Effect on methane digestion of decreased H2 partial pressure by means of phototrophic or sulfate-reducing bacteria grown in an auxiliary reactor

Summary H₂ is a central metabolite in the process of methane digestion. In this study, the partial pressure of H₂ was decreased by sparging the gas phase of the digester through an auxiliary reactor in which a Rhodomicrobium vaniellii culture or a mixed culture of sulfate-reducing bacteria was allowed to develop at the expense of H₂ and CO₂ present in the biogas. The decrease of the H₂ concentration in the gas phase was significant. A 18–23 percent increase of the gas production rate and a concomitantly improved removal of volatile fatty acids from the mixed liquor was obtained. The sulfate-reducing bacteria appeared to be slightly more effective than the phototrophs. The results suggest that the increased biogas production rate is due to the decrease of propionic acid formation and the concomitant stimulation of propionate degradation.Abbreviations COD_t Total chemical oxygen demand - COD_s Soluble chemical oxygen demand - SS Suspended solids - DM Dry matter - VFA Volatile fatty acids     

The Acyl-Proteome of Syntrophus aciditrophicus Reveals Metabolic Relationships in Benzoate Degradation

Syntrophus aciditrophicus is a model syntrophic bacterium that degrades fatty and aromatic acids into acetate, CO₂, formate, and H₂ that are utilized by methanogens and other hydrogen-consuming microbes. S. aciditrophicus benzoate degradation proceeds by a multistep pathway with many intermediate reactive acyl-coenzyme A species (RACS) that can potentially N^ε-acylate lysine residues. Herein, we describe the identification and characterization of acyl-lysine modifications that correspond to RACS in the benzoate degradation pathway. The amounts of modified peptides are sufficient to analyze the post-translational modifications without antibody enrichment, enabling a range of acylations located, presumably, on the most extensively acylated proteins throughout the proteome to be studied. Seven types of acyl modifications were identified, six of which correspond directly to RACS that are intermediates in the benzoate degradation pathway including 3-hydroxypimeloylation, a modification first identified in this system. Indeed, benzoate-degrading enzymes are heavily represented among the acylated proteins. A total of 125 sites were identified in 60 proteins. Functional deacylase enzymes are present in the proteome, indicating a potential regulatory system/mechanism by which S. aciditrophicus modulates acylation. Uniquely, N^ε-acyl-lysine RACS are highly abundant in these syntrophic bacteria, raising the compelling possibility that post-translational modifications modulate benzoate degradation in this and potentially other, syntrophic bacteria. Our results outline candidates for further study of how acylations impact syntrophic consortia.     

Metabolism of Monoterpenes : Evidence for the Function of Monoterpene Catabolism in Peppermint (Mentha piperita) Rhizomes

l-Menthone of peppermint leaves is reduced to d-neomenthol which is glucosylated and transported to the rhizome, whereupon the β-d-glucoside is hydrolyzed, the aglycone oxidized back to l-menthone, and this ketone converted to l-3,4-menthone lactone. l-[G-³H]-3,4-Menthone lactone and its labeled progenitors, when incubated with excised mint rhizomes, gave rise to nonvolatile lipids as well as polar metabolites. The lipids thus generated consisted of labeled squalene and phytosterols in the nonsaponifiable fraction and C₁₄-C₂₆ fatty acids in the saponifiable fraction. These results imply degradation of the terpenoid to acetylcoenzyme A and reduced pyridine nucleotide, and reincorporation of label via these products. Starch and soluble carbohydrates were also found to be labeled; however, chemical degradation of the [³H]glucose obtained on hydrolysis of starch indicated the presence of tritium only on interior carbons, suggesting that labeling had occurred via reduced pyridine nucleotides. Analysis of the labeled organic acids revealed the presence of several hydroxy methylacyl intermediates suggesting the operation of a modified β-oxidation pathway in the degradation of the acyclic terpenoid skeleton. The results indicate that monoterpenes transported to the rhizome are oxidized to yield acetyl-coenzyme A and reduced pyridine nucleotides, and suggest that metabolic turnover of monoterpenes in mint represents a mechanism for recycling carbon and energy from foliar terpenes into other metabolites of the rhizome.     

