In fact, the concentrations reported in the literature for AHLs in the culture media of the model microorganism Vibrio fischeri usually range between 0.4 and 400 nM (Kaplan & Greenberg, 1985; Schaefer et al., 2002; Burton et al., 2005), significantly lower than the concentrations exhibiting inhibitory activity against Anabaena sp. PCC7120. In conclusion, AHLs strongly inhibit nitrogen fixation in Anabaena sp. PCC7120, although they do not affect the process of heterocyst differentiation because no changes were observed in the frequency, pattern of differentiation, permeability of the heterocyst

cell wall or expression of regulatory Ku-0059436 cost genes whose products are involved in differentiation (ntcA). The strong inhibition of nitrogenase activity observed could be related to nitrogen fixation blockage at a post-transcriptional level, mainly on newly formed heterocysts. Moreover, a possible new activity of AHL signals was found for OC10-HSL in the presence of combined

nitrogen, differing from those activities described for oxo-substituted and AHL tetramic acid derivatives. Osimertinib concentration The presence of acylase activity against long-chain AHLs described in the biomass of Anabaena sp. PCC7120 (Romero et al., 2008) could be related to the negative effects of AHLs in this cyanobacterium. This AHL-degradation mechanism would protect the filaments, at normal environmental concentrations, from exogenous signals with potential cytotoxic and inhibitory activities on the cyanobacterium. This work was financed by a grant from Consellería de Innovación e Industria, Xunta de Galicia PGIDIT06PXIB200045PR. M.R. was supported by an FPU fellowship from the Spanish Ministry of Education and Science and a predoctoral fellowship from Diputación

de A Coruña. We would like to thank Prof. Kim D. Janda and Dr Gunnar F. Kaufmann for kindly providing us with OC12-tetramic acid. We also would like to thank Prof. Miguel Cámara for providing us with synthetic AHLs. “
“Helicobacter pylori is a unique bacterial Thiamet G species that assimilates various steroids as membrane lipid components. Our group has recently found, however, that certain steroids may impair the viability of H. pylori. In this study, we go on to reveal that estradiol, androstenedione, and progesterone (PS) all have the potential to inhibit the growth of H. pylori. Of these three steroid hormones, progesterone demonstrated the most effective anti-H. pylori action. 17α-hydroxyprogesterone caproate (17αPSCE), a synthetic progesterone derivative, had a much stronger anti-H. pylori action than progesterone, whereas 17α-hydroxyprogesterone, a natural progesterone derivative, completely failed to inhibit the growth of the organism. Progesterone and 17αPSCE were both found to kill H. pylori through their bacteriolytic action. Among five bacterial species investigated, H. pylori was the only species susceptible to the bactericidal action of progesterone and 17αPSCE.