Jared E. Fein

Effect of commercial feedstocks on growth and morphology of Zymomonas mobilis

The minimum inhibitory concentration for some compounds frequently present in commercial wood acid hydrolysates are presented for Zymomonas mobilis ATCC 29191. All of the compounds tested caused morphological disturbances at sub-inhibitory concentrations. Extensive filamentous growth was observed in the presence of a complex wood hydrolysate fraction, molasses, or various salts or urea. Steady-state filamentous growth of ATCC 29191 was demonstrated in continuous culture with an elevated (150 mM) level of NH4Cl.

Development of a simple defined medium for continuous ethanol production by Zymomonas mobilis

A simple defined medium for the production of ethanol by Zymononas mobilis in continuous culture is presented. Under comparable cultural conditions very similar fermentation kinetics were obtained using simple, complex and semi-synthetic rich media.

Optimization of process design for continuous ethanol production by Zymomonas mobilis ATCC 29191

A two-stage continuous-stirred-tank-reactor (CSTR) system is used to achieve high final alcohol concentrations (>100 g/l) with Zymononas mobilis ATCC 29191. By employing continuous cell recycle on the second stage CSTR of a two-stage process a high overall volumetric productivity (18.13 g/l/h) is achieved together with >100 g/l effluent alcohol.

High productivity continuous ethanol fermentation with a flocculating mutant strain of Zymomonas mobilis

High fermenter (volumetric) ethanol productivities (⩾80 g/lh−1) were attained in a simple single-stage continuous-stirred-tank-reactor (CSTR) employing a flocculent mutant of Zymomonas mobilis with a feed containing 100g/l glucose. Under these conditions a final ethanol concentration of 47.6 g/l was obtained, representing a maximum conversion efficiency of 97% of theoretical.

Comparative performance trials with yeast andZymomonas for fuel alcohol production from corn

Z.mobilis (ATCC 29191) produced ethanol in significantly greater yield thanS. cerevisiae, (0.49 vs 0.45 g ethanol/g glucose entering the system), in multistage continuous culture, on commercial feedstocks obtained from corn wet milling operations. In the same system, Z.mobilis showed higher volumetric productivity (4.14 vs 3.06 g/L/h) than S.cerevisiae. The approximately 9% increase improvement in ethanol production that should result from the improvement in yield makes the cost for retrofitting a plant for the Z.mobilis process minimal.

The Influence of Bioreactor Design on the Production of High-Quality Polymers

An examination into the effect of bioreactor design on the production of s-l,3-glucan exopolysaccharide (EPS) by selected strains of Alcaligenes faecalis and Agrobacterium radiobacter has revealed that the use of alternative means of agitation and mixing, whereby shear stress is reduced, leads to an increase in both the quantity and quality of the recoverable polymer. Whereas Rushton-type turbine impellers were effective in providing high rates of oxygen transfer for high cell density fermentations, the shear stress resulting from this type of agitation resulted in about a 30–40% reduction in the amount of recoverable polymer after a 5-day batch fermentation. With turbine impellers, the specific rate of polymer production (Qp) decreased significantly after 40–50hrs (stationary-phase). However, the Qp remained constant (approx. 100mg EPS/g cell/hr) over the entire time course of the batch fermentation (90 hrs) when ‘shear’ was reduced; for example, when (i) a marine-type propeller was substituted for the flat-blade turbine impellers, or (ii) mixing and oxygen transfer were accomplished in a non-rotary, vibro-fermentor. Systems with reduced ‘apparent shear’ also proved to be effective in the production of a higher quality polymer product as judged by such indicators as intrinsic viscosity and MW of the alkali-solubilized isolated polymer. The strength of the irreversible thermal gel was also markedly improved for polymer recovered from bioreactors configured with agitation devices designed to reduce shear stress on the cell/polymer complex. Other physicochemical properties were consistent with these high-quality novel polymers being ‘curdlan’-like, s-1,3-glucan exopolysaccharide.

EVALUATION OF TECHNOLOGIES FOR CONVERSION OF BIOMASS SUGARS TO ETHANOL AT PILOT SCALE USING ZYMOMONAS MOBILIS

ABSTRACT A state of the art pilot plant has been designed for the continuous conversion of 1 oven dried ton of wood per day. It has been equipped for process optimization and data acquistion in the demonstration of the Bio-hol process (European patent 0047641). Previous studies by our group and others have shown that the microorganism, Zymomonas mobilis, has considerable advantages over yeast. Better product yield and specific and volumetric productivity have been demonstrated for laboratory-scale continuous processes. These advantages have been confirmed at pilot-scale using several process configurations. A continuous process has been developed at the pilot plant for producing inexpensive sugar hydrolysates from wood and agricultural residues. Data will be presented on the fermentation performance of both Z. mobilis , and Saccharomyces cerevisiae on this feedstock, and on current efforts for increasing productivity through feedstock refining and strain optimization. (The Bio-hol Developments venture has had financial support through the Ontario Ministry of Energy and Energy, Mines and Resources, Canada (CREDA).)