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J. Bacteriol., 12 1996, 7221-7226, Vol 178, No. 24
D Canovas, C Vargas, LN Csonka, A Ventosa and JJ Nieto
The osmoregulatory pathways of the moderately halophilic bacterium
Halomonas elongata DSM 3043 have been investigated. This strain grew
optimally at 1.5 to 2 M NaCl in M63 glucose-defined medium. It required at
least 0.5 M NaCl for growth, which is a higher concentration than that
exhibited by the H. elongata type strain ATCC 33173. Externally provided
betaine, choline, or choline-O-sulfate (but not proline, ectoine, or
proline betaine) enhanced the growth of H. elongata on 3 M NaCl-glucose-M63
plates, demonstrating the utilization of these compounds as
osmoprotectants. Moreover, betaine and choline stimulated the growth of H.
elongata DSM 3043 over the entire range of salinity, although betaine was
more effective than choline at salinities below and above the optimum. We
found that H. elongata DSM 3043 has at least one high-affinity transport
system for betaine (K(m) = 3.06 microM and Vmax = 9.96 nmol of betaine
min(-1) mg of protein(-1)). Competition assays demonstrated that proline
betaine and ectoine, but not proline, choline, or choline-O-sulfate, are
also transported by the betaine permease. Finally, thin-layer
chromatography and 13C-nuclear magnetic resonance analysis showed that
exogenous choline was taken up and transformed to betaine by H. elongata,
demonstrating the existence of a choline-glycine betaine pathway in this
moderately halophilic bacterium.
Copyright © 1996, American Society for Microbiology
Osmoprotectants in Halomonas elongata: high-affinity betaine transport system and choline-betaine pathway
Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Seville, Spain.
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