Adaptive response of Haloferax mediterranei to low concentrations of NaCl (< 20%) in the growth medium
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© Springer-Verlag 1997
S H O RT C O M M U N I C AT I O N
Sandra E. D’Souza · Wijaya Altekar · S. F. D’Souza
Adaptive response of Haloferax mediterranei to low concentrations of NaCl (< 20%) in the growth medium
Received: 3 January 1997 / Accepted: 18 April 1997
Abstract Halobacteria require 20–25% NaCl for optimal growth and lyse when the salt concentration falls below 10%. The response of Haloferax mediterranei cells to low concentrations of NaCl (< 20%) in the medium was studied. The cells adapted to and grew in concentrations of NaCl as low as 10% and survived in concentrations lower than 5%. The cells synthesised a red pigment, bacterioruberin, in response to stress caused by a low concentration of NaCl (< 20%).
sea water (3% total salts or 1% NaCl) could play an important role in the dispersion of halobacteria. The present work describes the adaptive response of H. mediterranei cells with respect to bacterioruberin synthesis to low concentrations of NaCl (< 20%) in the medium.
Key words Haloferax mediterranei · Red pigment · Bacterioruberin · Osmotic stability
H. mediterranei ATCC 33 500 was a gift from Dr. RodriguezValera, University of Alicante, Spain. The organism was grown in a synthetic salts medium containing 20% NaCl, 0.5% glucose and 0.05 M Tris-HCl (pH 7.2) (Rodriguez-Valera et al. 1980). Growth was monitored at different time intervals (0–72 h) by following the OD600 of the cultures, and the glucose concentration and pH of the medium. The NaCl concentration in the medium was lowered to 15, 10, 5 and 0%, and the growth response of H. mediterranei cells was studied. The medium devoid of NaCl is referred to as basal salts medium. The cells were harvested and washed with 20% NaCl, and cell extracts were prepared by sonicating the cells in 0.05 M Tris-HCl (pH 7.5) containing 3.0 M KCl.
Introduction Extremely halophilic bacteria are adapted to life in highly saline conditions and require more than 15% (2.56 M) NaCl for growth (Kushner 1985); the cells lyse when the salt concentration falls below 10% (1.71 M). Environmental influences of salinity, Mg2+ concentration, pH, and oxygen tension together with the biochemical capability of the organisms play an important role in nature in the selection of certain groups or strains of aerobic halophilic archaebacteria (Tindall and Truper 1986). Haloferax mediterranei, in contrast to Halobacterium salinarium, has a low NaCl (1.5–2.5 M) dependence and an elevated Mg2+ (0.5–1.5 M) dependence for growth (Rodriguez-Valera et al. 1983; Tindall and Truper 1986). Since salt dilution is a common stress factor in the ever-changing salt environment, the ability to survive in
S. E. D’Souza (Y) · W. Altekar Radiation Biology and Biochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India Fax +91-22-556-0750 S. F. D’Souza Biotechnology Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
Materials and methods Organism and growth conditions
Analytical methods and chemicals Glucose in the medium was estimated by the glucose oxid
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