Improved system for heterologous expression of cytochrome c mutants in Escherichia coli.

We improved an already existing cytochrome c expression system to a reliable, tightly controllable one to achieve a higher expression yield for single cysteine mutants of horse cytochrome c. The protein is heterologously overexpressed in E. coli together with the maturation coordinating enzyme heme lyase from yeast. Various plasmid constructs and host strains were tested for protein expression yield and routinely around 35 mg/L yield was achieved, which is a good result for a post-translationally modified enzyme. The purpose of producing cysteine mutants is to position accessible cysteine residues on the surface of cytochrome c which can be labeled with a photoactive redox dye, 8-thiouredopyrene-1,3,6-trisulfonate, TUPS. TUPS labeled proteins have been used for intramolecular and intermolecular electron transfer measurements. Here, we initiate the photoreduction of cytochrome c oxidase, the natural electron acceptor partner of cytochrome c by an appropriate cytochrome c mutant labeled with TUPS. The electron transfer from cytochrome c to the first cytochrome oxidase redox cofactor, copper A, is shown to be very fast.

Overlaps between the various biodegradation pathways in Sphingomonas subarctica SA1.

A bacterium capable to grow on sulfanilic acid as sole carbon, nitrogen and sulfur source has been isolated. A unique feature of this strain is that it contains the full set of enzymes necessary for the biodegradation of sulfanilic acid. Taxonomical analysis identified our isolate as Sphingomonas subaretica SA1 sp. The biodegradation pathway of sulfanilic acid was investigated at the molecular level. Screening the substrate specificity of the strain disclosed its capacity to degrade six analogous aromatic compounds including p-aminobenzoic acid. Moreover, the strain was successfully used for removal of oil contaminations. S. subarctica SA1 seemed to use distinct enzyme cascades for decomposition of these molecules, since alternative enzymes were induced in cells grown on various substrates. However, the protein patterns appearing upon induction by sulfanilic acid and sulfocatechol were very similar to each other indicating common pathways for the degradation of these substrates. Cells grown on sulfanilic acid could convert p-aminobenzoic acid to some extent and vice versa. Two types of ring cleaving dioxygenases were detected in the cells grown on various substrates: one preferred protocatechol, while the other had higher activity with sulfocatechol. This latter enzyme, named as sulfocatechol dioxygenase was partially purified and characterized.

Recent advances in biohydrogen research.

A fundamental and principal difficulty of the future energy supply is that the formation of fossil fuels is much slower than the rate of their exploitation. Therefore the reserves which can be recovered in an energetically feasible manner are shrinking parallel with an increasing world-wide energy demand. Among the alternative energy carriers, hydrogen is preferred because it is easy to transport and store and it burns to environmentally friendly water vapour when utilized. Hydrogen can be produced in biological systems, however, our understanding of the molecular details is just emerging.

Cloning and sequence of the structural (hupSLC) and accessory (hupDHI) genes for hydrogenase biosynthesis in Thiocapsa roseopersicina.

The first molecular biology study on the purple sulfur photosynthetic bacterium Thiocapsa roseopersicina is reported, namely, the construction of cosmid libraries and isolation of a hydrogenase gene cluster by hybridization with hydrogenase structural genes from the purple non-sulfur bacterium, Rhodobacter capsulatus. The sequenced gene cluster contains six open reading frames, the products of which show significant degrees of identity (from 40 to 78%) with hydrogenase gene products necessary for biosynthesis of the group-I of [NiFe]hydrogenases. The structural hupSLC genes encode the small and large hydrogenase subunits and a hydrophobic protein shown to accept electrons from hydrogenase in R. capsulatus. They are followed downstream by three genes, hupDHI, which are similar to hydrogenase accessory genes found in other bacteria.

Hydrogen evolution from dithionite and H2 photoproduction by hydrogenase incorporated into various hydrophobic matrices.

The effects of surfactants, lipids and amphiphilic viologen mediators on H2 production from dithionite as well as on Ru(bpy) sensitized H2 photoproduction by hydrogenase from Thiocapsa roseopersicina was studied. Three systems which differed as to the nature of the hydrophobic matrix around the hydrogenase were tested. An enhanced hydrogenase activity was observed in the presence of surfactants, in the 1-6 mM concentration range. Hydrogenase showed a selectivity for the amphiphilic viologens, 2C7-diCl was the most efficient electron mediator in both reactions. H2 photoproduction seemed not to be feasible in the detergent-hydrogenase system because of intensive foaming. Hydrogenase incorporated into liposomes catalyzed H2 photoevolution efficiently but the rate was decreasing in time, though reversibly. Using intact bacterial cells instead of purified hydrogenase yielded stable H2 photoevolution for at least 12 hours. This system offers several advantages for potential practical applications.

