Verwertung vonn-Alkanen durch einen Stamm vonAcinetobacter calco-aceticus

A periplasmic insulin-cleaving proteinase (ICP) from Acinetobacter calcoaceticus sharing properties with protease III from Escherichia coli and IDE from eucaryotes

A periplasmic insulin-cleaving proteinase (ICP), purified to its electrophoretic homogeneity in the SDS-PAGE from the Gram-negative bacterium Acinetobacter calcoaceticus, was examined and compared in its properties with the protease III (protease Pi, pitrilysin, EC 3.4.99.44) of Escherichia coli and the insulin-destroying proteinase (IDE, insulinase, EC 3.4.99.45) from eucaryotes. The enzyme was proven to be a metalloprotease like protease III and IDE, as was shown by the inhibitory effects exerted by EDTA and o-phenanthroline. Furthermore, dialysis against EDTA and o-phenanthroline led to a complete loss of activity, which could be restored by addition of Co2+, and, to a lesser extent, but at a lower metal ion concentration by Zn2+. Similar to protease III and IDE, ICP prefers the cleavage of small polypeptides (insulin, insulin B-chain, glucagon) to the cleavage of proteins (casein, human serum albumin, globin) and was inactive against synthetic amino acid derivates (esters, p-nitranilides, and furoylacroleyl substrates) of subtilisin, thermolysin, trypsin, and chymotrypsin. The peptide-bond-specificity of the ICP in the cleavage of the oxidized insulin B-chain was investigated and the results were compared to the specificity of protease III of E. coli, IDE, protease-24,11, and thermolysin. Cleavage sites in the oxidized insulin B-chain generated by ICP are Asn3-Gln4, His10-Leu11, Ala14-Leu15, Leu17-Val18, Gly23-Phe24, Phe24-Phe25, and Phe25-Tyr26. Principally, ICP cleaves between hydrophobic amino acids and amides. The ICP shares one of the only two cleavage sites with the protease III and four sites with the IDE.

Genetics of alkane oxidation by Pseudomonas oleovorans

Many Pseudomonads are able to use linear alkanes as sole carbon and energy source. The genetics and enzymology of alkane metabolism have been investigated in depth for Pseudomonas oleovorans, which is able to oxidize C5-C12 n-alkanes by virtue of two gene regions, localized on the OCT-plasmid. The so-called alk-genes have been cloned in pLAFR1, and were subsequent analyzed using minicell expression experiments, DNA sequencing and deletion analysis. This has led to the identification and characterization of of the alkBFGHJKL and alkST genes which encode all proteins necessary to convert alkanes to the corresponding acyl-CoA derivatives. These then enter the beta-oxidation-cycle, and can be utilized as carbon- and energy sources. Medium (C6-C12)- or long-chain (C13-C20) n-alkanes can be utilized by many strains, some of which have been partially characterized. The alkane-oxidizing enzymes used by some of these strains (e.g. two P. aeruginosa strains, a P. denitrificans strain and a marine Pseudomonas sp.) appear to be closely related to those encoded by the OCT-plasmid.

Periplasmic aminopeptidases in Acinetobacter calcoaceticus and Pseudomonas aeruginosa

The greater part of the intracellular aminopeptidases in Pseudomonas aeruginosa and Acinetobacter calcoaceticus is soluble. The localization of aminopeptidases in the cells was examined using the osmotic shock method with some modifications. When the cells of A. calcoaceticus and P. aeruginosa of the logarithmic phase were subjected to an osmotic shock, all aminopeptidases investigated were mainly localized in the sucrose supernatants and in the periplasm. Acid phosphatase as marker enzyme for periplasm showed a similar distribution between the fractions as the aminopeptidases. The periplasmic aminopeptidases of both microorganisms were separated by FPLC on Superose 12 and their molecular masses were determined. The results obtained show that at least four different aminopeptidases occur in the periplasm, a leucyl aminopeptidase (LAP, cleaving Leu-NH-NH2, 400 kDa), a glutamyl aminopeptidase (GAP, 200 kDa), an alanyl aminopeptidase (AAP, 80 kDa) and a prolyl aminopeptidase (PAP, 65 kDa). The results are in agreement for both species. Our results show clearly that aminopeptidases of these typical members of Gram-negative bacteria are mainly periplasmic like degrading enzymes (alkaline and acid phosphatases, 5'-nucleotidase, cyclic phosphodiesterase), detoxifying enzymes and binding proteins for amino acids and sugars.

