Response to substrate limitation by a marine sulfate-reducing bacterium

Area of Science:

• Microbiology
• Environmental Science
• Biochemistry

Background:

• Sulfate-reducing microorganisms (SRM) inhabit energy-limited subsurface sediments.
• Adaptation strategies of SRM to substrate limitation are poorly understood.

Purpose of the Study:

• To investigate how Desulfobacterium autotrophicum adapts to lactate or sulfate limitation.
• To elucidate the metabolic and genetic responses of D. autotrophicum under substrate-limited conditions.

Main Methods:

• Controlled chemostat cultivation of Desulfobacterium autotrophicum.
• Transcriptomic analysis to examine gene expression.
• Determination of half-saturation uptake constants (K_m) for lactate and sulfate.

Main Results:

• First reported K_m values for lactate (1.2 µM) and sulfate (3 µM) in marine SRM.
• Lactate limitation led to complete lactate oxidation and amino acid metabolism gene upregulation.
• Sulfate limitation induced incomplete lactate oxidation and metabolic rerouting, under thermodynamic control.
• Upregulation of sulfate transporters with varying affinities was observed.

Conclusions:

• Desulfobacterium autotrophicum exhibits distinct metabolic adaptations to lactate versus sulfate limitation.
• Thermodynamic principles govern metabolic shifts in response to energy availability.
• SRM play a crucial role in controlling in situ substrate concentrations, such as lactate.