A field portable gas-exchange system for measuring carbon dioxide and water vapour exchange rates of leaves during fumigation with SO2

Abstract A field portable, steady-state gas-exchange system which measures both CO₂ and water vapour exchange of single intact leaves during fumigations with SO₂ is described. Within the leaf cuvette temperature, light, humidity and both CO₂ and SO₂ concentrations are controlled to preset levels. Gas flow and concentrations are controlled by mass flow controllers. Photosynthetic uptake of CO₂ can be determined either by differential depletion or null balance measurement. Water vapour exchange is measured differentially and transpiration and conductance to water vapour determined. Sulphur dioxide is measured directly within the cuvette exhaust gas line by UV-pulse fluorescence. The performance of this system under field conditions is described and the physiological measurements compared with those obtained with other systems.     

The Microbial Logic behind the Prevalence of Incomplete Oxidation of Organic Compounds by Acetogenic Bacteria in Methanogenic Environments

Microbial degradation of organic material in methanogenic ecosystems is a multistep process in which subsequent groups use the products of the first groups of organisms in the chain as substrates. The acetogenic bacteria in these systems produce both H₂ and acetate. In the present minireview a thermodynamic approach is taken to evaluate the logic behind this duality. The evaluation shows that at the H₂ partial pressures that usually occur in methanogenic ecosystems the acetogenic oxidation of known acetogenic substrates such as propionate, butyrate, and benzoate yields more energy than their complete oxidation to H₂/CO₂. Also, H₂ partial pressures needed to achieve complete hydrogenogenic oxidation of these acetogenic substrates would have to be so low that H₂ would be virtually unavailable to the hydrogenotrophic bacteria, in casu the methanogens.     

A laboratory study on biochemical degradation and microbial utilization of organic matter comprising a marine diatom,land grass,and salt marsh plant in estuarine ecosystems

We studied the biochemical degradation of organic matter comprising marine diatom, land grass, and salt marsh plant in estuarine ecosystems in two laboratory microcosms consisting of estuarine sediments and coastal seawater. The materials were incubated separately and together under controlled oxic and anoxic conditions to test effects of co-metabolism and redox on overall degradation of organic matter. We followed variations of bulk parameters [total organic carbon (TOC), total nitrogen (TN), C/N ratio, δ¹³C_TOC, and δ¹⁵N_TN], fatty acid concentrations, and compound-specific δ¹³C values over 3 months. Coexistence of marine diatom (relatively labile) with land grass/salt marsh plant (relatively refractory) in the microcosms yielded a negative co-metabolism effect (retardation rather than acceleration) on the overall degradation of organic matter. The ratios of oxic to anoxic degradation rate constants (k _ox/k _an) of TOC and most fatty acids were in a range of 1.1–1.7, implying that redox conditions per se had a limited influence on degradation of fresh organic materials in estuarine ecosystems. Variations of two bacteria-specific fatty acids (iso- and anteiso-15:0) and their δ¹³C values indicated that bacterial metabolism could use organic carbon (OC) from any available material when only one single-source material was dominant in the ecosystems. However, bacteria probably utilized OC preferentially from labile marine diatom when multiple-source materials were almost equally present in the ecosystems.     

Microbiological Degradation of Organic Components in Oil Shale Retort Water: Organic Acids

The losses of benzoic acid and a homologous series of both mono- and dibasic aliphatic acids in oil shale retort water were monitored with time (21 days) in liquid culture (4% retort water, vol/vol) inoculated with soil. The organic acids constituted approximately 12% of the dissolved organic carbon in retort water, which served as the sole source of carbon and energy in these studies. The levels of the acids in solution were reduced by 80 to 90% within 9 days of incubation. From mass balance calculations, the decrease in dissolved organic carbon with time of incubation was equal to the formation of CO₂ and bacterial cell carbon. The decrease in the level of the acid components, either from degradation to CO₂ or incorporation into bacteria, would account for ~70% of the loss in dissolved organic carbon within the first 9 days of incubation and would account for ~50% of the loss over the entire 21-day incubation period.     