Purification of a periplasmic insulin-cleaving proteinase from Acinetobacter calcoaceticus

Cells of Acinetobacter calcoaceticus contain a constitutive periplasmic metalloproteinase showing similar properties as the periplasmic metalloproteinase of Escherichia coli. The periplasmic proteinase of A. calcoaceticus was purified, starting from periplasm, by ammonium sulfate precipitation, hydrophobic interaction chromatography and chromatofocusing up to the homogeneity of the enzyme in SDS-electrophoresis with a yield of 6.7% and a purification factor of 417. The enzyme has a molecular mass of 108,000 (gel filtration) or 112,000 (native electrophoresis), and consists of four identical subunits with a molecular mass of 27,000 (SDS-electrophoresis). The purified enzyme degrades preferentially polypeptides such as glucagon and insulin. Larger proteins are accepted as substrates to a considerably lower extent. All tested synthetic substrates with trypsin, chymotrypsin, elastase and thermolysin specificity were not cleaved. Therefore, the described enzyme was designated "insulin-cleaving proteinase" (ICP).

Isolation and characterization of the extracellular lipase of Acinetobacter calcoaceticus 69 V

The extracellular lipase of Acinetobacter calcoaceticus 69 V was purified by hydrophobic interaction chromatography to homogeneity as suggested by gel electrophoretic analysis. The lipase existed as a high molecular complex of about 300 kDa, with a subunit molecular weight of 30.5 kDa being obtained by SDS-PAGE. The hydrodynamic molecular radius obtained by gel electrophoresis was 3.27 nm. The lipase had an isoelectric point of 5.5 and was stimulated by additions of deoxycholate. The activation energy for the hydrolysis of p-nitrophenyl palmitate was 39.9 kJ mol-1. Tri-, di- and monoacylglycerols were hydrolyzed. Hg2+ and p-hydroxymercuribenzoate inhibited the enzyme activity at very low concentrations. One sulfhydryl group was found per molecule of lipase.

[Proteases in different membrane fractions of Acinetobacter calcoaceticus]

Distinct protease activities were found in membrane fractions from Acinetobacter calcoaceticus grown on acetate-NH4+ medium until early stationary phase. Mechanical or enzymatic cell disintegration followed by membrane fractionation through sucrose gradient revealed higher activities in the outer membrane than in the cytoplasmic membrane. Using azocasein and synthetic p-nitroanilides as substrates we found very low proteinase activities in intracytoplasmic membrane fractions. However, these fractions contained a significant aminopeptidase activity which was absent from cell envelope membranes. Peptidolytic activities in intracytoplasmic membranes of gram-negative bacteria have not been described before.

Leucine aminopeptidase in intracytoplasmic membranes of Acinetobacter calcoaceticus

Cells of Acinetobacter calcoaceticus strain 69-V contain an aminopeptidase that cleaves L-leucine amide, leucylglycine or leucine hydrazide with high efficiency. Leucine 4-nitroanilide and hydrazide are hydrolyzed to less than 0.1% and 1%, resp. of leucine amide. Grown on acetate-NH4+ medium the activity of the enzyme in the cytoplasm is increased 5-fold compared with cells grown on a casamino acid medium or on yeast extract. In these cases the specific activity of the unpurified enzyme is about 5 nkat/mg for the cytoplasmic and membrane-bound enzyme species as well. Up to 30% of the aminopeptidase activity were found mainly in intracytoplasmic membranes, less in cytoplasmic membranes and only traces in outer membranes, presumably as contaminations. It is solubilized by detergents but not by high salt concentrations. An addition of antipain or Z-Ala2-Phe-CH3 before cell rupture did not change the distribution of the enzyme. A mixture of EDTA and 1.10-phenanthroline diminished the membrane-bound enzyme from 11.4% to 4.3% and leupeptin or E-64 increased it to 20%. The enzyme is regarded as leucine aminopeptidase (LAP) bound to intracytoplasmic membranes.

