Mutation in the a-subunit of F(1)F(O)-ATPase causes an increased motility phenotype through the sodium-driven flagella of Vibrio

Bacterial flagellar motors exploit the electrochemical potential gradient of a coupling ion as energy source and are composed of stator and rotor proteins. Vibrio alginolyticus has a Na(+)-driven motor and its stator is composed of PomA and PomB. Recently, we isolated increased motility strains (sp1-sp4) from the PomA-N194D/PomB-D24N mutant whose motility was quite weak. To detect the responsible mutation, we have used a next-generation sequencer and determined the entire genome sequences of the sp1 and sp2 strains. Candidate mutations were identified in the gene encoding the a-subunit of F1Fo-ATPase (uncB). To confirm this, we constructed a deletion strain, which gave the increased motility phenotype. The amount of membrane-bound ATPase was reduced in the sp2 and ΔuncB mutants. From these results, we conclude that a mutation in the uncB gene causes the increased motility phenotype in V. alginolyticus. They confer faster motility in low concentrations of sodium than in the parental strain and this phenotype is suppressed in the presence of KCN. Those results may suggest that the proton gradient generated by the respiratory chain is increased by the uncB mutation, consequently the sodium motive force is increased and causes the increased motility phenotype.

A conserved residue, PomB-F22, in the transmembrane segment of the flagellar stator complex, has a critical role in conducting ions and generating torque

Bacterial flagellar motors exploit the electrochemical potential gradient of a coupling ion (H+ or Na+) as their energy source, and are composed of stator and rotor proteins. Sodium-driven and proton-driven motors have the stator proteins PomA and PomB or MotA and MotB, respectively, which interact with each other in their transmembrane (TM) regions to form an ion channel. The single TM region of PomB or MotB, which forms the ion-conduction pathway together with TM3 and TM4 of PomA or MotA, respectively, has a highly conserved aspartate residue that is the ion binding site and is essential for rotation. To investigate the ion conductivity and selectivity of the Na+-driven PomA/PomB stator complex, we replaced conserved residues predicted to be near the conserved aspartate with H+-type residues, PomA-N194Y, PomB-F22Y and/or PomB-S27T. Motility analysis revealed that the ion specificity was not changed by either of the PomB mutations. PomB-F22Y required a higher concentration of Na+ to exhibit swimming, but this effect was suppressed by additional mutations, PomA-N194Y or PomB-S27T. Moreover, the motility of the PomB-F22Y mutant was resistant to phenamil, a specific inhibitor for the Na+ channel. When PomB-F22 was changed to other amino acids and the effects on swimming ability were investigated, replacement with a hydrophilic residue decreased the maximum swimming speed and conferred strong resistance to phenamil. From these results, we speculate that the Na+ flux is reduced by the PomB-F22Y mutation, and that PomB-F22 is important for the effective release of Na+ from PomB-D24.

Adsorption Kinetics of Polyvinyl Acetate Adsorbed at the Solid-Liquid Interface

The kinetics of adsorption of polyvinyl acetate at the solid-liquid interface has been studied to verify the correctness of a description in a paper [Peterson and Kwel, J.Phys.Chem. 65, 1330(1961)] : “the initial rate of adsorption of polyvinyl acetate was found to be rapid”. This is inconsistent with the widely accepted knowledge that polymer adsorption is a slow process. Polyvinyl acetate (Mw = 124,800) was adsorbed from benzene (0.001 to 0.05 mg ml−1) onto mica at 295.5 K. The adsorbed amount per unit area i.e. adsorbance has been determined as a function of incubation time using an ultramicrobalance [Mettler UM3]. The results obtained show that the adsorbance rises rapidly at the beginning of adsorption and then reaches an apparent plateau, where the adsorbance still increases at negligibly slow rate in comparison with the initial rate. The Peterson and Kwei's results have been confirmed to be correct. We regarded the plateau as an adsorption equilibrium and constructed adsorption isotherms, in which the Peterson and Kwei's results were incorporated. These isotherms are found to be less dependent on concentration in the dilute region concerned. This dependency is in agreement with the prediction of the Scheutjens and Fleer theory based on the loop-train-tail model.

