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Abstract.

To enhance the economics of lignocellulosic biomass utilization, lignin has been extensively studied as a promising feedstock for biofuels and bioproducts. This study aimed at lignin bioupgrading by a strain of marine protists, Thraustochytrium striatum, to high-value nutraceuticals/pharmaceuticals. It was found that this strain was able to transform various types of lignin compounds into polyunsaturated long-chain fatty acids (EPA and DHA) and carotenoids (e.g., β-carotene and astaxanthin). In screening of 14 lignin model compounds as carbon sources, T. striatum can grow in most compounds at different concentrations, while achieving the best growth in 3, 4-dihydroxybenzoic acid (3, 4-DHBA) and 4-hydroxybenzoic acid (4-HBA). The maximum biomass yield reached 2-3 g/L under 5 g/L of 3, 4-DHBA or 2 g/L of 4-HBA even without optimization. In both batch and fed-batch cultivation modes, T. striatum can accumulate decent amount of long-chain fatty acids (15% cell dry weight) and carotenoids (0.1 mg/g biomass). T. striatum was also proven to utilize polymeric lignin. Significant cell mass growth was observed with Kraft pine lignin as sole carbon source, as well as accumulation of fatty acids and carotenoids. A preliminary investigation on lignin degradation mechanism indicated that T. striatum utilized 4-HBA as central intermediate. The monomer released from lignin depolymerization was firstly converted into 4-HBA and then catabolized by microorganisms. The capability of T. striatum to digest a wide range of lignin materials makes it a novel and attractive platform for lignin utilization and upgrading.