New obligate methylotroph

Methylohalobius crimeensis gen. nov., sp. nov., a moderately halophilic, methanotrophic bacterium isolated from hypersaline lakes of Crimea

A novel genus and species are proposed for two strains of methanotrophic bacteria isolated from hypersaline lakes in the Crimean Peninsula of Ukraine. Strains 10KiT and 4Kr are moderate halophiles that grow optimally at 1–1·5 M (5·8–8·7 %, w/v) NaCl and tolerate NaCl concentrations from 0·2 M up to 2·5 M (1·2–15 %). This optimum and upper limit are the highest for any methanotrophic bacterium known to date. The strains are Gram-negative, aerobic, non-pigmented, motile, coccoid to spindle-shaped bacteria that grow on methane or methanol only and utilize the ribulose monophosphate pathway for carbon assimilation. They are neutrophilic (growth occurs only in the range pH 6·5–7·5) and mesophilic (optimum growth occurs at 30 °C). On the basis of 16S rRNA gene sequence phylogeny, strains 10KiT and 4Kr represent a type I methanotroph within the ‘Gammaproteobacteria’. However, the 16S rRNA gene sequence displays <91·5 % identity to any public-domain sequence. The most closely related methanotrophic bacterium is the thermophilic strain HB. The DNA G+C content is 58·7 mol%. The major phospholipid fatty acids are 18 : 1ω7 (52–61 %), 16 : 0 (22–23 %) and 16 : 1ω7 (14–20 %). The dominance of 18 : 1 over 16 : 0 and 16 : 1 fatty acids is unique among known type I methanotrophs. The data suggest that strains 10KiT and 4Kr should be considered as belonging to a novel genus and species of type I methanotrophic bacteria, for which the name Methylohalobius crimeensis gen. nov., sp. nov. is proposed. Strain 10KiT (=DSM 16011T=ATCC BAA-967T) is the type strain.

Oxidative and assimilative enzyme activities in continuous cultures of the obligate methylotroph Methylobacillus flagellatum

In methanol-limited continuous cultures of the obligate methylotrophic bacterium Methylobacillus flagellatum grown at rates from 0.05 to 0.63 h-1, and also in an oxyturbidostat culture of M. flagellatum growing at the rate of 0.73 h-1, levels of methanol dehydrogenase, enzymes of formaldehyde oxidation (both linear and cyclic) and assimilation (RuMP cycle), a number of intermediary metabolism and TCA cycle enzymes and also 'dye-linked' formaldehyde dehydrogenase were determined. It was shown that the activities of dissimilatory enzymes, with the exception of 'dye-linked' formaldehyde dehydrogenase, decreased with increasing growth rate. Activities of assimilative enzymes and activities of the TCA cycle enzymes detected as well as the 'dye-linked' formaldehyde dehydrogenase activity, increased with increasing growth rate. A periplasmic location was shown for the latter enzyme and a role in formaldehyde detoxification was proposed.

