Type III polyketide synthase (PKS) found in bacteria is known as 1,3,6,8-tetrahydroxynaphthalene synthase (THNS). Microbial type III PKSs synthesize various compounds that possess crucial biological functions and significant pharmaceutical activities. Based on our sequence analysis, we have identified a putative type III polyketide synthase from
Nocardia
sp. CS682 was named as ThnA. The role of ThnA, in
Nocardia
sp. CS682 during the biosynthesis of 1,3,6,8 tetrahydroxynaphthalene (THN), which is the key intermediate of 1-(
α
-L-(2-
O
-methyl)-6-deoxymannopyranosyloxy)-3,6,8-trimethoxynaphthalene (IBR-3) was characterized. ThnA utilized five molecules of malonyl-CoA as a starter substrate to generate the polyketide 1,3,6,8-tetrahydroxynaphthalene, which could spontaneously be oxidized to the red flaviolin compound 2,5,7-trihydroxy-1,4-naphthoquinone. The amino acid sequence alignment of ThnA revealed similarities with a previously identified type III PKS and identified Cys
138
, Phe
188
, His
270
, and Asn
303
as four highly conserved active site amino acid residues, as found in other known polyketide synthases. In this study, we report the heterologous expression of the type III polyketide synthase
thnA
in
S. lividan
TK24 and the identification of THN production in a mutant strain. We also compared the transcription level of
thnA
in
S. lividan
TK24 and
S. lividan
pIBR25-
thnA
and found that
thnA
was only transcribed in the mutant.
Spinosad, a combination of spinosyn A and D produced by Saccharopolyspora spinosa, is a highly efficient pesticide. There has been a considerable interest in the improvement of spinosad production because of a low yield achieved by wild‐type S. spinosa. In this study, we designed and constructed a pIBR‐SPN vector. pIBR‐SPN is an integrative vector that can be used to introduce foreign genes into the chromosome of S. spinosa. Different combinations of genes encoding forasamine and rhamnose were synthesized and used for the construction of different recombinant plasmids. The following recombinant strains were developed: S. spinosa pIBR‐SPN (only the vector), S. spinosa pIBR‐SPN F (forosamine genes), S. spinosa pIBR‐SPN R (rhamnose genes), S. spinosa pIBR‐SPN FR (forosamine and rhamnose genes), S. spinosa pIBR‐SPN FRS (forosamine, rhamnose, and SAM [S‐adenosyl‐L‐methionine synthetase] genes), and S. spinosa MUV pIBR‐SPN FR. Among these recombinant strains, S. spinosa pIBR‐SPN FR produced 1394 ± 163 mg/L spinosad, which was 13‐fold higher than the wild‐type. S. spinosa MUV pIBR‐SPN FR produced 1897 (±129) mg/L spinosad, which was seven‐fold higher than S. spinosa MUV and 17‐fold higher than the wild‐type strain.
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