An assessment of serial co-cultivation approach for generating novel Zymomonas mobilis strains
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RESEARCH NOTE
An assessment of serial co‑cultivation approach for generating novel Zymomonas mobilis strains Katsuya Fuchino* and Per Bruheim
Abstract Objective: The alphaproteobacterium Zymomonas mobilis is an efficient ethanol producer, and Z. mobilis-based biorefinery shows great potential for biofuel production. Serial co-cultivation is an emerging approach that promotes inter-species interactions which can improve or rewire the metabolic features in industrially useful microorganisms by inducing frequent mutations. We applied this method to assess if it improves or rewires the desirable physiological features of Z. mobilis, especially ethanol production. Results: We performed serial co-culture of Z. mobilis with the baker’s yeast, Saccharomyces cerevisiae. We observed filamentation of Z. mobilis cells in the co-culture, indicating that the Z. mobilis cells were exposed to stress due to the presence of a competitor. After 50 times of serial transfers, we characterized the generated Z. mobilis strains, showing that long term co-culture did not drive significant changes in either the growth or profile of excreted metabolites in the generated strains. In line with this, whole genome sequencing of the generated Z. mobilis strains revealed only minor genetic variations from the parental strain. 50 generations of Z. mobilis monoculture did not induce morphological changes or any significant genetic variations. The result indicates that the method needs to be carefully optimized for Z. mobilis strain improvement. Keywords: Zymomonas mobilis, Ethanol production, Adaptive evolution, Co-culture, Genomic stability Introduction The alphaproteobacterium Z. mobilis is the best bacterial ethanol producer endowed with unique physiological features [1]. Therefore, Z. mobilis based-biorefinery is a promising biofuel production system at an industrial scale [2]. Despite its efficient ethanol production capacity, there are challenges in employing Z. mobilis as a biocatalyst. For example, Z. mobilis consumes a limited range of feedstock as substrate [2]. It is also known to be sensitive to certain abiotic stress, such as acetic acid toxicity [2, 3]. Yet, recent advances in Z. mobilis metabolic engineering
*Correspondence: [email protected] Department of Biotechnology and Food Science, Norwegian University of Science and Technology, Trondheim, Norway
have overcome these drawbacks, advancing its potential use for environmentally-friendly biorefining [2, 3]. In addition to ethanol production, rewiring metabolic pathways to produce other useful compounds has lately been explored in Z. mobilis [3–7]. This is to utilize and exploit its intrinsic capacity of fast catabolism that comes with small biomass accumulation [1]. Considering that its prolific potential is expanding, a novel approach to engineer or generate desirable Z. mobilis strains should be assessed. Co-culture based adaptive evolution involves mixing several species in the same culture to stimulate interspecies interactions, this n
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