, 2007). Enzymatic QQ activity has been described in Gram-positive and -negative bacteria and more recently in the cyanobacterium Anabaena sp. PCC7120 (Romero et al., 2008). Anabaena sp. PCC7120 is a filamentous cyanobacterium simultaneously able to perform photosynthesis and dinitrogen fixation under aerobic conditions. In the presence of a source of combined nitrogen, filaments grow as undifferentiated

chains of vegetative cells. In contrast, when Anabaena sp. PCC7120 is deprived of combined nitrogen, approximately 10% of the cells differentiate into morphologically distinct heterocysts that supply the rest of the filament with fixed nitrogen and in return receive carbohydrate from this website vegetative cells (Wolk et al., 1994). In the absence of combined nitrogen the heterocysts are spaced along the filament in a semi-regular ABT-263 purchase pattern that is controlled by a regulatory loop established between two master regulators, NtcA and HetR (Muro-Pastor et al., 2002). Because AHLs have been described in natural environments where cyanobacteria are prevalent, such as microbial mats and algal blooms (McLean et al., 1997; Bachofen & Schenk, 1998), the acylase-type

QQ activity found in Anabaena sp. PCC7120 (Romero et al., 2008) could serve either to mitigate possible negative effects of AHLs themselves and/or their tetramic acid derivatives (Kaufmann et al., 2005; Schertzer et al., 2009) or to confer a competitive advantage against AHL-producing competitors through the disruption of their communication system. In this work, we study the effects of exogenous AHL addition to cultures of the filamentous

heterocyst-forming cyanobacterium Anabaena sp. PCC7120 over to assess the possible physiological role of the AHL-acylase present in this cyanobacterium. Stock cultures of Anabaena sp. PCC7120 were maintained photoautotrophically at 30 °C with a continuous irradiance of 75 μE m−2 s−1. Cultures were aerated by connecting each culture unit to an aeration system with a continuous filtered (0.45 μm) air flow or carbon dioxide (CO2)-enriched air (1% v/v). Diazotrophic cultures were carried out in BG110C medium [BG11 medium (Rippka et al., 1979) without NaNO3 and supplemented with 0.84 g L−1 of NaHCO3 (C)]. Nondiazotrophic cultures of Anabaena sp. PCC7120 were established in BG110C supplemented with either 17 mM NaNO3 (BG11C) or 6 mM NH4Cl and 12 mM of N-Tris(hydroxymethyl)methyl-2-aminoethanesulphonic acid-NaOH buffer pH 7.5 (BG110C+NH4+). To study the effect of AHL addition on the process of heterocyst differentiation, the biomass of nondiazotrophic cultures was collected by filtration (0.45 μm), washed and resuspended in fresh BG110C (nitrogen step-down procedure). Solid media plates were prepared mixing equal volumes of double-concentrated sterilized BG110 or BG110+NH4+ and agar 10 g L−1. Plates inoculated with Anabaena sp. PCC7120 were incubated at 30 °C with light.