Protein structural changes associated with active and inactive states of hydrogenase from Thiocapsa roseopersicina.

Electrophoretic and isoelectrofocusing behavior of the hydrogenase from Thiocapsa roseopersicina under various conditions revealed remarkable properties of this enzyme: there are two active forms which differ in their molecular masses as well as in oxygen sensitivity; the apparent molecular masses of the active hydrogenase forms (90 and 49 kDa) differ considerably from those in the inactive state (64, 34, and 15 kDa); the active forms and some of the inactivated ones can be transformed into each other reversibly; urea can unfold the 64 and 34 kDa proteins but not the 49 kDa form at room temperature; the pI of these proteins are different in the presence of urea. The results suggest large rearrangements in the hydrogenase protein structure which are associated with the enzymatically active and inactive states. It is concluded that reversible formation of disulfide bonds cannot be the major cause for maintaining the enzyme conformation. Strong hydrophobic interactions are suggested to be primarily responsible for the structural stability and for the rearrangements.

Bacterial triterpenoids of the hopane series from the methanotrophic bacteria Methylocaldum spp.: phylogenetic implications and first evidence for an unsaturated aminobacteriohopanepolyol.

The hopanoid content of the two methanotrophic bacteria Methylocaldum szegediense and Methylocaldum tepidum was investigated. 35-Aminobacteriohopane-30R,31R,32R,33S, 34S-pentol and its 3beta-methyl homologue were present in both strains. In M. tepidum, they were accompanied by 35-aminobacteriohopane-31R,32R,33S, 34S-tetrol and its 3beta-methyl homologue. The side chain structure was identical to those previously reported from two other obligate methanotrophs, Methylococcus capsulatus and Methylomonas methanica. The two Methylocaldum species shared with the Methylococcus species the presence of 3beta-methylhopanoid as well as of a hopanoid releasing adiantol upon H(5)IO(6)/NaBH(4) treatment. A rare feature was in addition found in M. szegediense. The saturated hopanoids were accompanied by an unsaturated aminobacteriohopanepentol with a Delta(11) double bond. Comparison of the hopanoid fingerprints was in accordance with the close phylogenetic relationship of Methylococcus and Methylocaldum. The major difference was the absence of sterols in Methylocaldum which were always detected in the Methylococcus species.

pH-dependent activation of the alternative transcriptional factor sigmaB in Bacillus subtilis.

The expression of the sigB gene of Bacillus subtilis was analysed in response to a mild acid shock. This gene is subject to sigmaB-dependent regulation. It has been found that the expression of sigB is induced as part of the acid-tolerant response. In that respect sigB is similar to the previously described gene gsiB which is also a member of the sigmaB regulon. Through this induction, the sigmaB regulon provides protection against acid shock. Besides its protective role against acid shock, no other general function could be directly associated with the sigmaB regulon. An acidification of the cytoplasmic environment induces synthesis of general stress proteins in B. subtilis.

Molecular characterization of structural genes coding for a membrane bound hydrogenase in Methylococcus capsulatus (Bath).

The first gene cluster encoding for a membrane bound [NiFe] hydrogenase from a methanotroph, Methylococcus capsulatus (Bath), was cloned and sequenced. The cluster consisted of the structural genes hupS and hupL and accessory genes hupE, hupC and hupD. A DeltahupSL deletion mutant of Mc. capsulatus was constructed by marker exchange mutagenesis. Membrane associated hydrogenase activity disappeared. The membrane associated hydrogenase appeared to have a hydrogen uptake function in vivo.

Genes involved in hydrogen and sulfur metabolism in phototrophic sulfur bacteria.

The dsr genes and the hydSL operon are present as separate entities in phototrophic sulfur oxidizers of the genera Allochromatium, Marichromatium, Thiocapsa and Thiocystis and are organized similarly as in Allochromatium vinosum and Thiocapsa roseopersicina, respectively. The dsrA gene, encoding the alpha subunit of 'reverse' siroheme sulfite reductase, is also present in two species of green sulfur bacteria pointing to an important and universal role of this enzyme and probably other proteins encoded in the dsr locus in the oxidation of stored sulfur by phototrophic bacteria. The hupSL genes are uniformly present in the members of the Chromatiaceae family tested. The two genes between hydS and hydL encode a membrane-bound b-type cytochrome and a soluble iron-sulfur protein, respectively, resembling subunits of heterodisulfide reductase from methanogenic archaea. These genes are similar but not identical to dsrM and dsrK, indicating that the derived proteins have distinct functions, the former in hydrogen metabolism and the latter in oxidative sulfur metabolism.

