A Medium Throughput Screening Device With Online Growth Data Collection of Multiple Small Volume Gas Phase Bioreactors

Open Access
Author:
Taylor, John Reed
Area of Honors:
Chemical Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Wayne Roger Curtis, Thesis Supervisor
  • Wayne Roger Curtis, Honors Advisor
  • Andrew Zydney, Faculty Reader
Keywords:
  • Clostridium ljungdahlii
  • Rhodobacter Capsulatus
  • syngas
  • synthesis gas
  • chemoautotrophic
  • fermentation
  • screening
  • biofuels
Abstract:
The national goal for a sustainable production platform for liquid fuels, and the difficulty in achieving economic feasibility on part with fossil fuels, has led to many different options being explored. Large scale corn to ethanol production plants, while a step in the right direction, have run up against an economic wall where the current model is not profitable without government subsidies. Beyond cellulosic biomass to fuel which are currently being deployed, there are next generation efforts to genetically engineer bacteria to produce higher energy fuel molecules like hydrocarbons and butanol from gas feeds like CO2/O2/H2 and synthesis gas (CO2/CO/H2). Since the substrate no longer involves simple addition of sugar to media, gas-consuming organisms present challenges for screening genetically modifications for product formation levels. Additional considerations for scale work are explosion risk (H2/O2) or toxicity (carbon monoxide) associated with these gas mixtures. This specific work was motivated by a project to develop liquid hydrocarbon (botryococeene) fuel for the ARPA-E Electrofuels Project. This project has genetically modified Rhodobacter capsulatus to produce the triterpene botryococcene—a “drop-in” fuel molecule native to an algae species. The growth modes of this organism includes autotrophic (CO2, H2, O2), therefore, there was a need for a safe method to increase the throughput of the screening process of this potentially explosive gas mixture. Experimental studies demonstrated that this device can obtain online optical density measurements of up to 12 separate 4 mL cultures simultaneously for gas phase fermentations. This device has been used to successfully grow both a chemoautotrophic bacteria as well as a syngas fermenting bacteria (Clostridium ljungdahlii). This device can provide kLa values up to 25 hr¬-1 and grow cultures to OD 1.0 while reducing the gas headspace volume of the screening process from 2.4 L in 250 mL shake flasks to only 60 mL. This device should enable faster and more quantitative screening of different organisms and feed gases for biofuels production.