Role of PQQ cofactor of Serratia sp. S119 in the modulation of bacterial antioxidant mechanisms

LUDUEÑA, L M; ANZUAY, M S; TAURIAN, T1

Congreso; XVI Symposium on Biological nitrogen fi xation with NON-LEGUMES IV Latinamerican Workshop of PGPR; 2018

EMBRAPA

Serratia sp. S119 is a plant growth promoting bacteria (PGPB) that improves peanut and maize growth. In early stages of interaction between these bacteria and plants they are initially detected as pathogens because plants response to its infection by an increase in ROS production. It is assumed that PGPB are able to avoid this response in order to achieve a successful rhizospheric and endophytic colonization, and to finally express its growth promotion ability. Bacteria present different antioxidant strategies to avoid the damage of ROS being both no enzymatic mechanisms (like gluthathione) and enzymatic mechanisms (specific enzymes activities). Cofactor PQQ is a prosthetic group in bacterial dehydrogenases involved in sugars and alcohol oxidation. It is capable of catalyzing continuous redox cycling and was reported as an efficient scavenger of O2-and OH-. In addition, it has been reported that PQQ could have a role in bacterial antioxidant enzymes activities during plant-bacterium interaction. The aim of this work was to study the role of PQQ molecule in the modulation of bacterial antioxidant mechanisms (enzymatic and no enzymatic). The strains used in this study were Serratia sp. S119 and the PQQ minus- mutant Serratia sp. RSL. Peroxide was used as ROS response molecule to evaluate antioxidant modulation in bacteria. Different concentrations of H2O2 (0, 5, 7, 10 mM) were added to the culture medium and CFU ml-1 was determined during 48 hours of growth. Enzymes activities; SOD, CAT and PX were determined according to Beauchamp and Fridovich (1973), Aebi (1984) and Alderete et al. (2009), respectively and GSH content was determined according to Anderson, (1985). All determinations were done during bacterial exponential growth phase. pqqE gene expression analysis was analyzed by qRT-PCR following methodology described by Ludueña et al. (2017). Results obtained indicated that 7 mM of H2O2 produced no differences between CFU ml-1 of both strains so this concentration was selected for further assays. Similar CAT, SOD and PX activities were observed when both bacteria were grown in the presence of H2O2. On the contrary, RSL showed an increase in its GSH content when it was grown in the presence of H2O2 meanwhile S119 showed a decreased in the level of this molecule. The expression of pqqE gene showed no differences in all conditions assayed. In conclusion it is possible to suggest that PQQ cofactor is not involved in these antioxidant mechanisms under these experimental conditions