Water sorption by human cells

Water sorption by powdered human callus was studied using a vacuum microbalance, X-ray powder diffraction and NMR relaxation. The sorption data were fitted to theoretical isotherms. At high relative vapour pressures an increase in the monolayer value was found which is probably related to the swelling of the material. Adsorption/desorption hysteresis is present below 0.75' relative vapour pressure (r.v.p.). Only a small increase in protein chain separation was observed on water uptake, indicating that the primary level of organization of the keratin is hardly affected. The effect of solvent extraction is to reduce the strength of water binding but to leave the monolayer values constant. Isosteric heats confirm the reduction in affinity for water on solvent extraction and show that totally extracted callus behaves as a mildly hydrophobic material. The results are consistent with a model in which the water binding properties of callus are determined by the presence of water soluble components which allow a monomolecular layer of water to be formed at low r.v.p. followed by physical multilayer formation.Adsorption of sodium dodecyl sulphate was found to increase the monolayer value while dodecyl trimethyl ammonium bromide left the monolayer value unchanged.The NMR relaxation behaviour of water in callus is very similar to that of water on human hair and wool fibres. An activation enthalpy of 48 kJ · mol⁻¹ was found for the T₂ relaxation and a very broad T₁ minimum was observed at about −20°C at an operating frequency of 45 MHz corresponding to a correlation time of 2.2 ns.     

Obligately phototrophic Chloroflexus: primary production in anaerobic hot spring microbial mats

Microbial mats which lack cyanobacteria occur at 50° to 65° C in the sulfide-containing Mammoth Springs of Yellowstone National Park. The principal organisms within these mats are filamentous bacteria which resemble Chloroflexus aurantiacus. The incorporation of [¹⁴C]-HCO ₃ ^- into mat material depended upon both light and sulfide, and was not inhibited when complete natural light was replaced with far-red and infra-red radiation. [¹⁴C]-acetate was incorporated in a light-dependent reaction which was stimulated by, but did not require, sulfide. In situ experiments with microelectrodes demonstrated net sulfide uptake by the mat in the light, and net sulfide production by the mat in the dark, suggesting the operation of a sulfur cycle.Filamentous phototrophic bacteria isolated from the mat were incapable of sustained growth in the presence of O₂.Simultaneous exposure of cultures to light and O₂ caused degradation of bacteriochlorophyll c. The stimulation of light-dependent [¹⁴C]-HCO ₃ ^- -uptake by sulfide was more pronounced in these isolates than in strains of Chloroflexus aurantiacus.     

Phytol Degradation by Marine Bacteria

Microbial degradation of phytol is often proposed to be the primary source of the acyclic isoprenoid acids observed in sediments, yet only a limited number of these acids have been found in bacterial cultures grown on phytol. This study reports detailed capillary gas chromatography and gas chromatography-mass spectrometry analyses of the products resulting from growth of marine bacteria on phytol as the sole carbon source. We examined two strains of bacteria which were able to oxidize phytol to phytenic acid but were unable to further degrade phytol. The third isolate studied converted phytol to a mixture of five saturated isoprenoid acids. The C₁₇ isoprenoid acid produced was of particular interest, since its genesis from phytol would have involved several unusual intermediates. It is suggested that this acid is produced by bacterial metabolism of the C₁₈ isoprenoid ketone (produced from phytol abiologically under oxic conditions) and that its abundance is thus a sensitive indicator of sedimentary depositional conditions.     

