Deletion of menaquinone (vitamin-K) biosynthetic gene menA restores ubiquinone (coenzyme Q) biosynthesis in ubiB mutant strain.
Carlson, Garrett Silo
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It is well established that for aerobic growth E.coli requires either Menaquinone (MK), Ubiquinone (Q) or 2-octaprenyl-3-methyl-6- methoxy-1,4-benzoquinone (MMQ) as electron carrier to grow on glycerol minimal medium (GMM). Therefore, a double mutant strain blocked in both the MK and Q pathways shouldn’t grow on GMM. The following double mutant strains were tested for growth on GMM (A ubiE Amen A, AubiH Amen A, AubiF Amen A, AubiB AmenA and AyigP AmenA). Surprisingly, it was found that the AubiB AmenA mutant grew after a long lag and AubiF AmenA mutant grew as expected due to the Q pathway intermediate MMQ serving as electron carrier. In GMM AubiB AmenA double mutant showed an increase in the rate of growth and growth yield. It is a known fact that all the Q pathway gene mutants including ubiB cannot grow on succinate minimal medium (SMM). The ubiB mutant has been previously shown to accumulate small amount of Q in stationary phase. To our surprise, the double mutant was also able to grow on succinate and lactate minimal media once adapted to grow in GMM. Quinone analysis of the AubiB AmenA mutant using HPLC revealed that it made significant amount of Q. Therefore, the reason behind the growth of double mutant strain is due to increase in the amount of Q.