Showing papers in "Fems Microbiology Letters in 1986"

Redox balances in the metabolism of sugars by yeasts

Abstract: The central role of the redox couples NAD+/NADH and NADP+/NADPH in the metabolism of sugars by yeasts is discussed in relation to energy metabolism and product formation. Besides their physical compartmentation in cytosol and mitochondria, the two coenzyme systems are separated by chemical compartmentation as a consequence of the absence of transhydrogenase activity. This has considerable consequences for the redox balances of both coenzyme systems and hence for sugar metabolism in yeasts. As examples, the competition between respiration and fermentation of glucose, the Crabtree effect, the Custers effect, adaptation to anaerobiosis, the activities of the hexose monophosphate pathway, and the fermentation of xylose in yeast are discussed.

Osmoregulation by potassium transport in Escherichia coli

Abstract: Cell turgor pressure determines the extent of K+ accumulation by Escherichia coli cells. K+ influx is mediated both by a constitutive system with a low affinity for K+ (Trk) and by an inducible high affinity system (Kdp). K+ efflux is controlled by as yet unidentified but independent systems. Cell K+ concentration may be the link between growth in media of high osmolarity and the concomitant accumulation of compatible solutes such as betaine.

Carbonic anhydrase and CO2 concentrating mechanisms in microalgae and cyanobacteria

Abstract: Among the microbial phototrophs, those belonging to the cyanobacteria utilize CO2 and HCO−3 for photosynthesis. Some Chlorophyceae mainly take up CO2 in photosynthesis, and others, which have carbonic anhydrase (CA) on their cell surface can utilize HCO−3 as well as CO2. Kinetic studies revealed that most of the HCO−3 is utilized after this ion is converted to CO2 via CA located on the cell surface. Therefore, the actual molecular species which crosses the plasmalemma is mostly free CO2. There is apparent variation in the mode of utilization of dissolved inorganic carbon (DIC) for photosynthesis in microalgae in other classes. The apparent Km(CO2) values for photosynthesis in most microalgae grown in ordinary air (low-CO2 cells) are as low as in terrestrial C4 plants, although the algal cells fix CO2 via the C3 pathway. In contrast, the apparent Km(CO2) values in cells grown on CO2-enriched air (high-CO2 cells) are as high as those in the terrestrial C3 plants. Most low-CO2 cells show low photorespiration; a low CO2 compensation point, low rates of glycolate excretion and no or low O2 inhibition of photosynthesis. These results indicate that the efficiency of DIC utilization for photosynthesis in low-CO2 cells is very high. The activity of CA in low-CO2 cells is higher than that in high-CO2 cells, while no difference has been confirmed in the activities of other photosynthetic enzymes between low- and high-CO2 cells. In addition, low-CO2 cells can accumulate large amounts of DIC internally, indicating the existence of CO2-concentrating mechanisms in these cells. When CA activity or CO2 concentrating ability is reduced by inhibitors or by mutation, the apparent Km(CO2) values for photosynthesis and the rate of photorespiration increased notably. These results indicate that the high efficiency of DIC utilization in low-CO2 cells depends on both CA and a CO2-concentrating mechanism. It is concluded that CA facilitates the diffusion of DIC from outside the cells to the site(s) of the carboxylation reaction and the concentration of DIC is achieved via an active transporter.

