Journal of Biotechnology & Biomaterials
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Ectoine (1, 4, 5, 6-tetrahydro-2-methyl-4-pyrimidine carboxylic acid) represents the major compatible solute in many
halophilic and halotolerant bacteria isolated from saline and hypersaline environments, the role of ectoine is to balance the
osmotic pressures inside and outside the cells (Rajanet al., 2010).M9 minimal medium with different concentrations of NaCl (0.5,
0.75, 1.0 M) was used to determine the ability of A. hydrophila ATCC 7966 to grow in low nutrient medium with high salinity. The
roles of organic compatible solutes (glycine betaine, ectoine) taken up from the medium or synthesised de novo were investigated,
this is an important process which allows bacteria to adapt and grow in high salinity. Growth of A. hydrophila ATCC 7966 in
M9 minimal medium at 0.5 M, 0.75 and 1 M NaCl was faster in the presence of glycine betaine or ectoine than in their absence.
However, glycine betaine and ectoine did not stimulate growth in medium without salt. These results suggest that exogenously
supplied glycine betaine and ectoine stimulated the growth of strains as a function of increasing external NaCl at 0.5, 0.75 and
1.0 M. Ectoine promoted the growth of A. hydrophilaat high salinity (0.75 M NaCl after 24 hours),betaine on the other hand did
not show a significant effect on growth until after 72 hours of incubation. However, there was only slight growth of cells of A.
hydrophilaat 0.75 M NaCl (even after 5 days of incubation), when no betaine or ectoine was added. In addition, ectoine was the
most effective compatible solute for A. hydrophila at 1 M NaCl.
The effects of compatible solutes (20 mMbetaine or ectoine) on rates of oxygen uptake (respiration rates) were also measured
under different NaCl concentrations (Nagata et al., 2002). Respiration rate of A. hydrophila decreased as a function of NaCl
concentration increases. However, betaine and ectoine were able to significantly protect the respiration rate of A. hydrophila. In all
cases, at 0.5 M NaCl and above, respiration rates in the presence of 20 mMbetaine or ectoine were higher than respiration rate of
the same cells grown without addition of betaine or ectoine. Glycine betaine and ectoine led to the recovery of respiratory activity
in A. hydrophilain the presence of 1.0 M NaCl, however ectoine was more effective.
The de novo synthesisof compatible solute was monitored in M9 minimal medium cultures by NMR spectroscopy. Glutamate
was present at 0.5 M NaCl, but at high salt concentrations (0.75, 1 and 1.25 MNaCl) only ectoine was present.
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