Anaerobic regulation of hydrogenase transcription in different bacteria

Fnr Negatively Regulates Prodigiosin Synthesis in Serratia sp. ATCC 39006 During Aerobic Fermentation

The well-known Crp/Fnr family regulator Fnr has long been recognized as an oxygen sensor to regulate multiple biological processes, including the switch between aerobic/anaerobic metabolism, nitrogen fixation, bioluminescence, infection, and virulence. In most cases, Fnr was found to be active under anaerobic conditions. However, its role in aerobic antibiotic metabolism has not yet been revealed. In this research, we report that in the model organism, Serratia sp. ATCC 39006, Fnr (Ser39006_013370) negatively regulates prodigiosin production by binding to the spacer between the −10 and −35 region in the promoter of prodigiosin biosynthetic gene cluster under aerobic conditions. Fnr was also shown to modulate the anti-bacterial activity and motility by regulating pathway-specific regulatory genes, indicating that Fnr acts as a global regulator in Serratia sp. ATCC 39006. For the first time, we describe that Fnr regulates antibiotic synthesis in the presence of oxygen, which expands the known physiological functions of Fnr and benefits the further investigation of this important transcriptional regulator.

A metabolic and physiological design study of Pseudomonas putida KT2440 capable of anaerobic respiration

BACKGROUND

Pseudomonas putida KT2440 is a metabolically versatile, HV1-certified, genetically accessible, and thus interesting microbial chassis for biotechnological applications. However, its obligate aerobic nature hampers production of oxygen sensitive products and drives up costs in large scale fermentation. The inability to perform anaerobic fermentation has been attributed to insufficient ATP production and an inability to produce pyrimidines under these conditions. Addressing these bottlenecks enabled growth under micro-oxic conditions but does not lead to growth or survival under anoxic conditions.

RESULTS

Here, a data-driven approach was used to develop a rational design for a P. putida KT2440 derivative strain capable of anaerobic respiration. To come to the design, data derived from a genome comparison of 1628 Pseudomonas strains was combined with genome-scale metabolic modelling simulations and a transcriptome dataset of 47 samples representing 14 environmental conditions from the facultative anaerobe Pseudomonas aeruginosa.

CONCLUSIONS

The results indicate that the implementation of anaerobic respiration in P. putida KT2440 would require at least 49 additional genes of known function, at least 8 genes encoding proteins of unknown function, and 3 externally added vitamins.

Attractor Concepts to Evaluate the Transcriptome-wide Dynamics Guiding Anaerobic to Aerobic State Transition in Escherichia coli

For any dynamical system, like living organisms, an attractor state is a set of variables or mechanisms that converge towards a stable system behavior despite a wide variety of initial conditions. Here, using multi-dimensional statistics, we investigate the global gene expression attractor mechanisms shaping anaerobic to aerobic state transition (AAT) of Escherichia coli in a bioreactor at early times. Out of 3,389 RNA-Seq expression changes over time, we identified 100 sharply changing genes that are key for guiding 1700 genes into the AAT attractor basin. Collectively, these genes were named as attractor genes constituting of 6 dynamic clusters. Apart from the expected anaerobic (glycolysis), aerobic (TCA cycle) and fermentation (succinate pathways) processes, sulphur metabolism, ribosome assembly and amino acid transport mechanisms together with 332 uncharacterised genes are also key for AAT. Overall, our work highlights the importance of multi-dimensional statistical analyses for revealing novel processes shaping AAT.

Hydrogenases and H2 metabolism in sulfate-reducing bacteria of the Desulfovibrio genus

Hydrogen metabolism plays a central role in sulfate-reducing bacteria of the Desulfovibrio genus and is based on hydrogenases that catalyze the reversible conversion of protons into dihydrogen. These metabolically versatile microorganisms possess a complex hydrogenase system composed of several enzymes of both [FeFe]- and [NiFe]-type that can vary considerably from one Desulfovibrio species to another. This review covers the molecular and physiological aspects of hydrogenases and H₂ metabolism in Desulfovibrio but focuses particularly on our model bacterium Desulfovibrio fructosovorans. The search of hydrogenase genes in more than 30 sequenced genomes provides an overview of the distribution of these enzymes in Desulfovibrio. Our discussion will consider the significance of the involvement of electron-bifurcation in H₂ metabolism.