Ultracytochemical localization of aldehyde dehydrogenase in Acinetobacter calcoaceticus

A membrane-bound aldehyde dehydrogenase is induced in Acinetobacter calcoaceticus grown on aliphatic hydrocarbons as sole carbon source. This enzyme is NADP-dependent and is able to oxidize medium- and long-chain aliphatic aldehydes to their corresponding fatty acids. Electron micrographs of sectioned alkane-adapted bacteria showed hydrocarbon inclusions in the cytoplasmic matrix. The cytochemical phenazine methosulphate-tetranitro tetrazolium blue capture reaction allowed to localize the activity of the aldehyde dehydrogenase near the surface of these inclusions. At the same location we also found a NADPH tetrazolium-reducing activity.

Emulsifier formation with Acinetobacter: search for an excretion-reduced mutant of Acinetobacter calcoaceticus 69-V

After growth on acetate three groups of Acinetobacter strains could be identified with respect to the excretion of a bioemulsifier. Mutants of A. calcoaceticus 69-V were selected which produced reduced amounts of emulsifier.

Localization of hydrolytic enzymes in Acinetobacter calcoaceticus

The localization of hydrolytic enzymes, phosphatase, esterase, lipase and palmitoyl-CoA hydrolase was analysed in the cytosol, cytoplasmic membrane, periplasmic fraction, outer membrane and culture supernatant in dependence on the growth rate of the bacteria. The unspecific phosphatase was found to be a cytosolic enzyme. A lipase was the only extracellular enzyme detected. The results pointed to a secretion of the lipase into the culture medium via cytoplasmic and outer membrane. The palmitoyl-CoA hydrolase was found to be attached to the outer membrane, but activities were also detected in the periplasmic fraction. Unspecific esterolytic activities were mainly measured in the cytosol and in the cytoplasmic membrane.

Alcohol oxidation by Acinetobacter calcoaceticus EB 104--a n-alkane-utilizing and cytochrome P-450-producing strain

A soluble, NADP+-dependent alcohol dehydrogenase (ADH) with a pH optimum at 8.7 was found in A. calcoaceticus EB 104 after growth on different carbon sources. n-Alkanols with short and medium chain length were employed as test substrates. The Km values decreased with increasing chain length. The Vmax values remained nearly unchanged. The activities determined were independent of the carbon source. Furthermore, a n-alkanol-dependent reduction of DCPIP was measured in membrane fractions of cells grown on different carbon sources. The optimum pH for this reaction was at 7.5. Further proof for the presence of a pyridine nucleotide-independent ADH was derived from the oxidation of 14C-decanol in the absence of NADP+ or NAD+.

Effect of oxygen limitation on the content of n-hexadecane-inducible cytochrome P-450 in Acinetobacter calcoaceticus strain EB 104

The content of cytochrome P-450 as a function of oxygen supply was studied during growth of Acinetobacter on n-hexadecane in batch cultures at constant pH and agitation. The rate of growth and the content of cytochrome P-450 were not affected as long as the dissolved oxygen tension ranged above 3 to 5% of saturation. The amount of cytochrome P-450 increased when the oxygen tension declined to zero. Cytochrome P-450 levels of about 0.3 to 0.4 nmol/mg protein, i.e. a more than a threefold increase, were observed under conditions where oxygen supply was strictly limited and allowed to maintain only a minimum of metabolism or growth. Limited oxygen supply exerted a special effect on the induction of the cytochrome P-450 as concluded from an increasing ratio between cytochrome P-450 and cytochrome o, and from the absence of cytochrome d in cells with elevated content of cytochrome P-450. The increased formation of cytochrome P-450 was a reversible process.

Solubilization of bacterial cells in organic solvents via reverse micelles

A reverse micellar system containing Tween 85 and water in isopropylpalmitate was developed which permitted the solubilization of bacteria in the form of homogenous organic solutions. The presence of the bacteria in solution was demonstrated by light microscopy. Immediately after solubilization, isolated bacterial cells were observed, which by aging tend to form larger aggregates. Cells of Escherichia coli remained viable in this system for at least one day and retained beta-galactosidase activity for an even longer period as indicated by the hydrolysis of x-gal. Cells of an alkane-degrading strain of Acinetobacter calcoaceticus remained viable in the system for several days.

