CONICET | Buscador de Institutos y Recursos Humanos

The Pseudomonas genus has a wide metabolic versatility that allows bacteria to adapt to changing environmental conditions, including variations in oxygen (O2) levels. The availability of O2 is relevant for species of agricultural importance since the soil and the different plant tissues are environments characterized by the presence of gradients. In Pseudomonas, the transition from aerobiosis to anaerobiosis is controlled by the global regulator Anr, which binds to consensus regions called Anr box. P. syringae pv. syringae B728a (B728a) is a foliar pathogen that causes bacterial brown spots in common bean (Phaseolus vulgaris), in other species of commercial importance, and in the model plant Nicotiana benthamiana. Genes involved in arginine fermentation, that produce ATP by phosphorylation at the substrate level in absence of oxygen, are present in the genome of B728a. In this work, the impact of O2 availability and the presence of L-arginine on important cellular functions for plant interaction were analyzed. B728a was capable of growing at low O2 conditions in L-arginine supplemented medium, thus microaerobic (M) and aerobic (A) cultures were used to investigate O2 impact on B728a physiology. Arginine was found to promote biofilm formation in vitro and repress the swarming capacity of B728a. M cultures of B728a showed deficiencies in the early stages of foliar infection of N. benthamiana, compared to A cultures, probably due to the lower resistance to oxidative stress of bacteria grown in microaerobic cultures, or by physiological differences affecting relevant traits, such as envelopes or expression of virulence factors, under these growth conditions. At 72 h the virulence halos formed by bacteria from aerobic and microaerobic cultures presented a similar area. Viable bacteria count indicated the presence of 2.8 x 103 CFU/cm2 from leaves inoculated with B728a (A) and 9.7 x 103 CFU/cm2 from leaves inoculated with B728a (M) (p