Singlet oxygen antioxidant capacity of carotenoids from Halorubrum salinarum.

Halorubrum salinarum RHB-CT, an archaeon known for its extreme halophilic, neutrophilic, and mesophilic characteristics, was studied for its carotenoids' potential as singlet oxygen antioxidants. This resilient organism thrives optimally at pH 7, 45°C temperature, and 25%-30% salinity. Optimization revealed that pH 7, 30°C temperature, and 25% salinity enhanced carotenoid production, likely due to oxidative stress and slower growth at lower temperatures, which in turn stimulate secondary metabolism. Carotenoids identified were haloxanthin (38%), bacterioruberin (BRB) (20%), monoanhydro-bacterioruberin (MABR) (20%), and one unidentified compound (23%). A 40 µM crude extract showed the highest singlet oxygen antioxidant activity at 19.68%, comparable to butylated hydroxyanisole and butylated hydroxytoluene.