DESCRIPTION OF A NOVEL ENDOPHYTIC PLANT GROWTH-PROMOTING Pseudomonas SPECIES WITH THE ABILITY TO MODULATE STOMATAL APERTURE, A TRAIT NOT PREVIOUSLY REPORTED FOR NON-PATHOGENIC BACTERIA

GONZALEZ, MARÍA E; CASTAGNO LN; SANNAZZARO AI; ESTRELLA MJ; RIOS C; GUDESBLAT G; PIECKENSTAIN FL

Congreso; XXIII Congreso de la Sociedad Argentina de Microbiología General; 2023

A previous bioprospection of endophytic bacteria associated to horticultural crops identified several strains that exerted biological control of tomato diseases caused by the phytopathogenic fungus Botrytis cinerea and the phytopathogenic bacterium Pseudomonas syringae pv tomato and also showed plant growth promoting traits (1). One of these strains, designed as NT2 and assigned to the genus Pseudomonas based on 16S-rRNA gene sequencing, attracted our attention because of its ability to both inhibit fungal growth and suppress plant stomatal immunity through the production of diffusible signals. Suppression of stomatal immunity could provide a means for endophytic leaf colonization and might also affect the regulation of plant transpiration through stomata. Modulation of stomatal aperture was reported for phytopathogenic bacteria belonging to the genera Pseudomonas and Xanthomonas (2,3), but was not shown for plant growth-promoting bacteria so far.The aim of this work was to establish the taxonomical identity of Pseudomonas sp. NT2. A preliminary taxonomical analysis showed that, despite being closely related to Pseudomonas veronii DSM11631T and Pseudomonas fildesensis KG01T, Pseudomonas sp. NT2 belongs to a separate clade, along with other Pseudomonas strains originally isolated by our group during the above mentioned bioprospection. Next, Pseudomonas sp. NT2 genome was fully sequenced and assembled. Phylogenomic and multilocus sequence analysis of housekeeping genes gyrB, rpoD and rpoB confirmed that strain NT2 belongs to a distinct clade within the genus Pseudomonas. Indexes obtained after in silico DNA-DNA hybridization and average nucleotide identity-based comparison of Pseudomonas sp. NT2 genome with closely related Pseudomonas species were below the threshold for species delineation. As a whole, our results suggest that NT2 and other strains isolated during the initial bioprospection correspond to a novel Pseudomonas species, for which NT2 is proposed as the type strain. To our knowledge, Pseudomonas sp. NT2 is the first example of a plant growth-promoting bacteria able to modulate stomatal aperture. Thus, Pseudomonas sp. NT2 might serve as a model for further studying the possible role of modulation of stomatal aperture in endophytic colonization of plant leaves by non-pathogenic bacteria, as well as its effects on gas exchange of the host plant.