High Canadian Arctic Pseudomonas spp. and their potential as biostimulants in cold growth conditions

This study investigated the potential of Pseudomonas strains isolated from the Canadian Arctic environment to be used as plant growth-promoting rhizobacteria (PGPR) in cold and temperate conditions. Forty bacterial strains were isolated from soil samples collected in the Cambridge Bay area, Nunavut. Their genomes were sequenced and annotated, their taxonomical affiliation determined, and genes/clusters associated with selected phytobeneficial traits were identified. In parallel, some of these traits, including atmospheric nitrogen fixation, siderophore production, auxin production, and phosphate solubilization, were evaluated in vitro . Based on these findings, the most promising strains were then tested for their ability to promote lettuce plant growth under cold (10°C) and temperate (20°C) conditions. The results revealed that most of the strains under study do not belong to species with validly published and correct names, representing 28 potential new species within the genus Pseudomonas . Substantial functional and taxonomic diversity among isolates was observed, highlighting the ecological complexity of Northern microbial communities. Interestingly, strains displaying higher phytobeneficial trait performance under in vitro assays did not consistently enhance plant growth. Yet, different strains significantly increased lettuce fresh and/or dry weight under cold and temperate conditions. The most efficient strains (LBUM1647, LBUM1648, LBUM1661, LBUM1666, and LBUM1675) do not share high taxonomical similarities, suggesting strain-specific rather than species-specific effects. These findings underscore the importance of considering PGPR trait expression in soil, strain-specific effects, and plant and microbe compatibility when selecting candidate Pseudomonas spp. More integrative screening strategies that better reflect rhizosphere conditions should therefore be developed.