Chemotaxis of Escherichia coli to norepinephrine (NE) requires conversion of NE to 3,4-dihydroxymandelic acid.

Norepinephrine (NE), the primary neurotransmitter of the sympathetic nervous system, has been reported to be a chemoattractant for enterohemorrhagic Escherichia coli (EHEC). Here we show that nonpathogenic E. coli K-12 grown in the presence of 2 µM NE is also attracted to NE. Growth with NE induces transcription of genes encoding the tyramine oxidase, TynA, and the aromatic aldehyde dehydrogenase, FeaB, whose respective activities can, in principle, convert NE to 3,4-dihydroxymandelic acid (DHMA). Our results indicate that the apparent attractant response to NE is in fact chemotaxis to DHMA, which was found to be a strong attractant for E. coli. Only strains of E. coli K-12 that produce TynA and FeaB exhibited an attractant response to NE. We demonstrate that DHMA is sensed by the serine chemoreceptor Tsr and that the chemotaxis response requires an intact serine-binding site. The threshold concentration for detection is ≤5 nM DHMA, and the response is inhibited at DHMA concentrations above 50 µM. Cells producing a heterodimeric Tsr receptor containing only one functional serine-binding site still respond like the wild type to low concentrations of DHMA, but their response persists at higher concentrations. We propose that chemotaxis to DHMA generated from NE by bacteria that have already colonized the intestinal epithelium may recruit E. coli and other enteric bacteria that possess a Tsr-like receptor to preferred sites of infection.

Chemotaxis to the quorum-sensing signal AI-2 requires the Tsr chemoreceptor and the periplasmic LsrB AI-2-binding protein.

AI-2 is an autoinducer made by many bacteria. LsrB binds AI-2 in the periplasm, and Tsr is the l-serine chemoreceptor. We show that AI-2 strongly attracts Escherichia coli. Both LsrB and Tsr are necessary for sensing AI-2, but AI-2 uptake is not, suggesting that LsrB and Tsr interact directly in the periplasm.

Molecular cloning and regulation of mRNA expression of the thyrotropin ß and glycoprotein hormone α subunits in red drum, Sciaenops ocellatus.

Full-length cDNAs for thyrotropin ß (TSHß) and glycoprotein hormone α (GSUα) subunits were cloned and sequenced from the red drum (Sciaenops ocellatus). The cDNAs for TSHß (877 bp) and GSUα (661 bp) yielded predicted coding regions of 126 and 94 amino acid proteins, respectively. Both sequences contain all invariant cysteine and putative glycosylated asparagines characteristic of each as deduced by comparison with other GSUα and TSHß sequences from representative vertebrate species. Multiple protein sequence alignments show that each subunit shares highest identity (79% for the TSHß and 86% for the GSUα) with perciform fish. Furthermore, in a single joint phylogenetic analysis, each subunit segregates most closely with corresponding GSUα and TSHß subunit sequences from closely related fish. Tissue-specific expression assays using RT-PCR showed expression of the TSHß subunit limited to the pituitary. GSUα mRNA was predominantly expressed in the pituitary but was also detected in the testis and ovary of adult animals. Northern hybridization revealed the presence of a single transcript for both TSHß and GSUα, each close in size to mRNA transcripts from other species. Dot blot assays from total RNA isolated from S. ocellatus pituitaries showed that in vivo T3 administration significantly diminished mRNA expression of both the TSHß and GSUα subunits and that goitrogen treatment caused a significant induction of TSHß mRNA only. Both TSHß and GSUα mRNA expression in the pituitary varied significantly in vivo over a 24-h period. Maximal expression for both TSHß and GSUα occurred during the early scotophase in relation to a peak in T4 blood levels previously documented. These results suggest the production of TSH in this species which may serve to drive daily cycles of thyroid activity. Readily quantifiable, variable, and thyroid hormone-responsive pituitary TSH expression, coupled with previously described dynamic daily cycles of circulating T4 and extensive background on the growth, nutrition, and laboratory culture of red drum, suggests that this species will serve as a useful model for experimental studies of the physiological regulation of TSH production.