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H van Keulen

Publications and source records attributed to H van Keulen.

At least 19 recordsLinked to original sources
PubMed2006

Evaluating farm performance using agri-environmental indicators: recent experiences for nitrogen management in The Netherlands.

Intensive agriculture, characterized by high inputs, has serious implications on the environment. Monitoring and evaluation of projects aiming at designing, testing and applying more sustainable practices require instruments to asses agronomic as well as environmental performance. Guidelines for Good Agricultural Practice (GAP) or Good Farming Practice (GFP) define sustainable practices but give limited insight into their environmental performance. Agri-environmental indicators (AEIs) provide information on environmental as well as agronomic performance, which allows them to serve as analytical instruments in research and provide thresholds for legislation purposes. Effective AEIs are quantifiable and scientifically sound, relevant, acceptable to target groups, easy to interpret and cost-effective. This paper discusses application of four AEIs for nitrogen (N) management in three Dutch research projects: 'De Marke', 'Cows and Opportunities' and 'Farming with a future'. 'De Marke' applied Nitrogen Surplus and Groundwater Nitrate Concentration in the design and testing of environmentally sound dairy systems. 'Cows and Opportunities', testing and disseminating dairy systems designed at 'De Marke', mainly applied Nitrogen Surplus, while 'Farming with a future' used Nitrogen Surplus, Groundwater Nitrate Concentration and Residual Mineral Soil Nitrogen to support arable farmers in complying with Dutch legislation (MINAS). Nitrogen Surplus is quantifiable, appealing and easy to interpret, but lacks scientific soundness or a good relationship with groundwater quality. Nitrogen Use Efficiency is sensitive to changes in management, while Residual Mineral Soil Nitrogen is appealing and cheap, but has difficulties in scaling. Groundwater Nitrate Concentration lacks clear rules for sampling, is labor consuming, expensive and mainly used in combination with other indicators. AEIs enhanced improvements in N management by facilitating (i) definition of project goals, (ii) design of desired systems, (iii) evaluation of applied systems and (iv) improving effective communication. AEI applications in other countries show a similar pattern as found in The Netherlands. Limitations to AEI application relate to inconsistencies between different indicators, heterogeneity of soil characteristics and linkages of N, carbon and water management. AEIs should be applied in an integrated evaluation, at a scale that reflects the farm's spatial variability. Simple AEIs like Nitrogen Surplus should be supported by other indicators and/or model calculations. The paper concludes that AEIs proved their value in design, implementation and testing of farming systems, but they should be used with care, always keeping in mind that indicators are simplifications of complex and variable processes.

Agriculture↗
PubMed1998

The sequence of Giardia small subunit rRNA shows that voles and muskrats are parasitized by a unique species Giardia microti.

The small subunit ribosomal RNA (eukaryotic 16S rRNA) gene from Giardia trophozoites, isolated from 8 different prairie voles and 8 different muskrats, was amplified by the polymerase chain reaction. The 16S rDNA was sequenced in its entirety for 2 prairie vole and 2 muskrat Giardia. In addition, the 5' 500 nucleotides of the 16S rDNA from Giardia isolates from each of 6 voles and 6 muskrats were amplified and sequenced. The results show that Giardia from voles and muskrats are very similar to each other but differ substantially from Giardia isolated from humans. We believe that the Giardia isolate from voles and muskrats constitutes a distinct species, which will be referred to as Giardia microti. These results suggest that both voles and muskrats are parasitized by the same species of Giardia, that this species is different from the Giardia that parasitizes humans, and that voles and muskrats do not contribute to the zoonotic character of human giardiasis.

Animals↗
PubMed1996

Prevalence of Giardia cysts and Cryptosporidium oocysts and characterization of Giardia spp. isolated from drinking water in Canada.

