Pyrobaculum yellowstonensis Strain WP30 Respires on Elemental Sulfur and/or Arsenate in Circumneutral Sulfidic Geothermal Sediments of Yellowstone National Park.

Thermoproteales (phylum Crenarchaeota) populations are abundant in high-temperature (>70°C) environments of Yellowstone National Park (YNP) and are important in mediating the biogeochemical cycles of sulfur, arsenic, and carbon. The objectives of this study were to determine the specific physiological attributes of the isolate Pyrobaculum yellowstonensis strain WP30, which was obtained from an elemental sulfur sediment (Joseph's Coat Hot Spring [JCHS], 80°C, pH 6.1, 135 µM As) and relate this organism to geochemical processes occurring in situ. Strain WP30 is a chemoorganoheterotroph and requires elemental sulfur and/or arsenate as an electron acceptor. Growth in the presence of elemental sulfur and arsenate resulted in the formation of thioarsenates and polysulfides. The complete genome of this organism was sequenced (1.99 Mb, 58% G+C content), revealing numerous metabolic pathways for the degradation of carbohydrates, amino acids, and lipids. Multiple dimethyl sulfoxide-molybdopterin (DMSO-MPT) oxidoreductase genes, which are implicated in the reduction of sulfur and arsenic, were identified. Pathways for the de novo synthesis of nearly all required cofactors and metabolites were identified. The comparative genomics of P. yellowstonensis and the assembled metagenome sequence from JCHS showed that this organism is highly related (∼95% average nucleotide sequence identity) to in situ populations. The physiological attributes and metabolic capabilities of P. yellowstonensis provide an important foundation for developing an understanding of the distribution and function of these populations in YNP.

Predominant Acidilobus-like populations from geothermal environments in yellowstone national park exhibit similar metabolic potential in different hypoxic microbial communities.

High-temperature (>70°C) ecosystems in Yellowstone National Park (YNP) provide an unparalleled opportunity to study chemotrophic archaea and their role in microbial community structure and function under highly constrained geochemical conditions. Acidilobus spp. (order Desulfurococcales) comprise one of the dominant phylotypes in hypoxic geothermal sulfur sediment and Fe(III)-oxide environments along with members of the Thermoproteales and Sulfolobales. Consequently, the primary goals of the current study were to analyze and compare replicate de novo sequence assemblies of Acidilobus-like populations from four different mildly acidic (pH 3.3 to 6.1) high-temperature (72°C to 82°C) environments and to identify metabolic pathways and/or protein-encoding genes that provide a detailed foundation of the potential functional role of these populations in situ. De novo assemblies of the highly similar Acidilobus-like populations (>99% 16S rRNA gene identity) represent near-complete consensus genomes based on an inventory of single-copy genes, deduced metabolic potential, and assembly statistics generated across sites. Functional analysis of coding sequences and confirmation of gene transcription by Acidilobus-like populations provide evidence that they are primarily chemoorganoheterotrophs, generating acetyl coenzyme A (acetyl-CoA) via the degradation of carbohydrates, lipids, and proteins, and auxotrophic with respect to several external vitamins, cofactors, and metabolites. No obvious pathways or protein-encoding genes responsible for the dissimilatory reduction of sulfur were identified. The presence of a formate dehydrogenase (Fdh) and other protein-encoding genes involved in mixed-acid fermentation supports the hypothesis that Acidilobus spp. function as degraders of complex organic constituents in high-temperature, mildly acidic, hypoxic geothermal systems.

Microbial community structure and sulfur biogeochemistry in mildly-acidic sulfidic geothermal springs in Yellowstone National Park.

