BISC209/F13: Lab2: Difference between revisions

You can directly count a random sample of microbes from the soil extract that you prepared last week and then extrapolate the number per gram of soil. To make the microbes easier to count, your lab instructors stained the nucleic acids of your soil community microbes (not just the bacteria) with a fluorescent 4'-6-Diamidino-2-phenylindole (DAPI) DNA stain. All the microbes in a 1ml aliquot of the 1% soil extract that you prepared last week were transferred in a Poisson distribution to a small piece of filter paper. She photographed the discreet bright "spots" of fluorescent DNA in several different areas of the filter paper distribution using fluorescence microscropy.  These photomicrographs will be made available to you and your partners today. You will each count the discreet "spots" as individual microorganisms (one fluorescent genome/cell) from one area and perform the calculations described below to assess the total microbial concentration in this ''culture-independent'' enumeration of your soil community's microorganisms. Compare this number to the calculation of CFUs/gram of wet soil (a culture-dependent assessment) that you will also obtain today. Compare the two counts that, in theory, should be the same since we are using two methods to figure out the same thing: how many microbes per gram comprise your soil community. The answer will provide evidence for one of our investigative goals: abundance or microorganisms in your soil community. What does it mean if your two experimental methods don't give the same answer? <BR><BR>