Pseudomonas machongensis sp. nov. and Stenotrophomonas capsici sp. nov., isolated from wilted pepper plants

Two Gram-stain-negative, aerobic, rod-shaped, non-endospore-forming bacteria, designated as strain MH1^T and MH2^T, were isolated from branches of wilted pepper plants (<i>Capsicum annuum</i>) collected from a farmland in Machong town, Guangdong, China, and investigated using a polyphasic approach. MH1^T grew at temperatures of 4-42 °C (optimum 28 °C), with 0-6.0 % (w/v) NaCl and at pH 4.0-10.0 (optimum pH 4.0). MH2^T grew at temperatures of 4-42 °C (optimum 28 °C), with 0-6.0% (w/v) NaCl and at pH 4.0-10.0 (optimum pH 5.0). Analysis of the 16S rRNA gene sequence indicated that MH1^T belongs to <i>Stenotrophomonas</i> and MH2^T belongs to <i>Pseudomonas</i>. Genome-based phylogenetic analysis further established that MH1^T shares the closest evolutionary relationships with <i>Stenotrophomonas humi</i> DSM 18929 and <i>Stenotrophomonas terrae</i> DSM 18941, and MH2^T is sister to <i>Pseudomonas wayambapalatensis</i> RW3S1. Whole-genome comparisons between MH1^T and known <i>Stenotrophomonas</i> species revealed average nucleotide identity (ANI) values up to 84.5%, as well as digital DNA-DNA hybridization (dDDH) values up to 28.3%, both substantially lower than the accepted thresholds for species delineation (ANI: 95%; dDDH: 70%). The ANI and dDDH values between MH2^T and known <i>Pseudomonas</i> species were at most 94.6 and 59.2 %, respectively. Additional biochemical and physiological analyses further support that MH1^T and MH2^T represent a novel species in <i>Stenotrophomonas</i> and <i>Pseudomonas</i>, respectively. Notably, the differences in carbon source utilization could differentiate MH1^T and its close relatives in <i>Stenotrophomonas</i>. The major fatty acids were iso-C_{15 : 0}, iso-C_{16 : 0} and iso-C_{14 : 0} for MH1^T and were C_{16 : 0}, C_{18 : 1} ω7c/C_{18 : 1} ω6c (summed feature 8), C_{16 : 1} ω7c/C_{16 : 1} ω6c (summed feature 3) and C_{17 : 0} cyclo for MH2^T. Therefore, we propose a new species <i>Stenotrophomonas capsici</i> sp. nov., with MH1^T (=GDMCC 1.3749^T=JCM 36317^T) as the type strain, and a new species <i>Pseudomonas machongensis</i> sp. nov., with MH2^T (=GDMCC 1.3750^T=JCM 36318^T) as the type strain. The MH1^T genome has a size of 4.18 Mb and a GC-content of 67.19 mol%, while the MH2^T genome has a size of 5.71 Mb and a GC-content of 63.12 mol%.