Paraburkholderia tropica is able to grow in chemostat under N2-fixing conditions

SOLIMANO, FRANCISCO; VIO, SANTIAGO ADOLFO; CHAVEZ MONTE, EMANUEL; LOPEZ, ANA CLARA; GARCIA, SABRINA SOLEDAD; BERNABEU, PAMELA; LUNA, MARIA FLAVIA

Foz de Iguazú

Simposio; XVI Symposium on Biological nitrogen Fixation with NON-LEGUMES ? IV Latinamerican Workchop of PGPR; 2018

EMBRAPA

The use of Plant Growth Promoting Bacteria (PGPB) as inoculants is a promising way to reduce the use of agrochemicals products. Plant growth stimulation by PGPB can be a consequence of phytohormones production, phytopathogens inhibition or facilitation in nutrients supply, such as Nitrogen (N2) fixation. In this work, physiological aspects of the diazotroph endophyte Paraburkholderia tropica growing in chemostat under limited carbon conditions have been defined. The results of this work showed that: 1- Paraburkholderia tropica MTo-293 was able to growth in chemostat with N2 as the sole nitrogen source provided that the dissolved oxygen was maintained at 1-2 % air saturation, but it was not a stable state: a small increase in the dissolved oxygen resulted in the inhibition of the nitrogenase and the culture washing. Nevertheless, a stable state of N2-fixing conditions was achieved with a starter dose of ammonium in the medium, that could be the growth condition that most resembles what it is found in its natural environment. 2- The biomass yields of P. tropica growing with glucose and a starter dose of ammonium were lower than those grown under non-N2-fixing conditions (0,39 vs 0,49 Cmol biomass/C-mol substrate), and the specific rates of oxygen consume were higher under N2-fixing conditions (3,0 vs 1,8 mol/g biomass.h). 3- The extracellular glucose oxidation via a PQQ-linked glucose dehydrogenase was expressed only under N2-fixing conditions, as it was also found in batch cultures. Carbon-limitation conditions were not enough to active the expression of this enzyme, suggesting that its synthesis is regulated by an efficient utilization of the Carbon source under circumstances where the energetic demand for growth functions are high (N2-fixing cultures). This work contributes to the knowledge of physiological aspects of an endophytic PGPB that are necessary to consider for its application in agriculture and to enhance plant-microbe interaction in non-legumes.