Development and application of monoclonal antibodies for in situ detection of indigenous bacterial strains in aquatic ecosystems

Nanoparticle immuno-fluorescent probes as a method for detection of viable E. coli O157:H7

Development of revolutionary sensitive biosensors for detecting the presence of harmful biological species in the environment is a necessity for countering disease outbreaks. This work examined the interaction of fluorescence-labeled antibody on amine functionalized gold nanoparticles (GNP) as a model system. The synthesized tetramethylrhodamine isothiocyanate (TRITC) labeled antibody-amine functionalized GNP interaction was characterized using UV-Vis spectroscopy and Fluorescent Microscopy imaging. Transmission Electron Microscopy (TEM) was also used to observe the morphology of the GNP. In contrast to TEM, the fluorescence microscopy imaging revealed the coating of the TRITC labeled antibody on the surface of the GNP. The signals were measured using a Photon Technology Inc. fluorometer at excitation of 541 nm and emission at 555 nm to 650 nm. Tests were conducted at near real-time with results obtained using the biosensor assay within 5 min. Results indicated that there was a shift of the wavelength from lower to higher wavelength (blue to red shift) when conjugated GNP (anti-E. coliO157:H7; IgY-TRITC-GNP) are compared to free GNP, a difference of about 28 nm. The GNP demonstrated a quenching capability when compared to the TRITC labeled antibody (degree of labeling of 15.41 mol dye per mole of IgY) using fluorometer. The lower and upper detection range of this method was found to be 10³-10⁵ CFU/mL with observed fluorescence of about 42,000 counts per seconds as against 24,000 counts per seconds that was observed when the specificity of the sensor was tested using Salmonella enterica.

Bacterial and mineral elements in an arctic biofilm: a correlative study using fluorescence and electron microscopy

Few simple labeling methods exist for simultaneous fluorescence and electron microscopy of bacteria and biofilms. Here we describe the synthesis, characterization, and application of fluorescent nanoparticle quantum dot (QD) conjugates to target microbial species, including difficult to label Gram-negative strains. These QD conjugates impart contrast for both environmental scanning electron microscopy (ESEM) and fluorescence microscopy, permitting observation of living and fixed bacteria and biofilms. We apply these probes for studying biofilms extracted from perennial cold springs in the Canadian High Arctic, which is a particularly challenging system. In these biofilms, sulfur-metabolizing bacteria live in close association with unusual sulfur mineral formations. Following simple labeling protocols with the QD conjugates, we are able to image these organisms in fully-hydrated samples and visualize their relationship to the sulfur minerals using both ESEM and fluorescence microscopy. We then use scanning transmission electron microscopy to observe precipitated sulfur around individual cells and within the biofilm lattice. All combined, this information sheds light on the possible mechanisms of biofilm and mineral structure formation. These new QD conjugates and techniques are highly transferable to many other microbiological applications, especially those involving Gram-negative bacteria, and can be used for correlated fluorescence and electron microscopy.

An immuno-PF2D-MS/MS proteomic approach for bacterial antigenic characterization: to Bacillus and beyond

We are confronted daily to unknown microorganisms that have yet to be characterized, detected, and/or analyzed. We propose, in this study, a multidimensional strategy using polyclonal antibodies, consisting of a novel proteomic tool, the ProteomeLab PF2D, coupled to immunological techniques and mass spectrometry (i-PF2D-MS/MS). To evaluate this strategy, we have applied it to Bacillus subtilis, considered here as our unknown bacterial model.

Recognition of individual genes in diverse microorganisms by cycling primed in situ amplification

Cycling primed in situ amplification-fluorescent in situ hybridization (CPRINS-FISH) was developed to recognize individual genes in a single bacterial cell. In CPRINS, the amplicon was long single-stranded DNA and thus retained within the permeabilized microbial cells. FISH with a multiply labeled fluorescent probe set enabled significant reduction in nonspecific background while maintaining high fluorescence signals of target bacteria. The ampicillin resistance gene in Escherichia coli, chloramphenicol acetyltransferase gene in different gram-negative strains, and RNA polymerase sigma factor (rpoD) gene in Aeromonas spp. could be detected under identical permeabilization conditions. After concentration of environmental freshwater samples onto polycarbonate filters and subsequent coating of filters in gelatin, no decrease in bacterial cell numbers was observed with extensive permeabilization. The detection rates of bacterioplankton in river and pond water samples by CPRINS-FISH with a universal 16S rRNA gene primer and probe set ranged from 65 to 76% of total cell counts (mean, 71%). The concentrations of cells detected by CPRINS-FISH targeting of the rpoD genes of Aeromonas sobria and A. hydrophila in the water samples varied between 2.1 x 10(3) and 9.0 x 10(3) cells ml(-1) and between undetectable and 5.1 x 10(2) cells ml(-1), respectively. These results demonstrate that CPRINS-FISH provides a high sensitivity for microscopic detection of bacteria carrying a specific gene in natural aquatic samples.

