Extremophilic bacteriorhodopsin from hypersaline salt pan: characterization and photoelectrochemical assessment for...

Salt pans host a diverse microbiome, including specialized extremophilic haloarchaea capable of producing industrially valuable biomolecules, yet remains underexplored extreme environment. Photosensitive bacteriorhodopsin (BR) is a naturally occurring seven helix trans-membrane protein with emerging relevance due to its light driven proton pumping activity, photochemical stability and efficient light to electrical energy conversion.

In this study, BR was extracted from haloarchaeal strains isolated from the Tuticorin salt pan using the Bead mix method and confirmed by SDS-PAGE. The extracted BR was further characterized using thin-layer chromatography (TLC), reverse-phase high performance liquid chromatography (R-HPLC), and Raman spectroscopy. The Purified BR was evaluated for its photovoltage response and a prototype biosensor was successfully developed.

Haloarchaeal isolate Halostagnicola larsenii (TP6) demonstrated a remarkable production yield of 360 mg/L of BR under native minimal saline medium conditions, the notably highest recorded for this native strain to date. This isolate was used for further optimization of BR production involving different carbon and nitrogen sources. Two different protein extraction methods were evaluated, of which the bead mix method proved to be effective, yielding around 48.4 mg/L of BR with 72.7% yield. We examined the morphological and physiological traits of these isolates and confirmed the presence of a 26 kDa protein using SDS-PAGE.

The isolated extremophilic haloarchaea have the potential to produce large amount of BR, and the characteristics were similar to those previously reported BR from native strains. The observed photoresponsive ability highlights the potential of BR as a bio-based functional component for food bio-sensing, optical devices, and photoelectrochemical biosensors. Overall, this highlights the feasibility of naturally occurring BR from haloarchaea as a sustainable source of photoactive biomolecules for emerging food biotechnology and sustainable biosensor development.