Many termites rely on diverse gut microbes to digest wood lignocellulose, but linking specific functions to these microorganisms has been challenging due to the incompleteness of their genomes. Our study aims to bridge this gap by generating complete bacterial genomes from the gut microbiota of the wood-feeding termite Nasutitermes takasagoensis and linking these genomes to specific functions in lignocellulose digestion and nitrogen metabolism.
Using PacBio HiFi reads, we generated 13.9 Gb of data, resulting in highly contiguous assemblies. We reconstructed 11 complete genomes of Leadbettera (Spirochaetota), two genomes of Candidatus Fibromonas (Fibrobacterota), and one genome of Chitinivibrionales (Fibrobacterota), the dominant bacterial lineages in the termite gut. These genomes revealed numerous CAZymes and genes associated with fermentation metabolism, indicating their crucial role in digesting and fermenting wood lignocellulose. Additionally, the presence of genes for essential amino acid biosynthesis and nitrogen fixation in Leadbettera and Chitinivibrionales highlights their importance in nitrogen cycling. Moreover, frequent horizontal gene transfers of nitrogen metabolism genes among Leadbettera, Candidatus Fibromonas, and Chitinivibrionales suggest a shared evolutionary adaptation to the termite gut environment. Notably, Leadbettera genomes lacked formate dehydrogenase, making their reductive acetogenesis pathway incomplete, which affects acetate production from H2, CO2, and formate, a key fermentation product.
Our results demonstrate the suitability of HiFi reads for reconstructing complete bacterial genomes from complex microbiota and inferring their metabolic functions. This study provides insights into the metabolic interactions within the termite gut, contributing to our understanding of microbial ecology and symbiosis in lignocellulose degradation. Less...