초록
<P><B>Background</B></P><P>Mannosylglycerate (MG) is one of the most widespread compatible solutes among marine microorganisms adapted to hot environments. This ionic solute holds excellent ability to protect proteins against thermal denaturation, hence a large number of biotechnological and clinical applications have been put forward. However, the current prohibitive production costs impose severe constraints towards large-scale applications. All known microbial producers synthesize MG from GDP-mannose and 3-phosphoglycerate via a two-step pathway in which mannosyl-3-phosphoglycerate is the intermediate metabolite. In an early work, this pathway was expressed in <I>Saccharomyces cerevisiae</I> with the goal to confirm gene function (Empadinhas et al. in <I>J Bacteriol</I> 186:4075–4084, 2004), but the level of MG accumulation was low. Therefore, in view of the potential biotechnological value of this compound, we decided to invest further effort to convert <I>S. cerevisiae</I> into an efficient cell factory for MG production.</P><P><B>Results</B></P><P>To drive MG production, the pathway for the synthesis of GDP-mannose, one of the MG biosynthetic precursors, was overexpressed in <I>S. cerevisiae</I> along with the MG biosynthetic pathway. MG production was evaluated under different cultivation modes, i.e., flask bottle, batch, and continuous mode with different dilution rates. The genes encoding mannose-6-phosphate isomerase (<I>PMI40</I>) and GDP-mannose pyrophosphorylase (<I>PSA1</I>) were introduced into strain MG01, hosting a plasmid encoding the MG biosynthetic machinery. The resulting engineered strain (MG02) showed around a twofold increase in the activity of <I>PMI40</I> and <I>PSA1</I> in comparison to the wild-type. In batch mode, strain MG02 accumulated 15.86 mg<SUB>MG</SUB> g<SUB>DCW</SUB><SUP>−1</SUP>, representing a 2.2-fold increase relative to the reference strain (MG01). In continuous culture, at a dilution rate of 0.15 h<SUP>−1</SUP>, there was a 1.5-fold improvement in productivity.</P><P><B>Conclusion</B></P><P>In the present study, the yield and productivity of MG were increased by overexpression of the GDP-mannose pathway and optimization of the mode of cultivation. A maximum of 15.86 mg<SUB>MG</SUB> g<SUB>DCW</SUB><SUP>−1</SUP> was achieved in batch cultivation and maximal productivity of 1.79 mg<SUB>MG</SUB> g<SUB>DCW</SUB><SUP>−1</SUP> h<SUP>−1</SUP> in continuous mode. Additionally, a positive correlation between MG productivity and growth rate/dilution rate was established, although this correlation is not observed for MG yield.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (10.1186/s12934-018-1023-7) contains supplementary material, which is available to authorized users.</P>