Extracellular electron transfer genes expressed by candidate flocking bacteria in cable bacteria sediment

Area of Science:

• Microbial Ecology
• Geomicrobiology
• Biogeochemistry

Background:

• Cable bacteria are filamentous, sulfide-oxidizing microbes found in sediments.
• They interact with other bacteria, forming 'flocks' that may facilitate extracellular electron transfer.
• The identity and function of these flocking bacteria in freshwater sediments were previously uninvestigated.

Purpose of the Study:

• To identify the bacteria flocking around cable bacteria in freshwater sediments.
• To elucidate their extracellular electron transfer capabilities and metabolic functions.
• To understand their role in sediment biogeochemical cycling.

Main Methods:

• Coupling metagenomics and metatranscriptomics with 16S rRNA amplicon sequencing over 155 days.
• Identifying candidate flocking bacteria based on motility and extracellular electron transfer genes (phenazines, flavins).
• Analyzing microbial community structure, gene expression, and metabolic pathways.

Main Results:

• Identified 22 MAGs (21.4% of total) as candidate flocking bacteria.
• 42.1% of candidate flockers expressed extracellular electron transfer genes.
• Flocking bacteria represent diverse, metabolically versatile groups across nine phyla.
• These bacteria are involved in sulfur, carbon, and iron cycling in anoxic sediment layers.

Conclusions:

• Cable bacteria in freshwater sediments engage in electric relationships with diverse exoelectrogenic microbes.
• These interactions enable indirect oxygen utilization in deeper anoxic sediment layers.
• This expands the understanding of microbial metabolism and biogeochemical cycling in sediments.