Insights into gas fermentation optimisation for enhanced acetate production
Date
2024
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Tartu Ülikool
Abstract
Conversion of CO2 utilising gas fermenting acetogens is a feasible and environmentally beneficial
solution to the global problem of greenhouse gas emissions. Homoacetogens are an especially
intriguing type of microorganisms since they can yield acetate as their primary metabolic product via
the Wood–Ljungdahl pathway. A product inhibition mechanism is observed when acetate
accumulates in high concentrations, adversely impacting bacterial growth and acetate production. The
tolerance of these microorganisms towards varying concentrations of acetate and under identical
conditions has not previously been investigated. However, it has been defined as crucial for selecting
the most robust acetogen for its use at industrial scale. The designed experimental setup for acetate
tolerance studies, including positive and negative controls, was intended to answer this scientific
question. Following the pre-screening test, it was observed that the carbon source affected the
microbial ability to tolerate acetate; bacteria performed substantially better when a more energy-rich
carbon source, glucose, was supplemented. The latter finding was accounted for when designing the
main screening setup for acetate tolerance in four well-known homoacetogenic strains, where
Moorella thermoacetica and Thermoanaerobacter kivui performed the best. Then, T. kivui was
utilised to perform pH-controlled fermentations in pressurised gas bioreactors. Furthermore, the
outcomes of this master's thesis support the hypothesis that gram-positive anaerobes undergo
variation in their Gram staining due to oxygen exposure. This thesis provides valuable information
for the future selection and screening of homoacetogenic strains and the effect of pH-controlled
cultivation in a pressurised bioreactor.
Description
Keywords
Acetate tolerance, Acetogens, Anaerobic, Gas fermentation, Screening