Kinetics of Pseudomonas veronii 2E biofilm development under different nutritional conditions for a proper bioreactor design

• An innovative method for biofilm structure analyses was developed.
• The applied image capture and processing is an easy and low cost/time technique.
• CV dying method by itself could lead to unreliable results.
• A biofilm structure study required the complementation of both techniques.
• P. veronii 2E homogeneous biofilms in complex media are applicable to bioreactors.

Biofilm-mediated bioreactors represent a proficient alternative, as extracellular materials of bacterial biofilms enhance metal immobilization by biosorption. Bacterial attachment or detachment is related to environmental conditions. The aim of this work is to study the nutritional dependence of Pseudomonas veronii 2E biofilm development to be applied in a future biofilm-reactor for wastewater treatments. For such purpose, biofilm establishment kinetics was explored over glass coverslips changing medium composition and nutrient concentration and in Fe(II) presence. After crystal violet cell staining, biofilm was visualized using direct microscopic observation; sample scanning-image analysis implemented in MATLAB and ethanol extraction-Absorbance 590 nm measurement. Biofilm structure developed with mineral basal medium appeared as a monolayer, but in complex basal media cell aggregates were appreciated. Optimal attachment was achieved with complex basal medium-5 g/L glucose at 55 h. The crystal violet concentration complemented with the image capturing supported these results. Biofilm establishment was enhanced by biosurfactant production in P. veronii 2E. The obtention of mutants deficient in biosurfactant secretion confirmed the influence of these compounds on cell motility and hence on cell attachment. The information of the biofilm structure defined under such conditions is the useful first step for the future bioreactor design.

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