Biomedical subjects

Jonathan D Rock

Publications and source records attributed to Jonathan D Rock.

3 recordsLinked to original sources

PubMed2006

Regulation of denitrification genes in Neisseria meningitidis by nitric oxide and the repressor NsrR.

The human pathogen Neisseria meningitidis is capable of growth using the denitrification of nitrite to nitrous oxide under microaerobic conditions. This process is catalyzed by two reductases: nitrite reductase (encoded by aniA) and nitric oxide (NO) reductase (encoded by norB). Here, we show that in N. meningitidis MC58 norB is regulated by nitric oxide via the product of gene NMB0437 which encodes NsrR. NsrR is a repressor in the absence of NO, but norB expression is derepressed by NO in an NsrR-dependent manner. nsrR-deficient mutants grow by denitrification more rapidly than wild-type N. meningitidis, and this is coincident with the upregulation of both NO reductase and nitrite reductase even under aerobic conditions in the absence of nitrite or NO. The NsrR-dependent repression of aniA (unlike that of norB) is not lifted in the presence of NO. The role of NsrR in the control of expression of aniA is linked to the function of the anaerobic activator protein FNR: analysis of nsrR and fnr single and nsrR fnr double mutants carrying an aniA promoter lacZ fusion indicates that the role of NsrR is to prevent FNR-dependent aniA expression under aerobic conditions, indicating that FNR in N. meningitidis retains considerable activity aerobically.

Aerobiosis↗

PubMed2006

Heme utilization in Campylobacter jejuni.

A putative iron- and Fur-regulated hemin uptake gene cluster, composed of the transport genes chuABCD and a putative heme oxygenase gene (Cj1613c), has been identified in Campylobacter jejuni NCTC 11168. Mutation of chuA or Cj1613c leads to an inability to grow in the presence of hemin or hemoglobin as a sole source of iron. Mutation of chuB, -C, or -D only partially attenuates growth where hemin is the sole iron source, suggesting that an additional inner membrane (IM) ABC (ATP-binding cassette) transport system(s) for heme is present in C. jejuni. Genotyping experiments revealed that Cj1613c is highly conserved in 32 clinical isolates. One strain did not possess chuC, though it was still capable of using hemin/hemoglobin as a sole iron source, supporting the hypothesis that additional IM transport genes are present. In two other strains, sequence variations within the gene cluster were apparent and may account for an observed negative heme utilization phenotype. Analysis of promoter activity within the Cj1613c-chuA intergenic spacer region revealed chuABCD and Cj1613c are expressed from separate iron-repressed promoters and that this region also specifically binds purified recombinant Fur(Cj) in gel retardation studies. Absorbance spectroscopy of purified recombinant His(6)-Cj1613c revealed a 1:1 heme:His(6)-Cj1613c binding ratio. The complex was oxidatively degraded in the presence of ascorbic acid as the electron donor, indicating that the Cj1613c gene product functions as a heme oxygenase. In conclusion, we confirm the involvement of Cj1613c and ChuABCD in heme/hemoglobin utilization in C. jejuni.

Bacterial Proteins↗

PubMed2005

The pathogen Neisseria meningitidis requires oxygen, but supplements growth by denitrification. Nitrite, nitric oxide and oxygen control respiratory flux at genetic and metabolic levels.

The human pathogen Neisseria meningitidis is the major causative agent of bacterial meningitis. The organism is usually treated as a strict aerobe and is cultured under fully aerobic conditions in the laboratory. We demonstrate here that although N. meningitidis fails to grow under strictly anaerobic conditions, under oxygen limitation the bacterium expresses a denitrification pathway (reduction of nitrite to nitrous oxide via nitric oxide) and that this pathway supplements growth. The expression of the gene aniA, which encodes nitrite reductase, is regulated by oxygen depletion and nitrite availability via transcriptional regulator FNR and two-component sensor-regulator NarQ/NarP respectively. Completion of the two-step denitrification pathway requires nitric oxide (NO) reduction, which proceeds after NO has accumulated during batch growth under oxygen-limited conditions. During periods of NO accumulation both nitrite and NO reduction are observed aerobically, indicating N. meningitidis can act as an aerobic denitrifier. However, under steady-state conditions in which NO is maintained at a low concentration, oxygen respiration is favoured over denitrification. NO inhibits oxidase activity in N. meningitidis with an apparent Ki NO = 380 nM measured in intact cells. The high respiratory flux to nitrite after microaerobic growth and the finding that accumulation of the denitrification intermediate NO inhibits oxygen respiration support the view that denitrification is a pathway of major importance in N. meningitidis.

Adult↗