Caulobacter endophyticus sp. nov., an endophytic bacterium harboring three lasso peptide biosynthetic gene clusters and producing indoleacetic acid isolated from maize root.

A novel Gram-stain-negative, aerobic and rod-shaped bacterium with a single polar flagellum or a stalk at the end of the cell, was isolated from maize roots in the Fangshan District of Beijing, People's Republic of China. The new strain designated 774T produced indole acetic acid (IAA). The 16S rRNA gene sequence analysis indicated that strain 774T belongs to the genus Caulobacter and is closely related to Caulobacter flavus RHGG3T, Caulobacter zeae 410Tand Caulobacter radices 695T, all with sequence similarities of 99.9%. The genome size of strain774T was 5.4 Mb, comprising 5042 predicted genes with a DNA G+C content of 68.7%.Three striking lasso peptide biosynthetic gene clusters and two IAA synthesis genes belonging to the TPM pathway were also found in the genome of strain 774T. The average nucleotide identity values and digital DNA-DNA hybridization values of the strain774T with its closely phylogenetic neighbours were less than 91.5% and 45.0%, respectively, indicating a new Caulobacter species. The major fatty acids of strain774T were identified as C16: 0 (27.7%), summed feature 3 (C16: 1ω6c and/or C16: 1ω7c) (12.6%) and summed feature 8 (C18: 1ω7c and/or C18: 1ω6c) (42.9%).The major polar lipids consisted of phosphatidyl-glycerol and glycolipids. The predominant ubiquinone was identified as Quinone 10. Based on the polyphasic characterization, strain 774T represents a novel species of the genus Caulobacter, for which the name Caulobacter endophyticus sp. nov. is proposed with 774T (= CGMCC 1.16558T = DSM 106777T) as the type strain.