Biology subjects

Aiyer, K.

Publications and source records attributed to Aiyer, K..

4 recordsLinked to original sources

bioRxiv2026

Artificial sediments enable reproducible cultivation and recapitulate ecological interactions of cable bacteria

Cable bacteria are filamentous microbes that couple sulfide oxidation to oxygen reduction over centimeter distances via long-distance electron transport. While their activity creates characteristic biogeochemical gradients that shape sediment ecology, the study of cable bacteria has been constrained by the chemical and physical heterogeneity of the natural sediments they inhabit. To date, laboratory cultivation efforts have relied on these undefined environmental matrices. Here, we established a reproducible enrichment and cultivation platform using an artificial sediment matrix coupled with chemically defined media. This matrix successfully supported the growth of both freshwater and marine cable bacteria and enabled serial propagation over multiple transfers. Microsensor profiling confirmed that the incubations recapitulated hallmark geochemical signatures, including the sulfide, oxygen and pH gradients associated with electrogenic sulfur oxidation. Scanning electron microscopy confirmed the presence of cable bacteria, while 16S rRNA sequencing confirmed enrichment of the cable bacteria together with a stable co-enriched community that included taxa associated with sulfur and iron cycling as well as cellulose decomposition. This defined cultivation system eliminates the variability inherent to natural samples, providing a controlled platform for dissecting the physiology, genetics, and microbial interactions of cable bacteria.

microbiology↗

bioRxiv2025

Extracellular electron transfer in cable bacteria enables growth rates comparable to aerobic respiration

Cable bacteria are filamentous sulphide-oxidisers performing long-distance electron transfer in redox-stratified sediments by transporting electrons over centimetre-scale distances to reduce oxygen. Here, we show that the freshwater cable bacterium Electronema aureum GS can respire insoluble electron acceptors under anoxic conditions via a versatile extracellular electron transfer (EET) system, supporting growth rates comparable to those under aerobic conditions. Using electrochemical and molecular biology analyses, we demonstrate that E. aureum GS engages in both direct and mediated electron transfer to electrodes, including at +600 mV vs. Ag/AgCl--an unusually high redox potential typically not accessed by electroactive bacteria. Two distinct cell-surface redox components were identified, which are metal-dependent, pH-sensitive, and heat-labile, consistent with outer-membrane-localised cytochromes. Moreover, the redox shuttle riboflavin accumulated extracellularly and enhanced current production in bioelectrochemical systems, indicating a role for soluble mediators in cable bacteria. Together, these findings reveal a previously unrecognised respiratory flexibility in E. aureum GS and highlight EET as a key alternative strategy for energy conservation in fluctuating redox environments.

microbiology↗

bioRxiv2024

A flavin-based extracellular electron transfer strategy in a novel gram-positive microbe Microbacterium deferre sp. nov. strain A1-JK, isolated from cable bacteria enrichments

Microbacterium deferre sp. nov. A1-JK is a metabolically versatile Gram-positive bacterium isolated from the oxic-anoxic interface of freshwater sediment, inhabited by cable bacteria. M. deferre A1-JK could simultaneously reduce oxygen and Fe(III), challenging the traditional view of microbial Fe(III)-reduction as a strictly anaerobic process. Electrochemical studies revealed extracellular electron transfer (EET) metabolism facilitated by soluble flavin shuttles, identified via HPLC. Genomic analyses uncovered EET pathways involving cytochrome FccA and flavin reductase FmnA. Its metabolic versatility also allowed for weak electroactivity in alkaline (pH 9-10) and saline conditions (0-4% NaCl). The ability to reduce Fe(III), in the presence of atmospheric oxygen highlights its adaptability to dynamic sediment environments with fluctuating oxygen and Fe(III) gradients. These findings underscore the metabolic versatility of M. deferre A1-JK at oxic-anoxic interfaces, providing insights into the coexistence of aerobic and anaerobic processes in a single cell. ImportanceMicrobacterium deferre A1-JK is a newly discovered gram-positive bacterium that employs flavin-mediated extracellular electron transfer to respire minerals and electrodes. Associated with cable bacteria in freshwater sediments, M. deferre A1-JK was able to simultaneously reduce oxygen and Fe(III). This makes it highly adaptable to changing environments, such as those found in (cable-bacteria-containing) sediments with fluctuating oxygen and Fe concentrations. The metabolic versatility of M. deferre A1-JK offers opportunities to fundamentally revise our understanding of microbial metabolism and nutrient cycling models that strictly separate aerobic and anaerobic metabolisms.

microbiology↗

bioRxiv2023

Electrically controlled interaction between cable bacteria and carbon electrodes

Cable bacteria couple the oxidation of sulphide in sediments to the reduction of oxygen via long-distance electron transfer through periplasmic wires. While direct electron transfer between cable bacteria cells belonging to the same filament is a well-known phenomenon, electron transfer from the filament to electrodes has remained elusive. In this study, we demonstrate that living cable bacteria are attracted to electrodes in different bioelectrochemical systems. Carbon felt and carbon fibre electrodes poised at +200 mV against an Ag/AgCl reference attracted live cable bacteria from the sediment. When the applied potential was switched off, cable bacteria retracted from the electrode. qPCR and scanning electron microscopy corroborated this finding and revealed cable bacteria adhered onto the electrode surface. These experiments raise new possibilities to cultivate cable bacteria and utilise them for important applications in bioelectrochemical systems.

microbiology↗