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Synonymous mutation of the N-terminal coding sequence (NCS) has been used to regulate gene expression. We here developed a statistical model to predict the effect of the NCSs on protein expression in Bacillus subtilis WB600. First, a synonymous mutation was performed within the first 10 residues of a superfolder green fluorescent protein to generate a library of 172 NCS synonymous mutants with different expression levels. A prediction model was then developed, which adopted G/C frequency at the third position of each codon and minimum free energy of mRNA as the independent variables, using multiple regression analysis between the 11 sequence parameters of the NCS and their fluorescence intensities. By designing the NCS of the 10 signal peptides de novo according to the model, the extracellular yield of B. subtilis pullulanase fused to each signal peptide was up-regulated by up to 515% or down-regulated by at most 79%. This work provided a candidate tool for fine-tuning gene expression or enzyme production in B. subtilis.

Blending high content of polyhydroxyalkanoates (PHAs ≥ 30 wt.%) with polylactide (PLA) provides an effective strategy to significantly improve heat resistance of PLA fibers. However, it has proven challenging to maintain good spinnability of the PLA/PHAs blends with the high content of PHAs. In this study, a series of poly(L‐lactide) (PLLA)/poly[(R)‐3‐hydroxybutyrate‐co‐4‐hydroxybutyrate] (P34HB) blend fibers with low P34HB content (≤ 8 wt.%) is successfully fabricated with excellent spinnability. The incorporation of P34HB contributes to a substantially improved heat resistance of the PLLA/P34HB blend fibers, as evidenced by a notable reduction in boiling water shrinkage from ca. 80% to 9%. This exceptionally improved heat resistance is closely related to substantial increase in crystallinity of PLLA in the blend fibers. Specifically, the addition of low P34HB content remarkably enhances chain mobility of PLLA chains, as such reduces crystallization half‐times (t1/2) and accelerates crystallization of PLLA. In fact, the amorphous P34HB phase favors crystal growth of PLLA phase rather than heterogeneous nucleation inferred previously. These results provide a facile and effective method to produce PLLA/P34HB blend fibers with enhanced heat resistance and sound spinnability.

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