Anaerobic degradation of organic compounds at high salt concentrations

A number of obligately anaerobic fermentative bacteria are known to degrade a variety of organic substrates such as sugars, amino acids, and others, in the presence of high salt concentrations (up to 3–4 M) to products such as hydrogen, CO₂, acetate and higher fatty acids, and ethanol. Our understanding of the fate of these products in hypersaline environments is still extremely limited. The occurrence of bacterial sulfate reduction is well established at salt concentrations of up to 24%; however, the bacteria involved have not yet been isolated in pure culture, and the range of electron donors used is unknown. Halophilic or halotolerant methanogenic bacteria using hydrogen/CO₂ or acetate as energy source are notably absent; methanogenesis under hypersaline conditions is probably limited to such substrates as methanol and methylamines, which cannot be expected to be major products of anaerobic degradation of most organic compounds.     

On the water balance ofPhytoseiulus persimilis A.-H. and its ecological significance

The net water vapour exchange ofPhytoseiulus persimilis A.-H. is described. Water loss by transpiration increases progressively with ambient temperature. The transpiration rate is directly proportional to the saturation deficit of the air (15 to 30° C) and at constant temperature linearly dependent on the water vapour activity: m_T=–0.81 a_v+0.91 (for a_v 0.0 to 0.85 at 20°C). Phytoseiulus persimilis is able to absorb water vapour from the unsaturated atmosphere. This occurs above a certain threshold (critical equilibrium activity, CEA), which is a_v=0.9 at 15 to 25°C and increases to a_v=0.935 at 30°C.The environmental humidity conditions influencingP. persimilis on the leaf surface are described. The diurnal water vapour profile within the laminar layer at the leaf surface includes periods with water vapour values high enough for these mites to utilize their water vapour sorption capability and to restore a previously-suffered water deficit. In addition,P. persimilis shows a positive hygrotactic behaviour when in a state of water deficit.The survival time of starvingP. persimilis is at least doubled when a possibility to absorb water vapour is available. The water balance at limited food resources is discussed. With a food supply (one prey mite, containing about 5.5 g water) every 3 days and a water vapour activity of a_v=0.76 (20°C), water balance is achieved and the survival time is maximal (approximately 120 days).     

Effect of Substrate on the Fatty Acid Composition of Hydrocarbon- and Ketone-utilizing Microorganisms

The fatty acid pattern in hydrocarbon- and ketone-utilizing bacteria after growth on various substrates was examined. The fatty acid composition of one hydrocarbon-utilizing organism (Mycobacterium sp. strain OFS) was investigated in detail after growth on n-alkanes, 1-alkenes, ketones, and n-alcohols. n-Alkanes shorter than C₁₃ or longer than C₁₇ were not incorporated into cellular fatty acids without some degradation. Strain OFS incorporated C₁₄ to C₁₇ 1-alkenes into cellular fatty acids as the ω-monoenoic fatty acid. Methyl ketones were incorporated into strain OFS after removal of one- or two-carbon fragments from the carbonyl end of the molecule. An organism isolated by enrichment on methyl ketones was incapable of n-alkane utilization but could grow on, although not incorporate, ketones or long chain n-alcohols into cellular fatty acids.     

Fatty acid metabolism by cutaneous bacteria and its role in axillary malodour

It is generally accepted that short (C₂-C₅) and medium (C₆-C₁₁) chain volatile fatty acids (VFAs) are among the primary causal molecules of axillary malodour. It is also widely acknowledged that malodour generation is attributable to the biotransformation of odourless natural secretions, into volatile odorous products, by cutaneous bacteria. However, little information is available on the biochemical origins of VFAs on axillary skin. In these studies, assay systems were developed to investigate the generation of VFAs from lipid substrates readily available to the bacteria resident on axillary skin. A major route to short and medium chain VFAs in the axilla was shown to be the partial catabolism of structurally unusual (e.g. methyl-branched) longer chain fatty acids by a previously uncharacterized sub-group of the Corynebacterium genus, corynebacteria (A). In contrast, corynebacteria (B) are incapable of growth on fatty acid. Structurally unusual fatty acids originate from the triacylglycerol component of sebum, and probably also apocrine sweat, by the action of bacterial lipases. Interestingly, VFA formation in the axilla is a dynamic process, with some cutaneous microorganisms, specifically micrococci and brevibacteria, capable of fully catabolizing these odorants. The results of these studies provide new understanding on the biochemical origins of VFA-based axillary malodour.     

