Abstract
A. succinogenes is well known for utilising various catabolic pathways. A multitude of batch fermentation studies confirm flux shifts in the catabolism as time proceeds. It has also been shown that continuous cultures exhibit flux variation as a function of dilution rate. This indicates a direct influence of the external environment on the proteome of the organism. In this work, ATP production efficiency was explored to evaluate the extent of bio-available energy on the production behaviour of A. succinogenes. It was found that the microbe successively utilised its most-to-least efficient energy extraction pathways, providing evidence of an energy optimisation survival strategy. Moreover, data from this study suggest a pyruvate overflow mechanism as a means to throttle acetic and formic acid production, indicating a scenario in which the external concentration of these acids play a role in the energy extraction capabilities of the organism. Data also indicates a fleeting regime where A. succinogenes utilises an oxidised environment to its advantage for ATP production. Here it is postulated that the energy gain and excretion cost of catabolites coupled to the changing environment is a likely mechanism responsible for the proteome alteration and its ensuing carbon flux variation. This offers valuable insights into the microbe’s metabolic logic gates, providing a foundation to understand how to exploit the system.
Highlights
IntroductionAs is often the case in microbial-catalysis, maximum theoretical yields are not attained due to mixed acid fermentative metabolic behaviours inherent in many strains of microbes
Homogenous compound production is regarded as the holy grail in chemical conversion
The peak in pyruvate excretion was found to coincide with the termination of growth, as well as being proximate to the peak of the PDH route
Summary
As is often the case in microbial-catalysis, maximum theoretical yields are not attained due to mixed acid fermentative metabolic behaviours inherent in many strains of microbes. One such an example is that of the bovine rumen bacterium Actinobacillus succinogenes. Its reductive pathway necessitates a net consumption of redox, which is supplied by the organism through the activation of complementary redox producing pathways. These pathways, in the case of A. succinogenes, lead to the co-production of acetic, formic, and pyruvic acid. These acids divert carbon away from succinic acid production and augment downstream processing costs
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