The life history of the plant pathogen Pseudomonas syringae is linked to the water cycle

Abstract

Pseudomonas syringae is a plant pathogen well known for its capacity to grow epiphytically on diverse plants and for its ice-nucleation activity. The ensemble of its known biology and ecology led us to postulate that this bacterium is also present in non-agricultural habitats, particularly those associated with water. Here, we report the abundance of P. syringae in rain, snow, alpine streams and lakes and in wild plants, in addition to the previously reported abundance in epilithic biofilms. Each of these substrates harbored strains that corresponded to P. syringae in terms of biochemical traits, pathogenicity and pathogenicity-related factors and that were ice-nucleation active. Phylogenetic comparisons of sequences of four housekeeping genes of the non-agricultural strains with strains of P. syringae from disease epidemics confirmed their identity as P. syringae. Moreover, strains belonging to the same clonal lineage were isolated from snow, irrigation water and a diseased crop plant. Our data suggest that the different substrates harboring P. syringae modify the structure of the associated populations. Here, we propose a comprehensive life cycle for P. syringae-in agricultural and non-agricultural habitats-driven by the environmental cycle of water. This cycle opens the opportunity to evaluate the importance of non-agricultural habitats in the evolution of a plant pathogen and the emergence of virulence. The ice-nucleation activity of all strains from snow, unlike from other substrates, strongly suggests that P. syringae plays an active role in the water cycle as an ice nucleus in clouds.

Atmospheric Processing and Variability of Biological Ice Nucleating Particles in Precipitation at Opme, France

“…Although no direct correlation of bacterial cell concentration with the freezing parameters was observed in our data (p > 0.17; n = 62; Table S3), it was also strongly linked with pH (p < 0.001; n = 62) and season, with more cells during the warmest periods of the year; these features were both observed earlier in the air and clouds, notably by our group at this location [61][62][63]. These indirect relationships suggest that a fraction of the biological particles involved in freezing could be ice-nucleation active bacterial cells, but the absence of a direct correlation also indicates that they represent an insignificant (in the statistical sense) number of individuals in the total airborne bacterial community (e.g., [11,12]). …”

“…To date, many INPs with possible impacts on precipitation have been identified in the atmosphere. These comprise abundant mineral and organic particles such as feldspar [2] and cellulose [3], and also fewer numerous biological particles [4][5][6][7] catalyzing freezing at much warmer temperatures (i.e., >−10 • C; [1,8]), notably fungi [9,10] and bacteria [11][12][13].…”

Vertical distribution of airborne bacterial communities in an Asian-dust downwind area, Noto Peninsula

“…The air sample at 3,000 m was dominated by terrestrial bacteria, such as Bacilli and Actinobacteria, which are thought to originate from continental areas, while the air samples at 1,000 m and 10 m contained bacterial populations of marine origin, including members of Cyanobacteria and Alpha-proteobacteria. Some species of Bacilli and Proteobacteria are well known as pathogens of plants, animals, and humans (Morris et al, 2008), whereas heterotrophic bacteria in these classes have been found to contribute to geochemical cycling in the oceans and terrestrial areas (Ulrich et al, 2008). Thus, the transport of bioaerosols plays an important role in dispersing bacterial populations that are potentially associated with microbial, plant and animal ecosystems, human health, organic matter cycles, and geochemical processes.…”

Local and regional influences over soil microbial metacommunities in the Transantarctic Mountains

“…Taxa that dominate the total bacterial community may represent groups that become entrained in the atmosphere (Morris et al 2008, Bowers et al 2011) and redistributed over broad scales. While the near-ground aeolian redistribution of cyanobacteria has been documented in the Dry Valleys (Wood et al 2008, Michaud et al 2012, cyanobacteria appear to be a minor component in more broadly dispersed bioaerosols (Bottos et al 2013).…”