Molecular structure of the resistant biopolymer in zygospore cell walls of Chlamydomonas monoica

The unicellular green alga Chlamydomonas monoica Strehlow is known to produce zygospores with a cell wall that is resistant against microbial and chemical attack. This resistance is thought to be due to the presence of a sporopollenin-like material. However, the resistant nature of sporopollenin-like materials seriously hampers their structural analysis. With complementary techniques such as ¹³C-nuclear magnetic resonance spectroscopy, Curie-point pyrolysis-gas chromatography/mass spectroscopy and RuO₄ chemical degradation, the chemical composition of resistant biopolymer in the isolated cell walls of C. monoica zygospores was determined. This material is composed of C₂₂–C₃₀ linear alcohols and carboxylic acids, intermolecularly linked via ester and ether-linkages similar to the resistant aliphatic biopolymers encountered in the walls of the vegetative cells of the algae Tetraedron minimum, Scenedesmus communis and Pediastrum boryanum. Received: 29 April 1998 / Accepted: 2 October 1998     

Anaerobic degradation of isobutyrate by methanogenic enrichment cultures and by a Desulfococcus multivorans strain

Methanogenic enrichment cultures with isobutyrate as sole source of carbon and energy were inoculated with sediment and sludge samples from freshwater and marine origin. Over more than 20 transfers, these cultures fermented 2 mol isobutyrate with 1 mol CO₂ via an intermediate formation of n-butyrate to 4 mol acetate and 1 mol CH₄. The primary isobutyrate-fermenting bacteria could not be purified. From one of the marine enrichment cultures, a sulfate-reducing bacterium was isolated which oxidized isobutyrate with sulfate completely to CO₂. Based on its physiological and morphological properties, this strain was assigned to the known species Desulfococcus multivorans. It also oxidized many other fatty acids without significant release of short-chain intermedeates. The enzymes involved in isobutyrate degradation by this bacterium were assayed in cell-free extracts. The results indicate that isobutyrate is activated to its CoA derivative and oxidized via methylmalonate semialdehyde to propionyl-CoA. Propionyl-CoA is further converted via the methylmalonyl-CoA pathway to acetyl-CoA which is finally cleaved by the CO-dehydrogenase system. It is evident that this is not the pathway used by the fermenting bacteria prevailing in the methanogenic enrichment cultures. There results are discussed on the basis of energetical considerations.     

Synthesis of Suberin during Wound-healing in Jade Leaves, Tomato Fruit, and Bean Pods

The structure and composition of the aliphatic monomers of the polymeric material deposited during wound-healing of tomato fruit, bean pods, and Jade leaves were examined. After removing the cuticle-containing layer of tissue, the wounds were healed for 14 days and the resulting surface layer was excised, lyophilized, solvent-extracted, and depolymerized by hydrogenolysis with LiAlH₄ or transesterified with BF₃ in methanol. The products obtained by the chemical depolymerization were subjected to thin layer chromatography and combined gas chromatography and mass spectrometry. The major aliphatic components isolated from the hydrogenolysate of the wound polymer produced by tomato fruit were hexadecane-1,16-diol and octadec-9-ene-1,18-diol, which were shown to be derived from a 1:1 mixture of ω-hydroxy and dicarboxylic acids of the appropriate chain length by LiAlH₄ reduction. Also identified in the wound polymer were long chain (>C₂₀) fatty acids and alcohols. This monomer composition is typical of suberin polymers and is in sharp contrast with that of the cutin of tomato fruit which contains dihydroxy C₁₆ acid as the major aliphatic component. The hydrogenolysis of the wound material from bean pods gave octadecene-1,18-diol as the major aliphatic component, and smaller amounts of hexadecane-1,16-diol and long chain alcohols. Similar treatment of the normal cuticular tissue of these pods gave hexadecane triol, as well as C₁₆ and C₁₈ alcohols. Hydrogenolysis of wound material from the Jade leaves gave octadecene-1,18-diol, C₁₆ and C₂₂ diols, as well as alcohols from C₁₆ to C₂₆, whereas similar treatment of the cutin-containing tissue from these leaves gave C₁₆ triol as the major aliphatic component. Thus, the major aliphatic monomers of the polymeric material deposited during the wound-healing of bean pods and Jade leaves are very similar to those of suberin, although the natural protective polymer of these tissues is cutin. From these results, it is concluded that suberization is a fundamental process involved in wound-healing in plants, irrespective of the chemical nature of the natural protective polymer of the tissue.     

