Author (Your Name)

Katherine M. AndreFollow

Date of Award


Document Type

Honors Thesis (Colby Access Only)


Colby College. Biology Dept.


Dr. Ronald Peck


Carotenoids, an important class of organic molecules used in a variety of industries, are produced by a wide selection of plants and microbes. Extraction from biological sources is energy-intensive so most carotenoid production is done via organic synthesis. The halophilic archaeon Haloferax volcanii may provide an excellent solution for sustainable carotenoid production since cells are easily lysed in water. Previous work in our lab revealed that increasing the expression of crtB, a gene encoding the carotenoid-synthetic enzyme phytoene synthase, resulted in high levels of carotenoid production but slowed the growth. However, we isolated a spontaneous mutant of this strain with high carotenoid production and a normal growth rate. Therefore, the overproduction of carotenoids may be possible without compromising growth rate. This mutant has a crtB encoding a phytoene synthase with a C-terminal truncation. Our current hypothesis is that crtB overexpression slows growth by saturating the essential LonB protease, known to play a role in controlling carotenoid production through degradation of phytoene synthase. The phytoene synthase in the spontaneous mutant may have lost its ability to be bound by LonB and thus does not affect growth when overexpressed. We have placed the LonB gene under the control of an inducible promoter to test whether significant differences in growth rate and carotenoid production are observed when LonB is overexpressed in strains with wild-type or mutated crtB. Our findings are consistent with our hypothesis that slow growth is caused by the diversion of LonB away from essential cell processes that it is involved in.


carotenoids, halophiles, archaea, protease, regulation, biosynthesis