Optimisation of feedstock utilisation by Geobacillus thermoglucosidasius

  • Alex Holland

Student thesis: Doctoral ThesisPhD


Geobacillus thermoglucosidasius (GT) is a thermophilic, ethanol-producing bacterium capable of utilising both hexose and pentose sugars for fermentation. One strategy to improve fermentation yields would be to engineer GT strains to secrete hydrolases to increase the amount of available sugars from various feedstocks. Therefore, optimised protein secretion would be vital to improve feedstock utilisation. Secretion in the related mesophile Bacillus subtilis (BS) has been well studied, and several strategies have been developed to improve secretion of heterologous proteins in BS, one such strategy being the manipulation or changing of the signal peptide. One aim is to identify any differences in the secretion machinery and signal sequences between GT and BS. Another aim is to analyse any effects of overproduction of hydrolases and to identify any bottlenecks in protein secretion in GT.Using bio-informatics tools we find that although GT is a thermophile, the signal peptides in this organism do not differ significantly from those in BS. From a shotgun mass spectrometry approach it was also observed that unlike BS, GT undergoes significant cell lysis during growth releasing cytoplasmic proteins into the extracellular milieu, which could have implications on the levels of secreted hydrolases.A model enzyme was selected and over-produced at high levels in order to stress the secretion system in GT so as to identify any bottlenecks in secretion. The results thus far indicate that the rate limiting step in secretion could be post-translocation where the enzyme is degraded by proteases in the cell wall and extracellular milieu. The addition of protease inhibitor to growth media, increases the activity and abundance of the enzyme, suggesting that proteolysis may be a major factor when over-producing secreted enzymes at high levels.
Date of Award27 Jun 2017
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorAlbert Bolhuis (Supervisor)


  • Geobacillus thermoglucosidasius
  • Geobacillus
  • protein secretion

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