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Bacterial oxygen production in the dark.

ABSTRACT: Nitric oxide (NO) and nitrous oxide (N(2)O) are among nature's most powerful electron acceptors. In recent years it became clear that microorganisms can take advantage of the oxidizing power of these compounds to degrade aliphatic and aromatic hydrocarbons. For two unrelated bacterial species, the "NC10" phylum bacterium "Candidatus Methylomirabilis oxyfera" and the ?-proteobacterial strain HdN1 it has been suggested that under anoxic conditions with nitrate and/or nitrite, monooxygenases are used for methane and hexadecane oxidation, respectively. No degradation was observed with nitrous oxide only. Similarly, "aerobic" pathways for hydrocarbon degradation are employed by (per)chlorate-reducing bacteria, which are known to produce oxygen from chlorite [Formula: see text]. In the anaerobic methanotroph M. oxyfera, which lacks identifiable enzymes for nitrogen formation, substrate activation in the presence of nitrite was directly associated with both oxygen and nitrogen formation. These findings strongly argue for the role of NO, or an oxygen species derived from it, in the activation reaction of methane. Although oxygen generation elegantly explains the utilization of "aerobic" pathways under anoxic conditions, the underlying mechanism is still elusive. In this perspective, we review the current knowledge about intra-aerobic pathways, their potential presence in other organisms, and identify candidate enzymes related to quinol-dependent NO reductases (qNORs) that might be involved in the formation of oxygen.

SUBMITTER: Ettwig KF

PROVIDER: S-EPMC3413370 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Bacterial oxygen production in the dark.

Ettwig Katharina F KF Speth Daan R DR Reimann Joachim J Wu Ming L ML Jetten Mike S M MS Keltjens Jan T JT

Frontiers in microbiology 20120807

Nitric oxide (NO) and nitrous oxide (N(2)O) are among nature's most powerful electron acceptors. In recent years it became clear that microorganisms can take advantage of the oxidizing power of these compounds to degrade aliphatic and aromatic hydrocarbons. For two unrelated bacterial species, the "NC10" phylum bacterium "Candidatus Methylomirabilis oxyfera" and the γ-proteobacterial strain HdN1 it has been suggested that under anoxic conditions with nitrate and/or nitrite, monooxygenases are us ...[more]

PMID: 22891064

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Project description:UnlabelledUnderstanding the mechanisms of lipid accumulation in microorganisms is important for several reasons. In addition to providing insight into assembly of biological membranes, lipid accumulation has important applications in the production of renewable fuels and chemicals. The photosynthetic bacterium Rhodobacter sphaeroides is an attractive organism to study lipid accumulation, as it has the ability to increase membrane production at low O2 tensions. Under these conditions, R. sphaeroides develops invaginations of the cytoplasmic membrane to increase its membrane surface area for housing of the membrane-bound components of its photosynthetic apparatus. Here we use fatty acid levels as a reporter of membrane lipid content. We show that, under low-O2 and anaerobic conditions, the total fatty acid content per cell increases 3-fold. We also find that the increases in the amount of fatty acid and photosynthetic pigment per cell are correlated as O2 tensions or light intensity are changed. To ask if lipid and pigment accumulation were genetically separable, we analyzed strains with mutations in known photosynthetic regulatory pathways. While a strain lacking AppA failed to induce photosynthetic pigment-protein complex accumulation, it increased fatty acid content under low-O2 conditions. We also found that an intact PrrBA pathway is required for low-O2-induced fatty acid accumulation. Our findings suggest a previously unknown role of R. sphaeroides transcriptional regulators in increasing fatty acid and phospholipid accumulation in response to decreased O2 tension.ImportanceLipids serve important functions in living systems, either as structural components of membranes or as a form of carbon storage. Understanding the mechanisms of lipid accumulation in microorganisms is important for providing insight into the assembly of biological membranes and additionally has important applications in the production of renewable fuels and chemicals. In this study, we investigate the ability of Rhodobacter sphaeroides to increase membrane production at low O2 tensions in order to house its photosynthetic apparatus. We demonstrate that this bacterium has a mechanism to increase lipid content in response to decreased O2 tension and identify a transcription factor necessary for this response. This is significant because it identifies a transcriptional regulatory pathway that can increase microbial lipid content.

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Bacterial oxygen production in the dark.

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Bacterial oxygen production in the dark.

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