Evaluation of productive biofilms for continuous lactic acid production

Abstract

In white biotechnology research, the putative superiority of productive biofilms to conventional biotransformation processes based on planktonic cultures has been increasingly discussed in recent years. In the present study, we chose lactic acid production as a model application to evaluate biofilm potential. A pure culture of Lactobacillus bacteria was grown in a tubular biofilm reactor. The biofilm system was cultivated monoseptically in a continuous mode for more than 3 weeks. The higher cell densities that could be obtained in the continuous biofilm system compared with the planktonic culture led to a significantly increased space-time yield. The productivity reached 80% of the maximum value 10 days after start-up and no subsequent decline was observed, confirming the suitability of the system for long-term fermentation. The analysis of biofilm performance revealed that productivity increases with the flow velocity. This is explained by the reduced retention time of the liquid phase in the reactor, and, thus, a minor pH drop caused by the released lactic acid. At low flow velocities, the pH drops to a value where growth and production are significantly inhibited. The biofilm was visualized by magnetic resonance imaging to analyze biofilm thickness. To deepen the understanding of the biofilm system, we used a simple model for cell growth and lactic acid production. K E Y W O R D Slactic acid production, long-term fermentation, magnetic resonance imaging, productive biofilm, simulation, tubular biofilm reactor

Advances on Bacterial and Fungal Biofilms for the Production of Added-Value Compounds

“…Additionally, membrane biofilm reactors with a porous gas-permeable membrane (e.g., silicone [ 28 , 29 ] and polysulphone [ 30 ]) are often used for these bioreactions [ 28 , 29 ]. Other configurations include fluidized-bed reactors [ 31 , 32 ], airlift reactors [ 33 , 34 ], bubble column reactors [ 35 , 36 ], rotating-disk reactors [ 37 , 38 ], or tubular biofilm reactors [ 39 ]. Thus, the choice of the reactor and feeding strategy (batch, fed-batch, and continuous mode) should be molded to the process conditions and nutritional requirements of the producing microorganisms.…”

“…The supports must be prone to adhesion of microorganisms, be widely available and inexpensive, resist high mechanical forces, and be non-toxic [ 16 , 18 , 19 ]. Synthetic materials employed as supports in biofilm reactors may include ceramics [ 26 , 40 ], silicone [ 41 , 42 ], polyethylene [ 43 , 44 , 45 ], polyurethane [ 46 , 47 ], clay bricks [ 27 ], polypropylene [ 48 ], and glass [ 39 ]. Natural polymers, such as alginate [ 49 , 50 ] and carrageenan [ 22 ], and some lignocellulosic materials, such as cotton [ 51 , 52 ], have also been used to immobilize microbial cells.…”

“…Moreover, the immobilization with the cotton cloth restrained control and operation problems in the reactor observed with freely suspended fungal cells. More recently, Cuny et al [ 39 ] used Lactobacillus delbrueckii to produce lactic acid in a horizontal tubular biofilm reactor. This biofilm system was operated in continuous mode for 3 weeks under different flow velocities and demonstrated good stability.…”

Microfluidic cultivation and analysis of productive biofilms

“…Recent research on productive biofilms generally uses model reactors of mesoscopic size, e.g. to study the continuous production of lactic acid (Cuny et al, 2019), cyclohexanol (Hoschek et al, 2019), or styrene oxide (Schmutzler et al, 2017). However, microfluidic reactors have also been used for this purpose (Karande et al, 2016), for instance, the segmented flow of microdroplets was utilized for the production of perillic acid (Willrodt et al, 2017).…”

Development and structure of Bacillus subtilis biofilms manipulated by Iron(II) addition during cultivation at different shear stress conditions

“…On one hand, these communities have several beneficial features, e.g. (i) in cleaning waste water (Van Loosdrecht & Heijnen, 1993); (ii) by producing valuable (platform) chemicals (Cuny et al, 2019), (iii) methane (as fuel) (Yeung et al, 2017) or (iv) bioplastics (Hackbarth et al, 2020), too. On the contrary, biofilms can have adverse effects, i.e.…”