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A sandwich hybridization assay for high-throughput, rapid, simple, and inexpensive quantification of specific microbial populations was evaluated. The assay is based on the hybridization of a target rRNA with differentially labeled capture and detector probes. Betaproteobacterial ammonia-oxidizing bacteria (AOB) were selected as the target group for the study, since they represent a phylogenetically coherent group of organisms that perform a well-defined geochemical function in natural and engineered environments. Reagent concentrations, probe combinations, and washing, blocking, and hybridization conditions were optimized to improve signal and reduce background. The detection limits for the optimized RNA assay were equivalent to approximately 10 3 to 10 4 and 10 4 to 10 5 bacterial cells, respectively, for E. coli rRNA and RNA extracted from activated sludge, by using probes targeting the majority of bacteria. Furthermore, the RNA assay had good specificity, permitted discrimination of rRNA sequences that differed by a 2-bp mismatch in the probe target region, and could distinguish the sizes of AOB populations in nitrifying and nonnitrifying wastewater treatment plants.Quantification of specific bacterial populations is key to understanding the mechanisms that underlie many biologically mediated processes, including nitrification. The use of rRNAbased cultivation-independent techniques may be one potentially useful means to do this. Numerous rRNA-based techniques are now commonly employed to quantify microbial communities in environmental samples. These include fluorescence in situ hybridization (FISH) (see, e.g., references 11, 12, 17, 27, 37, and 40), quantitative dot blot hybridization (see, e.g., references 14 and 34), PCR-based methods (e.g., real time PCR [19] and competitive PCR [15,33]), and microarray technology (see, e.g., references 1, 18, and 38).Each of these methods has particular advantages and disadvantages. For example, FISH allows direct identification and quantification of microorganisms in environmental samples and, because of its ability to measure individuals accurately, represents the "gold standard." However, FISH has a low sample throughput and is thus too slow for routine analysis. In contrast, PCR-based methods allow high sample throughput, which may be required for statistically valid spatial and temporal analysis. However, PCR-based methods are prone to biases (typically introduced during nucleic acid extraction and amplification) that may make quantification of natural bacterial populations difficult (see, e.g., references 20, 39, 39a, and 43). In addition, relatively pure preparations of DNA are required to avoid problems of inhibition of DNA polymerases. Quantitative dot blots and microarrays, on the other hand, often require the use of radioactive isotopes or expensive equipment and consumables.An alternative sensitive and specific method is a sandwich hybridization assay for the detection of rRNA, developed by Wicks and coworkers (46). The RNA assay is based on hybridization of...
A sandwich hybridization assay for high-throughput, rapid, simple, and inexpensive quantification of specific microbial populations was evaluated. The assay is based on the hybridization of a target rRNA with differentially labeled capture and detector probes. Betaproteobacterial ammonia-oxidizing bacteria (AOB) were selected as the target group for the study, since they represent a phylogenetically coherent group of organisms that perform a well-defined geochemical function in natural and engineered environments. Reagent concentrations, probe combinations, and washing, blocking, and hybridization conditions were optimized to improve signal and reduce background. The detection limits for the optimized RNA assay were equivalent to approximately 10 3 to 10 4 and 10 4 to 10 5 bacterial cells, respectively, for E. coli rRNA and RNA extracted from activated sludge, by using probes targeting the majority of bacteria. Furthermore, the RNA assay had good specificity, permitted discrimination of rRNA sequences that differed by a 2-bp mismatch in the probe target region, and could distinguish the sizes of AOB populations in nitrifying and nonnitrifying wastewater treatment plants.Quantification of specific bacterial populations is key to understanding the mechanisms that underlie many biologically mediated processes, including nitrification. The use of rRNAbased cultivation-independent techniques may be one potentially useful means to do this. Numerous rRNA-based techniques are now commonly employed to quantify