Effect of shear on morphology, viability and metabolic activity of succinic acid-producing Actinobacillus succinogenes biofilms

Abstract

Two custom designed bioreactors were used to evaluate the effect of shear on biofilms of a succinic acid producer, Actinobacillus succinogenes. The first bioreactor allowed for in-situ removal of small biofilm samples used for microscopic imaging. The second bioreactor allowed for complete removal of all biofilm and was used to analyse biofilm composition and productivity. The smooth, low porosity biofilms obtained under high shear conditions had an average cell viability of 79% compared to 57% at the lowest shear used. The maximum cell-based succinic acid productivity for high shear biofilm was 2.4 g g −1 DCW h −1 compared to the 0.8 g g −1 DCW h −1 of the low shear biofilm. Furthermore, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assays confirmed higher cell metabolic activities for high shear developed biofilm compared to biofilm developed at low shear conditions. Results clearly indicated that high shear biofilm cultivation has beneficial morphological, viability, and cell-based productivity characteristics.

Internal mass transfer considerations in biofilms of succinic acid producing Actinobacillus succinogenes

“…The complex nature of the model required a method to combine the interactions of the various parameters in a mechanistically interpretable way. A data set of pseudo-steady state biofilm results was compiled by combining results for pseudo-steady state fermentation studies by Maharaj et al [9], Brink & Nicol [10,26], Mokwatlo et al [21] (Error! Reference source not found.…”

“…Within a biofilm system, the biofilm properties are a strong function of the history of the biofilm. Mokwatlo et al [20,21] showed that metabolite accumulation, specifically CSA, and external shear are major factors in the development of A. succinogenes biofilms. The data for Maharaj et al [9] were obtained in a packed bed system under very low shear conditions (0.04 m.s −1 ) and dilution rates between 0.054 and 0.72 h −1 , corresponding to SA titres between 32.5 g.L −1 and 11 g.L −1 .…”

“…In addition, extracellular polymeric substances (EPS) in biofilms impede diffusion, a problematic property in pathogenic biofilms as it increases resistance to antimicrobial treatments [19]. Previous studies [20][21][22] have shown how both composition and properties of A. succinogenes biofilms vary depending on the hydrodynamic shear-and accumulated acid conditions. Low shear conditions would result in porous structures and be favourable in terms of mass transfer but tend to be unstable and prone to shedding events [23][24][25].…”

“…This work investigated internal mass transfer in biofilms of A. succinogenes by initially developing a theoretical transient internal mass transfer biofilm model, using intrinsic SA production kinetics estimated from resuspended batch biofilm fermentation experiments (i.e. to eliminate mass transfer limitations) in concert with known A. succinogenes biofilm properties [20][21][22]. The model was validated by accurate prediction of experimental transient batch biofilm behaviour.…”

Enhanced Oxygen Mass Transfer in Mixing Bioreactor Using Silica Microparticles

“…Still, this depends on the process's flow regime, which reduces the liquid layer of nearby air bubbles and increases the k L a. However, using solid particles in the fermenter can lead to the hydrodynamic shearing of the biomass, impacting the morphology and viability of bacterial biomass [22] and even filamentous fungi more susceptible to shearing [23]. In this sense, the use of particles can be administered by limiting the aeration and agitation conditions of the medium.…”