brasilense Sp245 (Pothier et al., 2008). Azospirillum brasilense is able to produce considerable quantities of NO under aerobic conditions, and as stated before, NO production is required for Azospirillum-induced lateral root formation (Creus et al., 2005). Interestingly,

the mutant Faj164 that produces 5% of NO compared to the Sp245 wt strain in supplemented media was unable to induce the promoting effect on the tomato root growth system (Molina-Favero et al., 2008). Consequently, NO production might be another beneficial trait for plants inoculated with Azospirillum (Molina-Favero et al., 2008; Bashan & de-Bashan, 2010; Fibach-Paldi et al., 2012). To produce beneficial effects, Azospirillum has to interact with the plant surface to form complex

multicellular assemblies such as aggregates and biofilms that are initiated by an attachment process (Burdman et al., 2000). Biofilms Inhibitor Library research buy are defined as surface-attached multicellular aggregates, typically encased in a self-produced extracellular polymeric matrix (Ramey et al., 2004). Several factors like mechanical and nutritional stress, and inorganic and quorum-sensing molecules among others, regulate biofilms assembly and disassembly (Karatan & Watnick, 2009). In response to these factors, secondary messengers like cyclic diguanosine monophosphate (c-di-GMP) are activated (Hengge, 2009) leading to biofilm formation or modification (Karatan & Watnick, 2009). Selleck Tenofovir Recently, it was shown that NO BAY 73-4506 cost stimulates biofilm formation by controlling the levels of

c-di-GMP (Plate & Marletta, 2012). On the other hand, Barraud et al. (2006, 2009) showed that NO triggered the disassembly of Pseudomonas aeruginosa biofilms acting upstream of c-di-GMP signaling pathway. More evidences of this complex picture are the results reported by Schmidt et al. (2004) who showed that cultures of Nitrosomonas europaea treated with exogenous NO gas enhanced biofilm formation. Considering that A. brasilense produces high amounts of NO in supplemented medium (Molina-Favero et al., 2008), it was interesting to test the effect of endogenous NO production on the ability of this beneficial bacterium to form biofilms. Hence, we proposed that NO could be involved in the signaling process for biofilm formation in A. brasilense. To determine this, we tested cultures of A. brasilense Sp245 and its isogenic Nap mutant Faj164 under static growth conditions for their ability to form biofilm on abiotic surfaces. We also evaluated the effects of the addition of a NO donor on biofilm formation. Azospirillum brasilense Sp245 wt, isolated from surface-sterilized wheat roots (Baldani et al., 1986), and A. brasilense Faj164, a knockout mutant of Sp245 with a Tn5 insertion in the napA gene of the operon (Steenhoudt et al., 2001a), were used.