This study was carried out to estimate the prevalence and potential for human infectivity of Giardia cysts in Canadian drinking water supplies. The presence of Cryptosporidium oocysts was also noted, but isolates were not collected for further study. A total of 1,760 raw water samples, treated water samples, and raw sewage samples were collected from 72 municipalities across Canada for analysis, 58 of which treat their water by chlorination alone. Giardia cysts were found in 73% of raw sewage samples, 21% of raw water samples, and 18.2% of treated water samples. There was a trend to higher concentration and more frequent incidence of Giardia cysts in the spring and fall, but positive samples were found in all seasons. Cryptosporidium oocysts were found in 6.1% of raw sewage samples, 4.5% of raw water samples, and 3.5% of treated water samples. Giardia cyst viability was assessed by infecting Mongolian gerbils (Meriones unguiculatus) and by use of a modified propidium iodide dye exclusion test, and the results were not always in agreement. No Cryptosporidium isolates were recovered from gerbils, but 8 of 276 (3%) water samples and 19 of 113 (17%) sewage samples resulted in positive Giardia infections. Most of the water samples contained a low number of cysts, and 12 Giardia isolates were successfully recovered from gerbils and cultured. Biotyping of these isolates by isoenzyme analysis and karyotyping by pulsed-field gel electrophoresis separated the isolates into the same three discrete groups. Karyotyping revealed four or five chromosomal bands ranging in size from 0.9 to 2 Mb, and four of the isolates had the same banding pattern as that of the WB strain. Analysis of the nucleotide sequences of the 16S DNA coding for rRNA divided the isolates into two distinct groups corresponding to the Polish and Belgian designations found by other investigators. The occurrence of these biotypes and karyotypes appeared to be random and was not related to geographic or other factors (e.g., different types were found in both drinking water and sewage from the same community). Biotyping and karyotyping showed that isolates from this study were genetically and biochemically similar to those found elsewhere, including well-described human source strains such as WB. We conclude that potentially human-infective Giardia cysts are commonly found in raw surface waters and sewage in Canada, although cyst viability is frequently low. Cryptosporidium oocysts are less common in Canada. An action level of three to five Giardia cysts per 100 liters in treated drinking water is proposed on the basis of the monitoring data from outbreak situations. This action level is lower than that proposed by Haas and Rose (C. N. Haas and J. B. Rose, J. Am. Water Works Assoc. 87(9):81-84, 1995) for Cryptosporidium spp. (10 to 30 oocysts per 100 liters).

Animals↗
PubMed1993

Unique phylogenetic position of Diplomonadida based on the complete small subunit ribosomal RNA sequence of Giardia ardeae, G. muris, G. duodenalis and Hexamita sp.

Complete small-subunit rRNA (SSU-rRNA) coding region sequences were determined for two species of the intestinal parasite Giardia: G. ardeae and G. muris, both belonging to the order Diplomonadida, and a free-living member of this order, Hexamita sp. These sequences were compared to published SSU-rDNA sequences from a third member of the genus Giardia, G. duodenalis (often called G. intestinalis or G. lamblia) and various representative organisms from other taxa. Of the three Giardia sequences analyzed, the SSU-rRNA from G. muris is the smallest (1432 bases as compared to 1435 and 1453 for G. ardeae and G. duodenalis, respectively) and has the lowest G+C content (58.9%). The Hexamita SSU-rRNA is the largest in this group, containing 1550 bases. Because the sizes of the SSU-rRNA are prokaryotic rather than typically eukaryotic, the secondary structures of the SSU-rRNAs were constructed. These structures show a number of typically eukaryotic signature sequences. Sequence alignments based on constraints imposed by secondary structure were used for construction of a phylogenetic tree for these four taxa. The results show that of the four diplomonads represented, the Giardia species form a distinct group. The other diplomonad Hexamita and the microsporidium Vairimorpha necatrix appear to be distinct from Giardia.

Animals↗
PubMed1992

The nucleotide sequence of the entire ribosomal DNA operon and the structure of the large subunit rRNA of Giardia muris.

The total nucleotide sequence of the rDNA of Giardia muris, an intestinal protozoan parasite of rodents, has been determined. The repeat unit is 7668 basepairs (bp) in size and consists of a spacer of 3314 bp, a small-subunit rRNA (SSU-rRNA) gene of 1429, and a large-subunit rRNA (LSU-rRNA) gene of 2698 bp. The spacer contains long direct repeats and is heterogeneous in size. The LSU-rRNA of G. muris was compared to that of the human intestinal parasite Giardia duodenalis, to the bird parasite Giardia ardeae, and to that of Escherichia coli. The LSU-rRNA has a size comparable to the 23S rRNA of E. coli but shows structural features typical for eukaryotes. Some variable regions are typically small and account for the overall smaller size of this rRNA. The structure of the G. muris LSU-rRNA is similar to that of the other Giardia rRNA, but each rRNA has characteristic features residing in a number of variable regions.

Animals↗
PubMed1992

Classification of subgroups of Giardia lamblia based upon ribosomal RNA gene sequence using the polymerase chain reaction.