Decomposition of specifically 14C-labelled phenols and dehydropolymers of coniferyl alcohol as models for lignin degradation by soft and white rot fungi

Several soft and white rot fungi were compared in their ability to degrade specifically ¹⁴C-labelled phenols and dehydropolymers of labelled coniferyl alcohol. Furthermore, plant material, which was expected to be specifically labelled in the lignin part was used in the degradation studies. The experiments showed that both groups of fungi were able to release CO₂ from methoxyl and carboxyl groups of phenol-carboxylic acids, to degrade side chains of cinnamic acids and cinnamyl alcohols and even to decompose aromatic structures. With the dehydropolymers and the plant material a CO₂ release from the methoxyl groups, the side chains and the aromatic carbons was observed. The time dependant course of the CO₂ release from these different groups showed in the beginning a higher CO₂ evolution from the side chain carbons than from the methoxyl groups, which were later on released to a higher extent. No laccase activity could be detected in the soft rot fungi and the peroxidase activity was lower than in the white rot fungi.     

Microbiological Studies of Coli-aerogenes Bacteria

α-Ketoglutarate was obtained in a very small amount by the oxidative fermentation of acetate with either a growing culture or the washed cells of Escherichia coli. This microorganism was also observed to accumulate a considerable amount of α-ketoglutarate as the oxidation-product of C₄-dicarboxylic acids such as succinate, fumarate, malate and oxalacetate. The addition of acetate to the reaction mixtures containing either C₃- or C₄-acids brought about an increase in the yield of α-ketoglutarate. The bacteria of coli-aerogenes revealed an ability of oxidizing tricarboxylic acids under suitable conditions, but there was no noticeable production of α-ketoglutarate. The formation of glyoxylate was observed to occur during the degradation of citrate by the bacteria of coli-aerogenes. Finally, a cyclic mechanism of aerobic carbon-metabolism in the bacteria was propounded and discussed.     

Investigation on bioremediation of oil-polluted wetland at Liaodong Bay in northeast China

An investigation on the effect of various microbes on degradation was carried out as part of the study on bioremediation of oil-polluted wetland at LiaoDong Bay in northeast China. The method used involved direct inoculation of selected bacteria, which were capable of degrading oil, to the soil samples. The combination of various bacteria showed better results in terms of oil degradation than any single ones due to their synergetic effects. The operation conditions [pH 8.0, 25°C, C/N/P (40:5.6:1)] for these bacteria to degrade the oil content in the soil samples were also studied and optimized. Addition of appropriate surfactants was helpful for bacteria growth, thus favoring the oil degradation. For instance, after adding Tween 80 (300 mg/kg) for 8 days, the number of bacteria was amplified 6.22 times and the rate of oil degradation increased by 20%. Adequate amount of H₂O₂ was also beneficial for microbes to decompose oil. However, overdosage may cause the death of the bacteria. The addition of 400 mg/l H₂O₂ each time was suitable. Seven thousand milligrams of H₂O₂ was added entirely in 11 days, and the rate of oil degradation increased significantly from 27% (without H₂O₂) up to 67%. The study clearly demonstrated that the direct soil inoculation was an effective method for environmental bioremediation.Foundation item: The National Key and Fundamental Research and Development Programming Projects (863, No2002AA648010)