CO2 fixation in acetogenic bacteria: Variations on a theme

Abstract: An increasing number of strict anaerobic bacteria are being found which use an alternative pathway to the ubiquitous Calvin cycle for CO2 fixation into cell compounds and the ubiquitous Krebs cycle for acetyl CoA oxidation to CO2. The principles of this non-cyclic pathway, the acetyl CoA pathway, have long been studied in acetogenic bacteria. These bacteria can catalyze the exergonic reduction of 2 CO2 with 8 reducing equivalents to acetate. In this pathway, CO2 reduction is part of a catabolic redox process which functions to accept reducing equivalents from a variety of dehydrogenated substrates. This process yields net ATP generated by electron transport phosphorylation. Acetyl CoA is an intermediate, formed from one CO2 via a tetrahydropteridine-bound 1-carbon unit (methyl group of acetate), and from another CO2 via a bound carbon monoxide (carboxyl group of acetate). The most characteristic and complex enzyme involved in acetyl CoA synthesis is carbon monoxide dehydrogenase (‘acetyl CoA synthase’). The enzymes of this acetyl CoA pathway not only participate in (1) acetate synthesis in energy metabolism of acetogenic bacteria, but also mediate (2) acetyl CoA oxidation in sulfate-reducing bacteria and possibly other anaerobes; (3) acetate disproportionation to CO2 and CH4 in the energy metabolism of many methanogenic bacteria; (4) autotrophic CO2 fixation in autotrophic acetogenic, methanogenic, and most autotrophic sulfate-reducing bacteria; (5) assimilation and/or dissimilation of 1-carbon compounds in many anaerobes; (6) CO oxidation to CO2 in anaerobes. A specialized group of anaerobes performs acetate synthesis from CO2 or from C1 units via a different pathway, the glycine synthase/glycine reductase pathway. Glycine is an intermediate which is formed from 2 C1 compounds, and is then reduced to acetate. The principal features of the two pathways and some open questions are discussed in this review. Emphasis is placed upon the acetyl CoA pathway in acetogenic bacteria, but important advances in the study of other strict anaerobes are also considered.

Survival of Pseudomonas fluorescens and Bacillus subtilis introduced into two soils of different texture in field microplots

Abstract: Antibiotic-resistant strains of Pseudomonas fluorescens and Bacillus subtilis, produced by transposon Tn5 mutagenesis and transformation with plasmid pFT30, respectively, were characterized. Both strains grew at a rate comparable to that of the wild-type strains, and the antibiotic resistance remained stable for over 50 generations without selective pressure. During the growing season, the survival of these strains was studied in two soils of different texture cropped with wheat. The B. subtilis populations declined rapidly in both soils and then stabilized at the levels of added spores. P. fluorescens showed a slow, steady decline in both soils; survival was better in the finer-textured soil, a silt loam, than in the coarser loamy sand. For both bacteria, some translocation to deeper soil layers was observed. No significant rhizosphere effects were detected in either of the two soils.

Organic solute accumulation in osmotically stressed cyanobacteria

Abstract: Three groups of cyanobacteria are recognized on the basis of their organic osmotica and upper salinity limit for growth. In general, the least halotolerant forms accumulate disaccharides, while cyanobacteria of intermediate halotolerance synthesize the heteroside glucosylglycerol and the most halotolerant isolates accumulate betaines in response to salt stress. However, certain strains also accumulate additional organic solutes, depending upon the growth temperature, the ambient salinity and the duration of salt stress.

Dinitrogen-fixing endogenous rhythm in Synechococcus RF-1

Abstract: Under continuous illumination this unicellular aerobic cyanobacterium fixes dinitrogen continuously at a variable and usually low rate. Exposure of the culture to diurnal light/dark cycles invariably results in the virtual restriction of nitrogenase activity to the dark periods. The rhythmic diurnal dinitrogen fixation pattern becomes a truely endogenous cycle which persists for at least 4 days with decreasing magnitude on exposing the culture to continuous illumination. The free running time of the rhythm appears to decrease from an initial 26 h to 22 h in the course of 4 days. This appears to be the first record of an endogenous rhythm in a prokaryote.

Osmoregulation and compatible solutes in eubacteria

Abstract: Osmotic adaption by halophilic and halotolerant bacteria is generally achieved by the accumulation or synthesis of several organic solutes. Accumulation by uptake from the medium is preferred over biosynthesis. The chemical nature of the major solute is important in determining the degree of osmotolerance of the organism. Glycine betaine accumulation confers a greater degree of osmotolerance than proline, which in turn confers more osmotolerance than glutamate accumulation. The occurrence and uptake of these solutes in a variety of eubacteria is reviewed.

