Abstract
The composition of culture media and the microbial cell mass influence on secondary metabolites production in fermentative procedures. The effect of two process variables, namely glucose and inoculum concentrations on biomass formation, bioactivity and surface tension of extract obtained during the cultivation of endophytic Paenibacillus polymyxa RNC-D was evaluated. Assays were performed using glucose and inoculum concentrations varying from 5.0 to 40.0 g.l −1 and from 2.5% to 5.0% (v/v), respectively, according to a 2 2 full factorial design. The microorganism was cultivated in orbital shaker (30 ◦ C, 180 rpm) for 96 h. Cell growth was estimated by optical density (600 nm) vs dry weight calibration curve. Bioassays were performed using two-fold serially diluted extract displayed in 96-well plates. Escherichia coli ATCC 25923 and Staphylococcus aureus ATCC 25922 were used as indicator strains. The minimal inhibitory concentration (MIC) was expressed in g.ml −1 . Surface tension (mN.m −1 ) of extracts was measured using a tensiometer. A significant (p<0.01) and positive effect of glucose and inoculum concentrations was observed on biomass formation. Bioactivity results were also affected by the two studied variables (p<0.01). The lowest MIC value of E. coli was obtained when the highest glucose and inoculum concentrations were used. Otherwise, MIC of S. aureus was increased when the maximum glucose was applied. Surface tension was affected by the two evaluated variables and also by their interaction (all of negative signal, p<0.1). The highest biomass formation (4.11 g.l−1) and the lowest MIC of E.coli (15.6g.ml −1 ) were attained under the highest concentrations of glucose and inoculum, while the surface tension reduction reached the maximum (20.0 mN.m −1 ) when using the lowest glucose and the highest inoculum concentrations. Such results can still be improved by performing additional assays for the establishment of the quadratic models, as suggested by analysis of the experimental design.
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