study the role of different glucose concentration along withfoaming, B. subtilis cells grown for 18 h were submitted to a foamingprocess (see Section 2.3). To this end, shake-flask cultivations, inoc-ulated with 0.038 g/L of wet biomass, were conducted in 500 mLErlenmeyer flasks containing 100 mL of M9 medium supplementedwith different glucose levels (3.5, 7, 10.5, and 21 g/L). The cells sub-mitted to a foaming process were compared with non-foamingsubmitted cells. These cultures were subsequently incubated onan orbital shaker (Innova 42, New Brunswick Sci.) at 200 rpmand 30◦C. Samples were aseptically withdrawn periodically todetermine cell growth. Biomass was removed by centrifugation at11,000 g for 5 min, the cell-free supernatants being stored frozen(−20◦C) until further analysis. Cultivations were carried out induplicate as independent trials.