Geothermal and hydrothermal waters often contain high concentrations of dissolved sulfide, which reacts with oxygen (abiotically or biotically) to yield elemental sulfur and other sulfur species that may support microbial metabolism. The primary goal of this study was to elucidate predominant biogeochemical processes important in sulfur biogeochemistry by identifying predominant sulfur species and describing microbial community structure within high-temperature, hypoxic, sulfur sediments ranging in pH from 4.2 to 6.1. Detailed analysis of aqueous species and solid phases present in hypoxic sulfur sediments revealed unique habitats containing high concentrations of dissolved sulfide, thiosulfate, and arsenite, as well as rhombohedral and spherical elemental sulfur and/or sulfide phases such as orpiment, stibnite, and pyrite, as well as alunite and quartz. Results from 16S rRNA gene sequencing show that these sediments are dominated by Crenarchaeota of the orders Desulfurococcales and Thermoproteales. Numerous cultivated representatives of these lineages, as well as the Thermoproteales strain (WP30) isolated in this study, require complex sources of carbon and respire elemental sulfur. We describe a new archaeal isolate (strain WP30) belonging to the order Thermoproteales (phylum Crenarchaeota, 98% identity to Pyrobaculum/Thermoproteus spp. 16S rRNA genes), which was obtained from sulfur sediments using in situ geochemical composition to design cultivation medium. This isolate produces sulfide during growth, which further promotes the formation of sulfide phases including orpiment, stibnite, or pyrite, depending on solution conditions. Geochemical, molecular, and physiological data were integrated to suggest primary factors controlling microbial community structure and function in high-temperature sulfur sediments.

Terminal oxidase diversity and function in "Metallosphaera yellowstonensis": gene expression and protein modeling suggest mechanisms of Fe(II) oxidation in the sulfolobales.

"Metallosphaera yellowstonensis" is a thermoacidophilic archaeon isolated from Yellowstone National Park that is capable of autotrophic growth using Fe(II), elemental S, or pyrite as electron donors. Analysis of the draft genome sequence from M. yellowstonensis strain MK1 revealed seven different copies of heme copper oxidases (subunit I) in a total of five different terminal oxidase complexes, including doxBCEF, foxABCDEFGHIJ, soxABC, and the soxM supercomplex, as well as a novel hypothetical two-protein doxB-like polyferredoxin complex. Other genes found in M. yellowstonensis with possible roles in S and or Fe cycling include a thiosulfate oxidase (tqoAB), a sulfite oxidase (som), a cbsA cytochrome b(558/566), several small blue copper proteins, and a novel gene sequence coding for a putative multicopper oxidase (Mco). Results from gene expression studies, including reverse transcriptase (RT) quantitative PCR (qPCR) of cultures grown autotrophically on either Fe(II), pyrite, or elemental S showed that the fox gene cluster and mco are highly expressed under conditions where Fe(II) is an electron donor. Metagenome sequence and gene expression studies of Fe-oxide mats confirmed the importance of fox genes (e.g., foxA and foxC) and mco under Fe(II)-oxidizing conditions. Protein modeling of FoxC suggests a novel lysine-lysine or lysine-arginine heme B binding domain, indicating that it is likely the cytochrome component of a heterodimer complex with foxG as a ferredoxin subunit. Analysis of mco shows that it encodes a novel multicopper blue protein with two plastocyanin type I copper domains that may play a role in the transfer of electrons within the Fox protein complex. An understanding of metabolic pathways involved in aerobic iron and sulfur oxidation in Sulfolobales has broad implications for understanding the evolution and niche diversification of these thermophiles as well as practical applications in fields such as bioleaching of trace metals from pyritic ores.

A geothermal-linked biological oasis in Yellowstone Lake, Yellowstone National Park, Wyoming.

Hundreds of active and dormant geothermal vents have been located on the floor of Yellowstone Lake, although characterization of the associated biology (macro or micro) has been extremely limited. Herein, we describe an aquatic moss (Fontinalis) colony closely associated with vent emissions that considerably exceeded known temperature maxima for this plant. Vent waters were supersaturated with CO(2), likely accommodating a CO(2) compensation point that would be expected to be quite elevated under these conditions. The moss was colonized by metazoa, including the crustaceans Hyalella and Gammarus, a segmented worm in the Lumbriculidae family, and a flatworm specimen tentatively identified as Polycelis. The presence of these invertebrates suggest a highly localized food chain that derives from the presence of geothermal inputs and thus is analogous to the deep marine vents that support significant biodiversity.

