, 1987; Cardinale & Clark, 2005 and references cited therein). A possible exception to this statement is the

report that Salmonella within macrophages might be exposed to up to 10 μM NO (Raines et al., 2006). However, nitrite was a more effective inducer of Phcp expression than growth-inhibitory concentrations of 10 or 20 μM NO added repeatedly at 30 min intervals. The smaller and slower response to NO was not due to the rapid decomposition of NO by oxygen because separate experiments with an NO-sensitive electrode confirmed that NO was stable under the anaerobic conditions used. Note that the high pKa value of nitrous acid means that at physiological pH, nitrous acid diffuses across the cytoplasmic membrane, and nitrite can be transported by at least three mechanisms, NarK,

NarU and NirC (see, e.g. Jia et al., 2009). Three of the Z VAD FMK obvious possible explanations for the minimal response of the hcp promoter to external NO are that derepression of NsrR was counter-balanced check details by loss of transcription activation by FNR; that derepression of the NsrR regulon resulted in sufficient capacity to repair nitrosative damage to FNR as rapidly as it occurred or that the capacity of the bacteria to reduce NO was sufficient to prevent its cytoplasmic accumulation. Control experiments with the Nsr-independent promoter, FF-37.5::lacZ, eliminated the first possibility and hence, by inference also, the second explanation (Table 2). The results of these experiments also challenged claims that FNR can function as a physiologically relevant sensor of NO (Cruz-Ramos et al., 2002; Corker & Roole, 2003; Pullan et al., 2007). Although the periplasmic

nitrite reductase, NrfAB, was the obvious candidate to provide protection against externally added NO by catalysing its reduction to ammonia in the periplasm (as proposed by van Wonderen et al., 2008), externally added NO still did not induce Phcp::lacZ transcription in a nrfAB deletion mutant as effectively as nitrite. The 10-fold higher rates of NO reduction than nitrite reduction by strains defective in both NirB and NrfA suggest that E. coli has a greater capacity to reduce NO than to produce it from nitrite. We recently reported that even in the absence of all currently characterized Tolmetin NO reductase activities, anaerobic cultures of E. coli still reduce NO rapidly (Vine & Cole, 2011). The data in the current study therefore reinforce our previous conclusion that a significant NO reduction activity remains to be characterized. We favour the explanation that this activity prevents significant damage to cytoplasmic proteins by concentrations of externally generated NO relevant to pathogenicity. We thank Merve Yasa for help with some of the control experiments. “
“Institute of Microbiology, AS ČR, Praha 4-Krč, Czech Republic SpoIISAB is a toxin–antitoxin module encoded on the chromosomes of Bacillus subtilis and related Bacilli species.