Production of AHLs of Serratia sp. S119 strain and its effects on properties involved in itrs promoting effect of plant growth.

LUCERO CT, LORDA GS, HALLIDAY N., AMBROSINO ML, CÁMARA M., TAURIAN T.

Los Cocos

Congreso; XVIII SAMIGE; 2022

Bacteria communicate with each other using a language that is based on the use of autoinducer (AI) molecules to collectively control gene expression through the process known as Quorum sensing (QS). In the case of plant growth promoting bacteria, the QS may be necessary for them to establish themselves successfully in the rhizosphere. In Gram-negative bacteria, the best known AI is the N-acylhomoserine lactone (AHL). Numerous genes belonging to QS systems have been reported in plant beneficial endophytic bacterial genomes although there are fewer studies evaluating the participation of QS in the direct mechanisms of plant growth promotion. The aim of this study was to describe the genetic background and the types of AHLs produced by a phosphate-solubilizing bacterium isolated from the roots of peanuts, and to evaluate the participation of these AIs in promoting the growth of plants of agronomic importance. Previous studies have shown that S119 strain stands out for its ability to solubilize significant amounts of phosphates and to promote the growth of peanut, soybean and maize plants. It presents features associated with the endophytic colonization of plants, such as mobility, ability to form biofilms and production of pectinase and cellulase enzymes. Toxicity tests showed that this PGPB does not represent a threat to human health. Bioinformatic analysis indicated that the genome of this strain harbours genes belonging to the production and detection of AHLs. A characterization of the AHLs produced by the strain under study was carried out by using LC-MS/MS. The S119 strains produced four different types of AHL molecules: C8-AHL, C10-AHL, 3-OH-C8-AHL and 3-OH-C10-AHL, being the last one produced in greater proportion. This finding was interesting since 3-OH-C10-AHL has not been described before in Serratia spp. In addition, 8 and 10 C-AHL are less frequently described within strains of genus Serratia. By overexpressing a heterologous lactonase enzyme in S119, this strain was depleted in the production of all AHLs with the exception of 3-OH-C10-AHL which levels were reduced by 50%. The ability to solubilize phosphate, produce biofilms and promote plant growth was analysed in the AHL attenuated strain. The biofilm formation capacity of this strain was decreased while its phosphate solubilizing ability was not affected. Inoculation of this AHL attenuated strain on peanut, maize and soybean plants showed differential effects and it was not possible to detect a common behaviour pattern in the evaluated growth parameters. Studies of this type are scarce and further analyses are required. It is possible to conclude that S119 strain has an active AHL-mediated QS signalling mechanism that would participate in the rhizospheric competence and plant colonization and that its effect on plant growth suggests a variable phenotype depending on the plant.