Oxygen, hydrogen and nitrogen fixation in Azotobacter

Yates, M. G.; Souza, Emanuel Maltempi de; Kahindi, Jhp

doi:10.1016/s0038-0717(96)00213-1

Cited by 14 publications

(10 citation statements)

References 30 publications

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“…A. chroococcum contains a membrane-bound H 2 -oxidizing enzyme which is highly related to the R. eutropha system (15). It has been shown that orf4 is able to complement an A. chroococcum mutant with a membrane-bound hydrogenase activity misassembled to the soluble fraction, but the molecular basis remains to be elucidated (45). To express the A. chroococcum orf4 gene we cloned the 2.7-kb BamHI/HindIII fragment of pGY12 into the broad-host-range vector pGE151, yielding pGE600.…”

Section: Resultsmentioning

confidence: 99%

Ralstonia eutropha TF93 Is Blocked in Tat-Mediated Protein Export

2000

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Ralstonia eutropha (formerly Alcaligenes eutrophus) TF93 is pleiotropically affected in the translocation of redox enzymes synthesized with an N-terminal signal peptide bearing a twin arginine (S/T-R-R-X-F-L-K) motif. Immunoblot analyses showed that the catalytic subunits of the membrane-bound [NiFe] hydrogenase (MBH) and the molybdenum cofactor-binding periplasmic nitrate reductase (Nap) are mislocalized to the cytoplasm and to the inner membrane, respectively. Moreover, physiological studies showed that the coppercontaining nitrous oxide reductase (NosZ) was also not translocated to the periplasm in strain TF93. The cellular localization of enzymes exported by the general secretion system was unaffected. The translocationarrested MBH and Nap proteins were enzymatically active, suggesting that twin-arginine signal peptidedependent redox enzymes may have their cofactors inserted prior to transmembrane export. The periplasmic destination of MBH, Nap, and NosZ was restored by heterologous expression of Azotobacter chroococcum tatA mobilized into TF93. tatA encodes a bacterial Hcf106-like protein, a component of a novel protein transport system that has been characterized in thylakoids and shown to translocate folded proteins across the membrane.Periplasmic enzymes binding redox cofactors play a central role in alternative energy metabolism of gram-negative bacteria. In contrast to cytochrome c-type proteins, various periplasmic enzymes binding constituents, such as the molybdenum cofactor, a [NiFe] site, copper centers, or iron-sulfur clusters, contain a conserved, positively charged -S/T-RRXFLK-(twinarginine) element within their N-terminal signal peptides, pointing to a special translocation pathway (2). Very recently, a system responsible for the membrane targeting and translocation of [NiFe] hydrogenases, as well as the molybdenum enzymes dimethylsulfoxide reductase, trimethylamine N-oxide reductase, and periplasmic nitrate reductase, has been characterized for Escherichia coli (32,43). Mutant analyses suggested that the translocation of the twin-arginine signal peptide-bearing enzymes proceeds independently of the general secretion machinery of the cell (Sec), presumably via intermediates which have their cofactors inserted (31).Ralstonia eutropha (formerly Alcaligenes eutrophus [7]) is the host of at least three periplasmic cofactor-containing enzymes synthesized with an N-terminal twin-arginine signal peptide: the membrane-bound hydrogenase (MBH) (involved in energy generation from H 2 ), the periplasmic nitrate reductase (Nap) (reduces nitrate to nitrite), and the nitrous oxide reductase (NosZ) (a component of the denitrification pathway). All three enzymes are encoded in R. eutropha H16 by megaplasmidborne genes.The MBH of R. eutropha is a member of the [NiFe] hydrogenases (15) composed of a heterodimer (HoxKG) attached to the periplasmic surface of the inner membrane by a cytochrome b-type anchor protein (HoxZ) (4, 13). Hydrogen is activated at the [NiFe] site of HoxG (62 kDa), and the electrons are tra...

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Section: Resultsmentioning

confidence: 99%

Ralstonia eutropha TF93 Is Blocked in Tat-Mediated Protein Export

2000

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“…Cultivation of A. chroococcum on chemically defined media was characterized by relatively low biomass yield coefficients (Y X/S ; 0.103 to 0.166 g/g), which is probably a consequence of relatively high energy demand for bacterial metabolism, as already reported in literature (Yates et al, 1997;Savenkova et al, 1999;Kisten et al, 2006).…”

Section: +mentioning

confidence: 53%

“…, Fe 2+ and Ca 2+ ) that are important for the growth of A. chroococcum (Page, 1986;Fallik et al, 1993;Yates et al, 1997). The complex media was composed of sugar beet molasses (47.6% w/w sucrose) as a carbon source and inorganic salts.…”

Section: +mentioning

confidence: 99%

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Cultivation of the bacterium Azotobacter chroococcum for preparation of biofertilizers

Oros¹,

Pavlečić²,

antek³

et al. 2011

Afr. J. Biotechnol.

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The biomass of the bacterium Azotobacter chroococcum can be used as a biofertilizer due to its ability to fix nitrogen from the atmosphere. In order to optimize the production of bacterial biomass for this purpose, a cultivation of A. chroococcum was done by using different media and cultivation techniques (batch, fed batch and repeated batch). Chemically defined and complex media with 20 g/l of sugar were selected as the most appropriate media for batch cultivation in stirred tank bioreactor. In order to obtain higher fed batch and repeated batch techniques were examined. During these cultivations, increase of bioprocess efficiency parameters (yield coefficient and productivity) were observed compared with the batch cultivation. On the basis of the obtained results, repeated batch technique appeared to be the most suitable for the bacterial biomass production at industrial scale.

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“…A recently described Sec-independent pathway mediates the export of proteins in a folded conformation. This alternative pathway has been designated the twin-arginine translocation (Tat) system because of the characteristic twin-arginine motif (S/T-R-R-x-F-L-K) present in the signal peptide of proteins translocated via this system (3,11,13,18,20; for a recent comprehensive review, see reference 9). In Escherichia coli, a functional Tat pathway requires a minimum set of three gene products: TatA, TatB, and TatC (4).…”

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confidence: 99%