Growth Dynamics of Bacterial Populations in a Two-Compartment Biofilm Bioreactor Designed for Continuous Surfactin Biosynthesis.

Hannah Luise Brück,François Coutte,Frank Delvigne,Philippe Jacques,Pascal Dhulster,Sébastien Gofflot

doi:10.3390/microorganisms8050679

Abstract

Biofilm bioreactors are promising systems for continuous biosurfactant production since they provide process stability through cell immobilization and avoid foam formation. In this work, a two-compartment biofilm bioreactor was designed consisting of a stirred tank reactor and a trickle-bed reactor containing a structured metal packing for biofilm formation. A strong and poor biofilm forming B. subtilis 168 strain due to restored exopolysaccharides (EPS) production or not were cultivated in the system to study the growth behavior of the planktonic and biofilm population for the establishment of a growth model. A high dilution rate was used in order to promote biofilm formation on the packing and wash out unwanted planktonic cells. Biofilm development kinetics on the packing were assessed through a total organic carbon mass balance. The EPS+ strain showed a significantly improved performance in terms of adhesion capacity and surfactin production. The mean surfactin productivity of the EPS+ strain was about 37% higher during the continuous cultivation compared to the EPS- strain. The substrate consumption together with the planktonic cell and biofilm development were properly predicted by the model (α = 0.05). The results show the efficiency of the biofilm bioreactor for continuous surfactin production using an EPS producing strain.

Highlights

Most of the biotechnological processes are based on planktonic cells in suspension in the cultivation medium [1]
In a previously designed trickle-bed biofilm reactor ([16,25]), the co-existence of a planktonic and biofilm population was recurrently observed during the cultivation of B. amyloliquefaciens GA1 which hindered data interpretation and probably decreased the production yield
Biofilm development on the packing elements gives important information about the process, but is difficult to monitor during cultivation

Summary

Introduction

Most of the biotechnological processes are based on planktonic cells in suspension in the cultivation medium [1]. Cell retention and a long-term cell viability represent the main challenges in a continuous reactor [1]. Natural cell immobilization through biofilm formation presents an interesting alternative technique to design new continuous bioprocesses. Due to the high biomass density in biofilms and their stability, biofilm reactors have a high potential for long-term fermentation processes [4,5]. The biofilm community is highly heterogeneous due to cell differentiation as a result of adaption to nutrients and oxygen gradients inside the biofilm. This heterogeneity makes it challenging to control the growth of the biofilm in the bioreactor

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