Increase in bacterial biosurfactant production by co-cultivation with biofilm-forming bacteria

Considering that bacterial biosurfactants (BSFs) are released as secondary metabolites involved in biotic relations within mixed bacterial assemblages, the hypothesis that the co-cultivation of BSF producing bacteria with biofilm-forming strains would enhance BSF synthesis was tested. Environmental BSF producing strains of Bacillus licheniformis and Pseudomonas sp. were cultivated with reference biofilm-forming strains (Pseudomonas aeruginosa and Listeria innocua). BSF production and quorum-quenching effects were tested in solid media. Tensioactive and anionic BSFs were also quantified in cell-free extracts (CFEs). BSF production increased in co-cultures with inducer strains although this was not demonstrated by all screening methods. Increased concentrations of anionic BSF were detected in CFEs of co-cultures in which Pseudomonas aeruginosa was included as inducer, which is in accordance with the observation of larger halos in cetyl trimethylammonium bromide-methylene blue agar. The results demonstrate that co-cultivation positively affects the efficiency of BSF production and that higher production yields may be attained by selecting convenient inducer partners in designed consortia. Significance and Impact of the Study The high production cost of biosurfactants (BSFs) still represents a major limitation to the industrial use of these otherwise advantageous alternatives to chemical surfactants. This work demonstrates that the co-cultivation of consortia of biosurfactant-producer and biofilm-forming bacteria enhances BSF production and may contribute to the cost-effectiveness of biosurfactant-based products.