2.1.3. Bacterial growth under increasing polyethylene glycol (PEG)
levels in the growing medium
Autochthonous bacterial isolates and the B. megaterium used as
a reference strain were grown at 28 C in an axenic medium
(nutrient broth, 8 g L1
) supplemented or not with increasing PEG
concentrations (0%, 15%, 30% and 40%) to generate osmotic stress
(equivalent to 1.02; 1.50; 3.60 and 3.99 MPa). This allows to
test bacterial osmotic stress tolerance along the time, by
estimating the number of viable cells, as centrifuged per milliliter.
Number of viable cells was estimated after 4 and 6 days of growth
following a conventional procedure: 1 mL of suspension was plated
in agar nutrient broth medium. The bacterial growth was
monitored by measuring optical density at 600 nm. The four
PEG treatments were replicated 3 times in the culture of each
bacterial strain giving a total of 48 tubes.