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a The listed NaCl was added to that present in the base media [10 g/liter for LB (Miller, 1972) and

50 mM for MOPS (Neidhardt et at., 1974)]. b LB medium (Miller, 1972) contains tryptone (a tryptic hydrolysate of casein, 10 g/liter), yeast extract (5 g/liter), andNaCl (10 g/liter). Note that LB medium formulations vary in NaCl content, and hence osmolality.

c MOPS is a minimal salts medium designed for the growth of enterobacteria (Neidhardt et at., 1974). For these osmolality measurements, MOPS medium was supplemented with D-glucose (11 mM) as carbon source and NH4Cl (9.5 mM) as nitrogen source.

a The listed NaCl was added to that present in the base media [10 g/liter for LB (Miller, 1972) and

50 mM for MOPS (Neidhardt et at., 1974)]. b LB medium (Miller, 1972) contains tryptone (a tryptic hydrolysate of casein, 10 g/liter), yeast extract (5 g/liter), andNaCl (10 g/liter). Note that LB medium formulations vary in NaCl content, and hence osmolality.

c MOPS is a minimal salts medium designed for the growth of enterobacteria (Neidhardt et at., 1974). For these osmolality measurements, MOPS medium was supplemented with D-glucose (11 mM) as carbon source and NH4Cl (9.5 mM) as nitrogen source.

as biofilms. New tools can now be applied to study osmoregulation by biofilm bacteria (see Methods in Enzymotogy, Volumes 336 and 337).

Light scattering is usually used as a measure of bacterial population density in liquid media. The relationship between light scattering and bacterial population density is affected by medium refractive index (in turn a function of solute content) and by bacterial aggregation, size, shape, and refractive index (all of which can be affected by osmotic pressure and osmotic adaptation). For a discussion of light scattering as a tool for the assessment of bacterial numbers and bacterial cell structure, see Wood (1999). Light scattering should therefore be supplemented with viable counts (enumeration of colonies arising when aliquots of culture dilutions are spread on petri plates) or measurements of the protein content of cell suspensions for studies of osmotolerance and osmoregulation (e.g., Culham et at., 2001; Romantsov et at., 2007).

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