The acetyl-CoA pathway of autotrophic growth

Abstract: The most direct conceivable route for synthesis of multicarbon compounds from CO2 is to join two molecules of CO2 together to make a 2-carbon compound and then polymerize the 2-carbon compound or add CO2 successively to the 2-carbon compound to make multicarbon compounds. Recently, it has been demonstrated that the bacterium, Clostridium thermoaceticum, grows autotrophically by such a process. The mechanism involves the reduction of one molecule of CO2 to a methyl group and then its combination with a second molecule of CO2 and CoA to form acetyl-CoA. We have designated this autotrophic pathway the acetyl-CoA pathway [1]. Evidence is accumulating that this pathway is utilized by other bacteria that grow with CO2 and H2 as the source of carbon and energy. This group includes bacteria which, like C. thermoaceticum, produce acetate as a major end product and are called acetogens or acetogenic bacteria. It also includes the methane-producing bacteria and sulfate-reducing bacteria. The purpose of this review is to examine critically the evidence that the acetyl-CoA pathway occurs in other bacteria by a mechanism that is the same or similar to that found in C. thermoaceticum. For this purpose, the mechanism of the acetyl-CoA pathway, as found in C. thermoaceticum, is described and hypothetical mechanisms for other organisms are presented based on the acetyl-CoA pathway of C. thermoaceticum. The available data have been reviewed to determine if the hypothetical schemes are in accord with presently known facts. We conclude that the formation of acetyl-CoA by other acetogens, the methanogens and sulphate-reducing bacteria occurs by a mechanism very similar to that of C. thermoaceticum.

Plasmid curing in bacteria

Abstract: Plasmids are extrachromosomal pieces of double-stranded circular DNA which have the capability to replicate independently of the host chromosome, yet coexist with it [1]. To date, many species of bacteria isolated from diverse habitats are known to contain plasmid DNA [2,3]. Some plasmids are stable and can be maintained through successive generations by being partioned to each daughter cell during cell division. This allows each cell to receive at least one plasmid copy. In recent years, plasmids have been observed in a wide variety of bacteria. In part, this is due to the development of new procedures that allow the detection, isolation, and molecular characterization of plasmid DNA. When working with some plasmid-containing bacteria, it is often desirable to obtain a plasmid-cured derivative. This allows a direct comparison to be made between the plasmid-containing and plasmid-cured cells. Some plasmids undergo spontaneous segregation and deletion. However, the majority are extremely stable, and require the use of curing agents or other procedures (elevated growth temperature, thymine starvation), to increase the frequency of spontaneous segregation [4]. The usefulness of curing agents is unpredictable in many bacterial strains, as there are no standard protocols applicable to all plasmids. However, there are some procedures that have provided good results with certain species. The aims of this manuscript are to summarize and review plasmid curing agents and procedures. In view of the importance of plasmids in specifying antibiotic and metal-resistance; metabolic properties; pathogenicity; host specificity and nodulation ( Rhizobium spp.); conjugal properties, and replication-maintenance properties [2], reproducible procedures for obtaining plasmid-cured derivatives are necessary.

The death and lysis of microorganisms in environmental processes

Abstract: Revue concernant divers aspects quantitatifs sur la mort cellulaire microbienne et la lyse (methodes d'etude). Classification physiologique d'une culture microbienne. Carence nutritive. Autolyse. Mort cellulaire. Modelisation mathematique de la mort et de la lyse

Metabolic control theory: its role in microbiology and biotechnology

Abstract: Many areas of microbiology and biotechnology are directly concerned with the isolation, study or engineering of cells capable of (over)producing metabolites of commercial significance. Yet the study, production or improvement of such strains has often been at best semi-empirical. The metabolic control theory developed by Kacser, Burns, Heinrich and Rapoport can provide a rational and quantitative basis for the description and improvement of such processes.

A highly active extracellular cellulase from the anaerobic rumen fungus Neocallimastix frontalis

Abstract: An extracellular cellulase which was highly active in solubilizing the highly hydrogen bond-ordered cellulose in cotton fibre was found in a culture filtrate of the anaerobic fungus, Neocallimastix frontalis, isolated from the rumen of a sheep. The cellulase was several-fold more active in solubilizing cotton fibre per unit of endo-1,4-β-glucanase than the cellulase of the aerobic fungus Trichoderma reesei mutant strain C-30, which is one of the most active cellulases isolated so far.

