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Background The bifunctional enzyme β-carotene hydroxylase (CrtZ) catalyzes the hydroxylation of carotenoid β-ionone rings at the 3, 3’ position regardless of the presence of keto group at 4, 4’ position, which is an important step in the synthesis of astaxanthin. The level and substrate preference of CrtZ may have great effect on the amount of astaxanthin and the accumulation of intermediates. Results In this study, the substrate preference of PC crtZ  from  Paracoccus  sp. PC1 and PA crtZ  from  Pantoea Agglomerans  were certified and were combined utilization for increase astaxanthin production. Firstly, PC crtZ  from  Paracoccus  sp. PC1 and PA crtZ  from  P. Agglomerans  were expressed in platform strains CAR032 (β-carotene producing strain) and Can004 (canthaxanthin producing strain) separately to identify their substrate preference for carotenoids with keto groups at 4,4’ position or not. The results showed that PC crtZ  led to a lower zeaxanthin yield in CAR032 compared to that of PA crtZ . On the contrary, higher astaxanthin production was obtained in Can004 by  PCcrtZ  than that of PA crtZ . This demonstrated that PCCrtZ has higher canthaxanthin to astaxanthin conversion ability than PACrtZ, while PACrtZ prefer using β-carotene as substrate. Finally, Ast010, which has two copies of PA crtZ  and one copy of PC crtZ  produced 1.82 g/L of astaxanthin after 70 h of fed-batch fermentation. Conclusions Combined utilization of  crtZ  genes, which have β-carotene and canthaxanthin substrate preference respectively, can greatly enhance the production of astaxanthin and increase the ratio of astaxanthin among total carotenoids.

Improving astaxanthin production in Escherichia coli by co-utilizing CrtZ enzymes with different substrate preference