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Influence of iron-limited continuous culture on physiology and virulence of Legionella pneumophila

Influence of iron-limited continuous culture on physiology and virulence of Legionella pneumophila
Influence of iron-limited continuous culture on physiology and virulence of Legionella pneumophila

A virulent strain of Legionella pneumophila serogroup 1, subgroup Pontiac, was grown in continuous culture at a constant growth rate under iron-replete and iron-limited conditions. Iron limitation was achieved by the removal of ferrous sulfate and hemin from the chemically defined medium. Residual contaminating iron, 0.45 μM, was sufficient to support iron-limited growth. Typical iron-replete cultures metabolized 3.3 μM iron. Serine provided the principal source of carbon and energy for both cultures, although iron- replete cultures also depleted a number of other amino acids. There was a 40% decrease in culture biomass under iron-restricted conditions. Iron limitation did not significantly affect carbohydrate metabolism, with the molar growth yield for carbon (Y(carbon)) comparable for both cultures. However, under iron-limited conditions a sixfold increase in Y(iron) correlated with a significant decrease in the iron content of the biomass, as the culture utilized the available iron more efficiently. Highly pleomorphic iron- replete cultures became uniform cultures of short fine rods when adapted to iron-deficient conditions. In addition to the morphological and physiological changes, iron limitation had a critical effect on culture virulence. The virulence of this strain was significantly (P < 0.05) reduced when the culture was subjected to iron-limited conditions. This phenomenon was reversible, with a significant increase in culture virulence upon reversion to iron-replete conditions. When compared in an in vitro macrophage assay, the number of culturable avirulent iron-limited cells located intracellularly after infection was significantly lower than for the virulent replete and control cultures. These results further support the role of environmental parameters in regulating the virulence of L. pneumophila.

0019-9567
4224-4230
James, B. W.
2982ef34-33f6-4dd1-bc54-03b0333f3339
Mauchline, W. S.
80ed42b2-235d-4e4b-998b-bb928a52daa2
Fitzgeorge, R. B.
af44691f-36fb-44fc-b2ac-f5125080667c
Dennis, P. J.
25bd2523-2802-498f-9a17-80ecea7db112
Keevil, C. W.
cb7de0a7-ce33-4cfa-af52-07f99e5650eb
James, B. W.
2982ef34-33f6-4dd1-bc54-03b0333f3339
Mauchline, W. S.
80ed42b2-235d-4e4b-998b-bb928a52daa2
Fitzgeorge, R. B.
af44691f-36fb-44fc-b2ac-f5125080667c
Dennis, P. J.
25bd2523-2802-498f-9a17-80ecea7db112
Keevil, C. W.
cb7de0a7-ce33-4cfa-af52-07f99e5650eb

James, B. W., Mauchline, W. S., Fitzgeorge, R. B., Dennis, P. J. and Keevil, C. W. (1995) Influence of iron-limited continuous culture on physiology and virulence of Legionella pneumophila. Infection and Immunity, 63 (11), 4224-4230.

Record type: Article

Abstract

A virulent strain of Legionella pneumophila serogroup 1, subgroup Pontiac, was grown in continuous culture at a constant growth rate under iron-replete and iron-limited conditions. Iron limitation was achieved by the removal of ferrous sulfate and hemin from the chemically defined medium. Residual contaminating iron, 0.45 μM, was sufficient to support iron-limited growth. Typical iron-replete cultures metabolized 3.3 μM iron. Serine provided the principal source of carbon and energy for both cultures, although iron- replete cultures also depleted a number of other amino acids. There was a 40% decrease in culture biomass under iron-restricted conditions. Iron limitation did not significantly affect carbohydrate metabolism, with the molar growth yield for carbon (Y(carbon)) comparable for both cultures. However, under iron-limited conditions a sixfold increase in Y(iron) correlated with a significant decrease in the iron content of the biomass, as the culture utilized the available iron more efficiently. Highly pleomorphic iron- replete cultures became uniform cultures of short fine rods when adapted to iron-deficient conditions. In addition to the morphological and physiological changes, iron limitation had a critical effect on culture virulence. The virulence of this strain was significantly (P < 0.05) reduced when the culture was subjected to iron-limited conditions. This phenomenon was reversible, with a significant increase in culture virulence upon reversion to iron-replete conditions. When compared in an in vitro macrophage assay, the number of culturable avirulent iron-limited cells located intracellularly after infection was significantly lower than for the virulent replete and control cultures. These results further support the role of environmental parameters in regulating the virulence of L. pneumophila.

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e-pub ahead of print date: 1 December 1995

Identifiers

Local EPrints ID: 431340
URI: http://eprints.soton.ac.uk/id/eprint/431340
ISSN: 0019-9567
PURE UUID: dbc96c3a-26b5-4979-ae6a-ef4d66b7187e
ORCID for C. W. Keevil: ORCID iD orcid.org/0000-0003-1917-7706

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Date deposited: 29 May 2019 16:30
Last modified: 07 Oct 2020 08:33

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