Description

Lignocellulosic biomass is attracting attention as the world's most abundant renewable resource, and its effective utilization is being sought. However, the development of an efficient and cost-effective technology for biomass saccharification is a challenge, and JIRCAS has developed the "microbial saccharification method," which does not rely on commercial cellulose saccharification enzymes (cellulases), but only on the cultivation of saccharifying microorganisms (see FY2022 Research Highlights: Technology development to saccharify cellulose “only by cultivating microorganisms” without using cellulase enzymes).

Some agricultural waste biomass contains not only cellulose but also a large amount of xylan. Since xylan inhibits the saccharification of cellulase enzyme, it is necessary to search for xylan-saccharifying microorganisms that can be incorporated into microbial saccharification methods and to develop saccharification technology using such microorganisms. We screened microorganisms that efficiently saccharify xylan at 60°C under anaerobic conditions using xylan as the sole carbon source and obtained DA-C8 bacteria. The characteristics of the DA-C8 bacteria isolated in this study are reported. 

We have screened microorganisms that efficiently saccharify xylan from Ishigaki Island compost at 60°C under anaerobic conditions using a medium containing xylan as the sole carbon source and obtained DA-C8 bacteria. This bacterium belongs to the same phylogenetic lineage as the known Xylanibacillus composti, but based on genetic, chemotaxonomic, and phylogenetic analyses (including digital DNA-DNA hybridization),
average amino acid sequence identity values, and major polar lipid composition, a new genus and species, Insulambacter and I. thermoxylanivorax, were proposed (Fig. 1). I. thermoxylanivorax DA-C8 not only can completely saccharify xylan (Fig. 2) but also hemicelluloses other than xylan, such as arabinoxylan and galactan. It also grows over a wide temperature (37–60°C; optimum temperature: 55°C) and pH range (4–11; optimum pH: 9). In a microbial saccharification test using oil palm fiber (EFB), which contains relatively high amounts of xylan, the saccharification capacity of Clostridium thermocellum alone was 24.7% and 13.2% for I. thermoxylanivorax DA-C8, which has a high cellulose saccharification capacity. When I. thermoxylanivorax DA-C8 and C. thermocellum were co-cultured, the saccharification efficiency was 58.1%, showing an extremely high saccharification efficiency. This is a 2- to 4-fold increase in saccharification efficiency compared to each alone (Fig. 3). I. thermoxylanivorax DA-C8 has been deposited as a reference strain at the RIKEN BioResource Center (JCM 34211T) and the German Microbial Cell Culture Collection Center (DSM 111723T) and is available for distribution.

Figure, table