Ecological succession among iron-oxidizing bacteria

Area of Science:

• Microbiology
• Environmental Science
• Ecology

Background:

• Factors controlling neutrophilic iron-oxidizing bacterial (FeOB) dominance are poorly understood despite extensive research.
• Ecological succession and niche differentiation are key concepts in microbial community dynamics.

Purpose of the Study:

• To investigate the ecological factors driving species dominance in freshwater wetland FeOB communities.
• To elucidate the niche separation between stalk-forming Gallionellales and sheath-forming Leptothrix ochracea.

Main Methods:

• Combined microscopy (light, scanning electron) with cultivation-independent molecular methods (FISH, SSU rRNA gene pyrosequencing).
• Quantified Fe-oxyhydroxide morphotypes and FeOB abundance.
• Analyzed physicochemical parameters of iron mats using redundancy analysis.

Main Results:

• Documented a clear ecological succession: Gallionellales dominated in early spring, transitioning to Leptothrix ochracea for the rest of the year.
• Species-specific FISH probes and SSU rRNA sequencing confirmed the Gallionellales to L. ochracea transition.
• Redundancy analysis revealed distinct environmental niches: Gallionellales favor low organic carbon and steep redoxclines; L. ochracea prefers high organic carbon, high Fe/Mn, and gentle redoxclines.

Conclusions:

• Ecological niches for stalk-forming Gallionellales and sheath-forming L. ochracea are defined by organic carbon levels and redoxcline steepness.
• A significant, previously underappreciated relationship exists between FeOB and organic carbon in aquatic ecosystems.