A sensitive and specific polymerase chain reaction-based assay has been developed to detect and analyze polymorphism in the Giardia lamblia 18S ribosomal RNA gene. Efficient amplification required the inclusion of cosolvents (glycerol and dimethyl sulfoxide) in the reaction. Following the optimization of conditions for amplification and subsequent hybridization of amplified product with radiolabeled oligonucleotide probe, a detection limit of less than one organism's worth of DNA was achieved. Thirty-five different G. lamblia strains obtained from various human and animal host types and geographic locations were analyzed by this method. The strains could be divided into 3 groups on the basis of defined nucleotide substitutions within the 183-bp amplified DNA fragment of the 18S ribosomal RNA gene. The groupings based upon the 18S ribosomal RNA gene sequence correlated with groupings previously assigned based upon patterns of surface antigens and restriction enzyme analysis. Analysis of the G. lamblia 18S ribosomal RNA gene sequences present in fecal specimens obtained from giardiasis patients revealed the presence of the different sequence types in these specimens. Some specimens contained more than one sequence type. The identification of subgroups of G. lamblia may facilitate studies of virulence, infectivity, and the epidemiology of giardia infection.

Amino Acid Sequence↗
PubMed1991

Cloning and restriction enzyme mapping of ribosomal DNA of Giardia duodenalis, Giardia ardeae and Giardia muris.

In an attempt to study Giardia at the DNA sequence level, the rRNA genes of three species, Giardia duodenalis, Giardia ardeae and Giardia muris were cloned and restriction enzyme maps were constructed. The rDNA repeats of these Giardia show completely different restriction enzyme recognition patterns. The size of the rDNA repeat ranges from approximately 5.6 kb in G. duodenalis to 7.6 kb in both G. muris and G. ardeae. These size differences are mainly attributable to the variation in length of the spacer. Minor differences exist among these Giardia in the sizes of their small subunit rRNA and the internal transcribed spacer between small and large subunit rRNA. The genetic maps were constructed by sequence analysis of the DNA around the 5' and 3' ends of the mature rRNA genes and between the rRNA covering the 5.8S rRNA gene and internal transcribed spacer. Comparison of the 5.8S rDNA and 3' end of large subunit rDNA from these three Giardia species showed considerable sequence variation, but the rDNA sequences of G. duodenalis and G. ardeae appear more closely related to each other than to G. muris.

Amino Acid Sequence↗
PubMed1991

Characterization of a 54-nucleotide gap region in the 28S rRNA gene of Schistosoma mansoni.

We have analyzed 572 bp in the 28S rDNA of the human blood fluke Schistosoma mansoni which correspond to expansion segment 5 of domain IV as defined by Clark et al. for the Xenopus laevis 28S rRNA. S1 nuclease mapping and primer extension analysis comparing this region with the mature 28S rRNA indicate that there are 54 nucleotides present in the 28S rDNA which are absent from the mature rRNA. This defines a gap that creates two 28S rRNA subunits (28S alpha and 28S beta). Comparison of the S. mansoni sequence with rDNAs of other organisms which contain gaps in their 28S rRNA shows that the overall features are conserved except that the S. mansoni gap is less A + T-rich. The conserved features include: (1) the location of the gap within the 28S rRNA; (2) the predicted secondary structure of the gap, containing a stem-loop with a UAAU sequence within the loop; and (3) a conserved CGAAAGGG on the 3' side of the gap.

Animals↗
PubMed1990

Giardia sp.: comparison of electrophoretic karyotypes.

Species in the genus Giardia have been named on the basis of host specificity, cell dimensions, and median body morphology. Despite these criteria, the species taxonomy of Giardia is still in question. To investigate Giardia taxonomy on a molecular level, Giardia chromosomal DNA was analyzed by orthogonal-field-alternation gel electrophoresis (OFAGE) and transverse alternating field electrophoresis (TAFE). Chromosomal DNA of G. duodenalis isolates (human, muskrat, sheep, dog, beaver), G. muris (mouse), and G. ardeae (great blue heron) were subjected to OFAGE and TAFE analyses. Comparable DNA patterns were obtained by both electrophoretic methods, but OFAGE required 8 days while TAFE required only 3 days. DNA patterns among all G. duodenalis isolates, although quite similar to each other, were distinctly different from those of G. muris and G. ardeae; G. muris and G. ardeae DNA patterns were distinctly different from each other. A G. duodenalis (Portland 1) total DNA probe hybridized to the DNA of all G. duodenalis isolates on Southern blots, but not detectably to G. muris and G. ardeae DNA. Similarly, G. muris and G. ardeae total DNA probes only hybridized detectably to their respective DNA. One probe that appears to hybridize to the DNA of all G. duodenalis and to G. ardeae DNA rather than G. muris DNA has been developed. Another probe that hybridizes only to G. muris and G. ardeae DNA has been developed. These data suggest that the differentiation of Giardia isolated from host and environmental samples may eventually be accomplished by DNA probes. Additionally, these techniques perhaps combined with other criteria may lead to the establishment of a sound taxonomic scheme for this genus.

