Biomedical subjects

Andrew J Daugulis

Publications and source records attributed to Andrew J Daugulis.

At least 19 recordsLinked to original sources

PubMed2007

Solvent selection for enhanced bioproduction of 3-methylcatechol in a two-phase partitioning bioreactor.

The biotransformation of toluene to 3-methycatechol (3MC) via Pseudomonas putida MC2 was used as a model system for the development of a biphasic process offering enhanced overall volumetric productivity. Three factors were investigated for the identification of an appropriate organic solvent and they included solvent toxicity, bioavailability of the solvent as well as solvent affinity for 3MC. The critical log P (log P(crit)) of the biocatalyst was found to be 3.1 and log P values were used to predict a solvent's toxicity. The presence of various functional groups of candidate solvents were used to predict the absorption of 3MC and it was found that solvents possessing polarity showed an affinity towards 3MC. Bis (2-ethylhexyl) sebecate was selected for use in the biphasic system as it fulfilled all selection criteria. A two-phase biotransformation with BES and a 50% phase volume ratio, achieved an overall volumetric productivity of 440 mg 3MC/L-h, which was an improvement by a factor of approximately 4 over previously operated systems. Additional work focused on reducing the toluene feed in order to minimize possible toxicity and decrease loss of substrate (toluene), a result of volatilization. Toluene losses were reduced by a factor of 4, compared to previously operated systems, without suffering an appreciable loss in overall volumetric productivity.

Bioreactors↗

PubMed2006

Ex situ bioremediation of phenol contaminated soil using polymer beads.

Polymer beads have been used to absorb high concentrations of phenol from soil decreasing the initial concentration of 2.3 g kg(-1) soil to 100 mg kg(-1) soil and achieving a phenol loading within the polymer beads of 27.5 mg phenol g(-1) beads. The phenol-loaded polymer beads were removed from the soil and placed in a bioreactor, which was then inoculated with a phenol-degrading microbial consortium. All of the phenol contained within the polymer beads was shown to desorb from the polymer matrix and was degraded by the microbial consortium. The beads were used again (twice) in a similar manner with no loss in performance.

Adsorption↗

PubMed2006

Benzene vapor treatment using a two-phase partitioning bioscrubber: an improved steady-state protocol to enhance long-term operation.

The performance and stability of a two-phase partitioning bioscrubber (TPPB) containing 33% (vol.) n-hexadecane as an immiscible phase was investigated during 30 days of continuous gaseous benzene treatment. Elimination capacities of 141 +/- 12 g/m(3) h were achieved by Achromobacter xylosoxidans Y234 while maintaining >99% removal throughout. A new steady-state operating strategy that limits excessive biomass production by directing substrate consumption to maintenance energy has eliminated the requirement for frequent exchange of liquid contents. Simplifying the operating protocols in this manner has dramatically reduced material costs and rendered the TPPB operational requirements as more comparable (in terms of frequency of required operator inputs) with other vapor-phase bioreactors. The practicality of the proposed simplification to the operating protocol was confirmed by demonstrating that intermediate metabolites were not accumulating in the TPPB, inorganic nutrient requirements were readily predictable, and that high culture viability could be sustained for prolonged cell retention times (30 days).

Achromobacter denitrificans↗

PubMed2006

Direct estimation of the oxygen requirements of Achromobacter xylosoxidans for aerobic degradation of monoaromatic hydrocarbons (BTEX) in a bioscrubber.

The O2 requirements for biomass production and supplying maintenance energy demands during the degradation of both benzene and ethylbenzene by Achromobacter xylosoxidans Y234 were measured using a newly proposed technique involving a bioscrubber. Using this approach, relevant microbial parameter estimates were directly and simultaneously obtained via linear regression of pseudo steady-state data. For benzene and ethylbenzene, the biomass yield on O2, Y(X/O2), was estimated on a cell dry weight (CDW) basis as 1.96 +/- 0.25 mg CDW mgO2(-1) and 0.98 +/- 0.17 mg CDW mgO2(-1), while the specific rate of O2 consumption for maintenance, m(O2), was estimated as 0.041 +/- 0.008 mgO(2) mg CDW(-1) h(-1) and 0.053 +/- 0.022 mgO(2) mg CDW(-1) h(-1), respectively.

