Fine structure mapping and complementation studies of the metD methionine transport system in Salmonella typhimurium

MtaR, a regulator of methionine transport, is critical for survival of group B streptococcus in vivo

The group B streptococcus (GBS) is an important human pathogen that infects newborns as well as adults. GBS also provides a model system for studying adaptation to different host environments due to its ability to survive in a variety of sites within the host. In this study, we have characterized a transcription factor, MtaR, that is essential for the ability of GBS to survive in vivo. An isogenic strain bearing a kanamycin insertion in mtaR was attenuated for survival in a neonatal-rat model of sepsis. The mtaR mutant grew poorly in human plasma, suggesting that its utilization of plasma-derived nutrients was inefficient. When an excess of exogenous methionine (200 microg/ml) was provided to the mtaR mutant, its growth rate in plasma was restored to that of the wild-type strain. The mtaR mutant grew poorly in chemically defined medium (CDM) prepared with methionine at a concentration similar to that of plasma (4 microg/ml) but was able to grow normally in CDM prepared with a high concentration of methionine (400 microg/ml). Both the wild-type strain and the mtaR mutant were incapable of growth in CDM lacking methionine, indicating that GBS cannot synthesize methionine de novo. When the abilities of the strains to incorporate radiolabeled methionine were compared, the mtaR mutant incorporated fivefold less methionine than the wild-type strain during a 10-min period. Collectively, the results from this study suggest that the ability to regulate expression of a methionine transport system is critical for GBS survival in vivo.

A transporter of Escherichia coli specific for L- and D-methionine is the prototype for a new family within the ABC superfamily

An ABC-type transporter in Escherichia coli that transports both L- and D-methionine, but not other natural amino acids, was identified. This system is the first functionally characterized member of a novel family of bacterial permeases within the ABC superfamily. This family was designated the methionine uptake transporter (MUT) family (TC #3.A.1.23). The proteins that comprise the transporters of this family were analyzed phylogenetically, revealing the probable existence of several sequence-divergent primordial paralogues, no more than two of which have been transmitted to any currently sequenced organism. In addition, MetJ, the pleiotropic methionine repressor protein, was shown to negatively control expression of the operon encoding the ABC-type methionine uptake system. The identification of MetJ binding sites (in gram-negative bacteria) or S-boxes (in gram-positive bacteria) in the promoter regions of several MUT transporter-encoding operons suggests that many MUT family members transport organic sulfur compounds.

The Escherichia coli metD locus encodes an ABC transporter which includes Abc (MetN), YaeE (MetI), and YaeC (MetQ)

We report that the genes abc, yaeC, and yaeE comprise metD, an Escherichia coli locus encoding a DL-methionine uptake system. MetD is an ABC transporter with Abc the ATPase, YaeE the permease, and YaeC the likely substrate binding protein. Expression of these genes is regulated by L-methionine and MetJ, a common repressor of the methionine regulon. We propose to rename abc, yaeE, and yaeC as metN, metI, and metQ, respectively.

Bacterial transporters for sulfate and organosulfur compounds

Microorganisms require sulfur for growth, and obtain it either from inorganic sulfate or from organosulfur compounds such as sulfonates, sulfate esters, or sulfur-containing amino acids. Transport of sulfate into the cell is catalyzed either by ATP binding cassette (ABC)-type transporters (SulT family) or by major facilitator superfamily-type transporters (SulP family). By contrast, the sulfonate and sulfate ester transporters identified to date are all ABC-type systems, whose synthesis is tightly regulated by the sulfur supply to the cell, mediated by the CysB protein and other transcriptional regulators of the LysR-family.

Genetic map of Salmonella typhimurium, edition VIII

We present edition VIII of the genetic map of Salmonella typhimurium LT2. We list a total of 1,159 genes, 1,080 of which have been located on the circular chromosome and 29 of which are on pSLT, the 90-kb plasmid usually found in LT2 lines. The remaining 50 genes are not yet mapped. The coordinate system used in this edition is neither minutes of transfer time in conjugation crosses nor units representing "phage lengths" of DNA of the transducing phage P22, as used in earlier editions, but centisomes and kilobases based on physical analysis of the lengths of DNA segments between genes. Some of these lengths have been determined by digestion of DNA by rare-cutting endonucleases and separation of fragments by pulsed-field gel electrophoresis. Other lengths have been determined by analysis of DNA sequences in GenBank. We have constructed StySeq1, which incorporates all Salmonella DNA sequence data known to us. StySeq1 comprises over 548 kb of nonredundant chromosomal genomic sequences, representing 11.4% of the chromosome, which is estimated to be just over 4,800 kb in length. Most of these sequences were assigned locations on the chromosome, in some cases by analogy with mapped Escherichia coli sequences.