Linking microbial oxidation of arsenic with detection and phylogenetic analysis of arsenite oxidase genes in diverse geothermal environments.

The identification and characterization of genes involved in the microbial oxidation of arsenite will contribute to our understanding of factors controlling As cycling in natural systems. Towards this goal, we recently characterized the widespread occurrence of aerobic arsenite oxidase genes (aroA-like) from pure-culture bacterial isolates, soils, sediments and geothermal mats, but were unable to detect these genes in all geothermal systems where we have observed microbial arsenite oxidation. Consequently, the objectives of the current study were to measure arsenite-oxidation rates in geochemically diverse thermal habitats in Yellowstone National Park (YNP) ranging in pH from 2.6 to 8, and to identify corresponding 16S rRNA and aroA genotypes associated with these arsenite-oxidizing environments. Geochemical analyses, including measurement of arsenite-oxidation rates within geothermal outflow channels, were combined with 16S rRNA gene and aroA functional gene analysis using newly designed primers to capture previously undescribed aroA-like arsenite oxidase gene diversity. The majority of bacterial 16S rRNA gene sequences found in acidic (pH 2.6-3.6) Fe-oxyhydroxide microbial mats were closely related to Hydrogenobaculum spp. (members of the bacterial order Aquificales), while the predominant sequences from near-neutral (pH 6.2-8) springs were affiliated with other Aquificales including Sulfurihydrogenibium spp., Thermocrinis spp. and Hydrogenobacter spp., as well as members of the Deinococci, Thermodesulfobacteria and beta-Proteobacteria. Modified primers designed around previously characterized and newly identified aroA-like genes successfully amplified new lineages of aroA-like genes associated with members of the Aquificales across all geothermal systems examined. The expression of Aquificales aroA-like genes was also confirmed in situ, and the resultant cDNA sequences were consistent with aroA genotypes identified in the same environments. The aroA sequences identified in the current study expand the phylogenetic distribution of known Mo-pterin arsenite oxidase genes, and suggest the importance of three prominent genera of the order Aquificales in arsenite oxidation across geochemically distinct geothermal habitats ranging in pH from 2.6 to 8.

Isolation and distribution of a novel iron-oxidizing crenarchaeon from acidic geothermal springs in Yellowstone National Park.

Novel thermophilic crenarchaea have been observed in Fe(III) oxide microbial mats of Yellowstone National Park (YNP); however, no definitive work has identified specific microorganisms responsible for the oxidation of Fe(II). The objectives of the current study were to isolate and characterize an Fe(II)-oxidizing member of the Sulfolobales observed in previous 16S rRNA gene surveys and to determine the abundance and distribution of close relatives of this organism in acidic geothermal springs containing high concentrations of dissolved Fe(II). Here we report the isolation and characterization of the novel, Fe(II)-oxidizing, thermophilic, acidophilic organism Metallosphaera sp. strain MK1 obtained from a well-characterized acid-sulfate-chloride geothermal spring in Norris Geyser Basin, YNP. Full-length 16S rRNA gene sequence analysis revealed that strain MK1 exhibits only 94.9 to 96.1% sequence similarity to other known Metallosphaera spp. and less than 89.1% similarity to known Sulfolobus spp. Strain MK1 is a facultative chemolithoautotroph with an optimum pH range of 2.0 to 3.0 and an optimum temperature range of 65 to 75 degrees C. Strain MK1 grows optimally on pyrite or Fe(II) sorbed onto ferrihydrite, exhibiting doubling times between 10 and 11 h under aerobic conditions (65 degrees C). The distribution and relative abundance of MK1-like 16S rRNA gene sequences in 14 acidic geothermal springs containing Fe(III) oxide microbial mats were evaluated. Highly related MK1-like 16S rRNA gene sequences (>99% sequence similarity) were consistently observed in Fe(III) oxide mats at temperatures ranging from 55 to 80 degrees C. Quantitative PCR using Metallosphaera-specific primers confirmed that organisms highly similar to strain MK1 comprised up to 40% of the total archaeal community at selected sites. The broad distribution of highly related MK1-like 16S rRNA gene sequences in acidic Fe(III) oxide microbial mats is consistent with the observed characteristics and growth optima of Metallosphaera-like strain MK1 and emphasizes the importance of this newly described taxon in Fe(II) chemolithotrophy in acidic high-temperature environments of YNP.