Effect of mineral media on trichloroethylene oxidation by aquifer methanotrophs

The effect of growth in different mineral media on subsequent oxidation of trichloroethylene (TCE) by type I and type II aquifer methanotrophs was evaluated. Mixed culture MM1, containing a type II methanotroph, and a type I pure culture tentatively identified as aMethylomonas sp., were enriched and isolated from an uncontaminated groundwater aquifer. The second-order rate coefficients (k/Ks) for TCE oxidation by these cultures varied by more than an order of magnitude when the cultures were grown in different mineral media. The presence of a chelator (NaEDTA) in one of these media, termed Whittenbury, significantly enhanced rates of TCE oxidation by all the cultures tested. When pregrown in this mineral medium, the resting cells of the pure cultureMethylomonas sp. MM2 exhibited second-order TCE oxidation rates as great as 0.78 liter/mg·day, whereas when pregrown in Whittenbury lacking the chelator, the rates did not exceed 0.018 liter/mg·day. The rate of TCE oxidation byMethylomonas sp. MM2 pregrown in another mineral medium formulation, devoid of chelators (termed Fogel), was intermediate in value (0.26 liter/mg·day), and adding EDTA to this medium did not affect the rate. Adding 1.6 μM copper to both Whittenbury and Fogel mineral media reduced the TCE oxidation rates about an order of magnitude; subsequent addition of 84 μM EDTA partially alleviated this effect. The maximal rate coefficients (k) for TCE oxidation byMethylomonas sp. MM2 were significantly higher, and the half saturation coefficients (Ks) for TCE significantly lower, following growth in the presence of EDTA. Stationary phase TCE oxidation rates as great as 2.3 liter/mg·day were achieved whenMethylomonas sp. MM2, grown in Whittenbury medium was provided formate as a source of reducing power. Omitting EDTA from Whittenbury medium also significantly reduced the methane oxidation rate and the growth yield. Copper addition did not significantly affect the methane oxidation rate or growth yield. The internal membrane structures ofMethylomonas sp. MM2 evaluated by transmission electron microscopy showed the presence of internal membranes, the ultrastructure of which was the same regardless of growth medium or TCE oxidation rate. The methane monooxygenase responsible for TCE oxidation inMethylomonas sp. MM2 under the conditions of this study appears to be associated with the particulate fraction.

Isolation and characterization of marine methanotrophs

Four new methane-oxidizing bacteria have been isolated from marine samples taken at the Hyperion sewage outfall, near Los Angeles, CA. These bacteria require NaCl for growth. All exhibit characteristics typical of Type I methanotrophs, except they contain enzyme activities of both the ribulose monophosphate pathway and the serine cycle. All four strains are characterized by rapid growth in liquid culture and on agar plates, and all have temperature optima above 35 degrees C. One strain, chosen for further study, has been shown to maintain broadhost range cloning vectors and is currently being used for genetic studies.

Autotrophic Growth of Gas Vacuolate Strains of Microcyclus aquaticus on Methanol and Hydrogen

Seven strains of Microcyclus aquaticus were found to be capable of growth on methanol and hydrogen as energy sources. Carbon was incorporated as CO 2 via the Calvin cycle, as shown by the presence of ribulosebisphosphate carboxylase activity in methanol-grown cells and by the absence of key enzymes of the ribulose monophosphate and serine pathways. In addition, incoporation of [ 14 C]methanol into cells was diminished when cultures were incubated in gas atmospheres enriched with carbon dioxide.

Arthrobacter P1, a fast growing versatile methylotroph with amine oxidase as a key enzyme in the metabolism of methylated amines

A facultative methylotrophic bacterium was isolated from enrichment cultures containing methylamine as the sole carbon source. It was tentatively identified as an Arthrobacter species. Extracts of cells grown on methylamine or ethylamine contained high levels of amine oxidase (E.C. 1.4.3) activity. Glucose- or choline-grown cells lacked this enzyme. Oxidation of primary amines by the enzyme resulted in the formation of H2O2; as a consequence high levels of catalase were present in methylamine- and ethylamine-grown cells. The significance of catalase in vivo was demonstrated by addition of 20 mM aminotriazole (a catalase inhibitor) to exponentially growing cells. This completely blocked growth on methylamine whereas growth on glucose was hardly affected. Cytochemical studies showed that methylamine-dependent H2O2 production mainly occurred on invaginations of the cytoplasmic membrane. Assimilation of formaldehyde which is generated during methylamine oxidation was by the FBP variant of the RuMP cycle of formaldehyde fixation. The absence of NAD-dependent formaldehyde and formate dehydrogenases indicated the operation of a non-linear oxidation sequence for formaldehyde via hexulose phosphate synthase. Enzyme profiles of the organism grown on various substrates suggested that the synthesis of amine oxidase, catalase and the enzymes of the RuMP cycle is not under coordinate control.

