Nazim Cicek
University of Manitoba, Canada
Title: Microbial conversion of biodiesel waste products into medium chain length polyhydroxyalkanoates (mcl-PHA) using Pseudomonas putida LS46
Biography
Biography: Nazim Cicek
Abstract
Medium chain-length polyhydroxyalkanoates (mcl-PHAs) are a class of polymers synthesized by certain species of bacteria as an energy storage mechanism. These polymers have shown promise as a potential renewable alternative to conventional petroleum-based plastics and fuels. Use of an inexpensive and renewable carbon source such as biodiesel waste glycerol and free fatty acids is a requisite for cost-effective mcl-PHA production. Under certain operating conditions, Pseudomonas putida LS46 has been shown to be capable of robust growth on these substrates while achieving relatively high cellular mcl-PHA content. Preliminary tests in reactors with a 3-5 L working volume have shown that for growth on substrates metabolized via β-oxidation pathways (pure octanoic acid, biodiesel waste fatty acids), the application of oxygen limitation (>0.01 mg/L O2) improved the cellular PHA content from 45% to 71% using pure octanoic acid, and from 17% to 35% using biodiesel waste fatty acids as compared to conventional nitrogen limitation. The improvement in cellular PHA content using oxygen limitation compensated for the slowed growth rate, resulting in a higher overall mcl-PHA productivity. For growth on waste glycerol, nitrogen limitation was found to be more effective than oxygen limitation, resulting in 25% cellular PHA content. For all substrates, fed batch strategies have been used to reliably achieve biomass yields of 12-15 g/L, in a reactor with working volumes up to 50 L. Further improvements to cell density and overall productivity may be achievable through the design and operation of continuous or semi-continuous feed bioreactors.