Abundance, transcription levels and phylogeny of bacteria capable of nitrous oxide reduction in a municipal wastewater treatment plant.

Nitrous oxide (N2O) production and expression of genes capable of its reduction were investigated in two full-scale parallel plug-flow activated sludge systems. These two systems continuously received wastewater with the same constituents, but operated under distinct nitrification efficiencies due to mixed liquor suspended solid (MLSS) concentration and the different hydraulic retention times (HRTs). A shorter HRT in system 2 resulted in a lower nitrification efficiency (40-60%) in conjunction with a high N2O emission (50.6 mg-N/L/day), whereas there was a higher nitrification efficiency (>99%) in system 1 with low N2O emission (22.6 mg-N/L/day). The DNA abundance of functional genes responsible for nitrification and denitrification were comparable in both systems, but transcription of nosZ mRNA in the lower N2O emission system (system 1) was one order of magnitude higher than that in the higher N2O emission system (system 2). The diversity and evenness of the nosZ gene were nearly identical; however, the predominant N2O reducing bacteria were phylogenetically distinct. Phylogenetic analysis indicated that N2O-reducing strains only retrieved in system 1 were close to the genera Rhodobacter, Oligotropha and Shinella, whereas they were close to the genera Mesorhizobium only in system 2. The distinct predominant N2O reducers may directly or indirectly influence N2O emissions.

Relationship between the cAMP levels in leukocytes and the cytokine balance in patients surviving gram negative bacterial pneumonia.

Lipopolysaccharide-stimulated leukocytes secrete proinflammatory cytokines including tumor necrosis factor-α and interleukin-12. Over-activation of host defense systems may result in severe tissue damage and requires regulation. Granulocyte colony-stimulating factor and interleukin-10 are candidate cytokines for inducing tolerance to lipopolysaccharide re-stimulation. We compared cytokines secreted by lipopolysaccharide-stimulated blood cells from patients who had survived gram negative bacterial pneumonia (Pseudomonas aeruginosa, Escherichia coli or Proteus mirabilis, n = 26) and age-matched healthy volunteers (n = 18). Interleukin-12p70 and tumor necrosis factor-α expression was significantly lower in patients (p = 0.0039 and p<0.001) compared to healthy controls, while granulocyte colony-stimulating factor production was markedly higher in patients (p<0.001). Levels of interleukin-10 were comparable. Granulocyte colony-stimulating factor expression was inversely correlated with interleukin-12p70 (R = -0.71, p<0.001) and tumor necrosis factor-α (R = -0.64, p<0.001) expression; interleukin-10 showed no significant correlation. In unstimulated leukocytes from patients, cAMP levels were significantly raised (p = 0.020) and were correlated inversely with interleukin-12p70 levels (R = -0.81, p<0.001) and directly with granulocyte colony-stimulating factor (R = 0.72, p = 0.0020), matrix metalloproteinase-9 (R = 0.67, p = 0.0067) and interleukin-10 (R = 0.54, p = 0.039) levels. Our results demonstrate that granulocyte colony-stimulating factor production by lipopolysaccharide-stimulated leukocytes is a useful indicator of tolerance induction in surviving pneumonia patients and that measuring cAMP in freshly isolated leukocytes may also be clinically significant.