Animals↗
PubMed1990

Axenic culture and characterization of Giardia ardeae from the great blue heron (Ardea herodias).

Trophozoites of Giardia ardeae were obtained from the great blue heron (Ardea herodias) and established in axenic culture using the TYI-S-33 medium. The generation time in culture for G. ardeae was 22-25 hr, which was 3-fold longer than for Giardia duodenalis (WB strain). A morphological comparison of trophozoites in the original intestinal isolate to those grown in culture revealed that they were identical for the following characteristics: a pyriform-shaped body, a ventral adhesive disc with a deep notch in the posterior border, teardrop-shaped nuclei, pleomorphism in median body structure ranging from a round-oval appearance (Giardia muris type) to that of a clawhammer (G. duodenalis type), and a single caudal flagellum on the right side (as viewed dorsally) with the left one being rudimentary. Analysis of the chromosomal migration patterns was performed by orthogonal-field-alternation gel electrophoresis and demonstrated that the pattern for G. ardeae was distinctly different from that for G. duodenalis (Portland 1-CCW strain). Bacterial symbionts were seen attached to trophozoites in the original isolate but could not be detected in cultured trophozoites using scanning electron microscopy, fluorescence light microscopy using the Hoechst 33258 dye for DNA localization, or by standard microbiological techniques using nonselective media for growing aerobic or anaerobic bacteria. This study demonstrated that avian-derived Giardia could be grown in axenic culture; based on morphological criteria and chromosomal migration patterns, that G. ardeae should be considered a distinct species; and that rationale for determining Giardia spp., based on median body structure alone, should no longer be considered adequate for classification at the species level.

Animals↗
PubMed1989

Schistosoma mansoni tropomyosin: cDNA characterization, sequence, expression, and gene product localization.

We have defined the polypeptide pattern of 3-hr Schistosoma mansoni schistosomula on nonequilibrium two-dimensional gels (NEPHGE). An acidic group of polypeptides with a molecular weight of about 40 kDa and a pI value of around 5.0 (numbered 48/59/53) were identified as antigens on Western blots probed with chronic human infection sera or vaccinated mouse sera. Polypeptides 48/49/53 from silver-stained NEPHGE gels produced antisera that were specific as demonstrated by Western blot analysis and immunoprecipitations of in vitro translation products. A cDNA clone (clone 1) from a S. mansoni adult worm pBR322 library was isolated by using cDNA probes made from size-fractionated mRNA and defined as encoding polypeptide 49 by hybridization selection of the mRNA which was in vitro translated and immunoprecipitated with specific mouse antiserum. A lambda gt 11 expression clone which contained an insert close to the full length mRNA was isolated from a S. mansoni cercariae library. The complete sequence of the mRNA was determined by sequencing the insert of this clone as well as primer extension of total RNA. The only open reading frame coding for 284 amino acids in the 1316 nucleotide sequence showed a 44.76 to 55.44% homology with the amino acid sequences of 18 different tropomyosins from various species. Computer-predicted secondary structure of schistosome tropomyosin was mainly alpha-helix which was very similar to other tropomyosins. Northern analysis showed the mRNA to be about 1.5 kb in size and detectable at much higher levels in the adult worm stage as compared to the cercariae and the egg stages. Western blot analysis likewise showed that greater amounts of tropomyosin were detected in extracts from adult worm stage as compared to extracts from cercariae and egg stages. Immunocytochemical analysis shows that tropomyosin is strongly associated with the tegument of adult worms. The restriction digestion pattern given by genomic Southern analysis suggests the existence of introns and/or multiple gene copies. Thus polypeptide 49, an immunodominant antigen, represents schistosome tropomyosin.

Amino Acid Sequence↗
PubMed1988

Schistosoma mansoni: identification and analysis of an mRNA and a gene encoding superoxide dismutase (Cu/Zn).

The sequence of an mRNA encoding superoxide dismutase (EC 1.15.1.1) of Schistosoma mansoni has been determined. The deduced amino acid sequence which it encodes shows 40 to 45% homology with the amino acid sequences of the cytosolic superoxide dismutase from 10 other species, as well as similar homology with the human extracellular form. Hybridization selection of the mRNA by cDNA clone pSM38 and in vitro translation of this mRNA have consistently produced a protein of 20,000 Da and occasionally, a 40,000-Da protein. Both are immunoprecipitable with sera pooled from patients with chronic schistosomiasis. The gene from which this mRNA is transcribed has also been isolated and characterized. It spans 5.1 kb of chromosomal DNA and possesses three exons and two introns which interrupt the coding region. These introns contain the splice junction sequences which fit the consensus sequences observed in mammalian genes. The upstream sequence of the gene shows a region for a potential 'TATA' box and the downstream sequence contains two polyadenylation sites.

