Evaluation of the ethanol tolerance for wild and mutant Synechocystis strains by flow cytometry

Abstract

HighlightsFlow cytometry was used to evaluate the effect of ethanol on Synechocystis strains.The three Synechocystis strains behaved differently in the presence of ethanol.UL 004 and UL 030 were more tolerant to the presence of ethanol than the WT strain.The most efficient ethanol producer (UL030) was also the most tolerant to ethanol.

Evaluation of New Genetic Toolkits and Their Role for Ethanol Production in Cyanobacteria

“…Furthermore, it has been shown that the catalytic activity of pdc ZM is a limiting factor, as the optimal molar ratio between pdc:adh would be 1:2.5 but is 1:30 to 1:40 so far [72]. [32] This result is supported by the fact that a double integration to increase the copy number of the genes further increased the ethanol yield. However, no significant difference in growth and ethanol production capacity was observed between a strain with double integration of the whole pdc ZM -adh SYN construct and a strain harbouring two copies of pdc ZM and one copy of adh SYN [31,72].…”

“…Therefore, alternative methods like for example different stripping methods need to be investigated [12,33]. Currently, so far the highest productivity of 0.285 g L −1 d −1 in cyanobacteria was achieved by Lopes da Silva et al [32] and the highest ethanol titre of 5.50 g L −1 in 26 days was reached by Gao et al [31]. Compared to the other model organisms like S. cerevisiae or E. coli with 130 g L −1 in 65 h and 20.7 g L −1 in 96 h, respectively, there is still a big step to be made in cyanobacteria [21].…”

“…This indicates that the redirection of carbon flux away from growth to product formation may contribute to impaired growth behaviour of ethanol producing Synechocystis. However, the most productive Synechocystis strain was presented by Armshaw et al [75] which was further characterized by Lopes da Silva et al [32]. The strain reached an ethanol titre of 2.6 g L −1 during a cultivation over 9 days, which corresponds to a STY of 0.285 g L −1 d −1 .…”

“…In order to achieve this, the ethanol tolerance of Synechocystis has to be taken into account, because a yield of 15 g L −1 is needed for commercial use. At this time, the Synechocystis wild type is 50% growth inhibited if this concentration is externally added to the media [12,32]. In various studies, the stress response of Synechocystis was further investigated and different genes and non-coding RNA sequences were identified to enhance the ethanol tolerance.…”

“…Underlining an increased ethanol tolerance is an important factor for commercial photoautotrophic ethanol production with cyanobacteria. Lopes da Silva et al [32] demonstrated with the ethanol producing strains generated by Armshaw et al [75] a positive correlation between an increasing ethanol production rate and enhanced ethanol tolerance. Proteomic analysis, comparing wild type and ethanol producing Synechocystis strains, provided a deeper insight into the stress response.…”