Achromobacter↗

PubMed2006

Transient performance of two-phase partitioning bioreactors treating a toluene contaminated gas stream.

Two-phase partitioning bioreactors (TPPBs) consist of a cell-containing aqueous phase and an immiscible organic phase that sequesters and delivers toxic substrates to cells based on equilibrium partitioning. The immiscible organic phase, which acts as a buffer for inhibitory substrate loadings, makes it possible for TPPBs to handle high volatile organic compound (VOC) loadings, and in this study the performance of liquid n-hexadecane and solid styrene butadiene (SB) polymer beads used as partitioning phases were compared to a single aqueous phase system while treating transient loadings of a toluene contaminated air stream by Achromobacter xylosoxidans Y234. The TPPBs operated as well-mixed stirred tanks, with total working volumes of 3 L (3 L aqueous for the single-phase system, 2 L aqueous and 1 L n-hexadecane for the solvent system, and 2.518 L aqueous volume and 500 g of SB beads for the polymer system). Two 60-min step changes (7 and 17 times the nominal loading rates, termed "small" and "large" steps, respectively) were imposed on the systems and the performance was characterized by the overall removal efficiencies, instantaneous removal efficiency recovery times (above 95% removal), and dissolved oxygen recovery times. For the small steps, with a nominal loading of 343 g/m3/h increasing to 2,400 g/m3/h, the TPPB system using n-hexadecane as the second phase performed best, removing 97% of the toluene fed to the system compared with 90% for the polymer beads system and only 69% for the single-phase system. The imposed large transient gave similar results, although the impact of the presence of a second sequestering phase was more pronounced, with the n-hexadecane system maintaining much reduced aqueous toluene concentrations leading to significantly improved performance. This investigation also showed that the presence of both n-hexadecane and SB beads improved the oxygen transfer within the systems.

Air Pollution↗

PubMed2006

Enhanced degradation of a mixture of polycyclic aromatic hydrocarbons by a defined microbial consortium in a two-phase partitioning bioreactor.

Biological treatment methods are effective at destroying polycyclic aromatic hydrocarbons (PAHs), and some of the highest rates of PAH degradation have been achieved using two-phase-partitioning bioreactors (TPPBs). TPPBs consist of a cell-containing aqueous phase and a biocompatible and immiscible organic phase that partitions toxic and/or recalcitrant substrates to the cells based on their metabolic demand and on maintaining the thermodynamic equilibrium of the system. In this study, the degradation of a 5-component mixture of high and low molecular weight PAHs by a defined microbial consortium of Sphingomonas aromaticivorans B0695 and Sphingomonas paucimobilis EPA505 in a TPPB was examined. The extremely low aqueous solubilities of the high molecular weight (HMW) PAHs significantly reduce their bioavailability to cells, not only in the environment, but in TPPBs as well. That is, in the two-phase system, the originally selected solvent, dodecane, was found to sequester the HMW PAHs from the cells in the aqueous phase due to the inherent high solubility of the hydrophobic compounds in this solvent. To circumvent this limitation, the initial PAH concentrations in dodecane were increased to sufficient levels in the aqueous phase to support degradation: LMW PAHs (naphthalene, phenanthrene) and fluoranthene were degraded completely in 8 h, while the HMW PAHs, pyrene and benzo[a]pyrene, were degraded by 64% and 11%, at rates of 42.9 mg l(-1) d(-1) and 7.5 mg l(-1) d(-1), respectively. Silicone oil has superior PAH partitioning abilities compared to dodecane for the HMW PAHs, and was used to improve the extent of degradation for the PAH mixture. Although silicone oil increased the bioavailability of the HMW PAHs and greater extents of biodegradation were observed, the rates of degradation were lower than that obtained in the TPPB employing dodecane.

