiment where organic substrate exclusively consisted of C2 and lactic acid was shown to enrich for both Clostridium sensu stricto 12 and Caproiciproducens while producing C4 (Detman et al, 2021). Thus, the co-utilization of C2 and lactic acid for the production of C4 may indeed have occurred in the DMB bioreactor.…”