Loss of production and animal health costs in assessing economic burden of animal disease.

This article focuses on identifying the loss of production and costs (or lack thereof) associated with livestock health as well as animal disease externalities, with the intent to estimate economy-wide burden. It limits its scope to terrestrial livestock and aquaculture, wherein economic burden is predominately determined by market forces. Losses and costs are delineated into both direct losses and costs and indirect losses and costs, as well as ex post costs and ex ante costs. These costs include not only private expenditures but also public expenditures related to the prevention of, treatment of, and response to livestock disease. This distinction is important because a primary role of government is to mitigate externalities. The article then discusses market impacts and investments. Finally, it provides selected examples and illustrative observations and discusses future directions for research and application.

Cet article examine les pertes de production et les coûts associés (ou non) à la santé animale ainsi que les externalités liées aux maladies animales, dans le but d'estimer le fardeau pour l'ensemble de l'économie. L'examen se limite à la production d'animaux terrestres et aquatiques, secteurs où le fardeau économique est principalement déterminé par les forces du marché. Les pertes et les coûts sont répartis en pertes et coûts directs et indirects, ainsi qu'en coûts ex post et ex ante. Ces coûts comprennent non seulement les dépenses privées, mais aussi les dépenses publiques liées à la prévention, au traitement et aux réponses aux maladies des animaux d'élevage. Il s'agit d'une distinction importante car l'une des fonctions premières d'un gouvernement est d'atténuer les externalités. Les auteurs examinent ensuite les impacts sur les marchés et les investissements. Pour conclure, à partir d'exemples choisis et d'observations illustrant leur propos, les auteurs proposent des voies d'exploration pour la recherche et ses applications.

Este artículo se centra en determinar las pérdidas de producción y los costos (o la ausencia de ellos) asociados con las externalidades de la sanidad del ganado y las enfermedades animales, con el objetivo de estimar su impacto en toda la economía. El ámbito del artículo se limita a la ganadería terrestre y la acuicultura, donde el impacto económico está principalmente determinado por las fuerzas del mercado. Las pérdidas y los costos se clasifican en pérdidas y costos directos e indirectos, así como en costos ex post y ex ante. Dichos costos incluyen no solo los gastos privados, sino también los gastos públicos relacionados con la prevención y el tratamiento de las enfermedades del ganado y la respuesta ante estas, una distinción que es importante habida cuenta de que una de las principales funciones del gobierno es mitigar las externalidades. En el artículo se analizan a continuación las repercusiones en el mercado y las inversiones y, por último, se presentan algunos ejemplos y observaciones ilustrativas y se examinan las orientaciones futuras de la investigación y sus aplicaciones.

A Collaborating Centre for animal health economics in the Americas.

Countries in the Americas play a vital role in global livestock and aquaculture production. With international trade of livestock and aquaculture products becoming an important source of income for countries, there has been an increased interest in using animal health economics for advocacy and allocation of resources. This article discusses the development of a new Collaborating Centre for the Economics of Animal Health and the applications of the Global Burden of Animal Diseases (GBADs) framework in the Americas region. Incentives for the increased use of economics in animal health decision-making and examples from the Americas region are examined. The article then discusses the newly formed World Organisation for Animal Health Collaborating Centre in the Americas region. Finally, it reviews two ongoing case studies that are implementing the GBADs framework in Peru and the United States of America.

Les pays des Amériques jouent un rôle crucial dans la production mondiale d'animaux d'élevage, qu'il s'agisse d'espèces terrestres ou aquatiques. Le commerce international des produits issus de l'élevage et de l'aquaculture étant désormais une source importante de revenus pour les pays, la possibilité d'utiliser les concepts de l'économie de la santé animale à des fins de plaidoyer et d'allocation des ressources suscite un intérêt croissant. Les auteurs abordent la désignation d'un nouveau Centre collaborateur pour l'économie de la santé animale ainsi que les applications du programme " Impact mondial des maladies animales " (GBADs) dans la région des Amériques. Ils examinent les avantages d'une meilleure prise en compte de l'économie dans les prises de décision en matière de santé animale, illustrés par quelques exemples concrets relevés dans la région. Ils décrivent ensuite la création du nouveau Centre collaborateur de l'Organisation mondiale de la santé animale dans la région des Amériques. Enfin, ils présentent deux études de cas menées actuellement concernant la mise en oeuvre du programme GBADs respectivement au Pérou et aux Etats-Unis d'Amérique.

