Presentation on theme: "Risk Assessment and Microbial Ecology Norman R. Pace MCD Biology University of Colorado, Boulder"— Presentation transcript:
Risk Assessment and Microbial Ecology Norman R. Pace MCD Biology University of Colorado, Boulder email@example.com
Questions Common to Microbial Ecology and Risk Assessment : 1. What organisms are present? 2. In what quantities?
Detection of Microbes: 1.Specific tests (e.g. antibodies) - Need to know what you are looking-for 2.Culture - Uncertain (EOP <0.1% in environment); tests expensive, complex, often ambiguous. 3.Gene sequences - In principle comprehensive and quantitative
Making Sense of Sequences: Molecular Phylogeny 1.Align sequences so that “homologous” residues are juxtaposed. 2.Count the number of differences between pairs of sequences; this is some measure of “evolutionary distance” that separates the organisms 3.Calculate the “tree”, the relatedness map, that most accurately represents all the pairwise differences
What Gene sequence to use to relate all life? Ribosomal RNA 1.rRNA is ubiquitous. 2.Sufficiently highly conserved to relate all life. (E.g., human-E. coli ca. 50% identity!) 3.Has resisted “lateral transfer” - tracks the “genetic line of descent. 4.Abundant in all active cells
Some Lessons from the Big Tree Three main relatedness groups: Eucarya, Bacteria and Archaea. Origin of life, the “root” of the Big Tree, is on the bacterial line of descent - Archaea and Eucarya are related to the exclusion of Bacteria. Many consistent biochemical correlates, e.g. transcription machinery. The eucaryal nuclear line of descent is as old as the archaeal line.
The major organelles, mitochondria and chloroplasts, are of bacterial ancestry. The biological clock, the rate of sequence-change, is not constant. You can’t date the deep past by sequences. The sequence-based framework is a quantitative articulation of biodiversity; most biodiversity is represented by microbial organisms. The sequence-based framework means that microbial organisms can be identified without the traditional requirement for culture
Prostatitis: Inflammation of prostate; pain in scrotum, pelvis, abdomen 50% of males expected to espress at some time Etiology not understood Diagnosed as bacterial or “nonbacterial” depending on culture results (positive ca. 10% of cases) What rDNAs in expressed prostatic secretion?
Prostatitis study conclusions All patients tested positive by rDNA for bacteria, regardless of culture success. Predominant organisms Actinobacteria and Low G+C bcteria. Corynebacteria prominent; four relatedness groups <98% identical to known organisms; likely new species. No clonal type identical between patients. Note potential for probe design for diagnostics
Some bacteria encountered in pool study [BLAST ID]: Mycobacterium ulcerans [99%] (262/325 clones in one air sample) Mycobacterium avium [99%] (36/357 clones, inside air Mycobacterium asiaticum [98%] (62/183 clones in poolwater/side biofilm Mycobacterium malomense [99%] (2/51 clones, pool water) Uncultured oral rDNA [99%] (15/51 clones in pool water sample) Uncultured archaeon [83%!] (11/51 clones in pool water) Blastomonas ursincola [99%] (107/183 clones in pool water/side biofilm)
Problems with the Molecular Approach Requires significant material (> a few hundred bacterial cells). Contaminants in reagents, enzymes, etc. a BIG problem. (Less problem with organism-specific primers.) General primers may not work with some rDNAs. Clone/Sequence/Phylogenetic analysis is cumbersome. Information on rRNA phylotype may not reflect phenotype.
Thanks to - Geothermal studies: Shower curtains Phil Hugenholtz Ulrike Theissen Anna-Louise Reysenbach Scott Kelley John Spear Prostatitis: Pool mycobacteria Mike Tanner Lars Angenent Dan Shoskes (UCLA) Mark Hernandez Support over the years from: NIH, NSF, DOE, NASA Astrobiology Institute