Combination of atmospheric and room temperature plasma (ARTP) mutagenesis, genome shuffling and dimethyl sulfoxide (DMSO) feeding to improve FK506 production in Streptomyces tsukubaensis.

FK506 is a clinically important macrocyclic polyketide with immunosuppressive activity produced by Streptomyces tsukubaensis. However, the production capacity of the strain is very low. To improve production, atmospheric and room temperature plasma (ARTP) mutagenesis was adopted to get the initial strains used in genome shuffling (GS). After three rounds of GS, S. tsukubaensis R3-C4 was the most productive strain, resulting in a FK506 concentration of 335 µg/mL, 2.6 times than that of the original wild-type strain. Moreover, exogenous DMSO 4% (v/v) addition could induce efflux of FK506 and increased FK506 production by 27.9% to 429 µg/mL. Finally, analyses of the differences in morphology, fermentation characteristics and specific gene expression levels between S. tsukubaensis R3-C4 and the wild-type strain revealed that R3-C4 strain: has hampered spore differentiation, thicker mycelia and more red pigment, which are likely related to the downregulation of bldD and cdgB expression. In addition, the expression levels of fkbO, fkbP, dahp, pccB and prpE all showed up-regulation at diverse degrees compared to the wild-type S. tsukubaensis. Overall, these results show that a combined approach involving classical random mutation and exogenous feeding can be applied to increase FK506 biosynthesis and may be applied also to the improvement of other important secondary metabolites.

The complete mitochondrial genome of Hyla annectans (Anura: Hylidae).

The complete mitochondrial genome sequence of the Hyla annectans (Anura: Hylidae) was determined in this study. It is a circular molecule of 17,973 bp in length including 37 genes for 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs and a control region, showing a typical neobatrachian-type arrangement. The A + T content of H-strand and the control region is 60.7% and 64.6%, respectively. The control region is 2554 bp in length and possesses distinct repeat regions at both 5' and 3' ends.