Los países de las Américas desempeñan un papel fundamental en la producción ganadera y acuícola mundial. Dado que el comercio internacional de productos ganaderos y acuícolas se ha convertido en una importante fuente de ingresos para los países, el interés por utilizar la economía de la sanidad animal en favor de la promoción y la asignación de recursos ha ido en aumento. En este artículo se analiza la creación de un nuevo Centro colaborador para la economía de la sanidad animal y las aplicaciones del marco del impacto global de las enfermedades animales (GBADs) en la región de las Américas. Se examinan los incentivos para un mayor uso de la economía en la toma de decisiones sobre sanidad animal, así como ejemplos de la región. A continuación, en el artículo se presenta el recién creado Centro colaborador de la Organización Mundial de Sanidad Animal en la región de las Américas. Por último, se examinan dos estudios de casos en los que se está poniendo en práctica el marco del GBADs en Perú y los Estados Unidos de América.

Low Prevalence of Screen-Detected Colorectal Cancer in an Average-Risk Population: The New Normal.

Prior studies have reported the prevalence of colorectal cancer (CRC) in average-risk screening population ages 50-75 to be 0.7%-1.0%.1,2 However, no estimates from studies enrolling individuals undergoing screening colonoscopy have been reported. The experience of ongoing studies enrolling average-risk individuals is that the prevalence rates are substantially lower. A 2020 study from a community-based cohort undergoing CRC screening with fecal immunochemical testing followed by diagnostic colonoscopy reported a CRC prevalence rate of 1.46 per 1000, or 0.15%.3 The aim of our study is to report the screen-detected prevalence of CRC and advanced neoplasia in average-risk asymptomatic individuals from selected academic and community medical centers in the United States, Canada, and Germany and describe associated risk factors.

Global Burden of Animal Diseases: a novel approach to understanding and managing disease in livestock and aquaculture.

Investments in animal health and Veterinary Services can have a measurable impact on the health of people and the environment. These investments require a baseline metric that describes the burden of animal health and welfare in order to justify and prioritise resource allocation and from which to measure the impact of interventions. This paper is part of a process of scientific enquiry in which problems are identified and solutions sought in an inclusive way. It poses the broad question: what should a system to measure the animal disease burden on society look like and what value would it add? Moreover, it aims to do this in such a way as to be accessible by a wide audience, who are encouraged to engage in this debate. Given that farmed animals, including those raised by poor smallholders, are an economic entity, this system should be based on economic principles. These poor farmers are negatively impacted by disparities in animal health technology, which can be addressed through a mixture of supply-led and demand-driven interventions, reinforcing the relevance of targeted financial support from government and non-governmental organisations. The Global Burden of Animal Diseases (GBADs) Programme will glean existing data to measure animal health losses within carefully characterised production systems. Consistent and transparent attribution of animal health losses will enable meaningful comparisons of the animal disease burden to be made between diseases, production systems and countries, and will show how it is apportioned by people's socio-economic status and gender. The GBADs Programme will produce a cloud-based knowledge engine and data portal, through which users will access burden metrics and associated visualisations, support for decisionmaking in the form of future animal health scenarios, and the outputs of wider economic modelling. The vision of GBADs, strengthening the food system for the benefit of society and the environment, is an example of One Health thinking in action.

