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Author ORCID Identifier
AccessType
Campus-Only Access for Five (5) Years
Document Type
dissertation
Degree Name
Doctor of Philosophy (PhD)
Degree Program
Microbiology
Year Degree Awarded
2019
Month Degree Awarded
May
First Advisor
Yasu S. Morita
Second Advisor
Michele M. Klingbeil
Third Advisor
Sloan Siegrist
Fourth Advisor
Peter Chien
Subject Categories
Bacteriology | Biochemistry | Microbial Physiology | Molecular Genetics
Abstract
The integrity of the multilaminate cell envelope surrounding mycobacteria is critical for survival and pathogenesis. The prevalence of phosphatidylinositol mannosides in the cell envelope suggests an important role in the mycobacterial life cycle. Indeed, deletion of the pimE gene (ΔpimE) encoding the first committed step in phosphatidylinositol hexamannoside biosynthesis in Mycobacterium smegmatis results in the formation of smaller colonies than wild-type colonies on Middlebrook 7H10 agar. To further investigate potential contributors to cell-envelope mannan biosynthesis while taking advantage of this colony morphology defect, we isolated spontaneous suppressor mutants of ΔpimE that reverted to wildtype colony size. Of 22 suppressor mutants, six accumulated significantly shorter lipomannan or lipoarabinomannan. Genome sequencing of these mutants revealed mutations in genes involved in the lipomannan/lipoarabinomannan biosynthesis, such as those encoding the arabinosyltransferase EmbC and the mannosyltransferase MptA. Furthermore, we identified three mutants carrying a mutation in a previously uncharacterized gene, MSMEG_5785, that we designated lmeA. Complementation of these suppressor mutants with lmeA restored the original ΔpimEphenotypes, and deletion of lmeA in wildtype M. smegmatis resulted in smaller lipomannan as observed in the suppressor mutants. LmeA carries a predicted N-terminal signal peptide, and density gradient fractionation and detergent extractability experiments indicated that LmeA localizes to the cell envelope. Using a lipid ELISA assay, we found that LmeA binds to plasma membrane phospholipids such as phosphatidylethanolamine and phosphatidylinositol. LmeA is widespread throughout the Corynebacteriales; therefore, we concluded that LmeA is an evolutionarily conserved cell-envelope protein critical for controlling the mannan chain length of lipomannan/lipoarabinomannan.
DOI
https://doi.org/10.7275/14218023
Recommended Citation
Rahlwes, Kathryn, "REGULATION OF LIPOMANNAN AND LIPOARABINOMANNAN BIOSYNTHESIS IN MYCOBACTERIA" (2019). Doctoral Dissertations. 1649.
https://doi.org/10.7275/14218023
https://scholarworks.umass.edu/dissertations_2/1649