The main activities carried out in the project were:
1. Cultivation and Characterization of Cable Bacteria in Synthetic Sediments
A major technical achievement was the successful cultivation of cable bacteria in defined synthetic sediments. Previously, growth relied on natural sediments, which introduced variability. Two reproducible sediment formulations were developed:
a sand–kaolinite–alpha cellulose mix, and
a pure alpha cellulose matrix.
Inoculation with Electronema aureum GS showed that the sand-based system reproduced the key biogeochemical fingerprints of cable bacteria, including sulfide oxidation and pH gradients. Microsensor profiling confirmed long-distance electron transport (LDET), the hallmark of cable bacteria activity.
Key achievements:
Long-term enrichment and subculturing of cable bacteria under controlled conditions.
Standardized synthetic medium eliminating inconsistencies from natural sediments.
Microsensor profiles (O2, sulfide, pH) matching natural sediment activity.
Microscopy and SEM confirmed multicellular filaments and conductive periplasmic fibers.
16S rRNA sequencing revealed co-existing sulfate-reducers and iron-reducers supporting cable bacteria metabolism.
This cultivation system provides a reliable experimental platform for future functional and genetic studies.
2. Mechanisms of Extracellular Electron Transfer (EET) in Cable Bacteria
Another major advance was the demonstration of cable bacteria interaction with electrodes in bioelectrochemical systems. Experiments under anoxic conditions revealed that cable bacteria are naturally attracted to electrodes poised at +0.25 V, producing significantly higher currents compared to controls.
Key findings:
Current generation in the presence of cable bacteria at +0.25 V.
Differential pulse voltammetry identified redox peaks (+0.25 V and +0.60 V) consistent with protein-mediated EET.
Elevated riboflavin concentrations suggested a role for flavins in electron transfer.
Redox activity was abolished by proteinase K treatment and heat, pointing to the involvement of extracytoplasmic redox proteins.
This provides the first evidence that cable bacteria possess protein-based extracellular electron transfer mechanisms, opening avenues for their use in microbial electrogenesis and bioelectronics.
3. Discovery of Simultaneous Aerobic and Anaerobic Respiration in Microbacterium, a bacerium in the vicinity of cable bacteria
The fellowship also led to the discovery of a previously unrecognized metabolic capacity in Microbacterium deferre sp. nov. A1-JK. Unlike the long-held dogma that bacteria switch between aerobic and anaerobic lifestyles, this strain was shown to perform both aerobic respiration and anaerobic iron reduction simultaneously.
This overturns a central paradigm in microbiology and provides new insights into microbial evolution and ecology. Beyond basic science, this capacity could be exploited for bioremediation, enabling pollutant degradation in fluctuating oxygen environments where conventional strategies fail.
Environmental and Biotechnological Implications
Together, these results contribute to three major fields:
Microbial ecology – reproducible cultivation and characterization of cable bacteria under laboratory conditions.
Electromicrobiology – identification of redox proteins and flavins mediating extracellular electron transfer.
Environmental biotechnology – discoveries with direct implications for pollutant remediation, methane mitigation, and the development of biohybrid devices that integrate microbial electron transfer with electrodes.
These achievements establish a scientific foundation for bioelectrochemical applications, from sustainable sensors to environmental cleanup, while opening a new frontier in understanding microbial metabolism.
