Serratia inhibens sp. nov., a new antifungal species isolated from potato ( Solanum tuberosum)

A novel bacterial strain, S40^T, with strong antifungal activity was isolated from the rhizosphere of green potato collected from Zealand, Denmark. Polyphasic analysis with a combined phenotypic, phylogenetic and genomic approach was used to characterize S40^T. Phylogenetic analysis based on the 16S rRNA gene and MLSA (concatenated gyrB, rpoD, infB and atpD sequences) showed that strain S40^T was affiliated with the genus Serratia and with Serratia plymuthica PRI-2C as the closest related strain [average nucleotide identity (ANI), 99.26 %; DNA-DNA hybridization (dDDH), 99.20%]. However, whole genome sequence analyses revealed that S40^T and S. plymuthica PRI-2C genomes displayed lower similarities when compared to all other S. plymuthica strains (ANI ≤94.34 %; dDDH ≤57.6 % relatedness). The DNA G+C content of strain S40^T was determined to be 55.9 mol%. Cells of the strain were Gram-negative, rod-shaped, facultative anaerobic and displayed growth at 10-37 °C (optimum, 25-30 °C) and at pH 6-9 (optimum, pH 6-7). Major fatty acids were C_{16 : 0} (27.9 %), summed feature (C_{16 : 1} ω6c/C_{16 : 1} ω7c; 18.0 %) and C_{17 : 0} cyclo (15.1 %). The respiratory quinone was determined to be Q8 (94 %) and MK8 (95 %) and the major polar lipids were phosphatidylethanolamine and phosphatidylglycerol. The results of phenotypic, phylogenetic and genomic analyses support the hypothesis that strain S40^T represents a novel species of the genus Serratia, for which the name Serratia inhibens sp. nov. is proposed. The type strain is S40^T (=LMG 31467^T=NCIMB 15235^T). In addition, we propose that S. plymuthica PRI-2C is reclassified and transferred to the species S. inhibens as S. inhibens PRI-2C.

Keywords: ANI; Serratia; antimicrobial activity; dDDH; potato; whole genome analysis.