Molecular analysis of microbial community structure in an arsenite-oxidizing acidic thermal spring.

Electron microscopy (EM), denaturing gradient gel electrophoresis (DGGE) and 16S rDNA sequencing were used to examine the structure and diversity of microbial mats present in an acid-sulphate-chloride (pH 3.1) thermal (58-62 degrees C) spring in Norris Basin, Yellowstone National Park, WY, USA, exhibiting rapid rates of arsenite oxidation. Initial visual assessments, scanning EM and geochemical measurements revealed the presence of three distinct mat types. Analysis of 16S rDNA fragments with DGGE confirmed the presence of different bacterial and archaeal communities within these zones. Changes in the microbial community appeared to coincide with arsenite oxidation activity. Phylogenetic analysis of 1400 bp 16S rDNA sequences revealed that clone libraries prepared from both arsenic redox active and inactive bacterial communities were dominated by sequences phylogenetically related to Hydrogenobacter acidophilus and Desulphurella sp. The appearance of archaeal 16S rDNA sequences coincided with the start of arsenite oxidation, and sequences were obtained showing affiliation with both Crenarchaeota and Euryarchaeota. The majority of archaeal sequences were most similar to sequences obtained from marine hydrothermal vents and other acidic hot springs, although the level of similarity was typically just 90%. Arsenite oxidation in this system may result from the activities of these unknown archaeal taxa and/or the previously unreported arsenic redox activity of H. acidophilus- or Desulphurella-like organisms. If the latter, arsenite oxidation must be inhibited in the initial high-sulphide zone of the spring, where no change in the distribution of arsenite versus arsenate was observed.

Agroterrorism, biological crimes, and biowarfare targeting animal agriculture. The clinical, pathologic, diagnostic, and epidemiologic features of some important animal diseases.

In the past 100 years, to our knowledge there have been approximately 12 events involving the intentional introduction of microbiologic agents into livestock and animal populations worldwide, of which three were World War I events in the United States. To the best of the authors' knowledge, there has been no recent intentional introduction of microbiologic agents (viruses or bacteria) into livestock and animal populations in the United States. The criminal or terrorist use of chemicals against animals and agriculture products have been more common. With the political, economic, and military new world order, however, the United States must maintain a vigilant posture. The framework for this vigilance must be an intelligence system sensitive to the needs of agriculture and a first-class animal disease diagnostic surveillance and response system.

Rapid oxidation of arsenite in a hot spring ecosystem, Yellowstone National Park.