Biodegradation, Environmental↗

PubMed2006

Biodegradation of a phenolic mixture in a solid-liquid two-phase partitioning bioreactor.

A solid-liquid two-phase partitioning bioreactor (TPPB) in which the non-aqueous phase consisted of polymer (HYTREL) beads was used to degrade a model mixture of phenols [phenol, o-cresol, and 4-chlorophenol (4CP)] by a microbial consortium. In one set of experiments, high concentrations (850 mg l(-1) of each of the three substrates) were reduced to sub-inhibitory levels within 45 min by the addition of the polymer beads, followed by inoculation and rapid (8 h) consumption of the total phenolics loading. In a second set of experiments, the beneficial effect of using polymer beads to launch a fermentation inhibited by high substrate concentrations was demonstrated by adding 1,300 and 2,000 mg l(-1) total substrates (equal concentrations of each phenolic) to a pre-inoculated bioreactor. At these levels, no cell growth and no degradation were observed; however, after adding polymer beads to the systems, the ensuing reduced substrate concentrations permitted complete destruction of the target molecules, demonstrating the essential role played by the polymer sequestering phase when applied to systems facing inhibitory substrate concentrations. In addition to establishing alternative modes of TPPB operation, the present work has demonstrated the differential partitioning of phenols in a mixture between the aqueous and polymeric phases. The polymeric phase was also observed to absorb a degradation intermediate (arising from the incomplete biodegradation of 4CP), which opens the possibility of using solid-liquid TPPBs during biosynthetic transformation to sequester metabolic byproducts.

Biodegradation, Environmental↗

PubMed2005

Biphenyl degradation kinetics by Burkholderia xenovorans LB400 in two-phase partitioning bioreactors.

Biphenyl could be successfully degraded by Burkholderia xenovorans LB400, initially described as Pseudomonas sp. LB400, in two-phase partitioning bioreactors (TPPBs). TPPBs are comprised of an aqueous, cell containing phase, and an immiscible, biocompatible organic phase that partitions toxic and/or poorly soluble substrates (in this case biphenyl) based on maintaining a thermodynamic equilibrium. The critical LogKO/W of the organism was found to be approximately 5.5, indicating that solvents with a LogKO/W larger than 5.5 are suitable as delivery phases for B. xenovorans LB400. Two solvents selected for the TPPB system were octadecene and bis(2-ethylhexyl)sebacate (BES). In one experiment a total of 6.6 g biphenyl per l aqueous-phase-equivalent (biphenyl delivered in solvent, at an aqueous phase to solvent ratio of 10) could be degraded in 25 h during batch operation with octadecene. The specific growth rate and the half saturation constant of the Monod model were estimated to be mumax=0.25 h-1 and KS=0.0001 g l-1, and the yield coefficient was YX/S=0.48 g biomass per g biphenyl. These parameter estimates were used to predict the time course of biphenyl degradation at different initial substrate concentrations and with biphenyl delivered from the two solvents with different partitioning behaviour for biphenyl. The predictions were validated by experimental data, confirming the microbial kinetics as well as the expected partitioning effects.

Biodegradation, Environmental↗

PubMed2005

Transient performance of a two-phase partitioning bioscrubber treating a benzene-contaminated gas stream.

