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

Abstract

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.