Nucleotide sequence of a plasmid‐encoded hemolysin determinant and its comparison with a corresponding chromosomal hemolysin sequence

Abstract: The complete sequence of the plasmid pHly152-encoded hemolysin (hly) determinant of Escherichia coli is presented and compared with a recently sequenced chromosomal hly determinant [1]. High sequence homology between the two hly determinants is observed within all four structural genes, hlyC, A, B and D, but little sequence similarities are found in the 3′- and 5′-noncoding flanking regions. In addition, the noncoding region upstream of hlyC which carries the promoter for hlyC, A and B, was sequenced for several chromosomal hly determinants. The comparison of these sequences indicates three distinct classes of promoter regions which share common putative −10 and −35 boxes at roughly the same location relative to the start of hlyC.

Thermodynamics of H2-consuming and H2-producing metabolic reactions in diverse methanogenic environments under in situ conditions

Abstract: In situ concentrations of hydrogen and other metabolites involved in H2-consuming and H2-producing reactions were measured in anoxic methanogenic lake sediments, sewage sludge and fetid liquid of cottonwood. The data were used to calculate the Gibbs free energies of the metabolic reactions under the conditions prevailing in situ. The thermodynamics of most of the reactions studied were exergonic with Gibbs free energies being more negative for H2-dependent sulfate reduction methanogenesis acetogenesis and for H2-producing lactate fermentation ethanol fermentation. Butyrate and propionate fermentation, on the other hand, were endergonic under in situ conditions. This observation is interpreted by suggesting that butyrate and propionate is degraded within microbial clusters which shield the fermentating bacteria from the outside H2 (and acetate) pool.

Polymerisation of lignins by ligninases from Phanerochaete chrysosporium

Abstract: Four major hemoproteins were purified by isoelectric focusing from an extracellular crude enzyme preparation, produced by the white rot fungus Phanerochaete chrysosporium under carbon-limited conditions. Both the crude enzyme and the purified proteins oxidised milled wood lignin, HCl-dioxane-extracted straw lignin and alkali straw lignin in the presence of hydrogen peroxide. The oxidation resulted mainly in further polymerisation of the lignins and was enhanced by addition of veratryl alcohol to the reaction mixture. Alkali straw lignin was also polymerised by horseradish peroxidase, although veratryl alcohol had no influence on this reaction.

Wheat inoculation with Azospirillum brasilense Sp6 and some mutants altered in nitrogen fixation and indole-3-acetic acid production

Abstract: Inoculation of wheat seedlings with Azospirillum brasilense Sp6 produced an increase in the number and length of the lateral roots as a plant response. Inoculation with a Nif− mutant, A. brasilense SpF103, which is producer of indole-3-acetic acid (IAA), yielded a very similar plant response. However, inoculation with a Nif− mutant, A. brasilense SpF57, which is a low producer of IAA, did not elitic any response from the plant. The data suggest that the root system response of wheat seedlings to bacterial inoculation is due mainly to production of auxin-type substances by the microorganism.

Research letterPolymerisation of lignins by ligninases from Phanerochaete chrysosporium

Abstract: Four major hemoproteins were purified by isoelectric focusing from an extracellular crude enzyme preparation, produced by the white rot fungus Phanerochaete chrysosporium under carbon-limited conditions. Both the crude enzyme and the purified proteins oxidised milled wood lignin, HCl-dioxane-extracted straw lignin and alkali straw lignin in the presence of hydrogen peroxide. The oxidation resulted mainly in further polymerisation of the lignins and was enhanced by addition of veratryl alcohol to the reaction mixture. Alkali straw lignin was also polymerised by horseradish peroxidase, although veratryl alcohol had no influence on this reaction.