The dynamic performance of a prototype, two-phase partitioning bioscrubber in response to fluctuating benzene waste gas feeds has been characterized through a series of spike, step, and shutdown-restart experiments. From stable operation at a nominal loading capacity of 62 +/- 6 g/(m3 h) and removal efficiencies of over 99%, the bioscrubber was subjected to influent benzene concentration step changes and spikes as high as 10- and 20-fold, respectively. The bioscrubber responded rapidly and effectively to all feed concentration spikes and steps, as well as to step changes in the feed flow rate, maintaining nearly undisturbed performance. Although benzene absorption by the two liquid phases was found to dominate the early stages of each transient, Achromobacter xylosoxidans Y234 responded quickly to prolonged disturbances, readily consuming most of the excess absorbed substrate. The results demonstrate that the two-phase partitioning bioscrubber can rapidly acclimate to and recover from fluctuations, ensuring that stable performance can be maintained both during and aftertransients. The presence of n-hexadecane promotes benzene capture in the two-phase system by increasing the absorption driving force, an important characteristic during high intermittent loadings. Rapid recovery from two different shutdown scenarios further demonstrates the practical potential of the two-phase partitioning bioscrubber as a high-performance biotechnology alternative for the treatment of toxic waste gases.

Achromobacter↗

PubMed2005

Challenges in the expression of disulfide bonded, threonine-rich antifreeze proteins in bacteria and yeast.

Certain freeze-intolerant insects produce antifreeze proteins (AFPs) during overwintering including the spruce budworm (Choristoneura fumiferana) and yellow mealworm (Tenebrio molitor) AFP gene families. However, only a few of the isoforms, encoded by their multiple-copy gene families, have been characterized. When expressed in bacterial systems the insect AFPs have to be denatured and refolded in vitro, a procedure that is not uniformly successful, presumably due to the beta-helix structure and the requirement for disulfide bonds. In an attempt to overcome these difficulties, bacterial vectors and hosts that have been developed to produce soluble, folded proteins, as well as a yeast expression system (Pichia pastoris) were employed. Bacterial expression resulted in low quantities of active recombinant protein for certain isoforms. In contrast, both small and large-scale fermentation of recombinant AFP in Pichia yielded substantial protein production (100 mg/L) but functional ice binding activity of protein produced in three different transformed yeast strains (KM71, X33 or GS115) was low. Inappropriate O-linked glycosylation of the Thr-rich AFPs appeared to be partially reversed by mild chemical deglycosylation, but activity remained low. Substantial quantities, as well as activity were recovered when a fish AFP, with disulfide bonds, but without potential Thr glycosylation sites was expressed in the yeast system.

Animals↗

PubMed2005

A restructured framework for modeling oxygen transfer in two-phase partitioning bioreactors.

This communication proposes a mechanistic modification to a recently published method for analyzing oxygen mass transfer in two-phase partitioning bioreactors (Nielsen et al., 2003), and corrects an oversight in that paper. The newly proposed modification replaces the earlier empirical approach, which treated the two liquid phases as a single, homogeneous liquid phase, with a two-phase mass transfer model of greater fundamental rigor. Additionally, newly developed empirical models are presented that predict the mass transfer coefficient of oxygen absorption in both aqueous medium and an organic phase (n-hexadecane) as a function of bioreactor operating conditions. Experimental values and theoretical predictions of mass transfer coefficients in two-phase dispersions, k(L)a(TP), are compared. The revised approach more clearly demonstrates the potential for oxygen mass transfer enhancement by organic phase addition, one of the motivations for employing a distinct second phase in a partitioning bioreactor.

Absorption↗

PubMed2005

Quantifying maintenance requirements from the steady-state operation of a two-phase partitioning bioscrubber.

An innovative method for directly and explicitly quantifying the maintenance energy requirements of pure cultures growing on volatile organic compound (VOC) substrates in a two-phase partitioning bioscrubber is described. Direct evidence of maintenance energy requirements of Achromobacter xylosoxidans Y234 is provided both through observed reductions in the macroscopic biomass-to-substrate yield with decreasing specific growth rates, but more remarkably through achievement of steady-state operation. The data conclusively show that maintenance activities do occur in the two-phase partitioning bioscrubber and clearly illustrate the importance of this phenomenon to the operation of this process, and similar bioreactor systems. While benzene was selected as the principal, sole substrate of interest in this study, ethylbenzene degradation experiments were also subsequently performed to illustrate and confirm the general applicability of the proposed technique, as well as the potential capabilities of the two-phase partitioning bioscrubber for the continuous treatment of waste gases containing various VOCs. The proposed method has been shown to generate maintenance energy estimates that are consistent with those obtained while employing more widely recognized estimation strategies, further validating its capabilities. The proposed steady-state mode also offers key operational advantages in terms of decreased disposal requirements in two-phase partitioning bioscrubbers. (c) 2005 Wiley Periodicals, Inc.

