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PubMed1993

Testing of some assumptions about biodegradability in soil as measured by carbon dioxide evolution.

Conversion to CO2 upon incubation in aerobic soil is one of the standard test procedures to assess biodegradability. It may be measured with unlabeled test compounds in biometer flasks. In this case, the background CO2 evolution by unamended soil is subtracted from the CO2 evolution by the amended soil and the resulting net CO2 evolution becomes the measure of biodegradation. Alternately, 14CO2 release from radiocarbon substrates is measured to assess biodegradability. Both approaches measure ultimate (complete) biodegradation and bypass the theoretical and technical limitations of residue analysis. This report examines the underlying assumptions that, except for carbon content, conversion percentage to CO2 is relatively independent of chemical composition, that CO2 production is proportional to the amount of added test compound, and that the background CO2 evolution of the soil is not influenced by the test substance. Work with unlabeled and radiolabeled substrates proved the first two assumptions to be essentially correct. However, more than half of net CO2 production may represent the mineralization of biomass and soil organic matter, some of it unrelated to the test compound. The soil microbial community in its nongrowing steady state appears to convert a much lower percentage of a radiocarbon substrate to 14CO2 than a growing soil community that responds to a substantial substrate addition. These findings may help to improve test methods and may aid in the interpretation of test results.

Adipates↗

PubMed1996

Quantifying the biodegradation of phenanthrene by Pseudomonas stutzeri P16 in the presence of a nonionic surfactant.

The low water solubility of polycyclic aromatic hydrocarbons is believed to limit their availability to microorganisms, which is a potential problem for bioremediation of polycyclic aromatic hydrocarbon-contaminated sites. Surfactants have been suggested to enhance the bioavailability of hydrophobic compounds, but both negative and positive effects of surfactants on biodegradation have been reported in the literature. Earlier, we presented mechanistic models of the effects of surfactants on phenanthrene dissolution and on the biodegradation kinetics of phenanthrene solubilized in surfactant micelles. In this study, we combined the biodegradation and dissolution models to quantify the influence of the surfactant Tergitol NP-10 on biodegradation of solid-phase phenanthrene by Pseudomonas stutzeri P16. Although micellized phenanthrene does not appear to be available directly to the bacterium, the ability of the surfactant to increase the phenanthrene dissolution rate resulted in an overall increase in bacterial growth rate in the presence of the surfactant. Experimental observations could be predicted well by the derived model with measured biokinetic and dissolution parameters. The proposed model therefore can serve as a base case for understanding the physical-chemical effects of surfactants on nonaqueous hydrocarbon bioavailability.

Biodegradation, Environmental↗

PubMed1997

Rhamnolipid (biosurfactant) effects on cell aggregation and biodegradation of residual hexadecane under saturated flow conditions.

The objective of this research was to evaluate the effect of low concentrations of a rhamnolipid biosurfactant on the in situ biodegradation of hydrocarbon entrapped in a porous matrix. Experiments were performed with sand-packed columns under saturated flow conditions with hexadecane as a model hydrocarbon. Application of biosurfactant concentrations greater than the CMC (the concentration at which the surfactant molecules spontaneously form micelles or vesicles [0.03 mM]) resulted primarily in the mobilization of hexadecane entrapped within the sand matrix. In contrast, application of biosurfactant concentrations less than the CMC enhanced the in situ mineralization of entrapped hexadecane; however, this effect was dependent on the choice of bacterial isolate. The two Pseudomonas isolates tested, R4 and ATCC 15524, were used because they exhibit different patterns of biodegradation of hexadecane, and they also differed in their physical response to rhamnolipid addition. ATCC 15524 cells formed extensive multicell aggregates in the presence of rhamnolipid while R4 cells were unaffected. This behavior did not affect the ability of the biosurfactant to enhance the biodegradation of hexadecane in well-mixed soil slurry systems but had a large affect on the extent of entrapped hexadecane biodegradation in the sand-packed-column system that was used in this study.

Alkanes↗

PubMed1999

Anaerobic benzene biodegradation linked to nitrate reduction.

