Moreover, it resembled the wt growth pattern in NH4Cl-supplemented medium (Fig. 1). Azospirillum brasilense Sp245 wt and Faj164 mutant strains were assayed for their ability to produce biofilm in two N sources, as indicated earlier. Biofilm formation was quantified with crystal violet. Moreover, attached cells in the biofilm were observed by CLSM. The amount of biofilm produced in each media was significantly different. In NH4Cl-supplemented medium, biofilm formation was similar for both strains

learn more (Fig. 2a). In this medium, biofilms formed at d1 and d3 showed loosely attachment to the well in comparison with d5 where adherence was tighter (Fig. 2b). Significantly, higher biofilm formation occurred in KNO3 Nfb, showing the wt strain a 10-fold increase in attached cell on d3 compared to NH4Cl Nfb and fourfold increase on d5 (Fig. 2a). Besides, the wt strain showed a twofold increase of attached cells on d3 compared to Faj164 (Fig. 2a and b). this website The fact that both strains grew similarly at d3 (Fig. 1) but the wt strain formed a greater biofilm (Fig. 2a) indicated a defect on biofilm formation caused by the deficiency of Nap activity. Nevertheless,

the difference observed between both strains at d5 was less pronounced (Fig. 2). The concentration was determined in the supernatants of biofilms in each N source (Fig. 3a). No detectable production occurred in medium supplemented with NH4Cl in both strains during the assay (Fig. 3a). However, remarkable differences were observed when the strains were grown with KNO3 (Fig. 3a). Whereas the Sp245 strain was able to produce measurable concentrations of after 24 h in the supernatant of biofilm (ca. 30 μmol mL−1), the Faj164 mutant did not produce detectable amounts of . While wt strain slightly decreased the production (arriving to ca. 20 μmol mL−1 on d5), no

concentration was found neither on d1 nor on d3 in mutant biofilm supernatant. Nevertheless, in Faj164 biofilm supernatant was detected at d5 (ca. 5 μmol mL−1) (Fig. 3a). Amperometric determination of NO production derived from was measured in wt and Faj164 static growing cultures. In situ production of NO Dichloromethane dehalogenase was determined at d3 (Fig. 3b), and data from both strains confirmed the preceding results on production (Fig. 3a). While wt strain produced ca.10 μM of NO in 40 min of measurement, the production of NO by mutant strain was < 2 μM (Fig. 3b). Amperometric measurements of NO were determined only in biofilms of d3 to compare similar grown cultures in both strains, evaluated by OD540nm (Fig. 1) and CFU mL−1 (data not shown). To assess the role of NO as a signal molecule inducing biofilm formation in A. brasilense, different concentrations of GSNO (NO donor) were added to the plates from culture initiation and every 24 h. The addition of GSNO to both media increased biofilm formation in both strains (Fig. 4).