Achromobacter denitrificans↗

PubMed2005

Enhanced biodegradation of phenol by a microbial consortium in a solid-liquid two phase partitioning bioreactor.

Two phase partitioning bioreactors (TPPBs) operate by partitioning toxic substrates to or from an aqueous, cell-containing phase by means of second immiscible phase. Uptake of toxic substrates by the second phase effectively reduces their concentration within the aqueous phase to sub-inhibitory levels, and transfer of molecules between the phases to maintain equilibrium results in the continual feeding of substrate based on the metabolic demand of the microorganisms. Conventionally, a single pure species of microorganism, and a pure organic solvent, have been used in TPPBs. The present work has demonstrated the benefits of using a mixed microbial population for the degradation of phenol in a TPPB that uses solid polymer beads (comprised of ethylene vinyl acetate, or EVA) as the second phase. Polymer modification via an increase in vinyl acetate concentration was also shown to increase phenol uptake. Microbial consortia were isolated from three biological sources and, based on an evaluation of their kinetic performance, a superior consortium was chosen that offered improved degradation when compared to a pure strain of Pseudomonas putida ATCC 11172. The new microbial consortium used within a TPPB was capable of degrading high concentrations of phenol (approximately 2000 mg l(-1)), with decreased lag time (10 h) and increased specific rate of phenol degradation (0.71 g phenol g(1) cell h). Investigation of the four-member consortium showed that it consisted of two Pseudomonas sp., and two Acinetobacter sp., and tests conducted upon the individual isolates, as well as paired organisms, confirmed the synergistic benefit of their existence within the consortium. The enhanced effects of the use of a microbial consortium now offer improved degradation of phenol, and open the possibility of the degradation of multiple toxic substrates via a polymer-mediated TPPB system.

Acinetobacter↗

PubMed2003

Degradation of xenobiotics in a partitioning bioreactor in which the partitioning phase is a polymer.

Two-phase partitioning bioreactors (TPPBs) are characterized by a cell-containing aqueous phase and a second immiscible phase that contains toxic and/or hydrophobic substrates that partition to the cells at subinhibitory levels in response to the metabolic demand of the organisms. To date, the delivery phase in TPPBs has been a hydrophobic solvent that traditionally needed to possess a variety of important properties including biocompatibility, nonbioavailability, low volatility, and low cost, among others. In the present work we have shown that the organic solvent phase can be replaced by inexpensive polymer beads that function in a similar fashion as organic solvents, delivering a toxic substrate to cells based on equilibrium considerations. Specifically, 3.4 mm diameter beads of poly(ethylene-co-vinyl acetate) (EVA) were used to reduce the aqueous concentration of phenol in a bioreactor from toxic levels ( approximately 2,000 mg/L) to subinhibitory levels ( approximately 750 mg/L), after which Pseudomonas putida ATCC 11172 was added to the system and allowed to consume the total phenol loading. Thus, the beads absorbed the toxic substrate and released it to the cells on demand. The EVA beads, which could be reused, were able to absorb 14 mg phenol/g EVA. This work has opened the possibility of using widely mixed cultures in TPPB systems without concern for degradation of the delivery material and without concern of contamination.

Adsorption↗

PubMed2003

A novel method of simulating oxygen mass transfer in two-phase partitioning bioreactors.