The electron-transport chains of the obligate methylotroph Methylophilus methylotrophus

The cytochrome complement of Methylophilus methylotrophus and its respiratory properties were determined during batch culture and in continuous culture under conditions of methanol-, nitrogen- and O(2)-limitation. About 35% of the cytochrome c produced by the bacteria was released into the growth medium, and of the remaining cytochrome c about half was membrane-bound and half was soluble. Two cytochromes c were always present on membranes (redox potentials 375mV and 310mV), and these probably correspond to the soluble cytochromes c described previously [Cross & Anthony (1980) Biochem. J.192, 421-427]. A third minor component of cytochrome c (midpoint potential 356mV) was only detected on membranes of methanol-limited bacteria. M. methylotrophus always contained two membrane-bound cytochromes b with alpha-band absorption maxima of about 556 and 563nm (measured at room temperature) and midpoint potentials of 110 and 60mV respectively. There appeared to be relatively more of the cytochrome b(563) in methanol-limited bacteria. A third b-type cytochrome with an alpha-band absorption maximum at 558 (at 77K) reacted with CO and had a high midpoint redox potential (260mV); it is thus a potential oxidase and hence is called cytochrome o. The roles of these cytochromes in electron transport were confirmed by investigating the patterns of respiratory inhibition. It is proposed that two cytochromes are physiological oxidases: cytochrome a+a(3), which is present only in methanol-limited conditions, and the cytochrome o, which is induced 10-fold in conditions of methanol excess. Schemes for electron transport from methanol and NAD(P)H to O(2) in M. methylotrophus under various limitations are proposed. Spectra and potentiometric titrations of cytochromes in whole cells and membranes of M. methylotrophus grown under various nutrient limitations have been deposited as Supplementary Publication SUP 50111 (10 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1978) 169, 5.

Characterization of Two New Facultative Methanotrophs

Two new facultative methane-oxidizing bacteria have been isolated from lake water enrichments. The organisms have been characterized in terms of colony types, growth characteristics, the guanine plus cytosine content of their deoxyribonucleic acid, thin sections, oxidation rates, and carbon assimilation pathways. Methane-grown cells of both organisms contained intracytoplasmic membranes similar to those described as type II in other methanotrophic bacteria. Neither organism had such membranes when grown heterotrophically. Both organisms assimilated methane by way of the isocitrate lyase-negative serine pathway for formaldehyde incorporation. The enzymes of this pathway were high in specific activity in cells grown on methane and were at low levels in cells grown either on heterotrophic substrates or on heterotrophic substrates plus methane. It is proposed that both organisms be classified in the genus Methylobacterium as two new species, Methylobacterium ethanolicum and Methylobacterium hypolimneticum.

Purification and characterization of a heme-containing amine dehydrogenase from Pseudomonas putida

The primary amine dehydrogenase of Pseudomonas putida NP was purified to homogeneity as judged by polyacrylamide gel electrophoresis. Cytochrome c or an artificial electron acceptor was required for amine dehydrogenase activity. The enzyme was nonspecific, readily oxidizing primary monoamines, benzylamine, and tyramine; little or no measurable activity was detected with isoamines, L-ornithine, L-lysine, and certain diamines or polyamines. The pH optima for n-butylamine, benzylamine, and n-propylamine were 7.0, 6.5, and 7.0, respectively. The molecular weight of the enzyme was 112,000 as determined by gel filtration and 95,300 as analyzed by sedimentation equilibrium. Subunit analysis by sodium dodecyl sulfate gel electrophoresis suggested that the enzyme was composed of two nonidentical subunits with molecular weights of 58,000 and 42,000. The absorption spectrum of the purified enzyme was indicative of a hemoprotein, exhibiting absorption maxima at 277, 355, and 408 nm. Reduction with sodium dithionite or amine substrates resulted in absorption maxima at 523 and 552 nm and a shift in the Soret peak to 416 nm. These results suggested that the enzyme is a hemoprotein of the type c cytochrome. There was no evidence that flavins were present.