Susceptibility of bacterial, eukaryotic and artificial membranes to the disruptive action of the cationic peptides Pep 5 and nisin

Abstract: The cationic bactericidal peptides Pep 5 and nisin render membranes permeable to low-M r compounds. All Gram-positive bacteria treated with these peptides showed an immediate efflux of entrapped radioactive markers. The uptake of α-[ 14 C] methylglucoside by the phosphoenolpyruvate-dependent phosphotransferase system was stimulated by Pep 5, supporting previous results that pep 5 abolishes the membrane potential. Oxygen consumption was inhibited, presumably due to lack of ADP. Escherichia coli became sensitive to Pep 5 and nisin when the outer membrane was bypassed by osmotic shock or by formation of cytoplasmic membrane vesicles. In contrast, Mycoplasma cells and erythrocytes were unaffected by Pep 5 and nisin in concentrations up to 1 mM. Human lung fibroblasts released only small amounts of ATP when treated with Pep 5 and nisin in μM concentrations. Eukaryotic and Mycoplasma cells were disrupted more effectively by the bee venom peptide melittin, which displays overall structural similarities to Pep 5 and nisin. Various artificial membranes were not affected by Pep 5, nisin, or melittin.

Genetics of osmoregulation in Escherichia coli: Uptake and biosynthesis of organic osmolytes

Abstract: Escherichia coli cells growing under osmotic stress activate systems for the transport or synthesis of several organic osmolytes. Glutamate and trehalose syntheses seem to represent mechanisms for achieving a low level of osmotic tolerance. The uptake and synthesis of betaines represent mechanisms of achieving a high level of osmotic tolerance. The osmotically-controlled ProP and ProU systems are involved in the uptake of glycine betaine and proline. However, glycine betaine synthesis occurs only in the presence of the precursor molecule choline. The osmotically controlled genes governing the high-affinity uptake of choline are located in close proximity to those encoding the dehydrogenases involved in the oxidation of choline to glycine betaine, but represent a different transcriptional unit. It is not known if each of these systems has its own osmotic sensor or whether a common osmotic sensor regulates all cell osmolytes.

Protozoan predation of bacterial cells in soil aggregates

Abstract: The development and survival of Aerobacter aerogenes IAM11022 in the inner and outer zones of soil aggregates (1–2 mm) was investigated in relation to a protozoan (Colpoda sp.). With different dilutions of the bacterial cell suspension, a constant partition ratio of these cells was observed between outer and inner zones of the aggregates. Protozoa inoculated in the same manner were generally recovered only from the outer zone of the aggregates. In the presence of protozoa, prey cell numbers of the outer zone were reduced from more than 108 to approx. 104 cells · g soil−1 in 12 days. In contrast, 108 cells · g soil−1 remained in the inner zone of the aggregates, even after 12 days. The increase in predator cell number was proportional to initial prey densities in the outer zone of the aggregates. At a constant initial prey density (1.8 × 107 cells · g soil−1), Colpoda sp. multiplied in proportion to the initial number of predators. When the initial density of the predator was low more prey cells survived in the outer zone. Prey persistence was associated with 3 different types of protection: (1) small pore necks of the inner zone space of the aggregates; (2) the division of the outer zone space into compartments; and (3) the distribution of protozoan cells among soil aggregates. The latter two were closely related to the moisture condition of the soil.

Viability and virulençe of Escherichia coli suspended by membrane chamber in semitropical ocean water

Abstract: Escherichia coli H10407 was suspended in seawater (38.5‰ salinity) contained in membrane chambers (0.4-μm polycarbonate membrane) incubated in situ at 25°C in Nixon's Harbor, South Bimini, Bahamas. Although colonies of E. coli could not be cultured after 13 h post chamber inoculation, the number of fluorescent-antibody staining cells remained constant. Direct viable counts revealed that viable cells were present, even though the cell suspension was not culturable on the media tested. After exposure to seawater for 112 h, cells were concentrated by centrifugation and introduced into ligated rabbit ileal loops. E. coli H10407 proved viable for recovery from inoculated loops and was confirmed by detection of characteristic plasmid bands. Results indicate that enteric pathogens remain viable in seawater long after they cease to be cultivable on laboratory media.