Les investissements réalisés en santé animale et dans les Services vétérinaires ont un impact mesurable sur la santé des personnes et de l'environnement. Le système de mesure appliqué à ces investissements doit reposer sur un référentiel de base décrivant l'impact de la santé et du bien-être animal de manière à justifier et classer par priorités les ressources allouées et à mesurer les effets des interventions. Les auteurs présentent une étude conduite dans le cadre d'une enquête scientifique destinée à identifier les problèmes et à rechercher des solutions de manière inclusive. L'étude pose la question de savoir à quoi devrait ressembler un système conçu pour mesurer l'impact sur la société des maladies animales, et quelle serait sa valeur ajoutée. En outre, l'étude est conduite de manière à être accessible à une large audience afin d'encourager cette dernière à participer aux discussions. Étant donné que les animaux d'élevage constituent une entité économique, y compris les animaux appartenant à des éleveurs pauvres, le système de mesure doit reposer sur des principes économiques. Les exploitants pratiquant une agriculture de subsistance subissent les effets négatifs des disparités entre les différentes technologies applicables à la santé animale, disparités auxquelles il est possible de remédier par le biais d'interventions associant des mesures dictées par l'offre et par la demande et en renforçant l'efficacité du soutien financier ciblé apporté par les organisations gouvernementales et non gouvernementales. Le Programme « L'impact mondial des maladies animales ¼ (GBADs) aura pour tâche de glaner les données existantes afin de mesurer les pertes associées à la santé animale au sein de systèmes de production qui auront été soigneusement caractérisés au préalable. Grâce à l'élucidation cohérente et transparente des pertes imputables à chaque problème de santé animale, des comparaisons pertinentes pourront être effectuées concernant l'impact des maladies animales par maladies, par systèmes de production et par pays, et la répartition de cet impact dans les populations concernées suivant le statut socio-économique et le genre des intéressés sera mieux comprise. Le Programme GBADs entend créer un moteur de recherche et un portail de données qui seront disponibles sur le Cloud et donneront aux utilisateurs l'accès à des outils de mesure de l'impact des maladies et à d'autres informations présentées sous forme graphique, ainsi qu'à des outils d'aide à la décision sous forme de scénarios prospectifs sur la santé animale et aux résultats d'études plus larges de modélisation économique. La vision du GBADs, renforcer le système de production de denrées alimentaires au profit de la société et de l'environnement, est un exemple de mise en oeuvre du concept Une seule santé.

Las inversiones en sanidad animal y en los Servicios Veterinarios pueden tener un efecto mensurable en la salud de las personas y el medio ambiente. Para efectuar estas inversiones se precisan parámetros que describan y cuantifiquen la situación de partida y el impacto de los problemas de sanidad y bienestar animales, a fin de poder, a partir de ahí, justificar y jerarquizar la asignación de recursos y medir los efectos de las intervenciones. Este artículo, inscrito en un proceso de indagación científica encaminado a detectar problemas y buscar soluciones de forma incluyente, plantea la cuestión general de cómo debería ser y qué valor añadido aportaría un sistema destinado a medir el impacto que imponen a la sociedad las enfermedades animales. Los autores, además, tratan de exponer la cuestión de manera que sea accesible a un público amplio, al que se alienta a participar en este debate. Dado que los animales de granja (incluidos los de pequeñas explotaciones) constituyen una entidad económica, tal sistema debería estar basado en principios económicos. Los productores que trabajan en régimen de subsistencia se ven negativamente afectados por las disparidades existentes en materia de tecnología zoosanitaria, disparidad que cabe corregir con una combinación de intervenciones marcadas por la oferta y otras marcadas por la demanda, dirigiendo así más selectivamente el apoyo económico de entidades gubernamentales y organizaciones no gubernamentales. El programa GBADs (El impacto global de las enfermedades animales) servirá para compilar datos ya existentes con el fin de medir las pérdidas zoosanitarias dentro de sistemas productivos cuidadosamente caracterizados. La atribución coherente y transparente de estas pérdidas zoosanitarias permitirá efectuar comparaciones significativas del impacto que representan las enfermedades animales en el caso de diferentes dolencias, sistemas productivos o países y pondrá de relieve cómo se distribuye este impacto en función del género y la condición socioeconómica de las personas. Por medio del programa GBADs se creará un motor de conocimiento y portal de datos ubicado en la nube que permita al usuario acceder a mediciones del impacto de enfermedades y representaciones gráficas conexas, a herramientas de apoyo a la adopción de decisiones, en forma de hipotéticas situaciones zoosanitarias futuras, y a los resultados de modelizaciones económicas más generales. La aspiración del programa GBADs ­ reforzar el sistema alimentario en beneficio de la sociedad y el medio ambiente ­ constituye un ejemplo de aplicación en la práctica del pensamiento en clave de Una sola salud.

Antagonistic Interactions and Biofilm Forming Capabilities Among Bacterial Strains Isolated from the Egg Surfaces of Lake Sturgeon (Acipenser fulvescens).