An empirical correlation, based on conventional forms, has been developed to represent the oxygen mass transfer coefficient as a function of operating conditions and organic fraction in two-phase, aqueous-organic dispersions. Such dispersions are characteristic of two-phase partitioning bioreactors, which have found increasing application for the biodegradation of toxic substrates. In this work, a critical distinction is made between the oxygen mass transfer coefficient, k(L)a, and the oxygen mass transfer rate. With an increasing organic fraction, the mass transfer coefficient decreases, whereas the oxygen transfer rate is predicted to increase to an optimal value. Use of the correlation assumes that the two-phase dispersion behaves as a single homogeneous phase with physical properties equivalent to the weighted volume-averaged values of the phases. The addition of a second, immiscible liquid phase with a high solubility of oxygen to an aqueous medium increases the oxygen solubility of the system. It is the increase in oxygen solubility that provides the potential for oxygen mass transfer rate enhancement. For the case studied in which n-hexadecane is selected as the second liquid phase, additions of up to 33% organic volume lead to significant increases in oxygen mass transfer rate, with an optimal increase of 58.5% predicted using a 27% organic phase volume. For this system, the predicted oxygen mass transfer enhancements due to organic-phase addition are found to be insensitive to the other operating variables, suggesting that organic-phase addition is always a viable option for oxygen mass transfer rate enhancement.

Bioreactors↗

PubMed2003

The use of Enterobacter cloacae ATCC 43560 in the development of a two-phase partitioning bioreactor for the destruction of hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX).

Research on the biodegradation of explosives has focussed exclusively on the treatment of contaminated soil and water. In the present work the anaerobic degradation of hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX) by Enterobacter cloacae ATCC 43560 was investigated, and a two-phase partitioning bioreactor (TPPB) was developed for the destruction of pure, past-date munitions. TPPBs are characterized by a cell-containing aqueous phase, and an immiscible and biocompatible organic phase into which very large amounts of toxic and/or insoluble substrates can be dissolved. Based on equilibrium partitioning, the substrate is then transported to the cells, in response to their metabolic requirements, providing a means of demand-based substrate delivery, and high bioreactor productivity. Through consideration of the critical logP of E. cloacae, whether various classes of solvents could be used as sole carbon and energy sources, the capacity of various organics to dissolve RDX, and solvent cost, 2-undecanone was ultimately selected as the delivery solvent for the TPPB. Using this solvent, both batch and fed-batch operation of the TPPB were undertaken, and the volumetric degradation rate of RDX was found to be higher in this arrangement than any previous values reported in the literature. This work has demonstrated the potential of a method for the destruction of decommissioned munitions involving the dissolution of RDX in 2-undecanone, the use of the RDX-rich solvent as the second phase in a TPPB to degrade this explosive, and the subsequent recycling and re-use of the solvent.

Anaerobiosis↗

PubMed2003

Delivery of benzene to Alcaligenes xylosoxidans by solid polymers in a two-phase partitioning bioreactor.

Toxic levels of benzene were decreased to sub-inhibitory levels in a bioreactor via absorption by polymer beads or cylinders (poly(ethylene-co-vinyl acetate) or poly(styrene-co-butadiene)). After inoculation with Alcaligenes xylosoxidans, the remaining benzene in the aqueous phase as well as the benzene taken up by the polymers was degraded to completion. The capacity of these polymers for benzene, and benzene diffusivity within the polymers were also determined.

Alcaligenes↗

PubMed2003

Microbial degradation of high and low molecular weight polyaromatic hydrocarbons in a two-phase partitioning bioreactor by two strains of Sphingomonas sp.

A mixture of six polyaromatic hydrocarbons (naphthalene, phenanthrene, fluoranthene, pyrene, chyrysene and benzo[a]pyrene), varying in size from 2 to 5 rings, was dissolved in dodecane, and used as the delivery phase of a partitioning bioreactor. Two species of Sphingomonas were then used individually, and as a consortium, to determine which of the PAHs were degraded. Only low molecular weight PAHs (naphthalene, phenanthrene and fluoranthene) were degraded by the individual strains, but the consortium degraded all substrates either to completion or near completion.

Biodegradation, Environmental↗