Effect of 8-MHz radiofrequency-capacitive regional hyperthermia with strong superficial cooling for unresectable or recurrent colorectal cancer

A well-known disadvantage of a radiofrequency-capacitive device for deep-seated tumours is preferential heating of the subcutaneous fat tissue. The authors previously developed the hyperthermia with their own external cooling unit and achieved strong superficial cooling, and reported its usefulness for the reduction of the preferential heating. The purpose of the present study was to evaluate the effect of hyperthermia with strong superficial cooling on the treatment results for unresectable or recurrent colorectal cancers. From 1986 to 2002, 44 patients with primary unresectable or locally recurrent colorectal cancer treated with thermoradiotherapy were analysed retrospectively. The patients with obesity as a subcutaneous fat thickness more than 3 cm, a high age or other serious complications did not undergo therapy. The results were compared between 17 cases with strong superficial cooling treated after 1997 (Group A) and 27 cases without strong superficial cooling treated before 1996 (Group B). Significant differences in thermometry data of T(max), T(ave) and T(min) were noted between Groups A (45.3, 44.4 and 43.6 degrees C, respectively) and B (42.9, 42.0 and 41.1 degrees C, respectively) (p<0.01). Complete response plus partial response rates were better for Group A than for Group B (59 versus 26%, p = 0.05). Multivariate analysis by logistic regression to evaluate the effects of certain factors on complete response plus partial response was strongly correlated with strong superficial cooling (p<0.05). The median survival times for overall survival were 24.3 months for Group A and 17.1 months for Group B (p<0.05). Eight-megahertz radiofrequency-capacitive regional hyperthermia with strong superficial cooling is potentially useful for improving treatment results in unresectable or recurrent colorectal cancers.

Comparative study of the ion flux pathway in stator units of proton- and sodium-driven flagellar motors

Flagellar motor proteins, MotA/B and PomA/B, are essential for the motility of Escherichia coli and Vibrio alginolyticus, respectively. Those complexes work as a H⁺ and a Na⁺ channel, respectively and play important roles in torque generation as the stators of the flagellar motors. Although Asp32 of MotB and Asp24 of PomB are believed to function as ion binding site(s), the ion flux pathway from the periplasm to the cytoplasm is still unclear. Conserved residues, Ala39 of MotB and Cys31 of PomB, are located on the same sides as Asp32 of MotB and Asp24 of PomB, respectively, in a helical wheel diagram. In this study, a series of mutations were introduced into the Ala39 residue of MotB and the Cys31 residue of PomB. The motility of mutant cells were markedly decreased as the volume of the side chain increased. The loss of function due to the MotB(A39V) and PomB(L28A/C31A) mutations was suppressed by mutations of MotA(M206S) and PomA(L183F), respectively, and the increase in the volume caused by the MotB(A39V) mutation was close to the decrease in the volume caused by the MotA(M206S) mutation. These results demonstrate that Ala39 of MotB and Cys31 of PomB form part of the ion flux pathway and pore with Met206 of MotA and Leu183 of PomA in the MotA/B and PomA/B stator units, respectively.

Cell-free synthesis of the torque-generating membrane proteins, PomA and PomB, of the Na+-driven flagellar motor in Vibrio alginolyticus

Flagellar motor proteins, PomA and PomB, are essential for converting the sodium motive force into rotational energy in the Na(+)-driven flagella motor of Vibrio alginolyticus. PomA and PomB, which are cytoplasmic membrane proteins, together comprise the stator complex of the motor and form a Na(+) channel. We tried to synthesize PomA and PomB by using the cell-free protein synthesis system, PURESYSTEM. We succeeded in doing so in the presence of liposomes, and showed an interaction between them using the pull-down assay. It seems likely that the proteins are inserted into liposomes and assembled spontaneously. The N-terminal region of in vitro synthesized PomB appeared to be lost, but this problem was suppressed by fusing GFP to the N-terminus of PomB or by mutagenesis at Pro-11 or Pro-12. A structural change of the N-terminal region of PomB by these modifications may prevent cleavage during protein synthesis in PURESYSTEM. The mutations did not affect the functioning of the motor. Using this system, biochemical analysis of PomA and PomB can be performed easily and efficiently.

Collaboration of FlhF and FlhG to regulate polar-flagella number and localization in Vibrio alginolyticus

Precise regulation of the number and placement of flagella is critical for the mono-polar-flagellated bacterium Vibrio alginolyticus to swim efficiently. We have shown previously that the number of polar flagella is positively regulated by FlhF and negatively regulated by FlhG. We now show that DeltaflhF cells are non-flagellated as are most DeltaflhFG cells; however, some of the DeltaflhFG cells have several flagella at lateral positions. We found that FlhF-GFP was localized at the flagellated pole, and its polar localization was seen more intensely in DeltaflhFG cells. On the other hand, most of the FlhG-GFP was diffused throughout the cytoplasm, although some was localized at the pole. To investigate the FlhF-FlhG interaction, immunoprecipitation was performed by using an anti-FlhF antibody, and FlhG co-precipitated with FlhF. From these results we propose a model in which FlhF localization at the pole determines polar location and production of a flagellum, FlhG interacts with FlhF to prevent FlhF from localizing at the pole, and thus FlhG negatively regulates flagellar number in V. alginolyticus cells.