The NiFe Hydrogenases of the Tetrachloroethene-Respiring Epsilonproteobacterium Sulfurospirillum multivorans: Biochemical Studies and Transcription Analysis

The organohalide-respiring Epsilonproteobacterium Sulfurospirillum multivorans is able to grow with hydrogen as electron donor and with tetrachloroethene (PCE) as electron acceptor; PCE is reductively dechlorinated to cis-1,2-dichloroethene. Recently, a genomic survey revealed the presence of four gene clusters encoding NiFe hydrogenases in its genome, one of which is presumably periplasmic and membrane-bound (MBH), whereas the remaining three are cytoplasmic. To explore the role and regulation of the four hydrogenases, quantitative real-time PCR and biochemical studies were performed with S. multivorans cells grown under different growth conditions. The large subunit genes of the MBH and of a cytoplasmic group 4 hydrogenase, which is assumed to be membrane-associated, show high transcript levels under nearly all growth conditions tested, pointing toward a constitutive expression in S. multivorans. The gene transcripts encoding the large subunits of the other two hydrogenases were either not detected at all or only present at very low amounts. The presence of MBH under all growth conditions tested, even with oxygen as electron acceptor under microoxic conditions, indicates that MBH gene transcription is not regulated in contrast to other facultative hydrogen-oxidizing bacteria. The MBH showed quinone-reactivity and a characteristic UV/VIS spectrum implying a cytochrome b as membrane-integral subunit. Cell extracts of S. multivorans were subjected to native polyacrylamide gel electrophoresis (PAGE) and hydrogen oxidizing activity was tested by native staining. Only one band was detected at about 270 kDa in the particulate fraction of the extracts, indicating that there is only one hydrogen-oxidizing enzyme present in S. multivorans. An enrichment of this enzyme and SDS PAGE revealed a subunit composition corresponding to that of the MBH. From these findings we conclude that the MBH is the electron-donating enzyme system in the PCE respiratory chain. The roles for the other three hydrogenases remain unproven. The group 4 hydrogenase might be involved in hydrogen production upon fermentative growth.

The HU regulon is composed of genes responding to anaerobiosis, acid stress, high osmolarity and SOS induction

BACKGROUND

The Escherichia coli heterodimeric HU protein is a small DNA-bending protein associated with the bacterial nucleoid. It can introduce negative supercoils into closed circular DNA in the presence of topoisomerase I. Cells lacking HU grow very poorly and display many phenotypes.

METHODOLOGY/PRINCIPAL FINDINGS

We analyzed the transcription profile of every Escherichia coli gene in the absence of one or both HU subunits. This genome-wide in silico transcriptomic approach, performed in parallel with in vivo genetic experimentation, defined the HU regulon. This large regulon, which comprises 8% of the genome, is composed of four biologically relevant gene classes whose regulation responds to anaerobiosis, acid stress, high osmolarity, and SOS induction.

CONCLUSIONS/SIGNIFICANCE

The regulation a large number of genes encoding enzymes involved in energy metabolism and catabolism pathways by HU explains the highly pleiotropic phenotype of HU-deficient cells. The uniform chromosomal distribution of the many operons regulated by HU strongly suggests that the transcriptional and nucleoid architectural functions of HU constitute two aspects of a unique protein-DNA interaction mechanism.

Shewanella oneidensis: a new and efficient system for expression and maturation of heterologous [Fe-Fe] hydrogenase from Chlamydomonas reinhardtii

BACKGROUND

The eukaryotic green alga, Chlamydomonas reinhardtii, produces H2 under anaerobic conditions, in a reaction catalysed by a [Fe-Fe] hydrogenase HydA1. For further biochemical and biophysical studies a suitable expression system of this enzyme should be found to overcome its weak expression in the host organism. Two heterologous expression systems used up to now have several advantages. However they are not free from some drawbacks. In this work we use bacterium Shewanella oneidensis as a new and efficient system for expression and maturation of HydA1 from Chlamydomonas reinhardtii.