Emerging waterborne infections: contributing factors, agents, and detection tools

Because microorganisms are easily dispersed, display physiological diversity, and tolerate extreme conditions, they are ubiquitous and may contaminate and grow in water. The presence of waterborne enteric pathogens (bacteria, viruses, and protozoa) in domestic water supplies represents a potentially significant human health risk. Even though major outbreaks of waterborne disease are comparatively rare, there is substantial evidence that human enteric pathogens that are frequently present in domestic water supplies are responsible for low-level incidence of waterborne microbial disease. Although these diseases are rarely debilitating to healthy adults for more than a few hours to a few days, enteric pathogens can cause severe illness, even death, for young children, the elderly, or those with compromised immune systems. As the epidemiology of waterborne diseases is changing, there is a growing global public health concern about new and reemerging infectious diseases that are occurring through a complex interaction of social, economic, evolutionary, and ecological factors. New microbial pathogens have emerged, and some have spread worldwide. Alternative testing strategies for waterborne diseases should significantly improve the ability to detect and control the causative pathogenic agents. In this article, we provide an overview of the current state of knowledge of waterborne microbial pathogens, their detection, and the future of new methods in controlling these infectious agents.

Production of a monoclonal antibody against Aeromonas hydrophila and its application to bacterial identification

AIMS

to develop a monoclonal antibody (MAb) for the rapid detection of Aeromonas hydrophila in human faeces.

METHODS AND RESULTS

A monoclonal antibody with strong specificity against Aer. hydrophila was obtained by the fusion of myeloma cells and splenocytes of a mouse immunized with vegetative cells of Aer. hydrophila ATCC 7966, followed by a two-step selection against other species of the genera. ELISA analyses revealed that MAb 5F3 strongly reacts with all the Aer. hydrophila strains evaluated, showing a just basal reactivity against other species of the genera, especially Aer. sobria and Aer. caviae.

CONCLUSIONS

MAb 5F3 was characterized as an IgG that recognized a polypeptide of approximately 110 kDa.

SIGNIFICANCE AND IMPACT OF THE STUDY

This MAb could be used to detect Aer. hydrophila in human stool samples.

Changes in bacterioplankton community structure and activity with depth in a eutrophic lake as revealed by 5S rRNA analysis

The community structure of bacterioplankton was studied at different depths (0 to 25 m) of a temperate eutrophic lake (Lake Plusssee in northern Germany) by using comparative 5S rRNA analysis. The relative amounts of taxonomic groups were estimated from 5S rRNA bands separated by high-resolution electrophoresis. Comparison of partial 5S rRNA sequences enabled detection of changes in single taxa over space and during seasons. Overall, the bacterioplankton community was dominated by 3 to 14 abundant (>4% of the total 5S rRNA) taxa. In general, the number of 5S rRNA bands (i.e., the number of bacterial taxa) decreased with depth. In the fall, when thermal stratification and chemical stratification were much more pronounced than they were in the spring, the correlation between the depth layers and the community structure was more pronounced. Therefore, in the fall each layer had its own community structure; i.e., there were different community structures in the epilimnion, the metalimnion, and the hypolimnion. Only three 5S rRNA bands were detected in the hypolimnion during the fall, and one band accounted for about 70% of the total 5S rRNA. The sequences of individual 5S rRNA bands from the spring and fall were different for all size classes analyzed except two bands, one of which was identified as Comamonas acidivorans. In the overall analysis of the depth profiles, the diversity in the epilimnion contrasted with the reduced diversity of the bacterioplankton communities in the hypolimnion, and large differences occurred in the composition of the epilimnion at different seasons except for generalists like C. acidivorans.

