A minimal gene set for cellular life derived by comparison of complete bacterial genomes

Xanthomonas species are primarily known as a group of phytopathogens infecting diverse plants. Recent molecular studies reveal the existence of potential novel species and strains of Xanthomonas following a nonpathogenic lifestyle. In the present study, we report whole-genome sequences of four nonpathogenic strains from citrus (NPXc). Taxonogenomics revealed the surprising diversity, as each of these three isolates were found to be potential novel species that together form a citrus-associated nonpathogenic Xanthomonas species complex (NPXc complex). Interestingly, this NPXc complex is related to another nonpathogenic species, Xanthomonas sontii, from rice (NPXr). On the other hand, the fourth NPXc isolate was found to be related to nonpathogenic isolates from walnut (NPXw); altogether, they form a potential taxonomic outlier of pathogenic Xanthomonas arboricola species. Furthermore, genomic investigation of well-characterized pathogenicity clusters in NPXc isolates revealed lifestyle-specific gene content dynamics. Primarily, genes essential for virulence (i.e., type 1 secretion system [T1SS], T2SS and its effectors, T3SS and its effectors, T4SS, T6SS, adhesins, and rpf gene cluster) and adaptation (i.e., gum, iron uptake and utilization, xanthomonadin, and two-component systems) were depicted by comparative genomics of a Xanthomonas community comprising diverse lifestyles. Overall, the present analysis confers that nonpathogenic isolates of diverse hosts phylogenomically converge and are evolving in parallel with their pathogenic counterparts. Hence, there is a need to understand the world of nonpathogenic isolates from diverse and economically important hosts. Genomic knowledge and resources of nonpathogenic strains will be invaluable in both basic and applied research of the genus Xanthomonas. IMPORTANCEXanthomonas citri is one of the top phytopathogenic bacteria and is the causal agent of citrus canker. Interestingly, Xanthomonas is also reported to be associated with healthy citrus plants. The advent of the genomic era enabled us to carry out a detailed evolutionary study of a Xanthomonas community associated with citrus and other plants. Our genome-based investigations have revealed hidden and extreme interstrain diversity of nonpathogenic Xanthomonas strains from citrus plants, warranting further large-scale studies. This indicates an unexplored world of Xanthomonas from healthy citrus plant species that may be coevolving as a species complex with the host, unlike the variant pathogenic species. The knowledge and genomic resources will be valuable in evolutionary studies exploring its hidden potential and management of pathogenic species.

https://msphere.asm.org/content/msph/5/2/e00087-20.full.pdf

Phylogenomic Insights into Diversity and Evolution of Nonpathogenic Xanthomonas Strains Associated with Citrus.

Bacteria Azospirillum brasilense Sp245 with mixed flagellation are able to form biofilms on various surfaces. A nonflagellated mutant of this strain with inactivated chromosomal copy of the flhB gene (flhB1) was shown to exhibit specific traits at the later stages of biofilm formation on a hydrophilic (glass) surface. Mature biofilms of the flhB1::Omegon-Km mutant Sp245.1063 were considerably thinner than those of the parent strain Sp245. The biofilms of the mutant were more susceptible to the forces of hydrodynamic shear. A. brasilense Sp245 cells in biofilms were not found to possess lateral flagella. Cells with polar flagella were, however, revealed by atomic force microscopy of mature native biofilms of strain Sp245. Preservation of a polar flagellum (probably nonmotile) on the cells of A. brasilense Sp245 may enhance the biofilm stability.

Changes in biofilm formation in the nonflagellated flhB1 mutant of Azospirillum brasilense Sp245

An actinobacterium strain BMG51109a was isolated from surface sterilized root nodules of Casuarina glauca collected in Tunisia. The 16S rRNA gene sequence of strain BMG51109a showed most similarity (96.53–96.55 %) to the type strains of Nocardia transvalensis, N. aobensis and N. elegans. Chemotaxonomic analysis supported the assignment of the strain to Nocardia genus. The major menaquinone was MK-8(H4c) while the polar lipid profile contained diphosphatidylglycerol, phosphatidylmonomethylethanolamine, glycophospholipid, phosphatidylinositol, one uncharacterized phospholipid and three glycolipids. Whole-cell sugar analysis revealed the presence of meso-diaminopimelic acid, arabinose and galactose as diagnostic sugars, complemented by glucose, mannose and ribose. The major cellular fatty acids were tuberculostearic, oleic, palmitoleic and stearic acids. Physiological and biochemical tests showed that strain BMG51109a could be clearly distinguished from its closest phylogenetic neighbours. On the basis of these results, strain BMG51109aT (= DSM 45978T = CECT 8469T) is proposed as the type strain of the novel species Nocardia casuarinae sp. nov.

Nocardia casuarinae sp. nov., an actinobacterial endophyte isolated from root nodules of Casuarina glauca.

Insight into the structure, function and conjugative transfer of pLPU83a, an accessory plasmid of Rhizobium favelukesii LPU83.

Plasticity in Plant-Growth-Promoting and Phytopathogenic Bacteria

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Plasticity in Plant-Growth-Promoting and Phytopathogenic Bacteria