초록
<P>The natural pigment astaxanthin is widely used in aquaculture, pharmaceutical, nutraceutical, and cosmetic industries due to superior antioxidant properties. The green alga <I>Haematococcus pluvialis</I> is currently used for commercial production of astaxanthin pigment. However, slow growing <I>H. pluvialis</I> requires a complex two-stage stress-induced process with high light intensity leading to increased contamination risks. In contrast, the fast-growing euryhaline cyanobacterium <I>Synechococcus</I> sp. PCC 7002 (<I>Synechococcus</I> 7002) is able to reach high density under stress-free phototrophic conditions, and is therefore a promising metabolic engineering platform for astaxanthin production. In the present study, genes encoding β-carotene hydroxylase and β-carotene ketolase, from the marine bacterium <I>Brevundimonas</I> sp. SD212, are integrated into the endogenous plasmid of <I>Synechococcus</I> 7002, and then expressed to biosynthesize astaxanthin. Although <I>Synechococcus</I> 7002 does not inherently produce astaxanthin, the recombinant ZW strain yields 3 mg/g dry cell weight astaxanthin from CO<SUB>2</SUB> as the sole carbon source, with significantly higher astaxanthin content than previous cyanobacteria reports. <I>Synechococcus</I> 7002 astaxanthin productivity reached 3.35 mg/L/day after just 2 days in a continuous autotrophic process, which is comparable to the best <I>H. pluvialis</I> astaxanthin productivities when factoring in growth times. Metabolomics analysis reveals increases in fractions of hexose-, pentose-, and triose phosphates along with intermediates involved in the nonmevalonate pathway. Dynamic metabolomics analysis of <SUP>13</SUP>C labeled metabolites clearly indicates flux enhancements in the Calvin cycle and glycolysis resulting from the overexpression of astaxanthin biosynthetic genes. This study suggests that cyanobacteria may enhance central metabolism as well as the nonmevalonate pathway in an attempt to replenish depleted pigments such as β-carotene and zeaxanthin.</P><BR>[FIG OMISSION]</BR>