Rapid detection and enumeration of Naegleria fowleri in surface waters by solid-phase cytometry

A new method for the rapid and accurate detection of pathogenic Naegleria fowleri amoebae in surface environmental water was developed. The method is based on an immunofluorescent assay combined with detection by solid-phase cytometry. In this study we developed and compared two protocols using different reporter systems conjugated to antibodies. The monoclonal antibody Ac5D12 was conjugated with biotin and horseradish peroxidase, and the presence of cells was revealed with streptavidin conjugated to both R-phycoerythrin and cyanine Cy5 (RPE-Cy5) and tyramide-fluorescein isothiocyanate, respectively. The RPE-Cy5 protocol was the most efficient protocol and allowed the detection of both trophozoite and cyst forms in water. The direct counts obtained by this new method were not significantly different from those obtained by the traditional culture approach, and results were provided within 3 h. The sensitivity of the quantitative method is 200 cells per liter. The limit is due only to the filtration capacity of the membrane used.

Detection and enumeration of coliforms in drinking water: current methods and emerging approaches

The coliform group has been used extensively as an indicator of water quality and has historically led to the public health protection concept. The aim of this review is to examine methods currently in use or which can be proposed for the monitoring of coliforms in drinking water. Actually, the need for more rapid, sensitive and specific tests is essential in the water industry. Routine and widely accepted techniques are discussed, as are methods which have emerged from recent research developments.Approved traditional methods for coliform detection include the multiple-tube fermentation (MTF) technique and the membrane filter (MF) technique using different specific media and incubation conditions. These methods have limitations, however, such as duration of incubation, antagonistic organism interference, lack of specificity and poor detection of slow-growing or viable but non-culturable (VBNC) microorganisms. Nowadays, the simple and inexpensive membrane filter technique is the most widely used method for routine enumeration of coliforms in drinking water.The detection of coliforms based on specific enzymatic activity has improved the sensitivity of these methods. The enzymes beta-D galactosidase and beta-D glucuronidase are widely used for the detection and enumeration of total coliforms and Escherichia coli, respectively. Many chromogenic and fluorogenic substrates exist for the specific detection of these enzymatic activities, and various commercial tests based on these substrates are available. Numerous comparisons have shown these tests may be a suitable alternative to the classical techniques. They are, however, more expensive, and the incubation time, even though reduced, remains too long for same-day results. More sophisticated analytical tools such as solid phase cytometry can be employed to decrease the time needed for the detection of bacterial enzymatic activities, with a low detection threshold. Detection of coliforms by molecular methods is also proposed, as these methods allow for very specific and rapid detection without the need for a cultivation step. Three molecular-based methods are evaluated here: the immunological, polymerase chain reaction (PCR) and in-situ hybridization (ISH) techniques. In the immunological approach, various antibodies against coliform bacteria have been produced, but the application of this technique often showed low antibody specificity. PCR can be used to detect coliform bacteria by means of signal amplification: DNA sequence coding for the lacZ gene (beta-galactosidase gene) and the uidA gene (beta-D glucuronidase gene) has been used to detect total coliforms and E. coli, respectively. However, quantification with PCR is still lacking in precision and necessitates extensive laboratory work. The FISH technique involves the use of oligonucleotide probes to detect complementary sequences inside specific cells. Oligonucleotide probes designed specifically for regions of the 16S RNA molecules of Enterobacteriaceae can be used for microbiological quality control of drinking water samples. FISH should be an interesting viable alternative to the conventional culture methods for the detection of coliforms in drinking water, as it provides quantitative data in a fairly short period of time (6 to 8 h), but still requires research effort. This review shows that even though many innovative bacterial detection methods have been developed, few have the potential for becoming a standardized method for the detection of coliforms in drinking water samples.

