Movement on surfaces, or swarming motility, is effectively mediated by the lateral flagellar (laf) system in Vibrio parahaemolyticus. Expression of laf is induced by conditions inhibiting rotation of the polar flagellum, which is used for swimming in liquid. However, not all V. parahaemolyticus isolates swarm proficiently. The organism undergoes phase variation between opaque (OP) and translucent (TR) cell types. The OP cell produces copious capsular polysaccharide and swarms poorly, whereas the TR type produces minimal capsule and swarms readily. OP7TR switching is often the result of genetic alterations in the opaR locus. Previously, OpaR, a Vibrio harveyi LuxR homolog, was shown to activate expression of the cpsA locus, encoding capsular polysaccharide biosynthetic genes. Here, we show that OpaR also regulates swarming by repressing laf gene expression. However, in the absence of OpaR, the swarming phenotype remains tightly surface regulated. To further investigate the genetic controls governing swarming, transposon mutagenesis of a TR (⌬opaR1) strain was performed, and SwrT, a TetR-type regulator, was identified. Loss of swrT, a homolog of V. harveyi luxT, created a profound defect in swarming. This defect could be rescued upon isolation of suppressor mutations that restored swarming. One class of suppressors mapped in swrZ, encoding a GntR-type transcriptional regulator. Overexpression of swrZ repressed laf expression. Using reporter fusions and quantitative reverse transcription-PCR, SwrT was demonstrated to repress swrZ transcription. Thus, we have identified the regulatory link that inhibits swarming of OP strains and have begun to elucidate a regulatory circuit that modulates swarming in TR strains.Vibrio parahaemolyticus is a gram-negative marine bacterium found in coastal and estuarine waters worldwide (11, 31). It possesses two distinct flagellar systems: the polar system produces a single sheathed flagellum designed for swimming motility, whereas the lateral flagellar (laf) system is adapted for movement over moist or viscous surfaces (3, 46). The lateral flagella are expressed only when the cell senses a surface environment (45). Swarmer cells are elongated (5 to 20 times the length of the swimmer cell) and multinucleoid, and they produce a multitude of lateral flagella. Two environmental signals are known to be required for laf expression: iron-limiting conditions and inhibition of polar flagellar rotation (32,43,44). The polar flagellum acts as a tactile sensor for the cell. When the cell encounters a surface or sufficiently viscous environment, flagellar rotation is impaired and laf is induced. Thus, the lateral flagellar system is intimately linked to the polar system. However, the molecular mechanism for sensing polar flagellar inhibition and the signal transduction pathway regulating laf expression are not known. It was the goal of this work to begin to elucidate the regulatory circuit controlling laf expression.Many bacterial species are known to swarm, including some with mixed polar and pe...

The bacterial flagellum is powered by a rotary motor capable of turning the helical flagellar propeller at very high speeds. Energy to drive rotation is derived from the transmembrane electrochemical potential of specific ions. Ions passing through a channel component are thought to generate the force to power rotation. Two kinds of motors, dependent on different coupling ions, have been described: proton-driven and sodium-driven motors. There are four known genes encoding components of the sodium-powered polar flagellar motor in Vibrio parahaemolyticus. Two, which are characterized here, are homologous to genes encoding constituents of the proton-type motor (motA and motB), and two encode components unique to the sodium-type motor (motX and motY). The sodium-channelblocking drugs phenamil and amiloride inhibit rotation of the polar flagellum and therefore can be used to probe the architecture of the motor. Mutants were isolated that could swim in the presence of phenamil or amiloride. The majority of the mutations conferring phenamil-resistant motility alter nucleotides in the motA or motB genes. The resultant amino acid changes localize to the cytoplasmic face of the torque generator and permit identification of potential sodium-interaction sites. Mutations that confer motility in the presence of amiloride do not alter any known component of the sodium-type flagellar motor. Thus, evidence supports the existence of more than one class of sodium-interaction site at which inhibitors can interfere with sodium-driven motility.Small but powerful rotary motors propel bacteria by turning semirigid helical propellers, the flagellar filaments (for recent reviews, see refs. 1-4). In Escherichia coli and Salmonella typhimurium, energy to power rotation derives from the proton motive force (5, 6). Somehow, the passage of protons through the torque generator is coupled to rotation of the flagellum (7). Although the molecular mechanism of coupling remains unsolved, the architecture of the proton-driven motor has been studied extensively. The stationary part of the torque generator consists of two cytoplasmic membrane proteins, MotA and MotB. MotA contains four transmembrane domains, and MotB possesses one transmembrane domain (8, 9). Together they form a proton channel (10-13). In addition, MotB contains a C-terminal domain, which is thought to anchor the MotA-MotB complex to the cell wall via an interaction with peptidoglycan (14,15).Torque is transmitted from the MotA͞B stator to the FliG protein, which acts as part of the rotor (16). FliG is found at the base of the flagellar basal body in a complex with FliM and FliN (17,18). This complex of interacting proteins, known as the ''switch complex,'' is essential for torque generation, flagellar assembly, and modulation of the direction of flagellar rotation (19)(20)(21)(22)(23)(24).Other bacteria, including alkalophilic Bacillus and marine Vibrio species, use the transmembrane electrochemical-potential gradient of Na ϩ to drive flagellar rotation (25). The sodiumdri...

