NDLI: Cysteine Metabolism in Legionella pneumophila: Characterization of an l-Cystine-Utilizing Mutant

Content Provider	PubMed Central
Author	Fanny, Ewann Hoffman, Paul S.
Copyright Year	2006
Abstract	Growth of Legionella pneumophila on buffered charcoal-yeast extract (BCYE) medium is dependent on l-cysteine (but not l-cystine), which is added in excess over what is required for nutrition. We investigated the biochemical and genetic bases for this unusual requirement and determined that much of the l-cysteine in BCYE medium is rapidly oxidized to l-cystine and is unavailable to the bacteria. Analysis of cysteine consumption during bacterial growth indicated that of the 11% consumed, 3.85% (∼0.1 mM) was incorporated into biomass. The activities of two key cysteine biosynthetic enzymes (serine acetyltransferase and cysteine synthase) were not detected in cell extracts of L. pneumophila, and the respective genes were not present in the genome sequences, confirming cysteine auxotrophy. Kinetic studies identified two energy-dependent cysteine transporters, one with high affinity (apparent Km , 3.29 μM) and the other with low affinity (apparent Km , 93 μM), each of which was inhibited by the uncoupling agent carbonyl cyanide m-chlorophenylhydrazone. Cystine was not transported by L. pneumophila; however, a mutant strain capable of growth on l-cystine (CYS1 mutant) transported l-cystine with similar kinetics (Km , 4.4 μM and 90 μM). Based on the bipartite kinetics, requirement for proton motive force, and inhibitor studies, we suggest that a high-affinity periplasmic binding protein and a major facilitator/symporter (low affinity) mediate uptake. The latter most likely is functional at high cysteine concentrations and most likely displays altered substrate specificity in the CYS-1 mutant. Our studies provide biochemical evidence to support a general view that L. pneumophila is restricted to an intracellular lifestyle in natural environments by an inability to utilize cystine, which most likely ensures that the dormant cyst-like transmissible forms do not germinate outside suitable protozoan hosts.
Related Links	http://dx.doi.org/10.1128/aem.00684-06
Ending Page	4000
Page Count	8
Starting Page	3993
File Format	PDF
ISSN	00992240
e-ISSN	10985336
Journal	Applied and Environmental Microbiology
Issue Number	6
Volume Number	72
Language	English
Publisher	American Society for Microbiology
Publisher Date	2006-06-01
Access Restriction	Open
Rights Holder	American Society for Microbiology
Subject Keyword	Biotechnology Food Science Ecology Applied Microbiology and Biotechnology Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Ecology Food Science Applied Microbiology and Biotechnology Biotechnology

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