Serratia rhizosphaerae sp. nov., a novel plant resistance inducer against soft rot disease in tobacco

A novel Gram-negative, facultatively anaerobic, non-spore-forming and rod-shaped bacterial strain (KUDC3025(T)) was isolated from rhizospheric soil of Artemisia japonica subsp. littoricola collected from the Dokdo Islands, Republic of Korea and bacterial strain MYb239 was isolated from compost from Kiel, Germany. Phylogenetic analysis based on 16S rRNA gene sequences, multilocus genes (atpD, gyrB, infB and rpoB), and whole-genome sequences indicated that both strains belonged to the genus Serratia and were most closely related to Serratia rubidaea KCTC 2927(T). The average nucleotide identity values based on blast and MUMmer, tetranucleotide usage pattern and genome-based digital DNA-DNA hybridization values were all below the 95.0%/95.0 %/0.998/70% cutoff points. The genome G+C content was 58.0mol%. The cellular quinone content contained ubiquinone-8 and the major components in the fatty acid profile were C-16:0, C-17:0 cyclo and C-14:0. The polar lipid profile included diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, four unknown amino lipids, two unknown phospholipids and an unknown lipid. Based on phenotypic, chemotaxonomic and genotypic data, strain KUDC3025(T) (DSM 106578(T)=CGMCC 1.18473(T)) and MYb239 represents a novel species, for which the name Serratia rhizosphaerae sp. nov. is proposed. Furthermore, strain KUDC3025(T) was able to suppress disease symptoms by priming the plant defence system components, including the salicylic acid and ethylene pathways, furthering our understanding of Serratia as potential plant growth promoting bacteria.