An analysis of the microbial communities of the Mojave Desert serving as a terrestrial model for the

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An analysis of the microbial communities of the
Mojave Desert serving as a terrestrial model for
the environment of Mars Elaine P. Bryant
NASA Spaceward Bound Mojave 2008
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Why the desert?

• If microbes exist on Mars (or other planets) one
  factor they must cope with is an extremely dry
  environment no liquid water.

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Terrestrial deserts
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Mojave Desert Region
Mojave Barstow
Zzyzx
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Overall research plan

• Examine the microbial communities at each site
  by
• collecting soil samples along a precipitation
  gradient
• analyzing the microbial community at each site
• comparing results to determine trends or patterns
  relating precipitation and the specified
  communities

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March 2007 Spaceward Bound Mojave

• Fieldwork
• Established 7 sample sites along precipitation
  gradient given from the Fire Resource
  Assessment Program
• Took 6 samples at each site ? 42 total soil
  samples
• Laboratory
• Performed two culture techniques
• Prepared DNA for molecular techniques

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07 Sample transect
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Sampling sites
Site 17 Cramer Junction
Site 15 Tehachapi
Site 21 soda lake bed
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Sampling procedure
1. Identify an appropriate area
4. Take sample from top 8 cm
2. Establish a 10m x10m sample area
3. Determine sample sites w/in sample area
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Analysis at Zzyzx

• Count plates to determine the relative number
  of microbes per gram of soil as a function of
  precipitation
• Biolog sole-carbon-source microplates to
  observe differences in the utilization of carbon
  sources as a function of precipitation
• Extraction of community DNA for molecular studies

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Count plates ? CFUs/gm soil
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Biolog sole-carbon-source micro plates
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Molecular analysis

• -Requires the extraction of DNA from the
  organisms in the soil.
• -Use community DNA and the amplification of a
  fragment of DNA the 16S ribosomal subunit,
  using Polymerase Chain Reaction (PCR)
• -Consist of two different techniques
• 1. Cloning 16S rDNA fragment ? phylogenetic
  trees
• 2. Denaturing Gradient Gel Electrophoresis (DGGE)

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Cloning basics

• Compare 16S rDNA fragments from all members of
  the microbial community
• Isolate unique fragments
• Identify (sequence) the nucleotide bases of the
  fragments
• Construct a tree relating one organism to the
  others
• Compare trees from each sample site

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DGGE

• Pass DNA fragments through a gel containing
  compounds to separate the two strands of DNA
  (denature) each resulting band represents a
  taxon or genus of organisms
• If two columns contain the same banding, those
  communities have the same taxons of organisms

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Summary of activities for SBM 08

• Collect 3 soil samples/site
• Inoculate 2 culture plates per site for count
  plates
• Inoculate 2 Biolog s-c-s plates/site
• Extract DNA samples