Methylamine dehydrogenase of Pseudomonas sp. J. Purification and properties

Methylamine dehydrogenase was purified in a homogeneous form from methylamine-grown Pseudomonas sp. J. The specific activity of the purified enzyme was 5.19 at 19 degrees C. The molecular weight was estimated to be 105 000, and the enzyme was composed of two kinds of subunit with molecular weights of 40 000 and 13 000, respectively. The enzyme contained little phosphorus, iron and copper. The enzyme had absorption maxima at 278, 330, 430 and 460 nm (shoulder). On addition of methylamine, the peaks at 430 and 460 nm decreased, while that at 330 nm increased. Primary amines served as substrates, but secondary and tertiary amines did not. Phenazine methosulfate was the most effective electron acceptor and oxygen was ineffective. The enzyme was inhibited by carbonyl reagents, cuprizone and HgCl2 but not by other chelators or sulfhydryl reagents. Some of other physical and biochemical properties of the enzyme were studied. These results show that the enzyme purified from Pseudomonas sp. J is essentially similar to the enzyme obtained from Pseudomonas AM1, although it differs slightly in some properties.

Methylamine dehydrogenase of Pseudomonase sp. J Isolation and properties of the subunits

Two kinds of subunits, light subunit (Mr =1300) and heavy subunit (Mr=40 000), were isolated from a methylamine dehydrogenase (Mr=105 000) of Pseudomonas sp. J. The isolation of the subunits was carried out by gel chromatography after the enzyme had been treated with 3M guanidine-HCl. Coexistence of both of the subunit exhibited an absorption maximum only at 278 nm but in addition to the peak at 278 nm. The results indicate that the prosthetic group, assumed to be a derivative of pyridoxal, was bound to the light subunit. The spectral changes of the light subunit were observed by addition of methylamine. Various physical and biochemical parameters of the subunits are reported.

Electron microscopy of methanol-utilizing bacteria

Two different groups of methanol-utilizing bacteria were studied by electron microsocpy. Bacteria using the serine pathway for the assimilation of methanol were found to have a thin cell envelope (outer membrane, periplasmic area and cytoplasmic membrane). Those using the assimilatory ribulose monophosphate pathway of formaldehyde fixation had a much thicker cell envelope and in the case of Pseudomonas C protrusions of the outer membrane were found.

The respiratory chain of a newly isolated Methylomonas Pl1

1. Whole cells of Methylomonas Pl1 contained ubiquinone, identified as ubiquinone-8. No naphthaquinone was detected. Ubiquinone was located predominantly in the particulate fraction, which also contained most of the NADH oxidase activity. 2. Aerobic incubation of cells with formaldehyde or methanol resulted in about 20% reduction of ubiquinone, irrespective of the presence or absence of dinitrophenol. On inhibition of the respiration by cyanide, ubiquinone became partly reduced by endogenous substrates (15--25%), and a further reduction occurred only in the presence of formaldehyde (up to 60%). When endogenous substrates were completely exhausted, then 44 and 23% of ubiquinone was reduced by formaldehyde or methanol respectively. 3. The difference spectra at room and liquid-N2 temperatures revealed the presence of cytochrome b and two cytochromes c (c-552.5 and c-549) all tightly bound to the membrane. Cytochrome c-552.5 was also found in the soluble fraction. 4. Redox changes of cytochromes b and c, with methanol or formaldehyde as substrates, respond to the aerobic and anaerobic states of the cell and to KCN inhibition in a manner characteristic of the electron carriers of the respiratory chain. 5. The merging point for electron transport from NADH dehydrogenase and formaldehyde dehydrogenase is suggested to be at the level of ubiquinone.

(14C)acetate assimilation by a type I obligate methylotroph, Methylococcus capsulatus

Methanol and formate oxidation supported the assimilation of [14C]acetate by cell suspensions of Methylococcus capsulatus; oxidation of other primary alcohols, except ethanol, did not. The extent of [1-14C]acetate assimilation supported by methanol oxidation was decreased in the presence of primary alcohols, except ethanol. Potassium cyanide (0.33 mM) completely inhibited the oxidation of formate and its stimulation of [1-14C]acetate assimilation. The amount of [1-14C]acetate assimilation supported by methanol oxidation was significantly inhibited by cyanide.