Amino Acid Sequence↗
PubMed1986

Characterization of a female-specific cDNA derived from a developmentally regulated mRNA in the human blood fluke Schistosoma mansoni.

We have isolated and characterized a cDNA clone that is derived from a developmentally regulated mRNA found only in mature female schistosomes. The mRNA is approximately 950 nucleotides in length and is not detectable in immature female schistosomes isolated from single-sex infections, in male worms, or in eggs. During normal bisexual infections, the mRNA species is first detected 28 days after infection (the time of worm pairing) and increases to a high level 35 days after infection, coinciding with the start of egg production. The nucleotide sequence of the cDNA shows two large open reading frames in the coding strand. Several features of the clone, including the deduced sequence of the polypeptide encoded by one of the reading frames, suggest a relationship to the silk moth chorion (egg shell) gene family. The isolation of this clone provides us with a probe for further studies of female schistosome development and is a first step toward a detailed understanding of this process at the molecular level.

Amino Acid Sequence↗
PubMed1985

Organization of the ribosomal RNA genes in Schistosoma mansoni.

The organization of the rRNA genes of Schistosoma mansoni has been determined by Southern blot analysis of genomic DNA digested with restriction enzymes, by isolation of the entire repeat on a single fragment of about 11 kilobase pairs from a genomic DNA library constructed in bacteriophage lambda and by characterization of three cloned EcoRI fragments which span the entire repeat. The segments encoding both the large and small rRNA subunits have been identified using specific cloned yeast rDNA fragments as probes and EcoRI, HindIII and BamHI restriction enzyme maps of the rRNA genes were constructed. The ends of the RNAs have been precisely mapped on the genomic DNA by S1 protection experiments. Our data indicate that the rRNA genes are present as a tight cluster. The total length of the rDNA repeat is about 10 kilobase pairs. There appears to be no variation in the size of transcribed and non-transcribed spacer DNA. At the RNA level we have characterized and mapped a small gap in the 28S RNA molecule. The interruption causes the RNA to dissociate into two equal sized fragments when analyzed under denaturing conditions.

Animals↗
PubMed1982

A yeast transcription system for the 5S rRNA gene.

A cell-free extract of yeast nuclei that can specifically transcribe cloned yeast 5S rRNA genes has been developed. Optima for transcription of 5S rDNA were determined and conditions of extract preparation leading to reproducible activities and specificities established. The major in vitro product has the same size and oligonucleotide composition as in vivo 5S rRNA. The in vitro transcription extract does not transcribe yeast tRNA genes. The extract does increase the transcription of tRNA genes packaged in chromatin.

Cell Nucleus↗
PubMedDate not supplied

Studies on P6, an important outer-membrane protein antigen of Haemophilus influenzae.

P6, a 16,600-dalton outer-membrane protein of Haemophilus influenzae, possesses many characteristics desired of a vaccine candidate. The protein is present in all strains of H. influenzae tested by analyses of outer-membrane protein profiles and with a monoclonal antibody. P6 is surface-exposed, as demonstrated by immunostaining techniques. Studies using monoclonal and polyclonal antisera indicate that P6 is a highly conserved antigen on the outer membrane of H. influenzae. Finally, experiments using affinity chromatography and normal human serum establish that P6 is a target of human bactericidal antibodies. The gene encoding P6 has been isolated and cloned into Escherichia coli, an accomplishment that will facilitate molecular analysis of the role of P6 in human immunity to H. influenzae.

Antigens, Bacterial↗
PubMedDate not supplied

A three nucleotide signature sequence in small subunit rRNA divides human Giardia in two different genotypes.

The nucleotide sequence of the 16S rRNA gene and the space DNA region was determined for Giardia duodenalis, obtained from humans in The Netherlands (AMC-4) and Washington State (CM). These rDNA sequences differ from other G. duodenalis isolates (Portland-1 and BRIS/83/HEPU/ 106) both of which have virtually identical rDNA sequences. The most characteristic feature was found close to the 5' end of the 16S rRNA. The Portland-1 -Bris/83/HEPU/ 106 type has GCG in position 22-24, while AMC-4 and CM have AUC in this position. These two sequences, present in an otherwise conserved region of the 16S rRNA, are "signature" sequences, which divide Giardia isolates into two different groups.

Animals↗