In: Biology
number of colonies in the range of 30 to 300 is used to calculate the CFU/mL
so let`s use dilution 10^-5 for the calculation of CFU/mL
CFU/mL= number of colonies/( dilution volume plated in mL)
volume plated =0.125 mL
dilution=10^-5
number of colonies=210
CFU/mL= 210/(10^-50.125)
= 1.6810^8/mL
bacterial concentration in the 50 mL is 1.6810^8/ mL
so total number of bacteria in the 50 mL= 501.6810^8=8.410^9 cells
50 mL of the solution contains 20 gram of soil, the number of bacteria in the20 grams of the soil is 8.410^9 cells so total number of cells per gram of the soil= number of bacteria in 20 grams of soil/20=8.410^9/20=4.210^8 /gram.