Mutant of Methylomonas methanolica and Its Characterization with Respect to Biomass Production from Methanol

A stable variant of Methylomonas methanolica , with a higher temperature optimum for growth, was obtained after mutagenic treatment and selection. The mutant strain M13V has an optimum growth temperature of 35 to 37°C and a maximum at 43°C, as compared with 30 and 40°C for the wild strain. Strain M13V and M. methanolica have similar basic characteristics and cell composition. An extracellular polysaccharide is produced by both strains, but this property is more pronounced in strain M13V. In strain M13V the production is favored by high temperature, low growth rate, and oxygen limitation. In continuous culture of strain M13V, the polysaccharide production was partly growth associated and partly independent of the growth rate. The extracellular polysaccharide acted as a flocculating agent. A relationship between polysaccharide concentration and sedimentation rate was found. Biomass production from strain M13V is most effective at 35°C with respect to both growth rate and substrate utilization. It was found that the yield coefficient for methanol was independent of the dilution rate, whereas the yield coefficient for oxygen increased and the production coefficient for carbon dioxide decreased at increasing dilution rates. These results are discussed in connection with the polysaccharide production.

Solubilization, partial purification and properties of N-methylglutamate dehydrogenase from Pseudomonas aminovorans

1. Extracts of amine-grown Pseudomonas aminovorans contained a particle-bound N-methylglutamate dehydrogenase (EC 1.5.99.5). The enzyme was not present in succinate-grown cells, and activity appeared before growth began in succinate-grown cells which had been transferred to methylamine growth medium. 2. Membrane-containing preparations from methylamine-grown cells catalysed an N-methylglutamate-dependent uptake of O2 or reduction of cytochrome c, which was sensitive to inhibitors of the electron-transport chain. 3. N-Methylglutamate dehydrogenase activity with phenazine methosulphate or 2,6-dichlorophenol-indophenol as electron acceptor could be solubilized with 1% (w/v) Triton X-100. The solubilized enzyme was much less active with cytochrome c as electron acceptor and did not sediment in 1 h at 150000g. Solubilization was accompanied by a change in the pH optimum for activity. 4. The solubilized enzyme was partially purified by Sepharose 4B and hydroxyapatite chromatograpy to yield a preparation 22-fold increased in specific activity over the crude extract. 5. The partially-purified enzyme was active with sarcosine, N-methylalanine and N-methylaspartate as well as with N-methylglutamate. Evidence suggesting activity with N-methyl D-amino acids as well as with the L-forms was obtained. 6. The enzyme was inhibited by p-chloromercuribenzoate, iodoacetamide and by both ionic and non-ionic detergents. 2-Oxoglutarate and formaldehyde were also inhibitors. 7. Kinetic analysis confirmed previous workers' observations of a group transfer (Ping Pong) mechanism. 8. Spectral observations suggested that the partially purified preparation contained flavoprotein and a b-type cytochrome. 9. The role of the enzyme in the oxidation of methylamine is discussed.

Purification and properties of 3-hexulosephosphate synthase from Methylomonas M 15

3-Hexulosephosphate synthase, the first enzyme of the ribulose monophosphate cycle, was purified 15-fold from methanol-grown Methylomonas M 15. The purification procedure involved chromatography on DEAE-cellulose, Sephadex G-75, and DEAE-Sephadex A-50. The purified enzyme was more than 95% pure as judged by analytical polyacrylamide gel electrophoresis. The molecular weight was calculated to be 43000 from sedimentation equilibrium experiments. Electrophoresis in sodium dodecylsulfate gels gave a single band corresponding to a molecular weight of 22000. The enzyme catalyzes specifically the condensation formaldehyde with ribulose 5-phosphate to yield D-arabino-3-hexulose 6-phosphate. The Km values were found to be 1.1 mM for formaldehyde and 1.6 mM for ribulose 5-phosphate. A bivalent cation is essential for activity and stability of the enzyme, Mg2+ and Mn2+ serve best for this purpose. The optimum of pH for enzyme activity is 7.5--8.0.

