PROKARYOTIC TRANSCRIPTOMICS AND METAGENOMICS
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After billions of years of evolution, prokaryotes have developed a huge diversity of regulatory mechanisms, many of which are probably uncharacterized. Now that the powerful tool of whole-transcriptome analysis can be used to study the RNA of bacteria and archaea, a new set of un expected RNA-based regulatory strategies might be revealed. Metagenomics, together with in vitro evolution and high-throughput screening technologies, provides industry with an unprecedented chance to bring biomolecules into industrial application.
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PROKARYOTIC TRANSCRIPTOMICS AND METAGENOMICS
- 2. LUBNA SHAKOOR M-PHIL “I” ADVANCES IN MICROBIAL GENETICS
- 3. PROKARYOTIC TRANSCRIPTOMICS AND METAGENOMICS
- 10. Wang et al. 2009
- 19. Affymetrix’s Photolithographic Approach GeneChip A Dan Nettleton, Department of Statistics, IOWA STATE UNIVERSITY, Copyright © 2008 Dan Nettleton mask mask mask mask mask mask mask mask A A C C G G T T T T T A A C C
- 23. Affymetrix GeneChip ® Affymetrix GeneChip ® Limits: 1: 100,000 transcripts ~ 5 transcripts/cell
- 27. From Figure 2 in Daniel, R. (2005) "The Metagenomics of Soil" Nature Reviews Microbiology 3: 470-478.
Notes de l'éditeur
- Arial Traditional genomics focuses on the sequencing and analysis of the genomes of individual organisms. When applied to microbes, it typically involves culturing the organism of interest followed by sequencing. Metagenomics is a new area of microbial genomics that aims to sequence the full or partial genomes of all members of a microbial community (also called a consortium). The term microbial community refers to the complex microbial ecosystems that exist almost everywhere in nature. For example, a project in soil metagenomics might extract DNA from a soil sample in a corn field and attempt to sequence all the DNA found in the sample. By directly sequencing the DNA, researchers bypass the need to culture organisms. Since only a very small minority of single-cell organisms have been successfully cultured in the laboratory, metagenomics becomes a very powerful technique for sequencing genes from organisms that can not be cultured. Alternatively, homologous genes from a variety of organisms in the microbial community can be selectively sequenced via PCR using tags that exist in known organisms.
- Arial Isolating DNA from an environmental sample is the first step of any metagenomics study. Different types of samples often require specialized extraction techniques; however, once the DNA is extracted most metagenomics projects will take one of several approaches. A schematic of the techniques used to study the soil metagenome is shown in the slide. Once DNA is isolated it is cloned, entered into some kind of vector (bacterial artificial chromosome, plasmid, cosmid, etc.), and then inserted into an appropriate bacterial host. The bacteria can then be used in functional screens for specific types of biochemical activity ( e.g. proteases). Alternatively, DNA from the metagenome can be used for sequencing. In some cases this can even result in the complete or almost complete genomes of individual species in the environmental sample.
- Arial The greatest challenge in studying metagenomes is their size. It is estimated that as many as 40,000 distinct species of microorganisms exist in a single soil sample, making the soil metagenome orders of magnitude larger than the human genome. Present sequencing technology makes it impossible to fully sequence that amount of DNA in a reasonable time or at a reasonable expense (though this may change in the not so distant future). To make matters worse, not all organisms are equally abundant in microbial communities, meaning that even greater amounts of DNA would have to be sequenced in order to obtain adequate coverage of rarer genomes. Nonetheless, significant progress has been made in studying metagenomes. For example, functional screens of metagenomic sequences have uncovered novel genes for antibiotics, antibiotic resistance, lipases, and proteases to name only a few. Phylogenetic studies have revealed the broad distributions of species within a particular microbial community. In some cases, it has even been possible to fully sequence the most common members of a particular community.
- Arial Though metagenomics is still in its infancy, it holds great promise for answering fundamental questions about the structure and dynamics of microbial communities. The slide poses a small sample of such questions. Metagenomics has already yielded several interesting discoveries. For example, a study of ocean surface water uncovered a new class of rhodopsin genes in alpha-proteobacteria. Rhodopsins are proteins that respond to light and serve a range of purposes in a wide variety of organisms, including the detection of light in the retinal cells of humans and other animals. Further studies of the newly discovered bacterial rhodopsins found that the light response of the proteins was tuned to match that of the light that was reaching the alpha-proteobacteria at different ocean depths. Metagenomics can also be used to observe the interactions of individual members of microbial communities. One such example is shown in the slide where fluorescence in situ hybridization (FISH) was used to visualize archaeal and bacterial species in an ocean sediment community. Bacteria are shown in green and archaea in red.