A novel Gram-negative, rod-shaped, motile, non-spore-forming bacterial strain, CMS(T), isolated from soil was characterized using phenotypic and molecular taxonomic methods. 16S rRNA gene sequence analysis revealed that the organism belongs phylogenetically to the genus Pseudomonas. Pseudomonas monteilii, P. plecoglossicida and P. mosselii were the most closely related species, with 16S rRNA gene sequence similarities to the respective type strains of 99.79, 99.73 and 99.59 %. Relatively low gyrB gene sequence similarities (<90 %) and DNA-DNA reassociation values (<51 %) were obtained between the strain and its phylogenetically closest neighbours. The G+C content of strain CMS(T) was 62.7 mol%. The major cellular fatty acids were C(18 : 1) �s 7c, summed feature 3 (C(16 : 1) �s 7c and/or iso-C(15 : 0) 2-OH), C(16 : 0) and C(10 : 0) 3-OH. Based on the phenotypic and genetic evidence, the strain is suggested to represent a novel species, for which the name Pseudomonas taiwanensis sp. nov. is proposed. The type strain is CMS(T) (=BCRC 17751(T) =DSM 21245(T)).

Rice bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most destructive rice diseases worldwide. Therefore, in addition to breeding disease-resistant rice cultivars, it is desirable to develop effective biocontrol agents against Xoo. Here, we report that a soil bacterium Pseudomonas taiwanensis displayed strong antagonistic activity against Xoo. Using matrix-assisted laser desorption/ionization imaging mass spectrometry, we identified an iron chelator, pyoverdine, secreted by P. taiwanensis that could inhibit the growth of Xoo. Through Tn5 mutagenesis of P. taiwanensis, we showed that mutations in genes that encode components of the type VI secretion system (T6SS) as well as biosynthesis and maturation of pyoverdine resulted in reduced toxicity against Xoo. Our results indicated that T6SS is involved in the secretion of endogenous pyoverdine. Mutations in T6SS component genes affected the secretion of mature pyoverdine from the periplasmic space into the extracellular medium after pyoverdine precursor is transferred to the periplasm by the inner membrane transporter PvdE. In addition, we also showed that other export systems, i.e., the PvdRT-OpmQ and MexAB-OprM efflux systems (for which there have been previous suggestions of involvement) and the type II secretion system (T2SS), are not involved in pyoverdine secretion.

Multilocus sequence analysis (MLSA) is one of the most accepted methods for the phylogenetic assignation of Pseudomonas strains to their corresponding species. Furthermore, updated databases are essential for correct bacterial identification and the number of Pseudomonas species is increasing continuously. Currently, 127 species are validly described in Euz?by's List of Species with Standing in Nomenclature, and 29 novel species have been described since the publication of the last comprehensive MLSA phylogenetic study based on the sequences of the 16S rDNA, gyrB, rpoB and rpoD genes. Therefore, an update of the sequence database is presented, together with the analysis of the phylogeny of the genus Pseudomonas. Whole-cell matrix-assisted laser-desorption/ionization time-of-flight (WC-MALDI-TOF) mass spectrometry (MS) analysis has been applied very recently to the identification of bacteria and is considered to be a fast and reliable method. A total of 133 type strains of the recognized species and subspecies in the genus Pseudomonas, together with other representative strains, were analyzed using this new technique, and the congruence between the WC-MALDI-TOF MS and MLSA techniques was assessed for the discrimination and correct species identification of the strains. The utility of both methods in the identification of environmental and clinical strains is discussed.