Potassium chemotaxis in <i>Rhodobacter sphaeroides</i>

Poole, Philip S.; Brown, Simon; Armitage, Judith P.

doi:10.1016/0014-5793(90)80073-r

Cited by 6 publications

(4 citation statements)

References 18 publications

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“…Membrane-spanning chemoreceptors (methyl-accepting chemotaxis proteins) (1,8) have not been found (3,17), and all identified chemoattractants are also metabolites (4,9). We have shown that attractants must be transported into the cell for a response to occur, but we had not conclusively identified whether the energetic process of transport caused the chemotactic signal or whether subsequent metabolism of the effector was required (9,12,13).…”

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confidence: 93%

Chemotactic signalling in Rhodobacter sphaeroides requires metabolism of attractants

1993

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Rhodobacter sphaeroides showed chemotaxis towards L-alanine but not towards the analog 2-aminoisobutyrate. 2-Aminoisobutyrate and alanine were shown to share a common transport system, but 2-aminoisobutyrate was not metabolized. Chemotaxis towards alanine was inhibited by structurally unrelated metabolites, suggesting cross-inhibition by common metabolic intermediates.Chemotactic sensing in the purple photosynthetic bacterium Rhodobacter sphaeroides is very different from that in enteric bacteria. Membrane-spanning chemoreceptors (methyl-accepting chemotaxis proteins) (1, 8) have not been found (3,17), and all identified chemoattractants are also metabolites (4, 9). We have shown that attractants must be transported into the cell for a response to occur, but we had not conclusively identified whether the energetic process of transport caused the chemotactic signal or whether subsequent metabolism of the effector was required (9, 12, 13).In Escherichia coli, the nonmetabolizable alanine analog 2-aminoisobutyrate is a strong chemoattractant, competing with alanine for methyl-accepting chemotaxis protein Tsr (11). We therefore examined the chemotactic response, transport, and metabolism of alanine and 2-aminoisobutyrate in R. sphaeroides.Chemotactic behavior. R. sphaeroides WS8 was grown photoheterotrophically as previously described (4) but with succinate, Casamino Acids, and ammonium sulfate replaced by 5 mM L-alanine. Cells, washed and resuspended in N2-sparged Na-HEPES (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid) buffer (10 mM, pH 7.2), were starved for at least 1 h before 0.6 ml was added to the bottom chamber of a chemotaxis well and covered with an 8-pumpore-size polycarbonate membrane and an attractant solution was added to the upper chamber (5). Figure 1 shows that after 90 min there was a threefold increase in bacteria swimming through the membrane in response to 10 mM alanine, whereas there was no chemotactic response to the alanine analog 2-aminoisobutyrate. The response saturated above 10 mM, and the reduced response at 50 mM indicated that the response was chemotaxis rather than chemokinesis (14,15).This result was confirmed in plug plate assays (Table 1) in which washed cells resuspended in HEPES as described above were mixed to approximately 2 x 109/ml with an equal volume of 0.5% agar containing 50 ,ug of chloramphenicol per ml to prevent growth. To test for competition, backgrounds of 10 or 20 mM metabolites were added to the agar. Plugs of attractant in 2.5% agar were placed in the soft agar plates, and chemotaxis was measured as cell accumulation around the plugs after approximately 2 and 5 h.R. sphaeroides showed a strong response to alanine and * Corresponding author.

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confidence: 93%

Chemotactic signalling in Rhodobacter sphaeroides requires metabolism of attractants

1993

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“…In the presence of the carbon source succinate there was no significant change in the speed at which the ceils swam after phosphate addition, in fact 0.1 mM caused an increase. Potassium is known to increase the swimming speed of R. sphaeroides [8], and indeed potassium phosphate had little effect on the swimming speed of R. sphaeroides, presumably because the potassium antagonised the effect of phosphate (data not shown).…”

Section: Resultsmentioning

confidence: 93%

“…It lacks the methyl accepting chemotaxis proteins found in the enteric bacteria and has consequently been studied as a model system of receptor independent chemotaxis [2][3][4][5][6][7]. Many chemoattractants, such as the organic acids and potassium cause an increase in the mean swimming speed and a decrease in the stopping frequency [4,8]. Further analysis of these effects suggests some compounds have two different effects on the flagellar motor of R. sphaeroides.First, there is a true chemotactic response, and secondly, some compounds cause an additional excitation of motility [6].…”

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confidence: 99%

The effect of phosphate on the motility of Rhodobacter sphaeroides

Poole

1991

FEMS Microbiology Letters

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Summary When Rhodobacter sphaeroides was resuspended in sodium phosphate buffer directly after growth on complete medium there was an almost complete loss of motility. The addition of 1 mM sodium phosphate to R. sphaeroides suspended in Hepes buffer also caused an immediate reduction in the mean swimming speed of 35%; an effect that was maintained for more than 60 min. This loss of motility was prevented by the inclusion of succinate in the resuspension medium. Addition of phosphate in the absence of succinate also increased the membrane potential by up to 35% and decreased the rate of respiration by 25%. These effects were reversed in the presence of succinate, phosphate addition decreased the membrane potential by up to 7% and increased the rate of respiration by 23%. These data show that the effect of phosphate buffer on R. sphaeroides is highly complex and its inhibition of motility is probably an indirect effect. The use of phosphate buffer in many physiological experiments may have unexpected side effects.

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“…shows chemokinesis, by the addition of certain chemoeffectors e.g. organic acids [12]. As *Corresponding author.…”

Section: Introductionmentioning

confidence: 99%

Swimming speed and chemokinetic response of Rhodobacter sphaeroides investigated by natural manipulation of the membrane potential

1994

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The AY of R sphaeroides, grown under high light to reduce the levels of light-harvesting bacteriochlorophyll, was naturally manipulated using light intensity. The relationship between AY and the swimming speed of free swimming populations of cells was investigated. After de-energisation by incubation in the dark there was an apparent threshold of about -13 mV which had to be overcome before functional motor rotation could resume and at -45 mV the motor saturated. Further increases in AY over -45 mV did not increase the free swimming velocity. However, when a chemokinetic effector was added there was an increase in swimming speed, even though the A!? was well above saturation, indicating that the chemokinetic response is independent of normal relationship between motor rotation and AY.

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Potassium chemotaxis in Rhodobacter sphaeroides

Cited by 6 publications

References 18 publications

Chemotactic signalling in Rhodobacter sphaeroides requires metabolism of attractants

Chemotactic signalling in Rhodobacter sphaeroides requires metabolism of attractants

The effect of phosphate on the motility of Rhodobacter sphaeroides

Swimming speed and chemokinetic response of Rhodobacter sphaeroides investigated by natural manipulation of the membrane potential

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