Breeding and fermentation medium optimization of Kluyveromyces marxianus with high-yield ribonucleic acid

Ribonucleic acid (RNA) is an important building block of living organisms and widely used in the food and pharmaceutical industries. In this study, recombinant strains TY20-HXT14 and TY20-HXT15 were constructed using lactose-capable Kluyveromyces marxianus TY-20 as the parent strain, and hexose transporter coding genes HXT14 and HXT15 were overexpressed by homologous recombination technology, in order to improve the lactose utilization and RNA content of the strain. On this basis, using the intracellular RNA content as evaluation index, the medium composition of the recombinant strain TY20-HXT14 was optimized by single factor tests and response surface tests. The results showed that the recombinant strain TY20-HXT14 had optimal growth performance and the highest intracellular RNA content. When cultured in lactose medium to the logarithmic stage (OD_{600 nm}=1.000), the intracellular RNA content of TY20-HXT14 was 14.48% higher than that of the parental strain TY-20. The optimal medium composition for RNA production of the recombinant strain TY20-HXT14 was lactose addition 14.8%, yeast extract powder addition 1.04%, KH₂PO₄ addition 0.31% and MgSO₄ addition 0.2%. Under the optimal medium composition, the intracellular RNA content of the recombinant strain TY20- HXT14 reached 18.04%, which was 26.77% higher than that before optimization (14.23%).