Glucose 6-phosphate (G6P) is a metabolic intermediate with many possible cellular fates. In mycobacteria, G6P is a substrate for an enzyme, F 420 -dependent glucose-6-phosphate dehydrogenase (Fgd), found in few bacterial genera. Intracellular G6P levels in six Mycobacterium sp. were remarkably higher (ϳ17-130-fold) than Escherichia coli and Bacillus megaterium. The high G6P level in Mycobacterium smegmatis may result from 10 -25-fold higher activity of the gluconeogenic enzyme fructose-1,6-bisphosphatase when grown on glucose, glycerol, or acetate compared with B. megaterium and E. coli. In M. smegmatis this coincided with up-regulation of the first gluconeogenic enzyme, phosphoenolpyruvate carboxykinase, when acetate was the carbon source, suggesting a cellular program for maintaining high G6P levels. G6P was depleted in cells under oxidative stress induced by redox cycling agents plumbagin and menadione, whereas an fgd mutant of M. smegmatis used G6P less well under such conditions. The fgd mutant was more sensitive to these agents and, in contrast to wild type, was defective in its ability to reduce extracellular plumbagin and menadione. These data suggest that intracellular G6P in mycobacteria serves as a source of reducing power and, with the mycobacteriaspecific Fgd-F 420 system, plays a protective role against oxidative stress.

Experiments were designed to detect regional disruptions of adrenergic neurons in the hearts of living dogs. The neuron disruption was achieved by the application of phenol to the epicardium of the left ventricle. Evidence for denervation was the reduction in endogenous norepinephrine (NE) concentrations in the myocardium beneath the region of phenol treatment and toward the apex. Radiolabeled meta-iodobenzylguanidine (MIBG) acts as an analog of NE and as such is concentrated in adrenergic nerve terminals. Following phenol application, MIBG labeled with 125I was found, 20 hours after injection, to be distributed within myocardium in patterns comparable to those of NE. However, left stellectomy did not alter the distributions of NE or 125I-MIBG in the myocardium and apparently did not disrupt adrenergic innervation. MIBG labeled with 123I enabled scintigraphic images of heart neurons in the living dog 3 and 20 hours after injection; these images portrayed the regions of adrenergic neuron disruption caused by phenol treatment. Concentrations of thallium-201 depicted on scintigraphic image and of triphenyltetrazolium observed on in vitro staining demonstrated no myocardial injury. Thus scintigraphy with 123I-MIBG will display regional adrenergic denervations in the heart.

The addition of dopamine to anterior pituitary incubations resulted in a marked decrease (88% for 3H prolactin and 69% for RIA prolactin) in prolactin release. Incubation with the cholinergic agonists carbacol, arecoline and nicotine resulted in no significant change in prolactin secretion.