Comparison of fluorescently labeled oligonucleotide and polynucleotide probes for the detection of pelagic marine bacteria and archaea

We compared the detection of bacteria and archaea in the coastal North Sea and at Monterey Bay, Calif., after fluorescence in situ hybridization (FISH) either with rRNA-targeted oligonucleotide probes monolabeled with the cyanin dye Cy3 (oligoFISH) or with fluorescein-labeled polyribonucleotide probes (polyFISH). During an annual cycle in German Bight surface waters, the percentages of bacteria visualized by polyFISH (annual mean, 77% of total counts) were significantly higher than those detected by oligoFISH (53%). The fraction of total bacteria visualized by oligoFISH declined during winter, whereas cell numbers determined by polyFISH remained constant throughout the year. Depth profiles from Monterey Bay showed large differences in the fraction of bacterial cells visualized by polyFISH and oligoFISH in the deeper water layers irrespective of the season. Image-analyzed microscopy indicated that the superior detection of cells by polyFISH with fluorescein-labeled probes in bacterioplankton samples was less a consequence of higher absolute fluorescence intensities but was rather related to quasi-linear bleaching dynamics and to a higher signal-to-background ratio. The relative abundances of archaea in North Sea and Monterey Bay spring samples as determined by oligoFISH were on average higher than those determined by polyFISH. However, simultaneous hybridizations with oligonucleotide probes for bacteria and archaea suggested that the oligoFISH probe ARCH915 unspecifically stained a population of bacteria. Using either FISH technique, blooms of archaea were observed in North Sea surface waters during the spring and summer months. Marine group II archaea (Euryarchaeota) reached >30% of total picoplankton abundances, as determined by polyFISH. We suggest that studies of pelagic microbial community structure using oligoFISH with monolabeled probes should focus on environments that yield detections > or =70% of total cell counts, e.g., coastal surface waters during spring and summer.

Biomonitoring of pJP4-carrying Pseudomonas chlororaphis with Trb protein-specific antisera

The transfer of catabolic genes on conjugative plasmids to indigenous organisms from which they may spread further into the community allows the introduction of new biodegradative pathways for metabolic conversion of pollutants to the community. Biomonitoring of IncP plasmid pJP4-carrying Pseudomonas chlororaphis from the rhizosphere of Arabidopsis thaliana was achieved using antisera specific for proteins from the plasmid transfer machinery. Antisera were generated that recognized TrbC and TrbF, the putative major and minor components of pJP4-determined pili, respectively, and the putative lipoprotein TrbH. Cell fractionation studies showed association of TrbC, TrbF and TrbH with the cells and suggested that TrbC and TrbF are part of extracellular pJP4-determined pili. TrbF and TrbH antisera allowed specific detection of IncP compared with IncN or IncW plasmid-carrying cells and even permitted differentiation between bacteria carrying IncPalpha plasmid RP4 and IncPbeta plasmid pJP4. Immunofluorescence microscopy was applied to detect TrbF and TrbH signal at the cell periphery, allowing distinction from autofluorescing cells and soil debris. In situ experiments showed specific recognition of pJP4-carrying cells from laboratory cultures, as well as from the rhizosphere of A. thaliana grown in natural soil. After co-inoculation of donor P. chlororaphis pJP4 and recipient Ralstonia eutropha, a combination of immunofluorescence and oligonucleotide hybridization techniques permitted the detection of plasmid transfer between both organisms in the A. thaliana rhizosphere. This strategy may be generally applicable for the analysis of plasmid transfer in natural ecosystems.

Flagellate predation on a bacterial model community: interplay of size-selective grazing, specific bacterial cell size, and bacterial community composition

The influence of grazing by the bacterivorous nanoflagellate Ochromonas sp. strain DS on the taxonomic and morphological structures of a complex bacterial community was studied in one-stage chemostat experiments. A bacterial community, consisting of at least 30 different strains, was fed with a complex carbon source under conditions of low growth rate (0.5 day(-1) when nongrazed) and low substrate concentration (9 mg liter(-1)). Before and after the introduction of the predator, the bacterial community composition was studied by in situ techniques (immunofluorescence microscopy and fluorescent in situ hybridization), as well as by cultivation on agar media. The cell sizes of nonspecifically stained and immunofluorescently labeled bacteria were measured by image analysis. Grazing by the flagellate caused a bidirectional change in the morphological structure of the community. Medium-size bacterial cells, which dominated the nongrazed community, were largely replaced by smaller cells, as well as by cells contained in large multicellular flocs. Cell morphological changes were combined with community taxonomic changes. After introduction of the flagellate, the dominating strains with medium-size cells were largely replaced by single-celled strains with smaller cells on the one hand and, on the other hand, by Pseudomonas sp. strain MWH1, which formed the large, floc-like forms. We assume that size-selective grazing was the major force controlling both the morphological and the taxonomic structures of the model community.