Electron transfer reactions in methanogens

Abstract: Methanogenic bacteria comprise a specialized group of obligately anaerobic microorganisms able to reduce a limited number of substrates to CH 4 . The intermediates involved in this reduction process remain bound to a series of typical C 1 -carriers. Reducing equivalents are either obtained from the oxidation of H 2 or from oxidation of carbon substrates to CO 2 . Electron transfer reactions thus constitute the very essence of the process of methanogenesis. In recent years much progress has been made in the elucidation of the special metabolic pathways and the nature of the C 1 -carriers involved in methanogenic bacteria. The energy generated at the oxidoreduction reactions, notably at the methylreductase step, is conserved by ATP synthesis. The energy is used for cell carbon synthesis and, in catalytic amounts, for the reductive activation of some methanogenic enzymes. Before the condensing reaction resulting in the formation of acetyl-CoA takes place, 2 C 1 -units are reduced or oxidized depending on the substrate to a carbonyl and a -CH 3 group. Formation of the latter proceeds via the methanogenic route. Intermediary cell carbon synthesis starting from acetyl-CoA involves reductive carboxylations and oxidoreductions by the participation of the enzymes of the tricarboxylic acid cycle.

Hydrogen cycling in a three-tiered food web growing on the methanogenic conversion of 3-chlorobenzoate

Abstract: A defined 3-chlorobenzoate-degrading methanogenic consortium was constructed by recombining key organisms isolated from a 3-chlorobenzoate-degrading methanogenic sludge enrichment. The organisms comprise a three-tiered food chain which includes: (1) reductive dechlorination of 3-chlorobenzoate; (2) oxidation of benzoate to acetate, H2 and CO2; (3) removal of H2 plus CO2 by conversion into methane. The defined consortium, consisting of a dechlorinating organism (DCB-1), a benzoate degrader (BZ-1) and a lithotrophic methanogen (Methanospirillum strain PM-1) grew well in a basal salts medium supplemented with 3-chlorobenzoate (3.2 mM) as the sole energy source. The chlorine released from the aromatic ringe was recovered in stoichiometric amounts as the chloride ion. The reducing power required for reductive dechlorination was obtained from the hydrogen produced in the acetogenic oxidation of benzoate. One-third of the benzoate-derived hydrogen was recycled via the reductive dechlorination of 3-chlorobenzoate, indicating that the consortium operated as a food web rather than a food chain.

Growth of Escherichia coli in the presence of trimethoprim-sulfamethoxazole facilitates detection of Shiga-like toxin producing strains by colony blot assay

Abstract: Subinhibitory concentrations of trimethoprim-sulfamethoxazole increased the total yield of Shiga-like toxin (SLT), produced by Shigella dysenteria 1 and by enterophathogenic and enterohemorrhagic strains of Escherichia coli . Stimulation of SLT synthesis by trimethoprim-sulfamethoxazole was demonstrated by an increase in cytotoxic activity for HeLa cells and the diameter of the zone formed around bacterial colonies probed with monoclonal antibodies to SLT. Thus, supplementation of culture media with trimetroprimsulfamethoxazol will facilitate SLT purification and detection of SLT-producing bacteria.

Bacterial microflora in the gastro‐intestinal tract of Dover sole (Solea solea L.), with emphasis on the possible role of bacteria in the nutrition of the host

Abstract: There was a progressive increase in the size of the aerobic heterotrophic bacterial populations along the gastro-intestinal tract of farmed Dover sole. Moreover, higher counts were recorded in juvenile than in adult animals. Thus, in juvenile fish, 5.2 × 105, 8.0 × 105 and 9.8 × 106 aerobic heterotrophs/g were recovered from the stomach/foregut, midgut and hindgut/rectum, respectively. In adult fish, comparative samples revealed the presence of only 3.0 × 104, 7.0 × 104 and 2.3 × 105 bacteria/g, respectively. There bacteria were equated with Acinetobacter, Alcaligenes, Enterobacteriaceae representatives, Flavobacterium, Micrococcus, Photobacterium, Staphylococcus and Vibrio. Of the compounds tested, many isolates, particularly those recovered from the hindgut/rectum, degraded p-nitrophenyl-β-N-acetylglucosaminide, chitin and collagen. Consequently, it is likely that such organisms may contribute to nutritional processes within Dover sole.

