Friend or foe? Exploring the fine line between Pseudomonas brassicacearum and phytopathogens

Abstract

Pseudomonas brassicacearum is one of over fifty species of bacteria classified into the P. fluorescens group. Generally considered a harmless commensal, these bacteria are studied for their plant-growth promotion (PGP) and biocontrol characteristics. Intriguingly, P. brassicacearum is closely related to P. corrugata , which is classified as an opportunistic phytopathogen. Twenty-one P. brassicacearum genomes have been sequenced to date. In the current review, genomes of P. brassicacearum and strains from the P. corrugata clade were mined for regions associated with PGP, biocontrol and pathogenicity. We discovered that ‘beneficial’ bacteria and those classified as plant pathogens have many genes in common; thus, only a fine line separates beneficial/harmless commensals from those capable of causing disease in plants. The genotype and physiological state of the plant, the presence of biotic/abiotic stressors, and the ability of bacteria to manipulate the plant immune system collectively contribute to how the bacterial-plant interaction plays out. Because production of extracellular metabolites is energetically costly, these compounds are expected to impart a fitness advantage to the producer. P. brassicacearum is able to reduce the threat of nematode predation through release of metabolites involved in biocontrol. Moreover this bacterium has the unique ability to form biofilms on the head of Caenorhabditis elegans, as a second mechanism of predator avoidance. Rhizobacteria, plants, fungi, and microfaunal predators have occupied a shared niche for millions of years and, in many ways, they function as a single organism. Accordingly, it is essential that we appreciate the dynamic interplay among these members of the community.

Comparative genomics of the Pseudomonas corrugata subgroup reveals high species diversity and allows the description of Pseudomonas ogarae sp. nov.

“…mediterranea and other strains from the P. corrugata subgroup is associated with a genetic island [37] and, more interestingly, this pathogenic ability only occurs towards certain plant species, while in others these bacteria act as PGPR/biocontrol agents [27, 39]. Another interesting group (group 7), composed of eight unclassified isolates, clearly diverges in its functional content from the rest of the observation groups (), which suggests the presence of specialized and distinctive traits.…”

The use of Pseudomonas spp. as bacterial biocontrol agents to control plant diseases

“…P. corrugata has also been reported on chrysanthemum and geranium (Catara, 2007). The line between plant-pathogenic and beneficial isolates in this subgroup is very thin (Gislason and de Kievit, 2020). P. corrugata strains have been isolated from soil and from the rhizosphere of non-diseased plants in various countries (see Catara (2007) for an overview).…”

“…Biocontrol activity in P. corrugata and P. mediterranea is mediated by these CLPs and volatiles such as HCN (Strano et al, 2017). P. corrugata and P. mediterranea strains do not produce the fluorescent siderophore, pyoverdine (Gislason and de Kievit, 2020).…”

Comparative genomic insights into the epidemiology and virulence of plant pathogenic pseudomonads from Turkey

“…However, P. fluorescens is more commonly known as a biocontrol [12, 13] or commensal bacterium associated with the plant rhizosphere [14, 15], although some strains are known to cause important diseases in animals (including humans), plants and fungi [16–23]. This phenotypic diversity is also reflected in their genomes, as the P.…”

“…P. syringae is primarily known for its ability to cause a wide spectrum of diseases on many agronomically important crops [2,6], but is also recovered from non-agricultural land and aquatic environments [3,[9][10][11]. However, P. fluorescens is more commonly known as a biocontrol [12,13] or commensal bacterium associated with the plant rhizosphere [14,15], although some strains are known to cause important diseases in animals (including humans), plants and fungi [16][17][18][19][20][21][22][23]. This phenotypic diversity is also reflected in their genomes, as the P. syringae and P. fluorescens species complexes are two of the most diverse Pseudomonas lineages [14,15,[24][25][26][27].…”