Coaggregation facilitates interspecies hydrogen transfer between Pelotomaculum thermopropionicum and...

Area of Science:

• Microbiology
• Biochemistry
• Environmental Science

Background:

• Syntrophic interactions are vital in microbial ecosystems, enabling the metabolism of complex substrates.
• Pelotomaculum thermopropionicum (SI) and Methanothermobacter thermautotrophicus (DeltaH) are key players in anaerobic digestion.
• Efficient interspecies hydrogen transfer is critical for the success of syntrophic consortia.

Purpose of the Study:

• To investigate the role of coaggregation in syntrophic propionate oxidation by Pelotomaculum thermopropionicum and Methanothermobacter thermautotrophicus.
• To determine the influence of different substrates on the coaggregation behavior of these two microorganisms.
• To quantify the physical proximity required for efficient interspecies hydrogen transfer.

Main Methods:

• Cultivation of Pelotomaculum thermopropionicum (SI) in monoculture and coculture with Methanothermobacter thermautotrophicus (DeltaH).
• Microscopic observation (including field emission-scanning electron microscopy) to assess cell aggregation and morphology.
• Application of Fick's diffusion law to calculate allowable distances for interspecies hydrogen transfer based on growth substrates.

Main Results:

• Coaggregation varied significantly with substrate: high aggregation on propionate, low aggregation on ethanol or 1-propanol.
• Flagellum-like filaments of SI cells were observed to mediate contact with DeltaH cells.
• Extracellular polymeric substance-like structures were present in intercellular spaces within aggregates.
• Calculated allowable distances for efficient hydrogen transfer were 2 µm (propionate), 16 µm (ethanol), and 32 µm (1-propanol).
• The mean cell-to-cell distance in dispersed cultures (approx. 30 µm) highlights the necessity of coaggregation for propionate oxidation.

Conclusions:

• Close physical contact through coaggregation is indispensable for efficient syntrophic propionate oxidation.
• The degree of coaggregation is substrate-dependent, influencing the efficiency of interspecies hydrogen transfer.
• Microbial cell arrangement and physical proximity are critical factors in the function of syntrophic consortia.