Improved method for polynucleotide probe-based cell sorting, using DNA-coated microplates

Basic Principles and Recent Advances in Magnetic Cell Separation

Magnetic cell separation has become a key methodology for the isolation of target cell populations from biological suspensions, covering a wide spectrum of applications from diagnosis and therapy in biomedicine to environmental applications or fundamental research in biology. There now exists a great variety of commercially available separation instruments and reagents, which has permitted rapid dissemination of the technology. However, there is still an increasing demand for new tools and protocols which provide improved selectivity, yield and sensitivity of the separation process while reducing cost and providing a faster response. This review aims to introduce basic principles of magnetic cell separation for the neophyte, while giving an overview of recent research in the field, from the development of new cell labeling strategies to the design of integrated microfluidic cell sorters and of point-of-care platforms combining cell selection, capture, and downstream detection. Finally, we focus on clinical, industrial and environmental applications where magnetic cell separation strategies are amongst the most promising techniques to address the challenges of isolating rare cells.

Autothermal Thermophilic Aerobic Digestion (ATAD) for Heat, Gas, and Production of a Class A Biosolids with Fertilizer Potential

Autothermal thermophilic aerobic digestion (ATAD) is a microbial fermentation process characterized as a tertiary treatment of waste material carried out in jacketed reactors. The process can be carried out on a variety of waste sludge ranging from human, animal, food, or pharmaceutical waste where the addition of air initiates aerobic digestion of the secondary treated sludge material. Digestion of the sludge substrates generates heat, which is retained within the reactor resulting in elevation of the reactor temperature to 70-75 °C. During the process, deamination of proteinaceous materials also occurs resulting in liberation of ammonia and elevation of pH to typically pH 8.4. These conditions result in a unique microbial consortium, which undergoes considerable dynamic change during the heat-up and holding phases. The change in pH and substrate as digestion occurs also contributes to this dynamic change. Because the large reactors are not optimized for aeration, and because low oxygen solubility at elevated temperatures occurs, there are considerable numbers of anaerobes recovered which also contributes to the overall digestion. As the reactors are operated in a semi-continuous mode, the reactors are rarely washed, resulting in considerable biofilm formation. Equally, because of the fibrous nature of the sludge, fiber adhering organisms are frequently found which play a major role in the overall digestion process. Here, we review molecular tools needed to examine the ATAD sludge consortia, what has been determined through phylogenetic analysis of the consortia and the nature of the dynamics occurring within this unique fermentation environment.

Application of recognition of individual genes-fluorescence in situ hybridization (RING-FISH) to detect nitrite reductase genes (nirK) of denitrifiers in pure cultures and environmental samples

Denitrification is an alternative type of anaerobic respiration in which nitrate is reduced to gaseous products via nitrite. The key step in this process is the reduction of nitrite to nitric oxide, which is catalyzed by two structurally different but functionally equivalent forms of nitrite reductase encoded by the nirK and nirS genes. Cultivation-independent studies based on these functional marker genes showed that in the environment there was a dominance of organisms with nirK and nirS genes presumably derived from organisms that have not been cultured yet. However, the phylogenetic affiliation of these organisms has not been resolved since the ability to denitrify is widespread in phylogenetically unrelated organisms. To unravel the phylogeny of the organisms from which the nitrite reductase (nirK) genes originated, one option is to use a special variant of whole-cell hybridization termed recognition of individual genes-fluorescence in situ hybridization (RING-FISH). In RING-FISH a multiply labeled transcript polynucleotide probe is used to detect a single gene on the bacterial chromosome during FISH. Here, RING-FISH was used with laboratory cultures and environmental samples, such as activated sludge. Furthermore, probe-based cell sorting using magnetic beads could also be carried out with mixtures of pure cultures, which led to effective depletion of the nirK-negative organism but capture of the nirK-positive organism, which was demonstrated by terminal restriction fragment length polymorphism analysis based on 16S rRNA genes. The results indicate that RING-FISH coupled with probe-based cell sorting could be used with environmental samples, which could provide a means for phylogenetic classification of nirK-type denitrifiers. Thus, the results of RING-FISH could increase our understanding of the phylogeny and function of denitrifying microorganisms in the environment.

Optimization of DGGE community fingerprinting for characterizing Escherichia coli communities associated with fecal pollution

We evaluated the use of DGGE fingerprinting to differentiate communities of Escherichia coli from animal and geographic sources. An initial screening of 15 gene candidates revealed the ability of three target genes (mdh, phoE and uidA-4) to effectively differentiate E. coli communities originating in horses, pigs, geese and goats. Cluster and jackknife analyses performed on the communities from a more extensive number of hosts (n=150) including humans (via raw sewage), horses, pigs, geese and cows revealed that the internal accuracy of classification of E. coli community fingerprints to their origin was similar for each of the three genes (85-86%). Each of the three genes were tested for their ability to associate E. coli source- and sink communities in two settings featuring contaminated water; (i) a stream receiving municipal wastewater effluent and (ii) a pond inhabited by geese. For each gene, DGGE fingerprints effectively matched effluent- and downstream E. coli communities (98-100% similarity) and excluded upstream communities, while communities from goose fecal material were 77-79% similar to communities in pond water, indicating fecal inputs from geese. Furthermore, each gene discriminated against E. coli communities from hosts non-indigenous to either setting. DGGE analysis of E. coli communities appears to be a promising tool to augment existing efforts aiming to address the dynamics of bacteria pollution in complex, natural environments.

Nucleic acid techniques in bacterial systematics and identification

Systematics and identification play central roles in any discipline of microbiology. The current prokaryotic taxonomic framework as proposed in Bergey's Manual of Systematic Bacteriology is mainly based on small subunit rRNA data. Alternative markers representing the conserved core of the prokaryotic genomes roughly support rRNA based phylogenetic inference. Consequently, many of the nucleic acid based techniques for identification target these molecules: i.e. comparative sequencing, specific probing, diagnostic PCR, and pattern techniques. For studies at species and lower taxonomic ranks, however, alternative less conserved targets have to be chosen. An overview of commonly used targets and methods for identification or differentiation is given below.

Confirmative electric DNA array-based test for food poisoning Bacillus cereus

Detection of the full set of toxin encoding genes involved in gastrointestinal diseases caused by B. cereus was performed. Eight genes determining the B. cereus pathogenicity, which results in diarrhea or emesis, were simultaneously evaluated on a 16-position electrical chip microarray. The DNA analyte preparation procedure comprising first 5 min of ultrasonic treatment, DNA extraction, and afterwards an additional 10 min sonication, was established as the most effective way of sample processing. No DNA amplification step prior to the analysis was included. The programmed assay was carried out within 30 min, once the DNA analyte from 10(8) bacterial cells, corresponding to one agar colony, was subjected to the assay. In general, this work represents a mature analytical way for DNA review. It can be used under conditions that require almost immediate results.

A microbial world within us

The microbial world within us includes a vast array of gastrointestinal (GI) tract communities that play an important role in health and disease. Significant progress has been made in recent years in describing the intestinal microbial composition based on the application of 16S ribosomal RNA (rRNA)-based approaches. These were not only instrumental in providing a phylogenetic framework of the more than 1000 different intestinal species but also illustrated the temporal and spatial diversity of the microbial GI tract composition that is host-specific and affected by the genotype. However, our knowledge of the molecular and cellular bases of host-microbe interactions in the GI tract is still very limited. Here an overview is presented of the most recent developments and applications of novel culture-independent approaches that promise to unravel the mechanisms of GI tract functionality and subsequent possibilities to exploit specifically these mechanisms in order to improve gut health.