GSE107996
Designing of Lactococcus lactis platform for isobutanol production using multiple rounds of adaptive laboratory evolution
This work was primarily focused on removing the main bottleneck for isobutanol production which is the toxicity of isobutanol towards its host and the major reason for its low-level production. Recently, there have been many reports where people have tried various strategies including continuous in-situ product removal from the bioreactor which led to a significant increase in the final product titers. Clearly, it is the intrinsic tolerance levels of the host which decides the end product titers. Importantly, if the host microbe can originally tolerate higher concentrations of toxin (here isobutanol) then it is likely to have a better potential for further improvement of tolerance levels. In our work, we tried to enhance the isobutanol tolerance of wild type NZ9000 using continuous culture. We used the principle of adaptive laboratory evolution to enhance the natural tolerance ability (0.8% isobutanol) of the wild type strain. The strain was cultivated for more than 60 days (>250 generations), while increasing the selection pressure (here isobutanol) gradually in the feed. This finally led to the strain that showed exceptionally higher tolerance (4%) for isobutanol. Transcriptomic analysis also showed fluctuations in gene expression levels from a wide range of categories, precluding any attempt to reverse engineer this phenotype. Overall design: Analysing the transcriptome of wild type (WT) and 4% isobutanol tolerant strain grown in absence of isobutanol (4B0) or in presence of 4% isobutanol (4B4). One biological replicate of wild type (WTD) was also included in the analysis.