Ivo Ganchev1 and Lev Tribis2
1 Trakia University, Faculty of Technics and Technologies of Yambol, 8602 Yambol, Bulgaria
2 Agriculture Academy,“Nikola Poushkarov“ Institute of Soil Science, Agrotechnologies and Plant Protection, 1331 Sofia, Bulgaria
Ganchev, I. & Tribis, L. (2025). Influence of osmolites on dual-species biofilm formation. Bulg. J. Agri. Sci., 31(2), 301–312
In a large part of ecological niches, bacterial species are united in communities and develop together in the form of heterogeneous structures called biofilms, which are formed on surfaces of different nature and nature with the participation and as a result of the interaction of two or more bacterial species. In this study, we evaluated effects of the osmolality of the cultivating on the biofilm development and architecture of biofilms of the bacterium (B. subtilis) during their interactions with Escherichia coli K-12 1655 strain. Effects of the osmolality of the cultivating on bacterial biofilm formation and the mechanisms were analyzed by the crystal violet staining method combined with cultivated microbial analysis, and confocal laser scanning microscopy. A 24 h mature Bacillus subtilis and Escherichia coli dual-species biofilms were exposed to different concentration of NaCl of the cultivating. To investigate the effect of NaCl concentration, a series of experiments on the cultivation of biofilms in M63 medium (0.02 M KH2PO4, 0.04 M K2HPO4, 0.02 M (NH4)2SO4, 0.1 mM MgSO4 and 0.04 M glucose) were carried out according to the indicated scheme at the concentration of NaCl of 100 mM, 150 mM, and 200 mM. At cultivation in the cultural medium without NaCl, the bacterial growth rates of single-species biofilms of Bacillus subtilis strains and biofilms as a result of their interaction with Escherichia coli strains were similar and determines the mutualism between two strains in the structure of biofilms, but the temperature of the cultivating of the concentration of NaCl in the cultural medium over of 100 mM lead to the impeded growth and affect adversely the process of biofilm formation by the participation of B. subtilis 170 and E. coli K-12 1655, B. subtilis 168 and E. coli K-12 1655 strains, as a result of which a decrease in the value of the optical density, average thickness and relative spreading area and an inversely proportional increase in the ratio of the spreading area of the structures to their volume, but inhibits spore formation.