Benzene oxidation to carbon dioxide linked to nitrate reduction was observed in enrichment cultures developed from soil and groundwater microcosms. Benzene biodegradation occurred concurrently with nitrate reduction at a constant ratio of 10 mol of nitrate consumed per mol of benzene degraded. Benzene biodegradation linked to nitrate reduction was associated with cell growth; however, the yield, 8.8 g (dry weight) of cells per mol of benzene, was less than 15% of the predicted yield for benzene biodegradation linked to nitrate reduction. In experiments performed with [14C]benzene, approximately 92 to 95% of the label was recovered in 14CO2, while the remaining 5 to 8% was incorporated into the nonvolatile fraction (presumably biomass), which is consistent with the low measured yield. In benzene-degrading cultures, nitrite accumulated stoichiometrically as nitrate was reduced and then was slowly reduced to nitrogen gas. When nitrate was depleted and only nitrite remained, the rate of benzene degradation decreased to almost zero. Based on electron balances, benzene biodegradation appears to be coupled more tightly to nitrate reduction to nitrite than to further reduction of nitrite to nitrogen gas.

Anaerobiosis↗

PubMed1973

Biodegradation of o-benzyl-p-chlorophenol.

The extent of biodegradation of o-benzyl-p-chlorophenol, marketed as a germicide under the name Santophen((R)) 1 (Monsanto Co.), in river water, sewage, and activated sludge was determined. Biodegradation was assessed by use of a colorimetric procedure for phenolic materials, carbon analysis, and CO(2) evolution. In unacclimated river water, 0.1 mg of Santophen 1 per liter was degraded within 6 days. In sewage, 0.5 and 1.0 mg/liter levels of Santophen 1 were degraded in 1 day. Acclimated activated sludge achieved 80% biodegradation of 1.0 mg/liter Santophen 1 in 8 h and 100% in 24 h. When effluent from a semicontinuous activated sludge unit, acclimated to 20 mg of Santophen 1 per liter was used as the inoculum for the CO(2) evolution procedure, 60% of the total theoretical CO(2) was evolved from Santophen 1. Based on the results of these studies, indicating Santophen 1 to be readily biodegraded in at least four biological systems, the continued use of present levels of Santophen 1 should present no significant environmental problems.

Alkanesulfonates↗

PubMed1995

Mechanisms of biodegradation of metal-citrate complexes by Pseudomonas fluorescens.

Biodegradation of metal-citrate complexes by Pseudomonas fluorescens depends on the nature of the complex formed between the metal and citric acid. Bidentate Fe(III)-, Ni-, and Zn-citrate complexes were readily biodegraded, but the tridentate Cd- and Cu-citrate, and U-citrate complexes were not. The biodegradation of Ni- and Zn-citrate commenced after an initial lag period; the former showed only partial (70%) degradation, whereas the latter was completely degraded. Uptake studies with 14C-labeled citric acid and metal-citrate complexes showed that cells grown in medium containing citric acid transported free citric acid at the rate of 28 nmol min-1 and Fe(III)-citrate at the rate of 12.6 nmol min-1 but not Cd-, Cu-, Ni-, U-, and Zn-citrate complexes. However, cells grown in medium containing Ni- or Zn-citrate transported both Ni- and Zn-citrate, suggesting the involvement of a common, inducible transport factor. Cell extracts degraded Fe(III)-, Ni-, U-, and Zn-citrate complexes in the following order: The cell extract did not degrade Cd- or Cu-citrate complexes. These results show that the biodegradation of the U-citrate complex was limited by the lack of transport inside the cell and that the tridentate Cd- and Cu-citrate complexes were neither transported inside the cell nor metabolized by the bacterium.

Adaptation, Physiological↗

PubMed1993

Biodegradation of cycloalkane carboxylic acids in oil sand tailings.

The biodegradation of both an n-alkane and several carboxylated cycloalkanes was examined within tailings produced by the extraction of bitumen from the Athabasca oil sands. The carboxylated cycloalkanes examined were structurally similar to naphthenic acids that have been associated with the acute toxicity of oil sand tailings. The biodegradation potential of naphthenic acids was estimated by determining the biodegradation of both the carboxylated cycloalkanes and hexadecane in oil sand tailings. Carboxylated cycloalkanes were biodegraded within oil sand tailings, although compounds with methyl substitutions on the cycloalkane ring were more resistant to microbial degradation. Microbial activity against hexadecane and certain carboxylated cycloalkanes was found to be nitrogen and phosphorus limited.

Alkanes↗

PubMed1996

Assessment of the biodegradation potential of psychrotrophic microorganisms.

