5 CONCLUSION
In summary, it is not desirable to disrupt the synthesis of amino acids
or nucleotides in order to construct a heterologous metabolic pathway in
metabolic engineering. Currently, the optimized CRISPR-Cas9 gene editing
tool may provide an alternative solution to achieve the recovery and
reuse of screening markers [16]. Meanwhile,
numerous
neutral
loci in S. cerevisiae have been characterized for multiple gene
integration [30]. The recovery of auxotrophic
markers to generate the prototrophic strain is supposed to be essential
to maximize bio-productions during the fermentation, and
alleviate
the interference of internal environment for the engineered strains.