Characterization of interactions within a host-associated microbiome can help elucidate the mechanisms of microbial community formation on hosts and can be used to identify potential probiotics that protect hosts from pathogens. Microbes employ various modes of antagonism when interacting with other members of the community. The formation of biofilm by some strains can be a defense against antimicrobial compounds produced by other taxa. We characterized the magnitude of antagonistic interactions and biofilm formation of 25 phylogenetically diverse taxa that are representative of isolates obtained from egg surfaces of the threatened fish species lake sturgeon (Acipenser fulvescens) at two ecologically relevant temperature regimes. Eight isolates exhibited aggression to at least one other isolate. Pseudomonas sp. C22 was found to be the most aggressive strain, while Flavobacterium spp. were found to be one of the least aggressive and the most susceptible genera. Temperature affected the prevalence and intensity of antagonism. The aggressive strains identified also inhibited growth of known fish pathogens. Biofilm formations were observed for nine isolates and were dependent on temperature and growth medium. The most aggressive of the isolates disrupted biofilm formation of two well-characterized isolates but enhanced biofilm formation of a fish pathogen. Our results revealed the complex nature of interactions among members of an egg associated microbial community yet underscored the potential of specific microbial populations as host probiotics.

Animal health economics: an aid to decisionmaking on animal health interventions - case studies in the United States of America.

For animal disease events the outcomes and consequences often remain unclear or uncertain, including the expected changes in benefits (e.g. profit to firms, prices to consumers) and in costs (e.g. response, clean-up). Moreover, the measurement of changes in benefits and costs across alternative interventions used to control animal disease events may be inexact. For instance, the economic consequences of alternative vaccination strategies to mitigate a disease can vary in magnitude due to trade embargoes and other factors. The authors discuss the economic measurement of animal disease outbreaks and interventions and how measurement is used in private and public decision-making. Two illustrative case studies in the United States of America are provided: a hypothetical outbreak of foot and mouth disease in cattle, and the 2014-2015 outbreak of highly pathogenic avian influenza in poultry.

Lors d'un événement sanitaire, les résultats et les conséquences d'une intervention sont souvent incertains ou imprécis, y compris pour ce qui concerne l'évolution attendue des bénéfices (par ex. le profit pour les entreprises ou le prix payé par le consommateur) et des coûts (par ex. le coût de la réponse ou de l'assainissement). De plus, la mesure de l'évolution des bénéfices et des coûts suivant les différentes interventions utilisées pour lutter contre les maladies animales peut s'avérer inexacte. Par exemple, les conséquences économiques de différentes stratégies de vaccination visant à atténuer l'impact d'une maladie peuvent varier en ordre de grandeur du fait des restrictions imposées au commerce suite à la vaccination, ou d'autres facteurs. Les auteurs examinent l'évaluation économique des foyers de maladies animales et des interventions sanitaires ainsi que l'utilisation de ces évaluations dans les prises de décision du secteur privé et public. L'analyse est illustrée par deux études de cas aux États- Unis d'Amérique : l'hypothèse d'un foyer de fièvre aphteuse survenant dans la population bovine, et le foyer d'influenza aviaire hautement pathogène survenu en 2014­2015 chez les volailles.

A menudo los resultados o efectos de ciertos episodios zoosanitarios quedan poco claros o generan incertidumbre, por ejemplo sobre el modo en que en principio modifican los beneficios (réditos para las empresas, precios para el consumidor) y los costos (p.ej. de respuesta o de saneamiento de la explotación). Además, la medición de los cambios que experimenten los costos y beneficios a resultas de distintas intervenciones posibles para combatir un episodio zoosanitario puede resultar inexacta. Por ejemplo: las consecuencias económicas de estrategias alternativas de vacunación para mitigar una enfermedad pueden ser de magnitud variable dependiendo de la existencia de embargos comerciales u otros factores. Los autores examinan la cuantificación económica de los brotes de enfermedades animales y las intervenciones para combatirlos y explican cómo se utilizan esas mediciones para tomar decisiones en los sectores público y privado, ofreciendo como ejemplo casos situados en los Estados Unidos de América: un brote hipotético de fiebre aftosa en el ganado vacuno y el brote de influenza aviar altamente patógena que en 2014 y 2015 afectó a las aves de corral.

Bacterial community dynamics during industrial malting, with an emphasis on lactic acid bacteria.