Location and quantification of metal ions in enzymes combining polyacrylamide gel electrophoresis and particle-induced X-ray emission.

A method is presented to identify and determine the relative amounts of protein-bound metal ions in situ. Proteins or their subunits are separated by SDS-PAGE, the appropriately dried gel sections are directly scanned by a collimated proton beam of 3 MeV energy, and the characteristic X-rays produced are detected. The determination of Fe content of an iron-sulfur protein (HiPiP), as well as the Fe and Ni analysis of the hydrogenase from Thiocapsa reseopersicina, have shown the feasibility of this technique.

Methane utilizing bacteria and their biotechnological applications.

Methanotroph microorganisms oxidize methane in four steps, producing methanol, formaldehyde, formate intermediers and eventually degrade methane to carbon dioxide and water. It is possible to separate the pathway into four steps in the cell free extract or after partial purification of the various enzymes. The key enzyme is a metalloenzyme, methane monooxygenase (MMO) which catalyses the oxidation of methane to methanol. MMO is also capable of biodegrading exceptionally harmful and stable chlorinated hydrocarbons. Produced by various industrial activities, most chlorinated hydrocarbons are toxic, potential and/or proven carcinogens and their decomposition challenges water treatment technologies.

[Identification and cloning of partial mbh2 gene cluster of hyperthermophile Aquifex pyrophilus].

A 0.8 kb fragment of mbhS2 gene of Aquifex pyrophilus was obtained by PCR with designed primers basing mbhS2 gene of A. aeolicus. It showed 85% homology with the corresponding region of A. aeolicus. Using it as probe, a 5.0 kb Nco I fragment was fished out from the partial genomic library of A. pyrophilus. Then this fragment was cloned, subcloned and sequenced. The result revealed that the fragment contains the full length gene for the mbhS2, the gene orf1 and the first 366 bp of orf2. Comparison with mbhS2 and orf963 of A. aeolicus shows 81% and 60% homologies in amino acid sequence, respectively.

Improvement of biogas production by bioaugmentation.

Biogas production technologies commonly involve the use of natural anaerobic consortia of microbes. The objective of this study was to elucidate the importance of hydrogen in this complex microbial food chain. Novel laboratory biogas reactor prototypes were designed and constructed. The fates of pure hydrogen-producing cultures of Caldicellulosiruptor saccharolyticus and Enterobacter cloacae were followed in time in thermophilic and mesophilic natural biogas-producing communities, respectively. Molecular biological techniques were applied to study the altered ecosystems. A systematic study in 5-litre CSTR digesters revealed that a key fermentation parameter in the maintenance of an altered population balance is the loading rate of total organic solids. Intensification of the biogas production was observed and the results corroborate that the enhanced biogas productivity is associated with the increased abundance of the hydrogen producers. Fermentation parameters did not indicate signs of failure in the biogas production process. Rational construction of more efficient and sustainable biogas-producing microbial consortia is proposed.

Anaerobic regulation of hydrogenase transcription in different bacteria.

Hydrogen metabolism is closely related to other important metabolic and energetic processes of bacterial cells, such as photosynthesis, anaerobic respiration and sulphur metabolism. Even small environmental changes influence these networks through different regulatory systems. The presence or absence of oxygen is one of the most important signals; how the cascades evolved to transmit this signal in different bacteria is summarized. In many instances, hydrogen is released only under anoxic conditions, because of bioenergetic considerations. Most [NiFe] hydrogenases are inactivated by oxygen, but many of them can be re-activated under reducing conditions. In addition to direct inactivation of the hydrogenases, oxygen can also regulate their expression. The global regulatory systems [FNR (fumarate and nitrate reduction regulator), ArcAB (aerobic respiratory control) and RegAB], which respond to alterations in oxygen content and redox conditions of the environment, have an important role in hydrogenase regulation of several bacteria. FNR-like proteins were shown to be important for the regulation of hydrogenases in Escherichia coli, Thiocapsa roseopersicina and Rhizobium leguminosarum, whereas RegA protein modulates the expression of hupSL genes in Rhodobacter capsulatus.

The hydrogenases of Thiocapsa roseopersicina.

