Effect of microaeration on cell growth and glucose/xylose fermentation of Kluyveromyces marxianus from the imitate lignocellulosic-derived hydrolysate

Kluyveromyces marxianus MTCC 1389 Augments Multi-stress Tolerance After Adaptation to Ethanol Stress

During fermentation, yeast cells undergo various stresses that inhibit cell growth and ethanol production. Therefore, the ability to tolerate multiple stresses during fermentation is one of the important characteristics for yeast cells that can be used for commercial ethanol production. In the present study, we evaluated the multi-stress tolerance of parent and ethanol adapted Kluyveromyces marxianus MTCC1389 and their relative gene expression analysis. Multi-stress tolerance was confirmed by determining its cell viability, growth, and spot assay under oxidative, osmotic, thermal, and ethanol stress. During oxidative (0.8% H2O2) and osmotic stress (2 M NaCl), there was significant cell viability of 90% and 50%, respectively, by adapted strain. On the other hand, under 45 °C of thermal stress, the adapted strain was 80% viable while the parent strain was 60%. In gene expression analysis, the ethanol stress responsive gene ETP1 was significantly upregulated by 3.5 folds, the osmotic stress gene SLN1 was expressed by 3 folds, and the thermal stress responsive gene MSN2 was expressed by 7 folds. This study shows adaptive evolution for ethanol stress can develop other stress tolerances by changing relative gene expression of osmotic, oxidative, and thermal stress responsive genes.

Carbon nanotubes mitigate copper-oxide nanoparticles-induced inhibition to acidogenic metabolism of Propionibacterium acidipropionici by regulating carbon source utilization

This study demonstrated that multi-walled carbon nanotubes (MWCNTs) could mitigate copper oxide nanoparticles (CuO NPs)-induced inhibition to acidogenic metabolism of propionic acid bacteria (i.e., Propionibacterium acidipropionici) by regulating carbon source utilization. CuO NPs severely inhibited the growth of P. acidipropionici, damaged its cell membrane, and down-regulated gene expressions and enzyme activities involved in acidogenic metabolism, thereby decreasing propionate production. However, although MWCNTs had a slightly negative impact on the growth and cell membrane, the gene expressions and catalytic activities were enhanced (glycolysis and pyruvate metabolism), resulting in the improved propionate production. Additionally, the gene expressions and catalytic activities of key enzymes (e.g., tpiA, pgk, PK, OTTAC, etc.) related to acidogenic metabolism were also enhanced by the co-existence of both nanomaterials, thereby promoting propionate production towards P. acidipropionici. This work demonstrated that the presence of MWCNTs could affect the inhibition of CuO NPs to fermentation processes via regulating carbon source utilization.