Dismantling and reorganizing Pseudomonas marginalis sensu lato

• Published in: Plant pathology 2023-05, Vol.72 (4), p.654-666
• Main Authors: Sawada, Hiroyuki, Fujikawa, Takashi, Satou, Mamoru
• Format: Article
• Language: English
• Subjects: Agricultural research; Cryptic species; Disease control; Ferns; Fluorescence; Genomic analysis; LOPAT; opportunistic infection; Phylogeny; Plant diseases; polyphasic taxonomy; Pseudomonas; Soft rot; Species; species complex; Strains (organisms); Taxonomy
• ISSN: 0032-0862; 1365-3059
• DOI: 10.1111/ppa.13690

Until recently, it had been a common practice in the field of plant disease control to identify bacterial strains with the following characteristics as Pseudomonas marginalis: fluorescent; oxidase‐, potato soft rot‐ and arginine dihydrolase‐positive; soft rot‐causing (here referred to as P. marginalis sensu lato). In contrast, as phylogenetic and genomic analyses have been introduced into the bacterial taxonomy, it became clear that P. marginalis sensu lato is heterogeneous, suggesting that it might be a species complex containing many cryptic species. Therefore, a preliminary survey was performed targeting the P. marginalis sensu lato strains preserved in the NARO (National Agriculture and Food Research Organization, Japan) Genebank to sort these into strains corresponding to P. marginalis sensu stricto (i.e., strains that would be included in the same species range as the type strain of P. marginalis) and strains that might not fit this category. Since then, attempts have been made to examine the taxonomic affiliations of the latter by using a polyphasic approach. As a result, some strains were proven to differ from any known species and are described as the following novel species: Pseudomonas kitaguniensis, Pseudomonas allii, Pseudomonas cyclaminis, Pseudomonas petroselini, Pseudomonas brassicae, Pseudomonas lactucae, Pseudomonas aegrilactucae and Pseudomonas morbosilactucae. In this article, the profiles of each of these novel species and a scheme for their identification are briefly introduced. In addition to the problem of cryptic species, reorganizing P. marginalis sensu lato still faces various challenges, which we discuss. Pseudomonas marginalis sensu lato identified based on a small number of phenotypic characteristics has been found to be a species complex containing many cryptic species and is currently being divided into multiple novel species.