Flagellar motility in bacteria structure and function of flagellar motor

Bacterial flagella are filamentous organelles that drive cell locomotion. They thrust cells in liquids (swimming) or on surfaces (swarming) so that cells can move toward favorable environments. At the base of each flagellum, a reversible rotary motor, which is powered by the proton- or the sodium-motive force, is embedded in the cell envelope. The motor consists of two parts: the rotating part, or rotor, that is connected to the hook and the filament, and the nonrotating part, or stator, that conducts coupling ion and is responsible for energy conversion. Intensive genetic and biochemical studies of the flagellum have been conducted in Salmonella typhimurium and Escherichia coli, and more than 50 gene products are known to be involved in flagellar assembly and function. The energy-coupling mechanism, however, is still not known. In this chapter, we survey our current knowledge of the flagellar system, based mostly on studies from Salmonella, E. coli, and marine species Vibrio alginolyticus, supplemented with distinct aspects of other bacterial species revealed by recent studies.

Regulation of polar flagellar number by the flhF and flhG genes in Vibrio alginolyticus

The number and location of bacterial flagella vary with the species. The Vibrio alginolyticus cell has a single polar flagellum, which is driven by sodium ions. We selected mutants on the basis of reduced swarming ability on soft agar plates. Among them, we found two mutants with multiple polar flagella, and named them KK148 and NMB155. In Pseudomonas species, it is known that FlhF and FleN, which are FtsY and MinD homologs, respectively, are involved in regulation of flagellar placement and number, respectively. We cloned homologous genes of V. alginolyticus, flhF and flhG. KK148 cells had a nonsense mutation in flhG; cells expressing transgenic flhG recovered the swarming ability and had a reduced number of polar flagella. NMB155 cells did not have a mutation in either flhF or flhG. In wild-type cells, expression of flhF increased the number of polar flagella; in contrast, expression of flhG reduced both the number of polar flagella and the swarming ability. These results suggest that FlhG negatively regulates the number of polar flagella in V. alginolyticus. KK148 cells expressing both flhF and flhG exhibited fewer polar flagella and better swarming ability than KK148 cells expressing flhG alone, suggesting that FlhG acts with FlhF.

High Speed and Reproducible Analysis of Nitrosamines by Capillary Electrophoresis with a Sulfonated Capillary

Recently environmental control is regarded as important for good human health conditions, and toxic substances, including carcinogens and endocrine disruptors should be eliminated from our living environment. Hence easy quantitative methods are expected for a high level of environmental control. Our previous paper describes an easy quantitative analysis of nitrosamines (NAs) by capillary electrophoresis with an untreated fused silica capillary installed in an ordinary apparatus. In this paper, utilizing a novel type capillary column having sulfonated inner wall was investigated for improvements of separation performance and reproducibility. A sulfonated capillary causes fast and stabile electroosmotic flow because its inner wall is strongly negative charged. On a performance comparison of a sulfonated capillary with an untreated fused silica, analysis time reduction of c.a. forty percent was achieved, and relative standard deviations of migration times and peak responses were less than one third. In addition sample concentrations giving detection and quantitation limits were also reduced to a half.

The Vibrio motor proteins, MotX and MotY, are associated with the basal body of Na-driven flagella and required for stator formation

The four motor proteins PomA, PomB, MotX and MotY, which are believed to be stator proteins, are essential for motility by the Na(+)-driven flagella of Vibrio alginolyticus. When we purified the flagellar basal bodies, MotX and MotY were detected in the basal body, which is the supramolecular complex comprised of the rotor and the bushing, but PomA and PomB were not. By antibody labelling, MotX and MotY were detected around the LP ring. These results indicate that MotX and MotY associate with the basal body. The basal body had a new ring structure beneath the LP ring, which was named the T ring. This structure was changed or lost in the basal body from a DeltamotX or DeltamotY strain. The T ring probably comprises MotX and MotY. In the absence of MotX or MotY, we demonstrated that PomA and PomB were not localized to a cell pole. From the above results, we suggest that MotX and MotY of the T ring are involved in the incorporation and/or stabilization of the PomA/PomB complex in the motor.