Metabolic and Kinetic impacts of the auxiliary energy source in model chemolithoheterotrophic Bacteria

Abstract

Chemolithoheterotrophy describes a type of microbial metabolism by which organisms oxidise an inorganic electron donor to supplement the generation of an electrochemical gradient. This results in higher overall growth yields and maximum specific growth rates as the organism does not need to generate as many reducing equivalents to fuel the respiratory chain and can instead
redirect that material into anabolic reactions to generate more biomass. Many aspects of this metabolism remain poorly understood due to the difficulty in observing genuine chemolithoheterotrophy, with significant increases in the maximum specific growth yield (YMAX) and maximum specific growth rate (µMAX) seen in continuous culture settings. This type of microbial metabolism offers several industrial benefits by offering a way to increase growth
parameters most important to industrial microbiology, those being yield and growth rate. The presented work investigates several aspects of chemolithoheterotrophy in organisms previously used to examine this type of metabolism, namely Pseudomonas trautweinii and Achromobacter
aegrifaciens culture B. Macromolecular fractions from lyophilised Pseudomonas trautweiniibiomass grown organoheterotrophically and chemolithoheterotrophically across carbon, phosphate and oxygen limited chemostats were examined to determine which cellular fraction or
what combination was responsible for the documented increase in growth yield. Respiratory chain inhibitors were also used to determine the route through which electrons oxidised from the auxiliary electron donor, in this case thiosulfate, enter the respiratory chain. The data presented
adds to the evidence that the main pathway of thiosulfate supported oxidative phosphorylation is through the terminal cytochrome-c oxidase via oxidation by thiosulfate dehydrogenase while also identifying the main macromolecular fraction which constitutes the observed increase in biomass.

Date of Award	2025
Original language	English
Awarding Institution	University of Plymouth
Supervisor	Anne Plessis (Director of Studies (First Supervisor)) & Rich Boden (Other Supervisor)