4). In KNO3-supplemented media, the wt strain showed gradual increase of biofilm up to 50 μM GSNO (Fig. 4). The addition of 50 μM GSNO to the Nap mutant restored the biofilm formation ability (Fig. 4). These data indicate the role of NO as an early signal Z-IETD-FMK order to induce formation of biofilm in A. brasilense. Neither lesser than 50 μM nor higher concentrations of GSNO restored the biofilm forming phenotype in the mutant strain, indicating that minor exogenous concentrations could be insufficient to trigger biofilm formation, and higher ones could be cytotoxic. The latter was corroborated by the diminished CFU mL−1 counts, where GSNO affected cell viability at 100 μM in KNO3-containing medium (data not

shown). On the other hand, in NH4Cl-containing medium, GSNO affects cell viability

only at 10 mM (data not shown). In natural environments, bacteria are often challenged by changing conditions, including different classes of nutrients availability, and various oxygen tensions (Danhorn & Fuqua, 2007). Some bacteria sense signals and environmental changes, and adjust their lifestyle from planktonic to sessile modes, triggering the formation of biofilms (Karatan & Watnick, 2009). Apart from providing different metabolic pathways, different N sources, NH4Cl or KNO3, generate different quantities of endogenous NO in A. brasilense Sp245 aerobic cultures (Molina-Favero et al., 2008). Therefore, we tested these two sources of N in the growing media in static conditions and concluded Atezolizumab clinical trial that there was a direct correlation between the presence of as a nitrogen source, and the quantity of biofilm formed (Fig. 2a and b). NO is a widespread intracellular and intercellular signaling molecule that regulates several functions that promote beneficial effects during the bacteria–plant interaction (Creus et al., 2005; Molina-Favero et al., 2008; Cohen et al., 2010). There are diverse reports on the function

Topoisomerase inhibitor of NO in biofilm formation. Schmidt et al. (2004) showed that treating N. europaea cultures with gaseous NO induced changes in growth characteristics, turning cells into nonmotile forms that produced biofilm on the reactor walls. Nevertheless, P. aeruginosa growing in aerobic conditions showed that a rise in the NO content in the preformed biofilm induced its dispersion and stimulated swarming motility (Barraud et al., 2006). This process occurred when the dominating conditions became anaerobic in the biofilm, inducing respiratory Nir activity. In addition, P. aeruginosa ΔnirS mutants, which produce less NO, showed a high degree of biofilm formation, while ΔNorCB mutants, which accumulate NO, showed an increased dispersion of the biofilm formed (Barraud et al., 2006). These results point to a different regulatory mechanism for biofilm formation or dispersion in ammonium-oxidizing bacteria and denitrifiers or pathogenic bacteria. Data presented in this paper could shed light on previous results obtained by Siuti et al.