Geothermal springs within Yellowstone National Park (YNP) often contain arsenic (As) at concentrations of 10-40 microM, levels that are considered toxic to many organisms. Arsenite (As(III)) is often the predominant valence state at the point of discharge but is rapidly oxidized to arsenate (As(V)) during transport in shallow surface water. The current study was designed to establish rates and possible mechanisms of As(III) oxidation and to characterize the geochemical environment associated with predominant microbial mats in a representative acid-sulfate-chloride (pH 3.1) thermal (58-62 degrees C) spring in Norris Basin, YNP. At the spring origin, total soluble As was predominantly As(III) at concentrations of 33 microM. No oxidation of As(III) was detected over the first 2.7 m downstream from the spring source, corresponding to an area dominated by a yellow filamentous S0-rich microbial mat However, rapid oxidation of As(III) to As(V) was observed between 2.7 and 5.6 m, corresponding to termination of the S0-rich mats, decreases in dissolved sulfide, and commencement of a brown Fe/As-rich mat. Rates of As(II) oxidation were estimated, yielding an apparent first-order rate constant of 1.2 min(-1) (half-life = 0.58 min). The oxidation of As(III) was shown to require live organisms present just prior to and within the Fe/As-rich mat. Complementary analytical tools used to characterize the brown mat revealed an As:Fe molar ratio of 0.7 and suggested that this filamentous microbial mat contains iron(III) oxyhydroxide coprecipitated with As(V). Results from the current work are the first to provide a comprehensive characterization of microbially mediated As(III) oxidation and the geochemical environments associated with microbial mats in acid-sulfate-chloride springs of YNP.

Microbial populations associated with the reduction and enhanced mobilization of arsenic in mine tailings.

Microbial reduction of arsenate [As(V)] to arsenite [As(III)] and the subsequent effects on As mobilization in contaminated mine tailings were studied under transport conditions. Molecular analysis of bacterial populations and traditional isolation techniques were used in conjunction with column experiments designed to observe relationships among pH (limed vs unlimed treatments), redox potential (Pt electrode), and mobilization of As. Liming increased pH values from approximately 4 to 8, resulting in a 5-fold increase in total As eluted from sterile columns. Elution of As from limed columns was further enhanced by microbial activity. As(III) was the predominant As species eluted from oxic, nonsterile columns. Conversely, in sterile treatments, As(V) was the predominant valence state in column effluent. Denaturing gradient gel electrophoresis coupled with sequence and phylogenetic analysis of 16S rRNA gene segments revealed that liming of the mine tailings stimulated specific Caulobacter-, Sphingomonas-, and Rhizobium-like populations. Pure culture isolates of these bacteria demonstrated the ability to rapidly reduce As(V) in aerated serum bottles. An intracellular As detoxification pathway was implicated in the reduction of As(V) by these isolates. These results indicate that microbial reduction of As(V) in As-contaminated soils may occur under aerobic conditions over relatively short time scales resulting in enhanced As mobilization.

Effect of model sorptive phases on phenanthrene biodegradation: different enrichment conditions influence bioavailability and selection of phenanthrene-degrading isolates.

The sorption of organic contaminants by natural organic matter (NOM) often limits substrate bioavailability and is an important factor affecting microbial degradation rates in soils and sediments. We hypothesized that reduced substrate bioavailability might influence which microbial assemblages are responsible for contaminant degradation under enrichment culture conditions. Our primary goal was to characterize enrichments in which different model organic solid phases were used to establish a range of phenanthrene bioavailabilities for soil microorganisms. Phenanthrene sorption coefficients (expressed as log K(D) values) ranged from 3.0 liters kg(-1) for Amberlite carboxylic acid cation-exchange resin (AMB) to 3.5 liters kg(-1) for Biobeads polyacrylic resin (SM7) and 4.2 liters kg(-1) for Biobeads divinyl benzene resin (SM2). Enrichment cultures were established for control (no sorptive phase), sand, AMB, SM7, and SM2 treatments by using two contaminated soils (from Dover, Ohio, and Libby, Mont.) as the initial inocula. The effects of sorption by model phases on the degradation of phenanthrene were evaluated for numerous transfers in order to obtain stable microbial assemblages representative of sorptive and nonsorptive enrichment cultures and to eliminate the effects of the NOM present in the initial inoculum. Phenanthrene degradation rates were similar for each soil inoculum and ranged from 4 to 5 micromol day(-1) for control and sand treatments to approximately 0.4 micromol day(-1) in the presence of the SM7 sorptive phase. The rates of phenanthrene degradation in the highly sorptive SM2 enrichment culture were insignificant; consequently, stable microbial populations could not be obtained. Bacterial isolates obtained from serial dilutions of enrichment culture samples exhibited significant differences in rates of phenanthrene degradation performed in the presence of SM7, suggesting that enrichments performed in the presence of a sorptive phase selected for different microbial assemblages than control treatments containing solid phase phenanthrene.