microbial communities in environmental samples. These include fluorescence in situ hybridization (FISH) (see, e.g., references 11, 12, 17, 27, 37, and 40), quantitative dot blot hybridization (see, e.g., references 14 and 34), PCR-based methods (e.g., real time PCR [19] and competitive PCR [15,33]), and microarray technology (see, e.g., references 1, 18, and 38).Each of these methods has particular advantages and disadvantages. For example, FISH allows direct identification and quantification of microorganisms in environmental samples and, because of its ability to measure individuals accurately, represents the "gold standard." However, FISH has a low sample throughput and is thus too slow for routine analysis. In contrast, PCR-based methods allow high sample throughput, which may be required for statistically valid spatial and temporal analysis. However, PCR-based methods are prone to biases (typically introduced during nucleic acid extraction and amplification) that may make quantification of natural bacterial populations difficult (see, e.g., references 20, 39, 39a, and 43). In addition, relatively pure preparations of DNA are required to avoid problems of inhibition of DNA polymerases. Quantitative dot blots and microarrays, on the other hand, often require the use of radioactive isotopes or expensive equipment and consumables.An alternative sensitive and specific method is a sandwich hybridization assay for the detection of rRNA, developed by Wicks and coworkers (46). The RNA assay is based on hybridization of...
Die Analytica in München bietet alle zwei Jahre den richtigen Anlaß, über die Veränderungen und Fortschritte in der Analytischen Chemie zu berichten. Die wichtigsten Stichworte im ersten Teil des Berichtes: Life Sciences, kombinierte Methoden, HTS, Chiptechniken…Ein Nachtrag “Spektroskopie” vervollständigt im nächsten Monat den Trendbericht.
Dye-encapsulating liposomes can serve as signaling reagents in biosensors and biochemical assays in place of enzymes or fluorophores. Detailed here is the use and preparation of streptavidin-coupled liposomes which offer a universal approach to biotinylated target detection. The universal approach provides two advantages, i.e. only one type of liposome is necessary despite varying target and probe sequences and the hybridization event can take place in the absence of potential steric hindrance occurring from liposomes directly conjugated to probes. One objective of this work was to optimize the one-step conjugation of SRB-encapsulating liposomes to streptavidin using EDC. Liposome, EDC, streptavidin concentrations, and reaction times were varied. The optimal coupling conditions were found to be an EDC:carboxylated lipid:streptavidin molar ratio of 600:120:1 and a reaction time of 15 min. The second goal was to utilize these liposomes in sandwich hybridization microtiter plate-based assays using biotinylated reported probes as biorecognition elements. The assay was optimized in terms of probe spacer length, probe concentration, liposome concentration, and streptavidin coverage. Subsequently, the optimized protocol was applied to the detection of DNA and RNA sequences. A detection limit of 1.7 pmol L(-1) and an assay range spanning four orders of magnitude (5 pmol L(-1)-50 nmol L(-1)) with a coefficient of variation =5.8% was found for synthetic DNA. For synthetic RNA the LOQ was half that of synthetic DNA. A comparison was made to alkaline phosphatase-conjugated streptavidin for detection which yielded a limit of quantitation approximately 80 times higher than that for liposomes in the same system. Thus, liposomes and the optimized sandwich hybridization method are well suited for detecting single-stranded nucleic acid sequences and compares favorably to other sandwich hybridization schemes recently described in the literature. The assay was then used successfully for the clear detection of mRNA amplified by nucleic acid sequence-based amplification (NASBA) isolated from as little as one Cryptosporidium parvum oocyst. The detection of mRNA from oocysts isolated from various water sample types using immunomagnetic separation was also assessed. Finally, to prove the wider applicability and sensitivity of this universal method, RNA amplified from the atxA gene of Bacillus anthracis was detected when the input to the preceding NASBA reaction was as low as 1.2 pg. This highly sensitive liposome-based microtiter plate assay is therefore a platform technology allowing for high throughput and wide availability for routine clinical and environmental laboratory applications.
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