Breakdown of dimethyl sulphide by mixed cultures and by Thiobacillus thioparus

Abstract: Dimethyl sulphide (DMS) was degraded by acclimatized activated sludge and by a mixed culture of Thiobacillus thioparus TK-1 and Pseudomonas sp. AK-2. While both these organisms persisted in stable co-culture on DMS, it was found that T. thioparus TK-1 and the derived strain TK-m grew in pure culture on DMS, and oxidized DMS with an apparent Km of 4.5 × 10−5 M. During growth, all the DMS-sulphur was oxidized stoichiometrically to sulphate but no methanol was detected in pure cultures of TK-m. DMS-carbon was probably converted to CO2, since the fixation of 14CO2 was progressively diluted during growth of a culture on 14CO2 and DMS. Growth yields were consistent with autotrophic growth, dependent on the oxidation of the methyl residues to CO2 (probably with formaldehyde as a first intermediate) and the sulphide to sulphate. The organism thus appears to exhibit a mixture, from the one substrate, of chemolithotrophic and methylotrophic energy generation supporting autotrophic growth with CO2 fixation.

Interspecies hydrogen transfer in co-cultures of methanol-utilizing acidogens and sulfate-reducing or methanogenic bacteria

Abstract: The metabolism of methanol by acidogenic bacteria (Butyribacterium methylotrophicum, Sporomusa ovata and Acetobacterium woodii) was studied in pure culture and in defined mixed cultures with sulfate-reducing bacteria (Desulfovibrio vulgaris) or methanogenic bacteria (Methanobrevibacter arboriphilus strain AZ). In the mixed cultures, less acids (acetate and/or butyrate) were formed per unit methanol converted than in pure cultures. In these mixed cultures, a significant production of sulfide or methane was observed despite the inability of the sulfate reducer and the methanogen to use methanol as an energy substrate. These results are explained in terms of interspecies hydrogen transfer between the acidogens (converting part of the methanol to 1 CO2 and 3 H2) and the Desulfovibrio or Methanobrevibacter species. The bioenergetic aspects of this process and its ecological implications are discussed.

PQQ and quinoprotein enzymes in microbial oxidations

Abstract: Pyrroloquinoline quinone (PQQ) is found in a wide range of microorganisms, and several bacteria even excrete this compound into their culture medium when grown on alcohols. The existence of different classes of quinoprotein (PQQ-containing) enzymes is now well established (alcohol dehydrogenases, aldose (glucose) dehydrogenases, amine dehydrogenases and amine oxidases) while several other enzymes are suspected to be quinoproteins. In addition, many bacteria produce a quinoprotein apoenzyme, e.g., Escherichia coli and Pseudomonas testosteroni, producing glucose and ethanol dehydrogenase apoenzyme, respectively. It is unclear why these bacteria do not produce the holoenzyme form, but the apoenzymes have the ability to become functional, as was shown when the organisms were provided with PQQ. With this approach it could be demonstrated that E. coli has a non-phosphorylative route of glucose dissimilation via gluconate. Also, results with mixed cultures indicate that PQQ is a growth factor for certain bacteria under certain conditions. Despite the relatively high redox potential of the PQQ/PQQH2 couple, quinoproteins transfer electrons to a variety of natural electron acceptors. Depending on the type of quinoprotein enzyme, the following components of the respiratory chain appear to be active: cytochrome c (sometimes with a copper protein as an intermediate), cytochrome b, and NADH dehydrogenase. PQQ is not restricted to a particular group of organisms, and reactions catalysed by quinoproteins can also be performed by NAD(P)-dependent or flavoprotein enzymes. Thus, these observations do not provide arguments for the view that quinoproteins have a unique role in microbial oxidations. Further comparative studies on oxidoreductases are necessary to reveal the special features of this novel group of enzymes.