Exploration of Carotenoid-Producing Microorganisms from the Kuril-Kamchatka Trench and Their Antioxidant Potential.

Despite its extreme conditions, the hadal environment harbors abundant but largely underexplored microbial resources. In this study, samples from the Kuril-Kamchatka Trench (KKT) were enriched at low temperature using R2A and 2216E media. Carotenoid-producing microorganisms (CPMs) were isolated from approximately one-third of the samples, yielding a total of 124 isolated strains spanning 4 phyla and 11 genera. Planococcus, Kocuria, Paracoccus, and Exiguobacterium collectively accounted for 75.8% of the isolates. The choice of culture medium significantly influenced CPM diversity at the family and genus levels, though not at the phylum or class level. Water depth, sample type, and sediment layer also significantly affected CPM community structure. Carotenoid spectral profiles correlated with phylogenetic lineage, and closer phylogenetic relationships corresponded to greater similarity in carotenoid biosynthesis gene clusters. Antioxidant assays (FRAP, ABTS, DPPH) demonstrated strong total antioxidant and radical scavenging capacities in carotenoid extracts from Citricoccus, Kocuria, Arthrobacter, and Olleya. Scavenging activity toward ABTS or DPPH radicals varied significantly among genera, suggesting genus-specific antioxidant mechanisms. These findings highlight the hadal zone as a promising reservoir of diverse CPMs and a valuable source of novel carotenoids and antioxidant-producing strains with potential biotechnological applications.