Previous Article | Next Article ![]()
J. Bacteriol., Nov 1996, 6496-6507, Vol 178, No. 22
MS Pavelka Jr and WR Jacobs Jr
Diaminopimelate (DAP) is a unique metabolite used for both the biosynthesis
of lysine in bacteria and the construction of the peptidoglycan of many
species of bacteria, including mycobacteria. DAP is synthesized by bacteria
as part of the aspartate amino acid family, which includes methionine,
threonine, isoleucine, and lysine. Aspartokinase, the first enzyme in this
pathway, is encoded by the ask gene in mycobacteria. Previous attempts to
disrupt this gene in Mycobacterium smegmatis were unsuccessful, even when
the cells were supplied with all the members of the aspartate family,
suggesting that unlike other bacteria, mycobacteria may have an absolute
requirement for this pathway even when growing in rich medium containing
DAP. The purpose of this study was to determine if the ask gene and the
aspartate pathway are essential to M. smegmatis. This study describes a
test for gene essentiality in mycobacteria, utilizing a counterselectable
marker (streptomycin resistance) in conjunction with a specially
constructed merodiploid strain. We have used this system to show that the
ask gene could not be disrupted in wild-type M. smegmatis, using selective
rich medium supplemented with DAP unless there was an extra copy of ask
provided elsewhere in the chromosome. Disruption of ask was also possible
in a lysine auxotroph incapable of converting DAP to lysine. The ask
mutant, mc21278 (ask1::aph), exhibits multiple auxotrophy (Met-, Thr-,
DAP-, and Lys-) and is complemented by the ask gene. This is the first
description of DAP auxotrophy in mycobacteria. The ask mutant lyses when
deprived of DAP in culture, a characteristic which can be exploited for the
reproducible preparation of protoplasts and mycobacterial extracts. The
evidence presented here indicates that the aspartate pathway is essential
to M. smegmatis and that DAP is the essential product of this pathway.
Copyright © 1996, American Society for Microbiology
Biosynthesis of diaminopimelate, the precursor of lysine and a component of peptidoglycan, is an essential function of Mycobacterium smegmatis
Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
This article has been cited by other articles:
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»