Purification and properties of a methanol-oxidizing enzyme in Pseudomonas C

A methanol-oxidizing enzyme has been purified from Pseudomonas C, grown on methanol as a sole source for carbon and energy. The purification procedure involved ammonium sulphate precipitation, ion-exchange chromatography and gel filtration and resulted in a yield of 35.4%. Enzyme activity can be coupled to phenazine methosulfate and requires the presence of ammonium ions in the assay mixtures. The enzymes possesses a broad specificity for primary alcohols. Formaldehyde is also oxidized by the purified enzyme. The Km value for methanol is 15 muM. The optimum pH for the oxidation of both methanol and formaldehyde is about 10.4. The enzyme has a molecular weight of about 128000 and consists of two subunits each having a molecular weight of 60000.

Regulation of citrate synthase activity in methylotrophs by reduced nicotinamide-adenine dinucleotide, adenine nucleotides and 2-oxoglutarate

Citrate synthase from two typical facultative methylotrophs, but not from four obligate methylotrophs or from two restricted facultative methylotrophs, is inhibited by 0.1 mM-NADH. ATP or ADP (both at 10mM) inhibits all the citrate synthases, whereas 2-oxoglutarate (10mM) inhibits those from only three of the eight methylotrophs.

Tricarboxylic acid-cycle and related enzymes in restricted facultative methylotrophs

The isolation is described of pure cultures of three non-methane-utilizing methylotrophic bacteria which, together with the previously described Bacillus PM6, have a very limited range of growth substrates; these organisms are designated "restricted facultative' methylotrophs. Two of these isolates, W6A and W3A1, grow only on glucose out of 50 non-C1 compounds tested, whereas the third isolate S2A1 and Bacillus PM6 grow on betaine, glucose, gluconate, alanine, glutamate, citrate and nutrient agar, but not on any of a further 56 non-C1 compounds. Crude sonic extracts of trimethylamine-grown and glucose-grown W6A and W3A1 isolates, and of trimethylamine-grown C2A1 (an obligate methylotroph) contain (i) no detectable 2-oxogltarate dehydrogenase activity, (ii) very low or zero specific activities of succinate dehydrogenase and succinyl-CoA synthetase and (iii) NAD+-dependent isocitrate dehydrogenase activity. Extracts of trimethylamine-grown PM6 and S2A1 methylotrophs have (i) very low 2-oxoglutarate dehydrogenase specific activities, (ii) comparatively high specific activities of succinate dehydrogenase, malate dehydrogenase and succinyl-CoA synthetase and (iii) NADP+-dependent isocitrate dehydrogenase activity but no NAD+-dependent isocitrate dehydrogenase activity. The activities of most of these enzymes are increased during growth on glucose, alanine, glutamate or citrate, but only very low 2-oxoglutarate dehydrogenase activities are present under all growth conditions. The restricted facultative methylotrophs grow on certain non-C1 compounds in the absence of 2-oxoglutarate dehydrogenase and, in some cases, of other enzymes of the tricarboxylic acid cycle; these lesions cannot therefore be the sole cause of obligate methylotrophy.

Enzymological aspects of the pathways for trimethylamine oxidation and C1 assimilation of obligate methylotrophs and restricted facultative methylotrophs