Bioremediation of polluted temperate and cold temperature environments may require the activity of psychrotrophic bacteria, because their low temperature growth range parallels the ambient temperatures encountered in these environments. In the present study, 135 psychrotrophic microorganisms isolated from a variety of ecosystems in Canada were examined for their ability to mineralize 14C-labelled toluene, naphthalene, dodecane, hexadecane, 2-chlorobiphenyl, and pentachlorophenol. A number of the psychrotrophic strains mineralized toluene, naphthalene, dodecane, and hexadecane. None of the psychrotrophs were capable of mineralizing 2-chlorobiphenyl or pentachlorophenol. Those strains demonstrating mineralization activity were subsequently screened by the polymerase chain reaction (PCR) and Southern hybridization of PCR products for the presence of catabolic genes (alkB, ndoB, todCl, and xylE) involved in known bacterial biodegradative pathways for these compounds. Some of the psychrotrophs able to mineralize toluene and naphthalene possessed catabolic genes that hybridized to xylE or todCl, and ndoB, respectively. The alkB PCR fragments obtained from the strains that mineralized dodecane and hexadecane did not hybridize to an alkB gene probe derived from Pseudomonas oleovorans. Psychrotrophic strain Q15, identified as a Rhodococcus sp., also mineralized the C28 n-paraffin octacosane. A gene probe constructed from the "alkB" PCR fragment from strain Q15 did hybridize with the alkB PCR fragments from most of the psychrotrophic alkane biodegraders, indicating that the alkB primers may be amplifying another gene(s), perhaps with low homology to P. oleovorans alkB, which may be involved in the biodegradation of both short chain (dodecane) and longer chain alkanes (hexadecane, octacosane). All of the psychrotrophic biodegradative isolates examined were capable of mineralization activity at both 23 and 5 degrees C, indicating their potential for low temperature bioremediation of petroleum hydrocarbon contaminated sites.

Arthrobacter↗

PubMed1997

Biodegradation of N-phosphonomethyliminodiacetic acid by microorganisms from industrial activated sludge.

A microbial population that biodegraded N-phosphonomethyliminodiacetic acid (PIA), a key component of glyphosate (N-phosphonomethylglycine) process waste, was established. The stoichiometric conversion of PIA to aminomethylphosphonic acid (AMPA) was observed in a laboratory sequencing batch reactor (SBR) containing activated sludge from a glyphosate-manufacturing facility and PIA as sole source of carbon. PIA degradation was determined by high-performance liquid chromatography and confirmed by radiolabeled studies. Greater than 90% of the [carboxymethyl-2-14C]-label of PIA was released as 14CO2 in 7 days using samples of sludge from the SBR. The cycle time required to biodegrade up to 7.5 mM PIA in SBRs was reduced from 21 to < 3 days. PIA biodegradation was also established in an immobilized bacteria column inoculated with mixed liquor from a SBR; > 99% PIA removal was achieved at an influent concentration of 2.2 mM and a hydraulic retention time of < 10 h. A pure bacterial culture was isolated from a SBR by streaking samples of sludge on solid media with PIA as sole carbon source. The isolate was identified as Xanthomonas maltophilia. In liquid culture, X. maltophilia degraded up to 4.4 mM PIA within 10 days and produced stoichiometric amounts of AMPA. The results demonstrate the biodegradation of PIA and suggest the potential for its treatment in industrial biological treatment systems.

Bacteria↗

PubMedDate not supplied

Biodegradable polymers for ocular drug delivery.

A variety of ocular drug delivery systems, including a controlled release of the drug, drug targeting, and penetration enhancement of the drug, have been investigated. Biodegradable polymers have been widely used as the drug carrier for controlled-release systems. Biodegradable polymers release the drug as they themselves degrade and are finally absorbed within the body. Several ocular drug delivery systems using different kinds of biodegradable polymers have been studied. In this article, we describe the fundamental mechanisms of drug delivery systems, polymer erosion and drug release, and then review those systems using the most popular biodegradable polymers, poly(lactic acid) and poly(lactic-glycolic acid).

Animals↗

PubMed1994

Controlled release of beta-estradiol from biodegradable microparticles within a silicone matrix.

