Aerobic carboxydobacteria.

Area of Science:

• Microbiology
• Environmental Science
• Biochemistry

Background:

• Bacterial consumption of atmospheric carbon monoxide (CO), a pollutant, has been documented but with inconsistent findings.
• Understanding the ecology of aerobic CO-oxidizing bacteria is crucial for environmental remediation and microbial metabolism studies.

Purpose of the Study:

• To isolate and characterize a broader spectrum of aerobic CO-utilizing bacteria.
• To elucidate the ecological roles and metabolic pathways of these bacteria, identified as carboxydobacteria.

Main Methods:

• Enrichment cultures from diverse environmental samples (soil, mud, water) under an atmosphere of 80% CO and 20% O2.
• Isolation and detailed characterization of seven carboxydobacteria strains.
• Spectroscopic analysis (cytochromes), isotope tracing (14C assimilation), and growth studies on various substrates (CO, H2, organic compounds).

Main Results:

• Isolation of multiple aerobic CO-utilizing bacterial strains, primarily from polluted, moist soil and mud.
• Six of seven characterized carboxydobacteria strains also utilized hydrogen; none utilized methane or formate.
• CO assimilation occurred via oxidation to CO2, utilizing the Calvin cycle, with evidence of functional electron transport chains (cytochromes b, c, a).
• Carboxydobacteria exhibited organotrophic growth on diverse organic compounds and were found in the neuston layer.

Conclusions:

• Carboxydobacteria are ecologically significant in environments where facultative anaerobes produce CO and H2.
• These bacteria possess functional electron transport chains for CO oxidation and utilize the Calvin cycle for carbon assimilation.
• The study provides a comprehensive description of carboxydobacteria, their metabolic capabilities, and ecological distribution.