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Growth phase‐dependent switch in osmolyte strategy in a moderate halophile: ectoine is a minor osmolyte but major stationary phase solute in Halobacillus halophilus
Author(s) -
Saum Stephan H.,
Müller Volker
Publication year - 2008
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/j.1462-2920.2007.01494.x
Subject(s) - ectoine , osmolyte , halophile , biology , operon , osmoprotectant , halotolerance , regulon , biochemistry , gene , gene expression , escherichia coli , proline , bacteria , genetics , amino acid
Summary The moderately halophilic, chloride‐dependent bacterium Halobacillus halophilus switches its osmolyte strategy with the salinity in its environment by the production of different compatible solutes. Ectoine is produced predominantly at very high salinities, along with proline. Interestingly, ectoine production is growth phase dependent which led to a more than 1000‐fold change in the ectoine : proline ratio from 0.04 in exponential to 27.4 in late stationary phase cultures. The genes encoding the ectoine biosynthesis pathway were identified on the chromosome in the order ectABC . They form an operon that is expressed in a salinity‐dependent manner with low‐level expression below 1.5 M NaCl but 10‐fold and 23‐fold increased expression at 2.5 and 3.0 M NaCl respectively. The temporal expression of genes involved in osmoresponse is different with gdh / gln and pro genes being first, followed by ect genes. Chloride had no effect on expression of ect genes, but stimulated cellular EctC synthesis as well as ectoine production. These data demonstrate, for the first time, a growth‐phase dependent switch in osmolyte strategy in a moderate halophile and, additionally, represent another piece of the chloride regulon of H. halophilus .