Production of high-concentration n-caproic acid from lactate through fermentation using a newly isolated Ruminococcaceae bacterium CPB6

Abstract

Background n-Caproic acid (CA), as a medium-chain carboxylic acid, is a valuable chemical feedstock for various industrial applications. The fermentative production of CA from renewable carbon sources has attracted a lot of attentions. Lactate is a significant intermediate waste in the anaerobic breakdown of carbohydrates that comprise 18–70% of the chemical oxygen demand (COD) in municipal and some industrial wastewaters. Recently, researchers (including our own group) reported the CA production using lactate as electron donor with newly identified microbiome systems. However, within such processes, it was hard to determine whether the CA production was completed by a single strain or by the co-metabolism of different microorganisms.ResultsHere, we report the CA production using lactate as electron donor using the strain CPB6, which we isolated from a microbiome for CA production as described previously. Strain CPB6 is affiliated with Clostridium cluster IV of the family of Ruminococcaceae based on 16S rRNA gene sequence analysis. The strain prefers acidic initial pH condition (pH 5.0–6.5), and the temperature ranging from 30 to 40 °C for CA production. In a fed-batch fermentation with non-sterilized lactate-containing organic wastewater as feedstock, strain CPB6 produced 16.6 g/L CA (from 45.1 g/L lactate) with a maximum productivity of 5.29 g/L/day. Enzyme assays with crude cell extract showed that CPB6 can metabolize acetate and butyryl-CoA to produce n-butyric acid, and acetate/n-butyrate and caproyl-CoA to produce CA, respectively.ConclusionThis study demonstrated that high concentration of CA production can be obtained by a newly isolated pure culture CPB6. This strain can be employed as a powerful workhorse for high-efficient CA recovery from lactate-containing waste streams. Our preliminary investigation suggested that the CA production from lactate in strain CPB6 might be via the chain elongation pathway of the reverse β-oxidation; the detailed mechanism, however, warrants further investigation using various molecular microbiology techniques.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0788-y) contains supplementary material, which is available to authorized users.

Complete genome sequence of Ruminococcaceae bacterium CPB6: A newly isolated culture for efficient n -caproic acid production from lactate

“…Even compared to strains that can produce CA from other substrates (e.g., ethanol, glucose, galactitol, etc), strain CPB6 showed the highest CA titer and very high productivity (comparable to the highest as reported so far) (Table 1). Additionally, the strain prefers initial pH-values of 5.0-6.5, and a temperature range 30-40°C for CA production (Zhu et al, 2017). These results indicated that strain CPB6 could be used as a powerful biocatalyst source for the biotechnological production of CA from lactate-containing waste streams.…”

“…Recently, we isolated a bacterial strain CPB6 from the CA-producing microbiome, and the isolate could produce 16.6 g/L of CA from lactatecontaining wastewater with a maximum production rate of 5.29 g/L/d (Zhu et al, 2017). The final CA titer of strain CPB6 was > 35-fold higher than that of M. elsdenii (Marounek et al, 1989) when lactate was used as the electron donor.…”

“…(For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) strain CPB6 belongs to the same Clostridium cluster IV branch as Clostridium leptum (16S rRNA sequence similarity: 92.6%) and Clostridium sporosphaeroides (91.7%), and is distant from the genus Clostridium and Ruminococcus (Zhu et al, 2017). To obtain the detailed genetic information involved in CA production, we performed the whole-genome sequencing of the strain CPB6 using the PacBio RSII platform (Tianjin Biochip Corporation, China).…”

Metatranscriptomic and thermodynamic insights into medium-chain fatty acid production using an anaerobic microbiome

“…The odd-chain valeric (C5) and heptanoic (C7) acids are products of reverse β-oxidation when the chain elongation process starts with propionyl-CoA. While there are demonstrations of this wide range of possible products from chain elongation (5, 18), and MCFA-bioreactors typically produce more than one product (4, 12, 14, 15, 19, 20), a strategy to control the final product length has not yet emerged. We are interested in obtaining the knowledge needed for the rational development and implementation of strategies to improve MCFA yields and control product formation in MCFA-producing microbiomes.…”

Multi-omic analysis of medium-chain fatty acid synthesis byCandidatusWeimerbacter bifidus, gen. nov., sp. nov., andCandidatusPseudoramibacter fermentans, sp. nov.

“…P. fermentans LDH clusters with proteins from organisms that consume lactate anaerobically ( Fig. 11 ), including two bacteria known to convert lactate to MCFA, Ruminococcaeae CPB6 and Megasphaera elsdenii (5, 7), and with the LDH from A. woodii that uses electron confurcation to couple lactate and ferredoxin oxidation with NAD + reduction to overcome the thermodynamic bottleneck of lactate oxidation (27). Pairwise correlation analyses of transcript abundance ( Fig.…”