Two-Stage Continuous Conversion of Carbon Monoxide to Ethylene by Whole Cells of Azotobacter vinelandii

ABSTRACT Azotobacter vinelandii is an obligate aerobic diazotroph with a verified transient ability to reduce carbon monoxide to ethylene by its vanadium nitrogenase. In this study, we implemented an industrially relevant continuous two-stage stirred-tank system for in vivo biotransformation of a controlled supply of air enriched with 5% carbon monoxide to 302 μg ethylene g−1 glucose consumed. To attain this value, the process required overcoming critical oxygen limitations during cell proliferation while simultaneously avoiding the A. vinelandii respiratory protection mechanism that negatively impacts in vivo nitrogenase activity. Additionally, process conditions allowed the demonstration of carbon monoxide’s solubility as a reaction-limiting factor and a competitor with dinitrogen for the vanadium nitrogenase active site, implying that excess intracellular carbon monoxide could lead to a cessation of cell proliferation and ethylene formation as shown genetically using a new strain of A. vinelandii deficient in carbon monoxide dehydrogenase. IMPORTANCE Ethylene is an essential commodity feedstock used for the generation of a variety of consumer products, but its generation demands energy-intensive processes and is dependent on nonrenewable substrates. This work describes a continuous biological method for investigating the nitrogenase-mediated carbon monoxide reductive coupling involved in ethylene production using whole cells of Azotobacter vinelandii. If eventually adopted by industry, this technology has the potential to significantly reduce the total energy input required and the ethylene recovery costs, as well as decreasing greenhouse gas emissions associated with current production strategies.

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A Novel Carbon Monoxide-Releasing Molecule Fully Protects Mice from Severe Malaria

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.05571-11 ◽

2011 ◽

Vol 56 (3) ◽

pp. 1281-1290 ◽

Cited By ~ 65

Author(s):

Ana C. Pena ◽

Nuno Penacho ◽

Liliana Mancio-Silva ◽

Rita Neres ◽

João D. Seixas ◽

...

Keyword(s):

Carbon Monoxide ◽

Severe Malaria ◽

Adjuvant Treatment ◽

Malaria Infection ◽

Severe Disease ◽

Inhalation Therapy ◽

Heme Oxygenase 1 ◽

Primary Therapy ◽

Content Type

ABSTRACTSevere forms of malaria infection, such as cerebral malaria (CM) and acute lung injury (ALI), are mainly caused by the apicomplexan parasitePlasmodium falciparum. Primary therapy with quinine or artemisinin derivatives is generally effective in controllingP. falciparumparasitemia, but mortality from CM and other forms of severe malaria remains unacceptably high. Herein, we report the design and synthesis of a novel carbon monoxide-releasing molecule (CO-RM; ALF492) that fully protects mice against experimental CM (ECM) and ALI. ALF492 enables controlled CO deliveryin vivowithout affecting oxygen transport by hemoglobin, the major limitation in CO inhalation therapy. The protective effect is CO dependent and induces the expression of heme oxygenase-1, which contributes to the observed protection. Importantly, when used in combination with the antimalarial drug artesunate, ALF492 is an effective adjunctive and adjuvant treatment for ECM, conferring protection after the onset of severe disease. This study paves the way for the potential use of CO-RMs, such as ALF492, as adjunctive/adjuvant treatment in severe forms of malaria infection.

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Enantioselective Dechlorination of Polychlorinated Biphenyls inDehalococcoides mccartyiCG1

Applied and Environmental Microbiology ◽

10.1128/aem.01300-18 ◽

2018 ◽

Vol 84 (21) ◽

Cited By ~ 10

Author(s):

Ling Yu ◽

Qihong Lu ◽

Lan Qiu ◽

Guofang Xu ◽

Yanhong Zeng ◽

...

Keyword(s):

Polychlorinated Biphenyls ◽

Critical Role ◽

Enrichment Factors ◽

Reductive Dehalogenation ◽

Content Type ◽

Whole Cells ◽

Dehalococcoides Mccartyi ◽

Cell Extracts

ABSTRACTReductive dehalogenation mediated by organohalide-respiring bacteria plays a critical role in the global cycling of organohalides. Nonetheless, information on the dehalogenation enantioselectivity of organohalide-respiring bacteria remains limited. In this study, we report the enantioselective dechlorination of chiral polychlorinated biphenyls (PCBs) byDehalococcoides mccartyiCG1. CG1 preferentially removed halogens from the (−)-enantiomers of the three major environmentally relevant chiral PCBs (PCB174, PCB149, and PCB132), and the enantiomer compositions of the dechlorination products depended on their parent organohalides. Thein vitroassays with crude cell extracts or concentrated whole cells and thein vivoexperiments with living cells showed similar enantioselectivities, in contrast with the distinct enantiomeric enrichment factors (εER) of the substrate chiral PCBs. Additionally, these results suggest that concentrated whole cells might be an alternative to crude cell extracts inin vitrotests of reductive dehalogenation activities. The enantioselective dechlorination of other chiral PCBs that we resolved via gas chromatography further confirmed the preference of CG1 for the (−)-enantiomers.IMPORTANCEA variety of agrochemicals and pharmaceuticals are chiral. Due to the enantioselectivity in biological processes, enantiomers of chiral compounds may have different environmental occurrences, fates, and ecotoxicologies. Many chiral organohalides exist in anaerobic or anoxic soils and sediments, and organohalide-respiring bacteria play a major role in the environmental attenuation and global cycling of these chiral organohalides. Therefore, it is important to investigate the dehalogenation enantioselectivity of organohalide-respiring bacteria. This study reports the discovery of enantioselective dechlorination of chiral PCBs byDehalococcoides mccartyiCG1, which provides insights into the dehalogenation enantioselectivity ofDehalococcoidesand may shed light on future PCB bioremediation efforts to prevent enantioselective biological side effects.

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