Pseudomonas sihuiensis sp. nov., isolated from a forest soil in South China

Phylogenomics studies and molecular markers reliably demarcate genus Pseudomonas sensu stricto and twelve other Pseudomonadaceae species clades representing novel and emended genera

Genus Pseudomonas is a large assemblage of diverse microorganisms, not sharing a common evolutionary history. To clarify their evolutionary relationships and classification, we have conducted comprehensive phylogenomic and comparative analyses on 388 Pseudomonadaceae genomes. In phylogenomic trees, Pseudomonas species formed 12 main clusters, apart from the "Aeruginosa clade" containing its type species, P. aeruginosa. In parallel, our detailed analyses on protein sequences from Pseudomonadaceae genomes have identified 98 novel conserved signature indels (CSIs), which are uniquely shared by the species from different observed clades/groups. Six CSIs, which are exclusively shared by species from the "Aeruginosa clade," provide reliable demarcation of this clade corresponding to the genus Pseudomonas sensu stricto in molecular terms. The remaining 92 identified CSIs are specific for nine other Pseudomonas species clades and the genera Azomonas and Azotobacter which branch in between them. The identified CSIs provide strong independent evidence of the genetic cohesiveness of these species clades and offer reliable means for their demarcation/circumscription. Based on the robust phylogenetic and molecular evidence presented here supporting the distinctness of the observed Pseudomonas species clades, we are proposing the transfer of species from the following clades into the indicated novel genera: Alcaligenes clade - Aquipseudomonas gen. nov.; Fluvialis clade - Caenipseudomonas gen. nov.; Linyingensis clade - Geopseudomonas gen. nov.; Oleovorans clade - Ectopseudomonas gen. nov.; Resinovorans clade - Metapseudomonas gen. nov.; Straminea clade - Phytopseudomonas gen. nov.; and Thermotolerans clade - Zestomonas gen. nov. In addition, descriptions of the genera Azomonas, Azotobacter, Chryseomonas, Serpens, and Stutzerimonas are emended to include information for the CSIs specific for them. The results presented here should aid in the development of a more reliable classification scheme for Pseudomonas species.

Contrasting genome patterns of two pseudomonas strains isolated from the date palm rhizosphere to assess survival in a hot arid environment

The plant growth-promoting rhizobacteria (PGPRs) improve plant growth and fitness by multiple direct (nitrogen fixation and phosphate solubilization) and indirect (inducing systematic resistance against phytopathogens, soil nutrient stabilization, and maintenance) mechanisms. Nevertheless, the mechanisms by which PGPRs promote plant growth in hot and arid environments remain poorly recorded. In this study, a comparative genome analysis of two phosphate solubilizing bacteria, Pseudomonas atacamensis SM1 and Pseudomonas toyotomiensis SM2, isolated from the rhizosphere of date palm was performed. The abundance of genes conferring stress tolerance (chaperones, heat shock genes, and chemotaxis) and supporting plant growth (plant growth hormone, root colonization, nitrogen fixation, and phosphate solubilization) were compared among the two isolates. This study further evaluated their functions, metabolic pathways, and evolutionary relationship. Results show that both bacterial strains have gene clusters required for plant growth promotion (phosphate solubilization and root colonization), but it is more abundant in P. atacamensis SM1 than in P. toyotomiensis SM2. Genes involved in stress tolerance (mcp, rbs, wsp, and mot), heat shock, and chaperones (hslJ and hslR) were also more common in P. atacamensis SM1. These findings suggest that P. atacamensis SM1could have better adaptability to the hot and arid environment owing to a higher abundance of chaperone genes and heat shock proteins. It may promote plant growth owing to a higher load of root colonization and phosphate solubilization genes and warrants further in vitro study.

Pseudomonas yangonensis sp. nov., isolated from wound samples of patients in a hospital in Myanmar

Strains of a Gram-negative, aerobic, rod-shaped, non-spore-forming bacterium, designated MY50^T, MY63 and MY101, were isolated from wound samples of three hospitalized patients in Yangon, Myanmar. Strains MY50^T, MY63 and MY101 grew at temperatures of 4-44 °C, in media containing 1.0-7.0 % (w/v) NaCl and at pH 6.0-9.5. Phylogenetic analysis based on 16S rRNA gene and whole genome sequences showed that these strains belonged to the genus Pseudomonas and were part of the Pseudomonas oleovorans group and located close to Pseudomonas guguanensis and Pseudomonas mendocina. Whole-genome comparisons, using average nucleotide identity and digital DNA-DNA hybridization analyses, confirmed that strains MY50^T, MY63 and MY101 were the same strain and they were a distinct species in the P. oleovorans group. Results of phenotypic characterization tests demonstrated that utilization of p-hydroxy-phenylacetic acid, glycerol, l-pyroglutamic acid and quinic acid could distinguish these strains from other species of the P. oleovorans group. These genetic and phenotypic characteristics suggest that they should be classified as representing a novel species, under the proposed name Pseudomonas yangonensis sp. nov. The type strain is MY50^T (=LMG 31602^T,=JCM 33396^T), with a DNA G+C content of 62.82 mol%.

A Novel Oligonucleotide Pair for Genotyping Members of the Pseudomonas Genus by Single-Round PCR Amplification of the gyrB Gene

Pseudomonas is a phylogenetically diverse bacterial genus which is broadly distributed in different ecological niches, and whose taxonomy is continuously under revision. For that purpose, gyrB is one of the housekeeping genes routinely used for multilocus sequence analysis (MLSA). As we noticed that there was not a single primer pair available in the literature suitable for direct sequencing of this gene, we decided to design a unique oligonucleotide pair and to set up a polymerase chain reaction (PCR) protocol to obtain a single amplicon for the entire Pseudomonas genus. Based on the available gyrB sequence from 148 Pseudomonas species, we identified highly conserved regions to design oligonucleotides without fully degenerate positions. We then set up cycling conditions for achieving high specificity and yield of the PCR protocol. Then, we showed that the amplicons produced with this procedure were appropriate for direct sequencing with both primers, obtaining more than 95% of amplicons coverage. Finally, we demonstrated that a PCR-RFLP (restriction fragment length polymorphism) approach served to differentiate among Pseudomonas species, and even between members of the same species.

The current status on the taxonomy of Pseudomonas revisited: An update

The genus Pseudomonas described in 1894 is one of the most diverse and ubiquitous bacterial genera which encompass species isolated worldwide. In the last years more than 70 new species have been described, which were isolated from different environments, including soil, water, sediments, air, animals, plants, fungi, algae, compost, human and animal related sources. Some of these species have been isolated in extreme environments, such as Antarctica or Atacama desert, and from contaminated water or soil. Also, some species recently described are plant or animal pathogens. In this review, we revised the current status of the taxonomy of genus Pseudomonas and the methodologies currently used for the description of novel species which includes, in addition to the classic ones, new methodologies such as MALDI-TOF MS, MLSA and genome analyses. The novel Pseudomonas species described in the last years are listed, together with the available genome sequences of the type strains of Pseudomonas species present in different databases.