Characterization of the microflora during malting is an essential step towards process management and optimization. Up till now, however, microbial characterization in the malting process has mostly been done using culture-dependent methods, probably leading to biased estimates of microbial diversity. The aim of this study was to characterize the bacterial communities using two culture-independent methods, including Terminal Restriction Fragment Length Polymorphism (T-RFLP) and 454 pyrosequencing, targeting the 16S rRNA gene. Studied samples originated from two harvest years and two malting houses malting the same batch of barley. Besides targeting the entire bacterial community (T-RFLP), emphasis was put on lactic acid bacteria (LAB) (T-RFLP and 454 pyrosequencing). The overall bacterial community richness was limited, but the community structure changed during the process. Zooming in on the LAB community using 454 pyrosequencing revealed a total of 47 species-level operational taxonomic units (OTUs). LAB diversity appeared relatively limited since 88% of the sequences were covered by the same five OTUs (representing members of Weissella, Lactobacillus and Leuconostoc) present in all samples investigated. Fluctuations in the relative abundances of the dominant LAB were observed with the process conditions. In addition, both the year of harvest and malting house influenced the LAB community structure.

Ribonuclease P catalysis differs from ribosomal RNA self-splicing.

Two RNA-catalyzed reactions have been described, the Tetrahymena self-splicing ribosomal RNA and ribonuclease P. The Tetrahymena self-splicing reaction proceeds through a transesterification cascade that is dependent upon nucleophilic attacks by ribose 3'-OH groups. Periodate oxidation of the catalytic (or substrate) RNA, which destroys the nucleophilicity of RNA 3' termini, did not inhibit ribonuclease P activity. Thus, catalysis by ribonuclease P differs from the self-splicing reaction.

Assessment of intraradicular bacterial composition by terminal restriction fragment length polymorphism analysis.

BACKGROUND: The aim of the study was to assess the bacterial community structures associated with endodontic infections using terminal restriction fragment length polymorphism (T-RFLP), and to investigate the correlation of whole community profiles with the manifestation of particular clinical features. METHODS: Intraradicular samples were collected from 34 subjects and classified into three study groups based on the observed clinical symptoms: acute (n = 16), sub-acute (n = 8), and asymptomatic (n = 10). Genomic DNA was extracted from each sample, submitted to polymerase chain reaction using a fluorescently labeled 16S ribosomal DNA forward primer, and digested with two tetrameric endonucleases (HhaI and MspI). The terminal restriction fragments (T-RFs) were subsequently discriminated in an automated DNA sequencer, and the results were filtered using a statistics-based criterion. RESULTS: Totals of 138 (HhaI) and 145 (MspI) unique T-RFs were detected (means 13.1 and 11.9) and there was high inter-subject variability in the bacterial assemblages. Odds-ratio analysis unveiled the existence of higher order groups of positively associated T-RFs, restating the concept that intricate ecological relationships may take place in the root canal space. A significantly greater T-RF prevalence was detected in acute cases, suggesting a straight correlation between species richness and spontaneous pain. CONCLUSION: Overall, no T-RFLP profile representing a specific bacterial consortium could be associated with the manifestation of symptoms of endodontic origin.

Terminal restriction fragment length polymorphism (T-RFLP): an emerging method for characterizing diversity among homologous populations of amplification products.

Terminal restriction fragment length polymorphism is a recent molecular approach that can assess subtle genetic differences between strains as well as provide insight into the structure and function of microbial communities. The technique has both high sensitivity and throughput making it ideal for comparative analyses.

The Ribosomal Database Project (RDP-II): previewing a new autoaligner that allows regular updates and the new prokaryotic taxonomy.

The Ribosomal Database Project-II (RDP-II) pro-vides data, tools and services related to ribosomal RNA sequences to the research community. Through its website (http://rdp.cme.msu.edu), RDP-II offers aligned and annotated rRNA sequence data, analysis services, and phylogenetic inferences (trees) derived from these data. RDP-II release 8.1 contains 16 277 prokaryotic, 5201 eukaryotic, and 1503 mitochondrial small subunit rRNA sequences in aligned and annotated format. The current public beta release of 9.0 debuts a new regularly updated alignment of over 50 000 annotated (eu)bacterial sequences. New analysis services include a sequence search and selection tool (Hierarchy Browser) and a phylogenetic tree building and visualization tool (Phylip Interface). A new interactive tutorial guides users through the basics of rRNA sequence analysis. Other services include probe checking, phylogenetic placement of user sequences, screening of users' sequences for chimeric rRNA sequences, automated alignment, production of similarity matrices, and services to plan and analyze terminal restriction fragment polymorphism (T-RFLP) experiments. The RDP-II email address for questions or comments is rdpstaff@msu.edu.

