Influence of Consistency and Composition of Growth Medium on Surface Physicochemical Properties of Streptomyces

Abstract

Streptomyces are known for their ability to produce various secondary metabolites used in biotechnology, human medicine and agriculture. Understanding of surface properties is very interesting in the control of interfacial phenomena. The objective of this study was to investigate the effect of consistency and composition of growth medium on the physicochemical properties of the surface of Streptomyces strains. To achieve this objective, Six Streptomyces strains belonging to bioprocess and bio-interfaces laboratory are cultivated in two media Bennett (rich) and GBA (minimum). Both media are tested in solid (agar) and liquid (broth) mode. The wettability θw, electron donor character ˠ (-), electron acceptor character ˠ (+) and Surface free energy ΔGiwi are determined using contact angle measurements. On the two solid media Bennett and GBA, Streptomyces strains develop a hydrophobic surface (96.9° <θw<167.9°) with a weak electron donor character (0.3 mJm-2 < (ˠ (-)) <12.14 mJm-2) and a strong electron acceptor character (0.26 mJm-2 < ˠ (+) < 17.8 mJm-2) and a negative surface free energy ((- 11.8 mJm-2) < ΔGiwi < (-110 mJm-2)). Whereas on both Bennett and GBA liquid media, the surfaces of Streptomyces strains are generally hydrophilic (1.3° < θw < 9.33°) with a strong electron donor character (13.76 mJm-2 < ( ˠ (-)) < 70.06 mJm-2) and a positive surface free energy. By changing the composition of the culture medium, only a slight change in the degree of hydrophobicity and surface free energy of Streptomyces is observed. Regarding the effect of medium composition on the surface properties of Streptomyces, the degree of wettability and the values of surface free energy are no longer the same when the composition of the medium changes. These results could be applied in further studies interested in interfacial phenomena and microbial adhesion in biotechnological fields.