Extracts of trimethylamine-grown W6A and W3A1 (type M restricted facultative methylotrophs) contain trimethylamine dehydrogenase whereas similar extracts of Bacillus PM6 and Bacillus S2A1 (type L restricted facultative methylotrophs) contain trimethylamine mono-oxygenase and trimethylamine N-oxide demethylase but no trimethylamine dehydrogenase. Extracts of the restricted facultatives and of the obligate methylotroph C2A1 contain hexulose phosphate synthase-hexulose phosphate isomerase activity; hydroxypyruvate reductase was not detected. Neither the restricted facultatives nor the obligates 4B6 and C2A1 contain all the enzymes of the hexulose phosphate cycle of formaldehyde assimilation as originally proposed by Kemp & Quayle (1967). Organisms PM6 and S2A1 lack transaldolase and use a modified cycle involving sedoheptulose 1,7-diphosphate and sedoheptulose diphosphatase. The obligates 4B6 and C2A1, and the type M organisms W6A and W3A1, use a different modification of the assimilatory hexulose phosphate cycle involving the Entner-Doudoroff-pathway enzymes phosphogluconate dehydratase and phospho-2-keto-3-deoxygluconate aldolase. The lack of fructose diphosphate aldolase and hexose diphosphatase in these organisms may be a partial explanation of their restricted growth-substrate range. Enzymological evidence suggests that all the obligates and the restricted facultatives use a dissimilatory hexulose phosphate cycle to accomplish the complete oxidation of formaldehyde to CO2 and water.

Growth of Pseudomonas C on C1 compounds: enzyme activites in extracts of Pseudomonas C cells grown on methanol, formaldehyde, and formate as sole carbon sources

Pseudomonas C can grow on methanol, formaldehyde, or formate as sole carbon source. It is proposed that the assimilation of carbon by Pseudomonas C grown on different C1 growth substrates proceeds via one of two metabolic pathways, the serine pathway or the allulose pathway (the ribose phosphate cycle of formaldehyde fixation). This contention is based on the distribution of two key enzymes, each of which appears to be specifically involved in one of the assimilation pathways, glycerate dehydrogenase (serine pathway) and hexose phosphate synthetase (allulose pathway). The assimilation of methanol in Pseudomonas C cells appears to occur via the allulose pathway, whereas the utilization of formaldehyde or formate in cells grown on formaldehyde or formate as sole carbon sources appears by the serine pathway. When methanol is present together with formaldehyde or formate in the growth medium, the formaldehyde or formate is utilized by the allulose pathway.

The carbon assimilation pathways of Methylococcus capsulatus, Pseudomonas methanica and Methylosinus trichosporium (OB3B) during growth on methane

d-arabino-3-Hexulose 6-phosphate was prepared by condensation of formaldehyde with ribulose 5-phosphate in the presence of 3-hexulose phosphate synthase from methane-grown Methylococcus capsulatus. The 3-hexulose phosphate was unstable in solutions of pH greater than 3, giving a mixture of products in which, after dephosphorylation, allulose and fructose were detected. A complete conversion of d-ribulose 5-phosphate and formaldehyde into d-fructose 6-phosphate was demonstrated in the presence of 3-hexulose phosphate synthase and phospho-3-hexuloisomerase (prepared from methane-grown M. capsulatus). d-Allulose 6-phosphate was prepared from d-allose by way of d-allose 6-phosphate. No evidence was found for its metabolism by extracts of M. capsulatus, thus eliminating it as an intermediate in the carbon assimilation process of this organism. A survey was made of the enzymes involved in the regeneration of pentose phosphate during C(1) assimilation via a modified pentose phosphate cycle. On the basis of the presence of the necessary enzymes, two alternative routes for cleavage of fructose 6-phosphate are suggested, one route involves fructose diphosphate aldolase and the other 6-phospho-2-keto-3-deoxygluconate aldolase. A detailed formulation of the complete ribulose monophosphate cycle of formaldehyde fixation is presented. The energy requirements for carbon assimilation by this cycle are compared with those for the serine pathway and the ribulose diphosphate cycle of carbon dioxide fixation. A cyclic scheme for oxidation of formaldehyde via 6-phosphogluconate is suggested.

Hexose phosphate synthase in trimethylamine-grown bacterium 2B2, a facultative methylotroph

Hexose phosphate synthase and hexulose phosphate isomerase activities were found in trimethylamine-grown bacterium 2B2, a facultative methylotroph. The activities were separated by column chromatography of cell extracts on DEAE-cellulose. Hexulose phosphate isomerase activity was measured spectrophotometrically by using the product of the hexose phosphate synthase reaction as substrate.