Kremer, T. A. | Search bioRxiv

bioRxiv2019

Cell aggregation and aerobic respiration facilitate survival of Zymomonas mobilis ZM4 in an aerobic minimal medium

Zymomonas mobilis produces ethanol from glucose near the theoretical maximum yield, making it a potential alternative to yeast for industrial ethanol production. A potentially useful industrial feature is the ability to form multicellular aggregates called flocs, which can settle quickly and exhibit higher resistance to harmful chemicals. While spontaneous floc-forming Z. mobilis mutants have been described, little is known about the natural conditions that induce Z. mobilis floc formation and the genetic factors involved. Here we found that wild-type Z. mobilis forms flocs in response to aerobic growth conditions but only in a minimal medium. We identified a cellulose synthase gene cluster and a single diguanylate cyclase that are essential for both floc formation and survival in an aerobic minimal medium. We also found that NADH dehydrogenase 2, a key component of the aerobic respiratory chain, is important for survival in an aerobic minimal medium, providing a physiological role for this enzyme which has previously been found to be disadvantageous in aerobic rich media. Supplementation of the minimal medium with vitamins also promoted survival but did not inhibit floc formation.

microbiology↗

bioRxiv2017

Pantothenate auxotrophy in Zymomonas mobilis ZM4 is due toa lack of aspartate decarboxylase activity

The bacterium Zymomonas mobilis naturally produces ethanol at near theoretical maximum yields, making it of interest for industrial ethanol production. Z. mobilis requires the vitamin pantothenate for growth. Here we characterized the genetic basis for the Z. mobilis pantothenate auxotrophy. We found that this auxotrophy is due to the absence of a single gene, panD, encoding aspartate-decarboxylase. Heterologous expression of Escherichia coli PanD in Z. mobilis or supplementation of the growth medium with the product of PanD activity, {beta}-alanine, eliminated the need for exogenous pantothenate. We also determined that IlvC, an enzyme better known for branched-chain amino acid synthesis, is required for pantothenate synthesis in Z. mobilis, as it compensates for the absence of PanE, another pantothenate synthesis pathway enzyme. In addition to contributing to an understanding of the nutritional requirements of Z. mobilis, our results have led to the design of a more cost-effective growth medium.

microbiology↗