Measurement Techniques to Resolve and Control Population Dynamics of Mixed-Culture Processes

Abstract

Microbial mixed cultures are gaining increasing attention as biotechnological production systems, since they offer a large but untapped potential for future bioprocesses. Effects of secondary metabolite induction and advantages of labor division for the degradation of complex substrates offer new possibilities for process intensification. However, mixed cultures are highly complex, and, consequently, many biotic and abiotic parameters are required to be identified, characterized, and ideally controlled to establish a stable bioprocess. In this review, we discuss the advantages and disadvantages of existing measurement techniques for identifying, characterizing, monitoring, and controlling mixed cultures and highlight promising examples. Moreover, existing challenges and emerging technologies are discussed, which lay the foundation for novel analytical workflows to monitor mixed-culture bioprocesses. Mixed Cultures: Opportunities and Challenges An old tradition is revolutionizing modern biotechnology: microbial collaboration. Mixed-culture applications, such as wastewater treatment, composting, and a broad spectrum of fermentative food preparations, are the historical foundation of current biotechnology. Now, a targeted assembly of microorganisms to perform concerted bioproductions is forming a new cutting edge in biotechnology. Over the past decade, the research field of defined mixed cultures has gained increased attention due to their potential for process intensification and the chance to produce unknown secondary metabolites [1]. In the old-school mixed-culture approach, the driving force to develop mixed culture-specific (online) measurement techniques was very limited. Reasons for this might be the rather low dynamic of these processes and the strong closeness to natural processes and equilibria with no need for control. In other words, there was simply no need for a deeper understanding of these robust systems. However, this is now changing. Since sustainability is currently the most important driving force in biotechnology, the number of published studies on mixed-culture consolidated bioprocesses (see Glossary) with plant biomass, waste streams, and gaseous waste substrates is increasing significantly [2-9]. The products of these processes are, in many cases, acids, alcohols, or enzymes for biomass pretreatment and hydrolysis [6,9]. Higher-value products of mixed cultures are secondary metabolites induced by interspecies communication [1,10-14]. Among these, antimicrobial substances, such as antibiotics, are of critical interest, especially in the context of increasingly multiresistant pathogens [15]. However, in-depth studies in this field are only possible with measurement tools for the identification and characterization of the microbial composition. To avoid the complexity of unknown natural microbial communities, synthetic co-culture systems allow defined combinations of microorganisms with beneficial metabolic pathways. Yet, in contrast to natural communities, which are typically stabilized by natu...

Advances in automated real‐time flow cytometry for monitoring of bioreactor processes

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