RESULTS

Based on codon usage bias and hydrogenase maturation ability, the bacterium S. oneidensis, which possesses putative [Fe-Fe] and [Ni-Fe] hydrogenase operons, was selected as the best potential host for C. reinhardtii [Fe-Fe] hydrogenase expression. Hydrogen formation by S. oneidensis strain AS52 (Delta hydA Delta hyaB) transformed with a plasmid bearing CrHydA1 and grown in the presence of six different substrates for anaerobic respiration was determined. A significant increase in hydrogen evolution was observed for cells grown in the presence of trimethylamine oxide, dimethylsulfoxide and disodium thiosulfate, showing that the system of S. oneidensis is efficient for heterologous expression of algal [Fe-Fe] hydrogenase.

CONCLUSION

In the present work a new efficient system for heterologous expression and maturation of C. reinhardtii hydrogenase has been developed. HydA1 of C. reinhardtii was purified and shown to contain 6 Fe atoms/molecule of protein, as expected. Using DMSO, TMAO or thiosulfate as substrates for anaerobic respiration during the cell growth, 0.4 - 0.5 mg l(-1)(OD600 = 1) of catalytically active HydA1 was obtained with hydrogen evolution rate of approximately 700 micromol H2 mg(-1) min(-1).

Transcription of hupSL in Anabaena variabilis ATCC 29413 is regulated by NtcA and not by hydrogen

Nitrogen-fixing cyanobacteria such as Anabaena variabilis ATCC 29413 use an uptake hydrogenase, encoded by hupSL, to recycle hydrogen gas that is produced as an obligate by-product of nitrogen fixation. The regulation of hupSL in A. variabilis is likely to differ from that of the closely related Anabaena sp. strain PCC 7120 because A. variabilis lacks the excision element-mediated regulation that characterizes hupSL regulation in strain PCC 7120. An analysis of the hupSL transcript in a nitrogenase mutant of A. variabilis that does not produce any detectable hydrogen indicated that neither nitrogen fixation nor hydrogen gas was required for the induction of hupSL. Furthermore, exogenous addition of hydrogen gas did not stimulate hupSL transcription. Transcriptional reporter constructs indicated that the accumulation of hupSL transcript after nitrogen step-down was restricted primarily to the microaerobic heterocysts. Anoxic conditions were not sufficient to induce hupSL transcription. The induction of hupSL after nitrogen step-down was reduced in a mutant in the global nitrogen regulator NtcA, but was not reduced in a mutant unable to form heterocysts. A consensus NtcA-binding site was identified upstream of hupSL, and NtcA was found to bind to this region. Thus, while neither hydrogen gas nor anoxia controlled the expression of hupSL, its expression was controlled by NtcA. Heterocyst differentiation was not required for hupSL induction in response to nitrogen step-down, but heterocyst-localized cues may add an additional level of regulation to hupSL.

Hydrogen independent expression of hupSL genes in Thiocapsa roseopersicina BBS

The expression of many membrane bound [NiFe] hydrogenases is regulated by their substrate molecule, hydrogen. The HupSL hydrogenase, encoded in the hupSLCDHIR operon, probably plays a role in hydrogen recycling in the phototrophic purple bacterium, Thiocapsa roseopersicina BBS. RpoN, coding for sigma factor 54, was shown to be important for expression, suggesting a regulated biosynthsis from the hup gene cluster. The response regulator gene, hupR, has been identified in the hup operon and expression of hupSL was reduced in a chromosomal hupR mutant, which indicated that HupR was implicated in the activation process. The hupT and hupUV genes were isolated, and show similarity to the histidine kinase element of the H2-driven signal transduction system and to the regulatory hydrogenases of Ralstonia eutropha and Rhodobacter capsulatus, respectively. Although the genes of the entire H2 sensing and regulation system were present, the expression of the hupSL genes was not affected by the presence or absence of H2. Using reverse transcription PCR, we could not detect any mRNA specific to the hupTUV genes in cells grown under diverse conditions. The hupT and hupUV mutant strains had the same phenotype as the wild-type strains. The hupT gene product, expressed from a plasmid, repressed HupSL synthesis as expected while introduction of actively expressed hupTUV genes together derepressed the HupSL activity in T. roseopersicina. The gene product of hupUV behaves similarly to other regulatory hydrogenases and shows H-D exchange activity.