Effect of model sorptive phases on phenanthrene biodegradation: molecular analysis of enrichments and isolates suggests selection based on bioavailability.

Reduced bioavailability of nonpolar contaminants due to sorption to natural organic matter is an important factor controlling biodegradation of pollutants in the environment. We established enrichment cultures in which solid organic phases were used to reduce phenanthrene bioavailability to different degrees (R. J. Grosser, M. Friedrich, D. M. Ward, and W. P. Inskeep, Appl. Environ. Microbiol. 66:2695-2702, 2000). Bacteria enriched and isolated from contaminated soils under these conditions were analyzed by denaturing gradient gel electrophoresis (DGGE) and sequencing of PCR-amplified 16S ribosomal DNA segments. Compared to DGGE patterns obtained with enrichment cultures containing sand or no sorptive solid phase, different DGGE patterns were obtained with enrichment cultures containing phenanthrene sorbed to beads of Amberlite IRC-50 (AMB), a weak cation-exchange resin, and especially Biobead SM7 (SM7), a polyacrylic resin that sorbed phenanthrene more strongly. SM7 enrichments selected for mycobacterial phenanthrene mineralizers, whereas AMB enrichments selected for a Burkholderia sp. that degrades phenanthrene. Identical mycobacterial and Burkholderia 16S rRNA sequence segments were found in SM7 and AMB enrichment cultures inoculated with contaminated soil from two geographically distant sites. Other closely related Burkholderia sp. populations, some of which utilized phenanthrene, were detected in sand and control enrichment cultures. Our results are consistent with the hypothesis that different phenanthrene-utilizing bacteria inhabiting the same soils may be adapted to different phenanthrene bioavailabilities.

Molecular analysis of surfactant-driven microbial population shifts in hydrocarbon-contaminated soil.

We analyzed the impact of surfactant addition on hydrocarbon mineralization kinetics and the associated population shifts of hydrocarbon-degrading microorganisms in soil. A mixture of radiolabeled hexadecane and phenanthrene was added to batch soil vessels. Witconol SN70 (a nonionic, alcohol ethoxylate) was added in concentrations that bracketed the critical micelle concentration (CMC) in soil (CMC') (determined to be 13 mg g(-1)). Addition of the surfactant at a concentration below the CMC' (2 mg g(-1)) did not affect the mineralization rates of either hydrocarbon. However, when surfactant was added at a concentration approaching the CMC' (10 mg g(-1)), hexadecane mineralization was delayed and phenanthrene mineralization was completely inhibited. Addition of surfactant at concentrations above the CMC' (40 mg g(-1)) completely inhibited mineralization of both phenanthrene and hexadecane. Denaturing gradient gel electrophoresis of 16S rRNA gene segments showed that hydrocarbon amendment stimulated Rhodococcus and Nocardia populations that were displaced by Pseudomonas and Alcaligenes populations at elevated surfactant levels. Parallel cultivation studies revealed that the Rhodococcus population can utilize hexadecane and that the Pseudomonas and Alcaligenes populations can utilize both Witconol SN70 and hexadecane for growth. The results suggest that surfactant applications necessary to achieve the CMC alter the microbial populations responsible for hydrocarbon mineralization.

Toxoplasmosis in Atlantic bottle-nosed dolphins (Tursiops truncatus).

