Biomedical subjects

Bruce A Ramsay

Publications and source records attributed to Bruce A Ramsay.

7 recordsLinked to original sources

PubMed2006

On-line estimation of dissolved methane concentration during methanotrophic fermentations.

Knowledge of the aqueous phase methane concentration is critical to understanding and controlling process kinetics in methanotrophic bioreactors. Unfortunately since no dissolved methane probe is commercially available, this data must be obtained off-line by the time-consuming gas-liquid partition method. In this study we demonstrate how knowledge of the reactor's k(L)a for oxygen combined with gas phase methane analysis can be used to continuously estimate the aqueous phase concentration of dissolved methane. The on-line estimation was verified in two reactor systems with greatly different values of k (L)a. In both systems the measured and calculated dissolved methane concentrations were in good agreement although dissolved methane was underestimated in both cases. The utility of this methodology was demonstrated by revealing a possible metabolic bottleneck in the model system.

Automation↗

PubMed2006

Carbon-limited fed-batch production of medium-chain-length polyhydroxyalkanoates from nonanoic acid by Pseudomonas putida KT2440.

Pseudomonas putida KT2440 grew on glucose at a specific rate of 0.48 h(-1) but accumulated almost no poly-3-hydroxyalkanoates (PHA). Subsequent nitrogen limitation on nonanoic acid resulted in the accumulation of only 27% medium-chain-length PHA (MCL-PHA). In contrast, exponential nonanoic acid-limited growth (mu = 0.15 h(-1)) produced 70 g l(-1) biomass containing 75% PHA. At a higher exponential feed rate (mu = 0.25 h(-1)), the overall productivity was increased but less biomass (56 g l(-1)) was produced due to higher oxygen demand, and the biomass contained less PHA (67%). It was concluded that carbon-limited exponential feeding of nonanoic acid or related substrates to cultures of P. putida KT2440 is a simple and highly effective method of producing MCL-PHA. Nitrogen limitation is unnecessary.

Biomass↗

PubMed2006

Acetone extraction of mcl-PHA from Pseudomonas putida KT2440.

A methodology was developed for the extraction of medium-chain-length poly-3-hydroxyalkanoates (mcl-PHA) from Pseudomonas putida. It was determined that if dry P. putida biomass containing mcl-PHA was washed in 20 volumes of methanol for 5 min followed by Soxhlet extraction in 10 volumes of acetone for 5 h, almost all of the PHA could be recovered with no detectable loss of molecular weight. Biomass containing higher amounts of PHA required less methanol during the pretreatment step but more acetone in the solvent extraction step than biomass containing less PHA. Further purification could be achieved by redissolving the PHA in acetone and reprecipitating in cold methanol. UV spectroscopy at 241 and 275 nm could be used as an indication of product purity.

Acetone↗

PubMed2005

Automated feeding strategies for high-cell-density fed-batch cultivation of Pseudomonas putida KT2440.

Four automatic substrate feeding strategies were developed and investigated in this study to obtain rapid, repeatable, and reliable high cell densities of Pseudomonas putida KT2440 from glucose. Growth yield data of the key nutrients, Y(X/Glucose), Y(X/NH4), Y(X/PO4), Y(X/Mg), and Y(CO2/Glucose), were determined to be 0.41, 5.44, 13.70, 236, and 0.65 g g(-1), respectively. Although standard exponential feeding strategy worked well when the predetermined mu was set at 0.25 h(-1), an exponential glucose feeding strategy with online mu(max) estimation resulted in a higher average biomass productivity (3.4 vs 2.8 g l(-1) h(-1)). A CO2 production rate based pulse glucose feeding strategy also resulted in good overall productivity (3.0 g l(-1) h(-1)) and can be used as an alternative to pH-stat or DO-stat feeding. A cumulative CO2 production based continuous feed with real-time cumulative glucose consumption estimation resulted in much higher biomass productivity (4.3 g l(-1) h(-1)) and appears to be an excellent and reliable approach to fully automating high-cell-density fed-batch cultivation of P. putida.

Biomass↗

PubMed2005

Pyrene mineralization capacity increases with compost maturity.

Experiments were conducted to determine the effects of composting or simple addition of compost to the mineralization of n-hexadecane, pyrene and benzo(a)pyrene in soil. Soil (contaminated or clean) was composted with maple leaves and alfalfa. Samples from different composting phases were spiked with radiolabeled and cold n-hexadecane, pyrene or benzo(a)pyrene, placed in aerated microcosms at different temperatures, and monitored for mineralization. It was determined that neither composting nor the addition of compost had any effect on n-alkane or benzo(a)pyrene mineralization. In contrast, the pyrene mineralization rate increased dramatically with the amount of time that soil had been composted. Highest pyrene mineralization rates and extents (more than 60% after 20 days) were obtained when pyrene was in contact with composted soil from the curing stage. Neither thermophiles (55 degrees C) nor fungi were responsible for pyrene mineralization.

Air↗

PubMed2005

Enhancement of PAH biomineralization rates by cyclodextrins under Fe(III)-reducing conditions.

Amendment of a soil slurry with low concentrations of a cyclodextrin, hydroxypropyl-beta-cyclodextrin (HPCD), (0.05-0.5 g l(-1)) increased the phenanthrene mineralization rate of a microbial consortium by 25% under Fe(III)-reducing conditions. Although a higher concentration (5.0 g l(-1)) resulted in a faster initial rate of mineralization, mineralization ceased after 25 days with maximum mineralization 17% lower than the control (no HPCD). At lower HPCD concentrations, mineralization was still taking place at day 76. Although pH should affect Fe(III) solubility, mineralization rates at pH 6.0 and 8.0 were comparable. Decreasing the temperature reduced the extent and rate of mineralization, but mineralization rates at 10 degrees C were still 60% of that obtained at 30 degrees C.

2-Hydroxypropyl-beta-cyclodextrin↗

PubMed2003

Naphthalene and anthracene mineralization linked to oxygen, nitrate, Fe(III) and sulphate reduction in a mixed microbial population.

A microbial consortium from a mixture of garden soil and an enrichment of a coal-tar contaminated sediment mineralized naphthalene and anthracene when oxygen, nitrate, Fe(III) (soluble and insoluble) or sulphate were provided as terminal electron acceptors (TEAs). Rates of polyaromatic hydrocarbon disappearance and mineralization were similar in the presence of oxygen and nitrate, and slower with the other TEAs. A maximum mineralization of 37.5% naphthalene and 8.5% anthracene occurred in 30 and 160 days respectively when oxygen was provided as the TEA. On the other hand, only 9.5% naphthalene and 3.2% anthracene were mineralized in 42 and 160 days respectively with FeOOH. Mineralization occurred only when a TEA was provided and ceased when the naphthalene concentration decreased to non-detectable levels (less than 0.008 micromoles/L), as measured by fluorescence spectroscopy. CH4 was not detected in the headspace of any microcosm. These results showed that mineralization of polyaromatic hydrocarbons such as naphthalene and anthracene can be linked to wide range of TEAs demonstrating that intrinsic polyaromatic hydrocarbon bioremediation is possible if any of these TEAs were available.

Anthracenes↗