Membrane functionality in adaptation to stressing factors in rhizobacteria of agronomic importance.

PAULUCCI NS; CESARI A; BIASUTTI A; DARDANELLI M.S; PERILLO M

MENDOZA

Jornada; Cuarta Reunión Conjunta de Sociedades de Biología de la República Argentina; 2020

SOCIEDADES DE BIOLOGIA DE ARGENTINA

An environmentally friendly alternative is the inoculation of legumes such as Medicago sativa (alfalfa) with rhizobia that can fix atmospheric nitrogen in symbiosis. To establish an effective symbiosis, the first step is a strict chemical signaling between the plant and the bacteria that involves the incorporation by the bacteria of the inducing flavonoid exuded by the alfalfa roots (luteolin), its binding to the NodD1 protein. and then the binding of the complex to the promoter of the box nod, which will allow the expression of the genes necessary for the Nod factors to be produced. Temperature is one of the most variable environmental factors and can cause important changes in the cell envelope of bacteria, which can then be translated into changes in their ability to signal and establish symbiosis with alfalfa. Recently, our working group characterized the response of outer and inner membrane of Sinorhizobium meliloti 1021 to cyclical temperature changes (10ºC–40ºC–10ºC), evaluating the biophysical state, the composition of phospholipids and fatty acids. The main findings indicate that the outer and inner membranes exhibited different biochemical and biophysical responses that cannot be predicted from whole cell data. The change in the degree of unsaturation of the esterified fatty acids in the most abundant phospholipids (phosphatidylcholine and phosphatidylethanolamine) seems to be the predominant mechanism for controlling the fluidity of both membranes. These changes in the bacterial envelope caused by temperature influenced the incorporation of luteolin, registering at 40ºC values well below those observed at 28ºC (48 ng/mg and 78 ng/mg of biomass, respectively), most of which was located in the outer membrane (77%). Cells exposed to 40ºC showed a delay in the ability to form infection threads in alfalfa roots. These results lay the biochemical bases for a successful and rapid rhizobia-legume interaction, taking into account the biochemical characteristics that the bacteria bring to the inoculant.