The purple sulphur phototrophic bacterium, Thiocapsa roseopersicina BBS, contains several NiFe hydrogenases. One of these enzymes (HynSL) is membrane associated, remarkably stable and can be used for practical applications. HupSL is also located in the photosynthetic membrane, its properties are similar to other known Hup-type NiFe hydrogenases. A third hydrogenase activity was located in the soluble fraction and was analogous to the NAD-reducing hydrogenases of cyanobacteria. The hoxEFUYH genes are transcribed together. HoxE is needed for the in vivo electron flow to and from the soluble hydrogenase. Some of the accessory genes were identified using random mutagenesis, and sequencing of the T. roseopersicina genome is in progress. The HupD, HynD and HoxW gene products corresponded to the proteases processing the C-termini of the three NiFe hydrogenases respectively. HypF and HupK mutants displayed significant in vivo H(2) evolution, which could be linked to the nitrogenase activity for the DeltahypF and to the bidirectional Hox activity in the DeltahupK strain. Both HypC proteins are needed for the biosynthesis of each NiFe hydrogenase. The hydrogenase expression is regulated at the transcriptional level through distinct mechanisms. The expression of hynSL is up-regulated under anaerobic conditions with the participation of an FNR (fumarate and nitrate reduction regulator)-type protein, FnrT. Although the genes encoding a typical H(2) sensor (hupUV) and a two-component regulator (hupR and hupT) are present in T. roseopersicina, the system is cryptic in the wild-type BBS strain. The hupR gene was identified in the gene cluster downstream from hupSL. Introduction of actively expressed hupT repressed the hupSL gene expression as expected by analogy with other bacteria.

Stereoselective crystallization induced by traces of dissolved optically active impurities.

Isothermal crystallization of D,L-sodium-ammonium tartrate with traces of different impurities admixed shows that the added chiral contaminations produce a preferential crystallization of the tartrate isomer of same handedness. The critical lowest concentration of effective seeding agents is 0.1-0.5%. 1% optically active excess material induces 1.0-3.6% optical purity in the deposited crystals. An analysis of the relevant data reported so far gives similar figures in different crystallization systems. The relation of the results to the suggested lattice energy difference between enantiomers is discussed.

Beta irradiation may induce stereoselectivity in the crystallization of optical isomers.

A novel approach has been introduced to detect the manifestation of symmetry breaking weak interactions at molecular level. In the racemic conglomerate crystallization of D,L-sodium-ammonium tartrate the effect of 32P irradiation was studied by measuring the weight and optical purity of the crystalline phase as well as the size distribution of the crystallites. The high number of independent experiments (over 1000) permitted statistical analysis of the results. The following observations have been made: 1. Beta irradiation influences the crystallization process, irradiated samples yield more crystalline material. 2. The effect involves presumably crystal seed formation because from the irradiated solutions more and smaller crystallites are formed. 3. The presence of beta particles induces stereoselective crystallization, the crystalline phase shows optical activity characteristic of the "unnatural" L-isomer. 4. The above changes are attributed to the beta irradiation as the magnitude of the effects depends on the amount of added radioactivity. Optically active contaminants are highly unlikely sources of the differences between irradiated and control series. 5. In the absence of 32P the tartrate enantiomers have equal probability to form crystals, i.e., the contribution of mixing of weak interaction into the electromagnetic one is not measurable in this system.

On the physical origin of biological handedness.

In the racemic conglomerate crystallization of over 1,000 samples of D,L-sodium-ammonium tartrate the effect of 32P beta irradiation on the weight, optical activity, and crystallite size was measured. Both weight and optical activity showed a statistical dependence on the intensity of beta irradiation. The crystallite size is also affected by the presence of 32P. Asymmetric crystals are suggested to have been potential mediators between asymmetric parity violating forces and molecular asymmetry so that stereo-selective prebiotic chemical reactions involving crystals need not be considered 'chance' processes. No measurable difference in the energy content of optical isomers was found. An upper limit for the direct contribution of weak interactions to electromagnetic ones has been calculated. The mechanism of stereoselective crystal seeding by beta particles is discussed.

Effect of enzyme concentration on apparent specific activity of hydrogenase.

The effect of enzyme concentration on the H2-uptake and H2-evolving activities of the reversible hydrogenase from Thiocapsa roseopersicina was examined. In the activity range assayed by a spectrophotometric technique the apparent H2-uptake specific activity varied greatly with hydrogenase concentration. Study of H2-evolving activity measured by the H2 electrode method and compared with a gas chromatographic assay also indicated that specific activity was highly dependent on enzyme concentration. The results indicate that the widely applied hydrogenase assays give systematically erroneous specific activity values. These assays should be used only for relative measurements and the hydrogenase concentration in the reaction mixture should be kept constant. To make the data from various laboratories comparable the assay parameters should be standardized.