Seasonal dynamics of bacterioplankton community structure in a eutrophic lake as determined by 5S rRNA analysis

Community structure of bacterioplankton was studied during the major growth season for phytoplankton (April to October) in the epilimnion of a temperate eutrophic lake (Lake Plusssee, northern Germany) by using comparative 5S rRNA analysis. Estimates of the relative abundances of single taxonomic groups were made on the basis of the amounts of single 5S rRNA bands obtained after high-resolution electrophoresis of RNA directly from the bacterioplankton. Full-sequence analysis of single environmental 5S rRNAs enabled the identification of single taxonomic groups of bacteria. Comparison of partial 5S rRNA sequences allowed the detection of changes of single taxa over time. Overall, the whole bacterioplankton community showed two to eight abundant (>4% of the total 5S rRNA) taxa. A distinctive seasonal succession was observed in the taxonomic structure of this pelagic community. A rather-stable community structure, with seven to eight different taxonomic units, was observed beginning in April during the spring phytoplankton bloom. A strong reduction in this diversity occurred at the beginning of the clear-water phase (early May), when only two to four abundant taxa were observed, with one taxon dominating (up to 72% of the total 5S rRNA). The community structure during summer stagnation (June and July) was characterized by frequent changes of different dominating taxa. During late summer, a dinoflagellate bloom (Ceratium hirudinella) occurred, with Comamonas acidovorans (beta-subclass of the class Proteobacteria) becoming the dominant bacterial species (average abundance of 43% of the total 5S rRNA). Finally, the seasonal dynamics of the community structure of bacterioplankton were compared with the abundances of other major groups of the aquatic food web, such as phyto- and zooplankton, revealing that strong grazing pressure by zooplankton can reduce microbial diversity substantially in pelagic environments.

Bacterial filament formation, a defense mechanism against flagellate grazing, is growth rate controlled in bacteria of different phyla

A facultatively filamentous bacterium was isolated from eutrophic lake water and was identified as Flectobacillus sp. strain MWH38 (a member of the Cytophaga-Flavobacterium-Bacteroides phylum) by comparative 16S rRNA gene sequence analysis. Filament formation by Flectobacillus sp. strain MWH38 and filament formation by Flectobacillus major, the closest known relative of strain MWH38, were studied in chemostat cultures under grazing pressure by the bacterivorous flagellate Ochromonas sp. strain DS and without predation at several growth rates. The results clearly demonstrated that filament formation by the two flectobacilli is growth rate controlled and thus independent of the presence of a predator. However, flagellate grazing positively influenced bacterial growth rates by decreasing bacterial biomass and thus indirectly stimulated filament formation. The results of investigations of cell elongation and filament formation by Comamonas acidovorans PX54 (a member of the beta subclass of the class Proteobacteria) supported the recent proposal that in this species the mechanism of filament formation is growth rate controlled. The finding that the grazing defense mechanism consisting of filament formation is growth rate controlled in the flectobacilli investigated and C. acidovorans PX54 (i.e., in bacteria belonging to divergent evolutionary phyla) may indicate that this mechanism is a phylogenetically widely distributed defense strategy against grazing.

Seasonal community and population dynamics of pelagic bacteria and archaea in a high mountain lake

The seasonal variations in community structure and cell morphology of pelagic procaryotes from a high mountain lake (Gossenkollesee, Austria) were studied by in situ hybridization with rRNA-targeted fluorescently labeled oligonucleotide probes (FISH) and image-analyzed microscopy. Compositional changes and biomass fluctuations within the assemblage were observed both in summer and beneath the winter ice cover and are discussed in the context of physicochemical and biotic parameters. Proteobacteria of the beta subclass (beta-proteobacteria) formed a dominant fraction of the bacterioplankton (annual mean, 24% of the total counts), whereas alpha-proteobacteria were of similar relative importance only during spring (mean, 11%). Bacteria of the Cytophaga-Flavobacterium cluster, although less abundant, constituted the largest fraction of the filamentous morphotypes during most of the year, thus contributing significantly to the total microbial biomass. Successive peaks of threadlike and rod-shaped archaea were observed during autumn thermal mixing and the period of ice cover formation, respectively. A set of oligonucleotide probes targeted to single phylotypes was constructed from 16S rRNA-encoding gene clone sequences. Three distinct populations of uncultivated microbes, affiliated with the alpha- and beta-proteobacteria, were subsequently monitored by FISH. About one-quarter of all of the beta-proteobacteria (range, 6 to 53%) could be assigned to only two phylotypes. The bacterial populations studied were annually recurrent, seasonally variable, and vertically stratified, except during the periods of lake overturn. Their variability clearly exceeded the fluctuations of the total microbial assemblage, suggesting that the apparent stability of total bacterioplankton abundances may mask highly dynamic community fluctuations.

