Sulfate-reducing bacterium with unusual morphology and pigment content

Area of Science:

• Microbiology
• Environmental Science
• Biochemistry

Background:

• Dissimilatory sulfate-reducing bacteria (SRB) are crucial in biogeochemical sulfur cycling.
• Previous research has characterized various SRB species, but novel strains with distinct properties continue to be discovered.

Purpose of the Study:

• To isolate and characterize a novel dissimilatory sulfate-reducing bacterium.
• To investigate its unique morphological, physiological, and biochemical characteristics.

Main Methods:

• Isolation and cultivation of the bacterium under anaerobic conditions.
• Microscopic examination for morphology and flagellation.
• Spectroscopic analysis for pigment identification (fluorescence, c-type cytochrome, CO-binding pigment).
• Growth studies with various substrates and electron acceptors.
• DNA buoyant density and guanine-plus-cytosine (GC) content determination.

Main Results:

• A mesophilic, obligately anaerobic, gram-negative, nonsporulating bacterium with a single polar flagellum was isolated.
• Whole cells exhibited red fluorescence at neutral pH due to a pink pigment; Desulfoviridin was present.
• Spectra indicated the presence of c-type cytochrome and unique peaks at 629 and 603 nm, along with a CO-binding pigment at 593 nm.
• Growth was supported by lactate and pyruvate with sulfate as the electron acceptor; sulfate, sulfite, and thiosulfate served as acceptors.
• DNA buoyant density was 1.722 g/cm³, with a GC content of 61.2-63.2%.

Conclusions:

• The isolated bacterium represents a novel species of dissimilatory sulfate-reducing bacteria with distinct phenotypic and genotypic features.
• Its unique pigment and spectral characteristics warrant further investigation into its biochemical pathways and ecological role.
• The high GC content suggests a unique evolutionary lineage within sulfate-reducing bacteria.