Novel, biodegradable controlled release systems were prepared from biodegradable microparticles of poly(lactic acid-co-glycolic acid) containing beta-estradiol in the presence or absence of silicone. The release behavior of beta-estradiol from free microparticles as well as from microparticles embedded within a silicone matrix was compared with the release behavior shown by nonencapsulated beta-estradiol within a silicone matrix. It was found that incorporating biodegradable microparticles within a silicone matrix lessens the initial burst of release often seen with these types of formulations and provides a controlled rate of drug release. In addition, the release rate of beta-estradiol from biodegradable microparticles within silicone is higher than for unencapsulated beta-estradiol in silicone. This type of formulation may be useful in a number of instances such as release of drugs from implants for which a simple drug-silicone formulation does not yield desired release behavior, formulations which are currently developed for microparticles but which may need to be removed if necessary, and implant formulations containing drugs which will not diffuse through silicone.

Biodegradation, Environmental↗

PubMed1997

The effect of phospholipids on the biodegradation of polyurethanes by lysosomal enzymes.

Although biodegradation of model poly(ester-urethane)s and poly(ether-urethane)s has been demonstrated using a single enzyme system (cholesterol esterase (CE) in vitro, in vivo biodegradation most likely involves many processes acting together. In this study, the physical (film vs textured surface) and chemical (poly(urethane)s containing polycaprolactone (PCL) vs poly(tetramethylene oxide) (PTMO)) nature of the materials as well as the products of enzymatic reactions known to occur during the inflammatory response (CE and phospholipase A2 (PLA)) were assessed for their effects on poly(urethane) (PU) biodegradation in vitro. A mixed micelle (phosphatidylcholine (PC):lysoPC (LPC):oleic acid (OA): 2:1:1) significantly increased the release of radiolabelled products from a C-labelled poly(ester-urethane) (TDI/PCL/ED) caused by CE. This effect was further enhanced when this material was cast as a textured surface. A model poly(ether-urethane) showed no significant enhancement of CE-mediated hydrolysis in the presence of phospholipids and their breakdown products whether cast as a film or a textured surface. PLA caused a small but significant release of radiolabel from TDI/PCL/ED which was enhanced in the presence of its substrate, PC, and a mixture of PC with its breakdown products, LPC and OA. Based on the results of this study, it may be possible to hypothesize that during the inflammatory response when PLA is activated, enhancement of the biodegradation of a PU could occur by direct action of PLA on the poly(ester-urethane) and by stimulation of CE due to the formation of LPC and OA occurring when PLA hydrolyses PC, its natural substrate

Biocompatible Materials↗

PubMed1999

Biodegradation of commercial dental composites by cholesterol esterase.

The research literature suggests that current dental polymeric composites are not chemically inert at the material/biological interface. Several studies have investigated the process of "biodegradation" on dental composites in the presence of enzymes, by monitoring changes in weight loss and surface hardness properties. However, it is hypothesized that these methods can provide an erroneous measure of biochemically induced degradation, since they are less sensitive to molecular events and lack the ability to provide chemical information. Knowledge of the latter is important because it relates to the biological significance of biodegradation, i.e., the identification and quantification of released compounds that may be capable of influencing cell, bacteria, or enzyme function. It was the objective of this study to compare three methods (weight loss, surface micro-hardness, and liquid chromatography combined with mass spectrometry) for their ability to measure the effect of enzyme-induced biodegradation on three commercial composite resin materials. The enzyme was cholesterol esterase, and the composites were Silux Plus XL, Z100 A2 (3M), and TPH XL (L.D. Caulk). Biodegradation was readily detected by liquid chromatography, and its sensitivity was shown to be substantially greater than that of weight loss or surface hardness measurements, although surface hardness measurements did show some agreement with liquid chromatography data. The data also indicated that the levels and distribution of released degradation products can vary substantially from one product to the next, and that this merits further investigation if the potential impact of different commercial restorative materials on cell and bacteria function is to be assessed.

Bacteria↗

PubMedDate not supplied

Biodegradable interference screw fixation exhibits pull-out force and stiffness similar to titanium screws.

Recently, increased interest in biodegradable interference screws for bone-tendon-bone graft fixation has led to numerous screws becoming available. The implants are made from different polymers and have different designs, which might influence their mechanical properties. Several studies have reported a wide range of mechanical results for these screws using different biomechanical models. The aim of the present study is to compare reliable biomechanical data for six different biodegradable interference screws, consisting of five different polymers, with a conventional titanium screw in a standardized model. Seventy proximal calf tibias were used to determine maximal pull-out force, stiffness of fixation, and insertion torque for interference screw fixation of bone-tendon-bone grafts. Additionally, maximal torque at failure was determined. Data were analyzed with respect to aspects of screw design, such as drive and thread shape. Five of the six biodegradable screws provided initial pull-out force and stiffness of fixation comparable with that of a conventional titanium screw. Torque at failure can be greatly increased by adapting the drive design to the mechanical properties of the polymeric raw material. A correlation between pull-out force and thread height indicates that fixation rigidity depends on screw design, even in a biodegradable implant.