A female Atlantic bottle-nosed dolphin (Tursiops truncatus) and her calf were found beached on Picnic Island in Tampa Bay, Florida, USA. Despite therapy the animals died. Necropsy revealed severe pneumonia and lymphadenopathy in the mother and the calf, gastric ulcers and infection with the stomach digenean Braunina cordiformis in the mother, and a large, pale liver in the calf. Toxoplasma gondii was identified by light and electron microscopy and by immunohistochemistry in tissues of both animals. Toxoplasma gondii was associated with interstitial pneumonia, necrotizing adrenalitis, and cardiac myonecrosis in the mother and with lymphoid necrosis in both dolphins. The source of infection and the relationship to the recent dolphin beachings along the eastern seacoast of North America are unknown. This is the first report of toxoplasmosis in cetaceans.

Extinction coefficients of chlorophyll a and B in n,n-dimethylformamide and 80% acetone.

We found inconsistencies in the commonly used data for chlorophyll analysis in 80% acetone. Recently developed extinction coefficients for chlorophyll b in N,N-dimethylformamide (DMF) based on values from 80% acetone are low as a result of these inconsistencies. We determined extinction coefficients of chlorophyll a (Chl a) and chlorophyll b (Chl b) in DMF for wavelengths of 618 to 665 nanometers. The simultaneous equations necessary for quantifying Chl a, Chl b, or total Chl in DMF in the absence of other chlorophyllous pigments are: Chl a = 12.70A(664.5) - 2.79A(647); Chl b = 20.70 A(647) - 4.62A(664.5); total Chl = 17.90A(647) + 8.08A(664.5), where A = absorbance in 1.00 centimeter cuvettes and Chl = milligrams per liter.N,N-Dimethylformamide is a very convenient solvent for Chl extraction since it is effective on intact plant parts and Chl is quite stable in DMF. There was no difference in the amount of Chl extracted when plant tissue was stored for 1 or 3 days at three temperatures, with or without solvent added.

Characterisation of the unsteady transport of labelled species in permeable capillaries: role of convective dispersion.

A mathematical model of transcapillary exchange has been developed which considers in detail the contribution of Taylor dispersion (i.e., non-uniform velocity and inequalities in radial concentration) to the uptake and wash-out of multiple tracers from single capillaries. A numerical solution to the two-dimensional unsteady-state species continuity equation for a single capillary is obtained (by the use of an array processor) which simulates the convective dispersion of labelled indicators in permeable capillaries. Particular attention is directed toward an analysis of the roles of capillary permeability, transport regime as characterised by the Peclet number, velocity profile and the length of the exchange region on the development of time-concentration profiles and on the importance of convective dispersion. For the physiologic range of parameters consistent with pulmonary capillary transport of multiple indicators (e.g., labelled urea, albumin, etc.), we find that the magnitude of convective dispersion is insufficient to markedly affect the shapes of simulated tracer concentration profiles. The implication in these circumstances is that the use of one-dimensional models, which do not account for Taylor dispersion, does not lead to significant errors in parameter estimates derived from data of multiple indicator dilution.

Role of longitudinal diffusion in the extravascular pulmonary space on parameter estimates derived from data of multiple indicator dilution.

A mathematical model of transcapillary exchange has been developed that considers in detail the role of axial diffusion in the extravascular tissue region on estimates of such physiological parameters as lung water (VE) and pulmonary capillary permeability-surface area products (PS), obtained from multiple indicator dilution studies. The experimental cases considered correspond to two animal models of pulmonary oedema in which the integrity of the pulmonary capillary membrane is disrupted and the effects of extravascular axial diffusion may be important. A novel feature of the computational scheme is the use of an Array Processor in the solution of the governing equations, initial and boundary conditions. Computer time is reduced to 2-3 min for parameter identification, thereby allowing a wide range of values for extravascular axial diffusion coefficients (D'/L2) to be studied at little computational expense. The results indicate that diffusion in the extravascular region does not influence parameter estimates for PS to urea. A statistical correlation is suggested between values for VE, PS to water, and D'/L2.