Summary auto-generated
This study describes two novel pathogenic Pseudomonas species isolated from diseased plants in France and Africa. Researchers analyzed 26 bacterial strains—15 from garlic plants showing 'Café au lait' disease symptoms in southern France and 11 from rice in Cameroon, Madagascar, and Réunion. Using polyphasic taxonomy, including phenotypic analysis of 167 biochemical tests, siderotyping (pyoverdine patterns), DNA-DNA hybridization, 16S rRNA sequencing, and G-C content determination, the garlic and rice strains clustered into two distinct groups. DNA-DNA hybridization revealed garlic strains shared 79-100% relatedness among themselves but only 10-39% with rice strains and reference species. Rice strains showed 68-100% internal relatedness but low relatedness to other groups. Siderotyping confirmed distinct pyoverdine profiles for each group. Pathogenicity tests demonstrated garlic strains were highly pathogenic to garlic but non-pathogenic to rice, while rice strains showed weak pathogenicity to rice and no pathogenicity to garlic. The authors propose Pseudomonas salomonii for garlic strains and Pseudomonas palleroniana for rice strains as novel species within γ-Proteobacteria.
Key findings
- Two novel Pseudomonas species identified: P. salomonii from garlic showing 'Café au lait' disease and P. palleroniana from rice
- DNA-DNA hybridization confirmed strains form two distinct genomospecies with 79-100% intragroup and only 10-47% intergroup relatedness
- Siderotyping revealed unique, species-specific pyoverdine patterns allowing rapid differentiation between the two groups
- Pathogenicity tests demonstrated host-specific virulence: P. salomonii highly pathogenic to garlic but non-pathogenic to rice; P. palleroniana weak on rice and non-pathogenic to garlic
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Abstract
L. Gardan, P. Bella, J. M. Meyer, R. Christen, P. Rott, W. Achouak and R. Samson
UMR 077 de Pathologie Vegetale INRA-INH-Universite, BP 57, 42 rue G. Morel, 49071 Beaucouze cedex, France
A total of 26 strains, including 15 strains isolated from garlic plants with the typical symptoms of 'Cafe au lait' disease and 11 strains isolated from diseased or healthy rice seeds and sheaths infested by Pseudomonas fuscovaginae, were compared with 70 type or reference strains of oxidase-positive pathogenic or non-pathogenic fluorescent pseudomonads. The strains were characterized by using a polyphasic taxonomic approach. Numerical taxonomy of phenotypic characteristics showed that the garlic and rice strains were related to each other. However, they clustered into separate phenons, distinct from those of the other strains tested, and were different in several nutritional tests. On the basis of DNA--DNA hybridization, the garlic and rice strains constituted two distinct DNA hybridization groups, indicating that they belonged to separate species. The two groups of strains were also well differentiated by siderotyping. Garlic strains were pathogenic to garlic plants and either weakly pathogenic or non-pathogenic on rice; rice strains were either weakly pathogenic or non-pathogenic on rice and non-pathogenic on garlic. A phylogenetic analysis of 16S rRNA gene sequences confirmed that the two groups of strains belonged to the gamma-Proteobacteria and to the genus Pseudomonas. The names Pseudomonas salomonii sp. nov. and Pseudomonas palleroniana sp. nov. are respectively proposed for the garlic strains and the rice strains. The type strains are P. salomonii CFBP 2022(T) (=ICMP 14252(T)=NCPPB 4277(T)) and P. palleroniana CFBP 4389(T) (=ICMP 14253(T)=NCPPB 4278(T)).