Bacillus velezensis T971 genome informs starch degradation in tobacco

Starch is an important reserve polysaccharide in tobacco leaves. An endophytic bacterium, <i>Bacillus velezensis</i> T971, was isolated from the leaves of <i>Nicotiana tabacum</i> L. Yunyan 97 and showed strong starch-degrading activity on the agar plate containing 1% starch (w/v). The complete genome of T971 was determined using PacBio long-read sequencing technology, revealing a single circular chromosome of 3,930,941 bp encoding 3,692 proteins. The T971 genome was compared with 242 other complete genomes of <i>B. velezensis</i>. Pan-genome analysis revealed a sporadic distribution of the plantazolicin (PZN) biosynthetic gene cluster (BGC) and mobile genetic elements (MGEs) (e.g., genomic islands (GIs) and prophages), which have contributed to the variability of <i>B. velezensis</i> genomes. Carbohydrate-active enzyme (CAZyme) analysis found 113 CAZymes in the T971 genome, including 41 glycoside hydrolases (GHs), 40 glycosyltransferases (GTs), and 14 carbohydrate esterases (CEs). One (GH13_28 family) of the four <i>α</i>-amylases is the most promising candidate for starch degradation in tobacco leaves, possessing a signal peptide and two carbohydrate-binding modules (CBMs). This study identifies <i>B. velezensis</i> T971 as a potential strain for industrial amylase production.