Relationship between carbon monoxide dehydrogenase and a small plasmid in Pseudomonas carboxydovorans

Abstract Isolation of plasmid DNA followed by plasmid curing was carried out to examine the relationship of plasmid to carbon monoxide dehydrogenase (CO-DH) production in carboxydobacteria. A small plasmid of almost identical size (1.52−1.76 × 10⁶) was present in Pseudomonas carboxydovorans, Azotobacter sp.1, and Azomonas sp.2. Azomonas sp.1 contained two kinds of plasmids (1.5 × 10⁶ and 2.47 × 10⁶). No plasmids were found in Pseudomonas carboxydohydrogena , JC1, and HY1. A plasmid-cured clone of P. carboxydovorans was obtained by growing the cells at 37°C. The cured cell was able to grow CO autotrophically on solid, but not in liquid, medium. CO-DH of the cured cell was active and consisted of three subunits similar to those found in the wild-type enzyme, with the exception that the β subunit of the enzyme was larger than that of the wild-type enzyme. These results suggest that the small plasmids do not carry genes encoding CO-DH but may have gene(s) for processing the β subunit of the enzyme.     

Carbon monoxide dehydrogenase in mycobacteria possesses a nitric oxide dehydrogenase activity

CO dehydrogenase (CO-DH) catalyzes the oxidation of CO to CO(2) in carboxydobacteria. Cell-free extracts prepared from several mycobacteria, including Mycobacterium tuberculosis H37Ra, showed NO dehydrogenase (NO-DH) activity in a reaction mixture containing sodium nitroprusside (SNP) as the source of NO. The association of the NO-DH activity with CO-DH was revealed by activity staining and confirmed by enzyme assay with purified CO-DH from Mycobacterium sp. strain JC1, a carboxydotrophic mycobacterium. SNP stimulated the production of CO-DH with a coincidental increase in NO-DH activity in the bacterium, further supporting this association and implying the existence of a possible SNP-induced CO-DH gene expression. The addition of purified CO-DH to cultures of Escherichia coli revealed that the enzyme protected E. coli from SNP-induced killing in a dose-dependant way. The present results indicate that mycobacterial CO-DH also acts as a NO-DH, which may function in the protection of mycobacterial pathogens from nitrosative stress during infection.     

Physiological characteristics of various species of strains of carboxydobacteria

Seven strains of aerobic carbon monoxide-oxidizing bacteria (carboxydebacteria) when growing on CO as sole source of carbon and energy had doubling times which ranged from 12–42 h. The activity profiles obtained after discontinuous sucrose density gradient centrifugation indicated that the CO-oxidizing enzymes are soluble and the hydrogenases are membrane-bound in all strains examined. The CO-oxidizing enzymes of Pseudomonas carboxydohydrogena, Pseudomonas carboxydoflava, Comamonas compransoris, and the so far unidentified strains OM2, OM3, and OM4 had a molecular weight of 230,000; that of Achromobacter carboxydus amounted to 170,000. The molecular weights of the CO-oxidizing and H₂-oxidizing enzymes turned out to be identical. The cell sonicates were shown to catalyze the oxidation of both CO and H₂ with methylene blue, thionine, phenazine methosulfate, toluylene blue, dichlorophenolindophenol, cytochrome c or ferricyanide as electron acceptors. Methyl viologen, benzyl viologen, FAD⁺, FMN⁺, and NAD(P)⁺ were not reduced. The spectrum of electron acceptors was identical for all strains tested. Neither free formate, hydrogen nor oxygen gas were involved in the CO-oxidation reaction. Methylene blue was reduced by CO at a 1:1 molar ratio. The results indicate that CO-oxidation by carboxydobacteria is catalyzed by identical or similar enzymes and that the reaction obeys the equation CO+H₂OCO₂+2H⁺+2e^- as previously shown for Pseudomonas carboxydovorans.Dedicated to Otto Kandler remembering almost three decades of enjoyable cooperation     

Polyamines of carbon monoxide-utilizing bacteria, Pseudomonas thermocarboxydovorans and Pseudomonas carboxydohydrogena

A slightly thermophilic, CO-utilizing pseudomonad, Pseudomonas thermocarboxydovorans grown under both autotrophic and heterotrophic growth conditions was found to contain 2-hydroxyspermidine and 2-hydroxyputrescine in addition to putrescine, diaminopropane and spermidine. A mesophilic CO — utilzing hydrogen bacterium, Pseudomonas carboxydohydrogena contained putrescine and homospermidine under both autotrophic and heterotrophic growth conditions. Although these two carboxydobacteria are classified to the same genus Pseudomonas , the difference in their polyamine distribution patterns suggests that they may belong to different subclasses of Proteobacteria .     

Physical evidence for plasmids in autotrophic,especially hydrogen-oxidizing bacteria

Agarose gel electrophoresis of crude lysates from 23 species of autotrophic bacteria revealed plasmids of various sizes in 12 species. The plasmid pattern varied considerably. While the majority of the plasmid-bearing species harbored one or two plasmids, one species, Alcaligenes latus, exhibited more than six ccc-DNA bands. With one exception the molecular masses of the plasmids were 50×10⁶ or higher. In Achromobacter carboxydus, Alcaligenes latus, Derxia gummosa and three strains of Paracoccus denitrificans large plasmids of molecular masses higher than 300×10⁶ were resolved. The examination of Thiobacillus A2 resulted in the discovery of two plasmids while Pseudomonas oxalaticus was apparently free of resident plasmid DNA. So far these plasmids can only be characterized as cryptic. Future studies may allow to correlate them with specific metabolic activities of their hosts such as the ability to grow on carbon monoxide or thiosulfate, to fix molecular nitrogen and to form soluble NAD-reducing and/or membrane-bound hydrogenases.     

Induction of carbon monoxide dehydrogenase during heterotrophic growth of Acinetobacter sp. strain JC1 DSM 3803 in the presence of carbon monoxide

Abstract Experiments with crude cell extracts of Acinetobacter sp. JC1 revealed that CO dehydrogenase in this bacterium is inducible not only during chemoautotrophic growth with CO but also during heterotrophic growth in the presence of CO. The results indicate that Acinetobacter sp. JC1 can grow mixotrophically with organic material and CO.