Caproicibacter fermentans gen. nov., sp. nov., a new caproate-producing bacterium and emended description of the genus Caproiciproducens

Abstract

Caproicibacter fermentans gen. nov., sp. nov., a new caproateproducing bacterium and emended description of the genus Caproiciproducens Abstract A strictly anaerobic bacterial strain designated EA1 T was isolated from an enrichment culture inoculated with biogas reactor content. Cells of strain EA1 T are spore-forming rods (1-3×0.4-0.8 µm) and stain Gram-negative, albeit they possess a Grampositive type of cell-wall ultrastructure. Growth of strain EA1 T was observed at 30 and 37 °C and within a pH range of pH 5-9. The major components recovered in the fatty acid fraction were C 14:0 , C 16:0 , C 16:0 DMA (dimethyl acetal) and C 16:1 ω7c. Strain EA1 T fermented several mono-and disaccharides. Metabolic end products from fructose were acetate, butyrate, caproate and lactate. Furthermore, ethanol, CO 2 and H 2 were identified as products. The genome consists of a chromosome (3.9 Mbp) with 3797 predicted protein-encoding genes and a G+C content of 51.25 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain EA1 T represents a novel taxon within the family Oscillospiraceae. The most closely related type strains of EA1 T , based on 16S rRNA gene sequence identity, are Caproiciproducens galactitolivorans BS-1 T (94.9 %), [Clostridium] leptum DSM 753 T (93.8 %), [Clostridium] sporosphaeroides DSM 1294 T (91.7 %) and Ruminococcus bromii ATCC 27255 T (91.0 %). Further phenotypic characteristics of strain EA1 T differentiate it from related, validly described bacterial species. Strain EA1 T represents a novel genus and novel species within the family Oscillospiraceae. The proposed name is Caproicibacter fermentans gen. nov., sp. nov. The type strain is EA1 T (DSM 107079 T =JCM 33110 T ).

The isolateCaproiciproducenssp. 7D4C2 producesn-caproate at mildly acidic conditions from hexoses: genome and rBOX comparison with related strains and chain-elongating bacteria

“…All three strains produced H , but H 2 production by C. galactitolivorans was the highest (Additional File 1: Figure S7B). Similar to strain 7D4C2 and C. galactitolivorans, C. fermentans also produced lactate, acetate, n-butyrate, n-caproate, and H 2 /CO 2 from hexoses (Flaiz et al, 2020).…”

“…To identify phenotypic differences between strain 7D4C2, C. fermentants, and C. galactitolivorans, we studied the carbohydrate utilization of strain 7D4C2 using the AN MicroPlate TM from Biolog (Hayward, CA) (Additional File 1: Figure S8) and we compared the results to those reported for C. fermentans (Flaiz et al, 2020) and C. galactitolivorans (Kim et al, 2015). From the seven carbohydrates compared between strain 7D4C2 and C. fermentans, all but glycerol (oxidized by strain 7D4C2 and C. galactitolivorans) and D-galactose (oxidized by C. fermentans and C. galactitolivorans) showed similar utilization (Additional File 1: Table S4).…”

“…Recently, Caproicibacter fermentans, which is an n-caproate producer from carbohydrates, was isolated (Flaiz et al, 2020). While open cultures can effectively perform chain elongation at mildly acidic pH conditions with in-line MCCs extraction, strain CPB6 and C. fermentans are the only known chain-elongating bacteria that can satisfactorily produce MCCs at mildly acidic pH levels (Flaiz et al, 2020;Zhu et al, 2017).…”

“…W14A, and C. fermentans, are very similar strains of a new species within the 16 Caproiciproducens. We propose Caproiciproducens fermentans as the name for these three strains based on the work byFlaiz et al (2020).The six rBOX genes in Caproiciproducens species are located next to each other, forming a gene clusterTo further study the chain-elongation metabolism of strain 7D4C2, we identified the rBOX genes(thl, hbd, crt, acdh, and etf-α andβ Figure 1) in its genome and we compared them to those in: (1) closely related bacteria (i.e., the proposed Caproiciproducens species); (2) bacteria with similar rBOX genes (i.e., Anaeromassilibacillus senegalensis, Eubacterium limosum, and several Clostridium species); and (3) well known chain-elongating bacteria (i.e., C. kluyveri, Oscillibacter valerigenes, unclassified Ruminococcaceae CPB6, M. hexanoica, and M. elsdenii). The number of copies for each gene varied from 1 to 14 for the included bacteria (Additional File 2).…”

Fermentation of Organic Residues to Beneficial Chemicals: A Review of Medium-Chain Fatty Acid Production

“…In the first nine months of 2020, five additional MCFA-producing bacteria have been isolated. Caproicibacter fermentans is a C6-producing bacterium isolated from a methanogenic bioreactor [58]. Clostridium sp.…”