Investigations on the growth of Rhodococcus rubra in relation to the formation of stable biological foams

The growth characteristics of a foam-forming species, Rhodococcus rubra wer e studied on different substrates. The basic medium contained Czapek (3.34% ), yeast extract (0.2%), potassium dihydrogen phosphate (0.12%), dipotassiu m hydrogen phosphate (0.25%) and ammonium chloride (0.1%). This was supplem ented with varying concentrations of glucose (0-2%). The same basic medium was also used to examine the growth of R. rubra in combination with varying concentration of n-hexadecane (0.0-0.5%) as a source of energy while varyi ng the concentration of ammonium chloride in the range 1-3 g l(-1). Studies based on determining the biomass concentration, the surface activity relat ed to the cell suspensions and measuring the variations in broth pH reveale d that glucose encouraged the growth of R. rubra, compared to the control. However, increasing the glucose concentration from 0.1 to 2.0% had no furth er effect on growth. The surface activity of the cell suspensions increased with increasing glucose concentration. Results similar to glucose were exh ibited by the addition of n-hexadecane, suggesting same degree of growth am ong different concentrations with higher surface activity increasing with i ncrease in substrate concentration. Results have also shown that the pH of all the culture broths decreased as the ammonium chloride concentration inc reased, suggesting that there was a production of hydrogen ions during the course of its metabolism.