Characterization of carotenoid production and antioxidant capacity in an Egyptian soil bacterium

Bacterial carotenoids are of significant industrial interest due to their bioactive properties. This study aimed to isolate carotenoid-producing bacteria from Egyptian agricultural land and screen key parameters to enhance their pigment yield. The most productive isolatesse were identified as Exiguobacterium acetylicum and Arthrobacter gandavensis. A one-variable-at-a-time approach revealed that maximum carotenoid production was highly strain-specific. Following cell disruption via mild acid hydrolysis, the optimal extraction solvents were pure acetone for A. gandavensis (4.74 mg L-1) and a 1:1 acetone:methanol mixture for E. acetylicum (5.87 mg L-1). While both strains achieved peak carotenoid production in nutrient broth at 48 hours and pH 6.0, their optimal growth temperatures diverged; A. gandavensis thrived at 35°C and E. acetylicum at 25°C. Liquid chromatography mass spectrometery analysis of A. gandavensis revealed a carotenoid profile containing zeaxanthin, decaprenoxanthin, bacterioruberin, and arthroxanthin. The extract exhibited mechanism-dependent antioxidant activity, most notably a robust peroxyl radical scavenging capacity (421.13 µM TE/mg in ORAC). These findings underscore the necessity of strain-specific screening to maximize the potential of bacterial sources for producing natural carotenoids with distinct antioxidant profiles.