Isoprene Formation in Bacillus subtilis: A Barometer of Central Carbon Assimilation in a Bioreactor?
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- 作者：Megan C. Shirk ; William P. Wagner ; and Ray Fall
- 刊名：Biotechnology Progress
- 出版年：2002
- 出版时间：October 2002
- 年：2002
- 卷：18
- 期：5
- 页码：1109 - 1115
- 全文大小：185K
- 年卷期：v.18,no.5(October 2002)
- ISSN：1520-6033
文摘
Isoprene (2-methyl-1,3-butadiene) is a volatile hydrocarbon of uncertain function inBacillus subtilis, and we hypothesized that it is an overflow metabolite produced duringexcess carbon utilization. Here we tested this idea for phase 2 of isoprene release, aphase that occurs during extracellular acetoin accumulation and its reassimilation.Phase 2 isoprene formation could be disrupted in three different ways, all related toacetoin metabolism. Disruption of a gene essential for acetoin biosynthesis (acetolacticacid synthase, alsS) blocked acetoin formation and led to cessation of phase 2 isopreneformation as well as a variety of pleiotropic effects related to loss of pH control. Growthof the alsS mutant with external pH control reversed most of these effects. Disruptionof acetoin catabolism (acetoin dehydrogenase, acoA), also eliminated phase 2 isopreneformation and caused cells to transition directly from phase 1 to phase 3; the latter isattributed to amino acid catabolism. A third alteration of acetoin metabolism wasdetected in the widely used strain 168 (trpC2) but not in strain MS175, a trpC mutantconstructed in the Marburg strain genetic background. Strain 168 exhibited slowacetoin assimilation compared to that of MS175 or the parental strain, with little orno isoprene formation during this growth phase. These findings support the idea thatisoprene release occurs primarily when the rate of carbon catabolism exceeds anabolismand that this volatile hydrocarbon is a product of overflow metabolism when precursorsare not required for higher isoprenoid biosynthesis. It is suggested that isoprene releasemight serve as a useful barometer of the rise and fall of central carbon fluxes duringthe growth of Bacillus strains in industrial bioreactors.