Animals↗

PubMed2005

Enhancement of cometabolic biodegradation of trichloroethylene (TCE) gas in biofiltration.

A biofilter column inoculated with Pseudomonas putida F1 was operated to study cometabolic biodegradation of trichloroethylene (TCE) gas using toluene as a primary substrate. Variations in the efficiency and capacity of TCE elimination with different inlet concentrations of toluene and TCE were investigated in order to understand the competitive inhibition between toluene and TCE. Two toluene feeding methods, stage feeding along the column and cyclic feeding, were examined as strategies to enhance TCE cometabolic biodegradation by avoiding the toluene inhibition of TCE biodegradation and the toxic effect of TCE on cells and toluene dioxygenase enzymes. It was concluded that both methods are promising and that the determination of a suitable feeding frequency, recovery period, and inlet toluene concentration was required to optimize cyclic feeding in the cometabolic biodegradation of TCE.

Air Pollutants↗

PubMed1997

Biodegradabilities of ethylenediamine-N,N'-disuccinic acid (EDDS) and other chelating agents.

Biodegradabilities of chelating agents were tested with activated sludge. Ethylenediaminetetraacetic acid (EDTA) remained intact in the effluent even after acclimation for 100 days, but propanediamine-N,N'-disuccinic acid (PDDS) and nitrilotriacetic acid (NTA) were biodegraded after acclimation for 5 and 23 days, respectively. Optical isomers of ethylenediamine-N,N'-disuccinic acid (EDDS) had different biodegradabilities: SS- and RS-isomers were susceptible to biodegradation, but the RR-isomer was resistant. SS-isomer was degraded even by activated sludge without acclimation.

Biodegradation, Environmental↗

PubMed2003

Impact of metals on the biodegradation of organic pollutants.

Forty percent of hazardous waste sites in the United States are co-contaminated with organic and metal pollutants. Data from both aerobic and anaerobic systems demonstrate that biodegradation of the organic component can be reduced by metal toxicity. Metal bioavailability, determined primarily by medium composition/soil type and pH, governs the extent to which metals affect biodegradation. Failure to consider bioavailability rather than total metal likely accounts for much of the enormous variability among reports of inhibitory concentrations of metals. Metals appear to affect organic biodegradation through impacting both the physiology and ecology of organic degrading microorganisms. Recent approaches to increasing organic biodegradation in the presence of metals involve reduction of metal bioavailability and include the use of metal-resistant bacteria, treatment additives, and clay minerals. The addition of divalent cations and adjustment of pH are additional strategies currently under investigation.

Biodegradation, Environmental↗

PubMed2005

Biodegradable microspheres for parenteral delivery.

Nowadays, emphasis is being laid to development of controlled release dosage forms. Interest in this technology has increased steadily over the past few years. Although oral administration of drugs is a widely accepted route of drug delivery, bioavailability of drug often varies as a result of gastrointestinal absorption, degradation by first-pass effect, and hostile environment of gastrointestinal tract. Transdermal administration for percutaneous absorption of drug is limited by the impermeable nature of the stratum corneum. Ocular and nasal delivery is also unfavorable because of degradation by enzymes present in eye tissues and nasal mucosa. Hence, the parenteral route is the most viable approach in such cases. Of the various ways of achieving long-term parenteral drug delivery, biodegradable microspheres are one of the better means of controlling the release of drug over a long time. Because of the lipidic nature of liposomes, problems such as limited physical stability and difficulty of freeze-drying are encountered. Similarly, for emulsions, stability on long-term basis and in suspensions, rheological changes during filling, injecting, and storage poses limitation. Also, in all these systems, the release rate cannot be tailored to the needs of the patient. Parenteral controlled-release formulations based on biodegradable microspheres can overcome these problems and can control the release of drug over a predetermined time span, usually in the order of days to weeks to months. Various FDA-approved controlled-release parenteral formulations based on these biodegradable microspheres are available on the market, including Lupron Depot Nutropin Depot and Zoladex. This review covers various molecules encapsulated in biodegradable microspheres for parenteral delivery.

Biodegradation, Environmental↗