Insight into a single halobacterium using a dual-bacteriorhodopsin system with different functionally optimized pH...

Area of Science:

• Microbiology
• Biochemistry
• Extremophile Biology

Background:

• Bacteriorhodopsin (BR) is a light-driven proton transporter crucial for energy production via ATP synthase.
• Halobacterium salinarum uses a single BR (HsBR), while Haloarcula marismortui exhibits a unique dual-BR system (HmBRI and HmBRII).
• The Dead Sea's resource-limited and acidic environment poses survival challenges for archaea.

Purpose of the Study:

• To investigate the contribution of Haloarcula marismortui's dual-BR system to its survival in extreme conditions.
• To compare the proton transport functionality of H. marismortui's dual-BR system with H. salinarum's solo-BR system under simulated Dead Sea conditions.

Main Methods:

• Testing native H. marismortui and H. salinarum cell functionality in simulated Dead Sea water.
• Measuring proton accumulation and periplasmic pH changes in both archaea.
• Conducting pH-dependent photocurrent measurements on purified HsBR, HmBRI, and HmBRII proteins.

Main Results:

• H. marismortui maintained proton transport functionality in simulated Dead Sea water, unlike H. salinarum.
• HsBR and HmBRI function optimally at pH > 5.0, while HmBRII functions optimally at pH > 4.0.
• The dual-HmBR system collectively maintains proton transport activity at pH > 4.0.

Conclusions:

• The dual-BR system in H. marismortui, with distinct pH optima, is essential for maintaining proton transport.
• This functional adaptability likely contributes to H. marismortui's survival in the acidic Dead Sea environment.
• The dual-BR system represents a key adaptation for extremophile survival.