Economic Assessment of Zoonotic Diseases: An Illustrative Study of Rift Valley Fever in the United States.

This study evaluates the economic consequences of a Rift Valley Fever outbreak, a virus that spreads from livestock to humans, often through mosquitoes. Developing a 'one health' economic framework, economic impacts on agricultural producers and consumers, government costs of response, costs and disruptions to non-agricultural activities in the epidemiologically impacted region, and human health costs (morbidity and mortality) are estimated. We find the agricultural firms bear most of the negative economic impacts, followed by regional non-agricultural firms, human health and government. Further, consumers of agricultural products benefit from small outbreaks due to bans on agricultural exports.

Developing historical food production and consumption data for 131I dose estimates: the Hanford experience.

This paper describes the methods used to reconstruct the movement of commercial foods in and through the study area of the Hanford Environmental Dose Reconstruction Project. The most dose-relevant radionuclide released from Hanford separations plants was 131I via the atmospheric pathway. As a result of atmospheric deposition of 131I, commercial food supplies may have been contaminated. Because the half-life of 131I is relatively short, foods consumed soon after production, such as milk and produce, presented the highest risk. For that reason, this paper deals primarily with the reconstruction of milk and produce production, marketing, and consumption from 1945-1951, the period with the highest known 131I releases. The reconstructed food production and consumption information was used as input to radiation dose estimates for representative individuals and as default values for real individuals who may not remember where they obtained food or how much they consumed during that period. Specific methods for tracing the movement of commercial milk and produce back from the point of human consumption, through commercial markets, to original production are presented. Results include the characteristics of food consumption exhibited by representative individuals, examples of commercial milk and produce market structures, and a review of commercial milk production and processing practices from 1945-1951.

Diversity of fish-associated flavobacteria of Michigan.

Flavobacteriosis poses a serious threat to wild and propagated fish stocks alike, accounting for more fish mortality in Michigan and its associated state fish hatcheries than all other pathogens combined. Although this consortium of fish diseases has primarily been attributed to Flavobacterium psychrophilum, F. columnare, and F. branchiophilum, herein we describe a diverse assemblage of Flavobacterium and Chryseobacterium spp. isolates recovered from diseased as well as apparently healthy wild, feral, and farmed fish of Michigan. Among 254 fish-associated flavobacterial isolates recovered from 21 fish species during 2003-2010, 211 were identified as Flavobacterium spp., whereas 43 were identified as Chryseobacterium spp. according to ribosomal RNA partial gene sequencing and phylogenetic analysis. Although F. psychrophilum and F. columnare were indeed associated with multiple fish mortality events, many previously uncharacterized flavobacteria were recovered from systemically infected fish showing overt signs of disease, and in vitro protease assays demonstrated that these isolates were highly proteolytic to multiple substrates that comprise host tissues. Indeed, the majority of the isolates either (1) were most similar to recently described fish-associated Flavobacterium and Chryseobacterium spp. that have never before been reported in North America (e.g., F. oncorhynchi, F. araucananum, C. viscerum, C. piscicola, and C. chaponense) or (2) did not cluster with any described species and most likely represent novel flavobacterial taxa. This study highlights the extreme diversity of flavobacteria that are potentially associated with flavobacteriosis in Michigan.

Relationship of hydrogen bioavailability to chromate reduction in aquifer sediments.

Biological Cr(VI) reduction was studied in anaerobic sediments from an aquifer in Norman, Okla. Microcosms containing sediment and mineral medium were amended with various electron donors to determine those most important for biological Cr(VI) reduction. Cr(VI) (about 340 microM) was reduced with endogenous substrates (no donor), or acetate was added. The addition of formate, hydrogen, and glucose stimulated Cr(VI) reduction compared with reduction in unamended controls. From these sediments, an anaerobic Cr(VI)-utilizing enrichment was obtained that was dependent upon hydrogen for both growth and Cr(VI) reduction. No methane was produced by the enrichment, which reduced about 750 microM Cr(VI) in less than six days. The dissolved hydrogen concentration was used as an indicator of the terminal electron accepting process occurring in the sediments. Microcosms with sediments, groundwater, and chromate metabolized hydrogen to a concentration below the detection limits of the mercury vapor gas chromatograph. In microcosms without chromate, the hydrogen concentration was about 8 nM, a concentration comparable to that under methanogenic conditions. When these microcosms were amended with 500 microM Cr(VI), the dissolved hydrogen concentration quickly fell below the detection limits. These results showed that the hydrogen concentration under chromate-reducing conditions became very low, as low as that reported under nitrate- and manganese-reducing conditions, a result consistent with the free energy changes for these reactions. The utilization of formate, lactate, hydrogen, and glucose as electron donors for Cr(VI) reduction indicates that increasing the availability of hydrogen results in a greater capacity for Cr(VI) reduction. This conclusion is supported by the existence of an enrichment dependent upon hydrogen for growth and Cr(VI) reduction.