Distribution and life strategies of two bacterial populations in a eutrophic lake

Monoclonal antibodies and epifluorescence microscopy were used to determine the depth distribution of two indigenous bacterial populations in the stratified Lake Plusssee and characterize their life strategies. Populations of Comamonas acidovorans PX54 showed a depth distribution with maximum abundances in the oxic epilimnion, whereas Aeromonas hydrophila PU7718 showed a depth distribution with maximum abundances in the anoxic thermocline layer (metalimnion), i. e., in the water layer with the highest microbial activity. Resistance of PX54 to protist grazing and high metabolic versatility and growth rate of PU7718 were the most important life strategy traits for explaining the depth distribution of the two bacterial populations. Maximum abundance of PX54 was 16,000 cells per ml, and maximum abundance of PU7718 was 20,000 cells per ml. Determination of bacterial productivity in dilution cultures with different-size fractions of dissolved organic matter (DOM) from lake water indicates that low-molecular-weight (LMW) DOM is less bioreactive than total DOM (TDOM). The abundance and growth rate of PU7718 were highest in the TDOM fractions, whereas those of PX54 were highest in the LMW DOM fraction, demonstrating that PX54 can grow well on the less bioreactive DOM fraction. We estimated that 13 to 24% of the entire bacterial community and 14% of PU7718 were removed by viral lysis, whereas no significant effect of viral lysis on PX54 could be detected. Growth rates of PX54 (0.11 to 0.13 h-1) were higher than those of the entire bacterial community (0.04 to 0.08 h-1) but lower than those of PU7718 (0.26 to 0.31 h-1). In undiluted cultures, the growth rates were significantly lower, pointing to density effects such as resource limitation or antibiosis, and the effects were stronger for PU7718 and the entire bacterial community than for PX54. Life strategy characterizations based on data from literature and this study revealed that the fast-growing and metabolically versatile A. hydrophila PU7718 is an r-strategist or opportunistic population in Lake Plusssee, whereas the grazing-resistant C. acidovorans PX54 is rather a K-strategist or equilibrium population.

Grazing Pressure by a Bacterivorous Flagellate Reverses the Relative Abundance of Comamonas acidovorans PX54 and Vibrio Strain CB5 in Chemostat Cocultures

The response of the bacterial strains Comamonas acidovorans PX54 (beta subclass of the class Proteobacteria) and Vibrio strain CB5 (gamma subclass of the class Proteobacteria) to grazing by the bacterivorous flagellate Ochromonas sp. was examined in one-stage chemostat experiments under conditions of low growth rates with a complex carbon source. The two bacterial strains were cultured together; they were cultured without flagellates in the first phase of the experiments and in the presence of the flagellates in the second phase. Monoclonal and polyclonal antibodies were used to determine the numbers and sizes of C. acidovorans PX54 and Vibrio strain CB5 cells. The flagellates caused strong changes in total bacterial cell numbers, in the relative abundances of the individual bacterial strains, and in bacterial cell size distribution. Vibrio strain CB5 dominated the total bacterial cell numbers during the flagellate-free phase of the experiments with a relative abundance of 93%, but this declined to 33% after inoculation with the flagellate. In contrast to Vibrio strain CB5, C. acidovorans PX54 responded to grazing with a strong expansion of cell length distribution toward large, filamentous cells. These changes in cell morphology resulted in a high percentage of inedible cells in the C. acidovorans PX54 population but not in the Vibrio strain CB5 population, which caused the observed change in the relative abundances of the strains. Batch culture experiments without the flagellate demonstrated that the elongation of C. acidovorans PX54 cells was dependent on their growth rate. This indicates that the occurrence of filamentous C. acidovorans PX54 cells is not a direct response to chemical stimuli released by the flagellates but rather a response to increased growth rates due to flagellate grazing.