[Rubredoxin reductase in crude extracts of Acinetobacter calcoaceticus in relation to carbon source and growth phase]

By immunization of rabbits with discelectrophoretically purified rubredoxin-reductase from Ac. calcoaceticus an antiserum against this enzyme was prepared. The antiserum was monospecifical to a diaphoretic activity, which had a RF-value identical with the rubredoxin-reductase-RF value. It has been shown by discelectrophoresis, immunoelectrophoresis, OUCHTERLONY technique and kinetic investigations that crude extracts of bacteria grown on C16, malate, succinate or acetate contain rubredoxin-reductase. By the LAURELL technique we demonstrated that the amount of the enzyme is nearly independent of the carbon source. There are only differences during the different growth phases.

Influence of growth phase and carbon source on the content of rubredoxin in Acinetobacter calcoaceticus

The rubredoxin content of Acinetobacter calcoaceticus in dependence on the carbon source (acetate, n-alkanes, succinate, L-malate) and on the growth phase was studied by means of a radioimmunoassay. The method used was specific for rubredoxin and Acinetobacter calcoaceticus. The formation of rubredoxin increased with time up to the end of the logarithmic phase when n-alkanes were the sole carbon source. After growth of Acinetobacter calcoaceticus on non-hydrocarbon substrates, rubredoxin was not detected.

[Interrelationships between carnitine metabolism and fatty acid assimilation in Pseudomonas putida (author's transl)]

The carnitine metabolism and some relations to the fatty acid metabolism were studied in Pseudomonas putida by means of control of growth, analysis of metabolites, and determination of enzyme activites. The strain grew on gamma-butyrobetaine, D,L- and L-carnitine, glycinebetaine, choline, D,L-norcarnitine, D,L-gamma-amino-beta-hydroxybutyrate, and D,L-beta-hydroxybuty-rate. Although the strain used straight-chain fatty acids of 2-16 C-atoms, it was only able to grow on O-acyl-L-carnitines of 10 or more C-atoms in the acyl-group. Addition of carnitine stimulated the growth on long-chain fatty acis. The formation of trimethylamine increased, if L-carnitine or gamma-butyrobetaine were the only carbon sources, and decreased, if these trimethylammonium compounds were carbon as well as nitrgen sources. L-Carnitine induced the carnitine dehydrogenase as well as the beta-hydroxybutyrate dehydrogenase, gamma-Butyrobetaine as carbon and nitrogen source induced the carnitine dehydrogenase, too. In the crude extract the specific activiteis of beta-hydroxybutyrate dehydrogenase were 0.7 or 1.6 mumoles.min-1.mg-1 after growth on L-carnitine and D,L-beta-hydroxybutyrate, respectively. The synthesis of both enzymes was repressed by glycinebetaine, glucose and long-chain fatty acis. Dependent on the nitrogen source L-carnitine was catabolized via two different pathways.

[Utilization of trimethylammonium-compounds by Acinetobacter calcoaceticus (author's transl)]

The utilization of carnitine and carnitine derivatives (O-acylcarnitines, carnitine carboxylderivatives) and structure-related trimethylammonium-compounds (betaines and nitrogen-bases) by Acinetobacter calcoaceticus was studied by means of the control of growth and the quantitative detection of metabolites. The strain grew only on L-carnitine, L-O-acylcarnitines, and gamma-butyrobetaine as the sole carbon sources. The utilization of these compounds and the growth correlated with the cleavage of the C-N bond and thereby with the formation of trimethylamin. D-Carnitine was metabolized, if an additional carbon source, like L-carnitine, was present in the incubation mixture, or if the bacteria were preincubated with L- or DL-carnitine, but no growth was observed on D-carnitine as the sole carbon source. The bacteria oxidized choline to glycinebetaine in the presence of additional carbon sources, glycinebetaine itself was not assimilated. With regard to the catabolism of quaternary nitrogen compounds Acinetobacter calcoaceticus shows a different pathway in comparison with other bacterial species metabolizing carnitine.