RNA catalysis and the origin of life.

Until the discovery of catalytic RNAs, first the self-splicing intron in Tetrahymena and then the bacterial RNAse P, cellular enzymes had always seemed to be protein in nature. The recognition that RNA can catalytically make and break phosphodiester bonds simplifies some of the assumptions required of a rudimentary self-replicating entity. Available information on the chemistry of RNA-catalyzed reactions is reviewed, with particular attention to self-splicing introns and tRNA processing by RNase P. An explicit model for a self-replicating RNA is described. The model postulates a nucleotide binding/polymerization site in the RNA, and takes advantage of intrinsic fluidity in RNA higher order structure to dissociate parent and progeny complementary strands.

Purification and characterization of RNase P from Clostridium sporogenes.

RNase P is a multi-subunit enzyme responsible for the accurate processing of the 5' terminus of all tRNAs. The RNA subunit from Clostridium sporogenes has been partially purified and characterized. The RNA is approximately 400 nucleotides long and makes a precise endonucleolytic cleavage at the mature 5' terminus of tRNA. The RNA requires moderate concentrations of Mg2+ (20 mM) and relatively high concentrations of NH4Cl (800 mM) for optimal activity. Mn2+ effectively substitutes for Mg2+ at 2 mM. Zn2+, Ni2+, Ca2+, and Co2+ are ineffective at stimulating activity. Monovalent ions are, in general, more effective the greater the ionic radius (NH+4 greater than Cs greater than Rb greater than K greater than Na). In contrast to the activity of Bacillus subtilis, C. sporogenes RNase P RNA is significant more active in (NH4)2SO4 than in NH4Cl.

Nucleotides in precursor tRNAs that are required intact for catalysis by RNase P RNAs.

Precursor tRNAAsp molecules, containing a 26-base 5' leader, were treated with diethylpyrocarbonate, 50% hydrazine or anhydrous hydrazine/3M NaCl and then subjected to processing by RNase P RNAs from Escherichia coli or Bacillus subtilis. Fully processed tRNAs and material not successfully cleaved by the catalytic RNAs were analyzed for their content of chemically altered nucleotides. Several bases were identified as being required intact for optimal activity as substrate as judged by exclusion of chemically modified residues from processed molecules, and simultaneous enhancement in material that was not recognized as substrate. Such nucleotides cluster near the site of cleavage at the mature 5' end and in the T stem and loop. Purines at residues 1 and 2 adjacent to the site of cleavage, position 57 in the T loop, and site 64 in the T stem exhibited the most pronounced effects. These results suggest a model of recognition of substrate by RNase P RNAs in which the ribozyme interacts with the corner of the precursor tRNA's three dimensional structure, where the T- and D-loops are juxtaposed, and extends along the top of the molecule back towards the site of catalysis.

Ion dependence of the Bacillus subtilis RNase P reaction.

The properties of the Bacillus subtilis RNase P are characterized with regard to the types and concentrations of monovalent and divalent ions required to potentiate precursor tRNA cleavage by the protein-RNA holoenzyme and the catalytic RNA alone. The ionic dependence of the RNase P RNA-catalyzed reaction in part seems due to a requirement for ion shielding between substrate and catalytic RNAs. The RNase P protein, which binds to RNA nonspecifically and tightly, likely serves, in part, as a cation screen. However, the character of the ion dependence of the RNA catalysis, the inhibition by high SO2-4 concentration, and potentiation by solvents suggest that RNA conformational transition may be involved in the reaction. It is proposed that the reason for catalysis by RNA in the RNase P reaction may be a requirement for fluidity in the structure of the catalyst, so that it can accommodate many tRNA substrates, which vary in their structural details.