Oxygen-dependent autoaggregation in Shewanella oneidensis MR-1

Area of Science:

• Microbiology
• Bacterial Physiology
• Biochemistry

Background:

• Shewanella oneidensis MR-1 is a facultative anaerobe known for its diverse electron acceptors.
• Cellular aggregation can influence microbial physiology and environmental interactions.
• Oxidative stress is a significant challenge for aerobic microbial metabolism.

Purpose of the Study:

• To investigate the mechanisms and environmental triggers of Shewanella oneidensis MR-1 autoaggregation.
• To understand the role of aggregate formation in response to oxygen availability and oxidative stress.
• To identify genetic factors involved in MR-1 aggregation and their physiological implications.

Main Methods:

• Chemostat cultures under varying dissolved oxygen tensions.
• Calcium chloride supplementation to induce aggregation.
• Confocal microscopy for extracellular matrix analysis.
• Global transcriptome analysis (RNA sequencing).
• Genetic analysis of pilD mutants and associated pili biogenesis pathways.

Main Results:

• MR-1 rapidly aggregated in aerobic conditions (50% dissolved O2) with CaCl2, disaggregating under oxygen-limited growth.
• Extracellular DNA, protein, and glycoconjugates constitute the aggregate matrix.
• Transcriptome analysis revealed increased expression of adhesion factors, anaerobic electron transfer, and metal reduction genes (e.g., mtrDCFE) in aerobic aggregated cells.
• PilD, a putative prepilin peptidase, is crucial for MR-1 autoaggregation; pilD mutants showed increased sensitivity to H2O2.

Conclusions:

• Aggregate formation in S. oneidensis MR-1 is a dynamic, oxygen-dependent process regulated by calcium and PilD-mediated pathways.
• Aggregation may serve as a strategy to reduce oxidative stress by creating internal hypoxic microenvironments.
• The study links aggregation to enhanced anaerobic respiration and metal reduction capabilities, potentially impacting biogeochemical cycling.