Abstract
To research the potential ability of marine-derived actinomycetes to act as biocatalysts, 8 Micromonospora strains and 5 Streptomyces strains were screened. Two recommended media (227 and 1076 media) and 2 modified media (1076-25% and P-1076-25% media) for liquid culture of these marine-derived actinomycetes were tested. As a result, 2 Micromonospora strains (Micromonospora sp. NBRC107096 and 107097) cultured with the 1076-25% medium and 2 Streptomyces strains (Streptomyces tateyamensis NBRC105048 and Streptomyces sp. NBRC105896) cultured with P-1076-25% medium showed a good growth. The stereoselective reduction of α-keto esters using these 4 actinomycetes was tested. As a result, it was found that these strains had a reducing activity toward various α-keto esters. The introduction of L-glutamate or sucrose as an additive remarkably increased the conversion ratios in the reduction of substrates by the Micromonospora strain. Furthermore, in the presence of L-alanine, Streptomyces tateyamensis NBRC105048 reduced ethyl pyruvate, ethyl 2-oxobutanoate, ethyl 2-oxopentanoate, ethyl 2-oxohexanoate, and ethyl 3-methyl-2-oxobutyrate to the corresponding α-hydroxy ester with a high conversion ratio and with excellent enantiomeric excess. Thus, we found that these marine-derived actinomycetes have great potential to be used as biocatalysts for stereoselective reduction of carbonyl compounds.
Highlights
Actinobacteria comprise one of the largest taxonomic units among the 18 major lineages currently recognized within the domain Bacteria, which consists of 5 subclasses and 14 suborders [1,2]
Actinomycetes have a capacity for biotransformation; they are used as biocatalysts for the preparation of chiral alcohols from carbonyl compounds [11,12,13,14]
This study describes the stereoselective reduction of α-keto esters by marine-derived Micromonospora and Streptomyces strains as novel biocatalysts (Figure 1)
Summary
Actinobacteria comprise one of the largest taxonomic units among the 18 major lineages currently recognized within the domain Bacteria, which consists of 5 subclasses and 14 suborders [1,2]. Among the 5 subclasses, Actinobacteria (commonly called actinomycetes) are widely distributed in soil and are well known to produce secondary metabolites [3,4,5,6], notably antibiotics [7], antitumor agents [8], immunosuppressive agents [9] and industrially important enzymes [10]. It was found that strains of Salinispora—marine actinomycetes—produce useful bioactive compounds such as arenimycin and salinosporamide A [21,22]. It has been reported that Salinispora strains reduce toward α-keto esters and their derivatives stereoselectively [23]. The potential biocatalyst activity of other marine-derived actinomycetes has not been investigated. This study describes the stereoselective reduction of α-keto esters by marine-derived Micromonospora and Streptomyces strains as novel biocatalysts (Figure 1)
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