We do human and animal population surveys. According to http://www.worldometers.info/world-population/ as on April 06, 2014 world population is around 7.224 billions and animal population is increasing day by day. We can easily do the census of the human and animal population but can we do the same for microorganisms? if yes, how? Is there any website or organization that counts the microbial population?
Yes, microbial population can be determined through total microbial count for a particular sample using General Purpose Media, depending on the type and nature of the microbe.
It may actually not be possible through culture methods because all the microbes are not culturable and we may not be able provide them with all the required nutrients in appopriate amounts in lab conditions as well as the interrelationships within microbial communities also determines their type and numbers. At present stage we havn't been able to isolate all types of microbes present in soil (only less than 1% are culturable) leave alone estimating their numbers. However, any expert may throw more light on this.
Culture methods are completely biased. Not only they stimulate the growth of some part of the microbial population but also, most of the microbes are not culturable or require extremely specific conditions.
Methods for community analysis of microbial populations are normally DNA-based: pyrosequencing is now pretty common as high throughput sequencing method; a lot of data is generated, though expensive it can be the less laborious. Clonning and sequencing of colonies was used time ago for the same purpose. Both methods give percentages of the given OTU in the community.
FISH and variants like CARD-FISH can give absolute numbers but they use specific DNA probes so you need to know beforehand what type of microbes thrive in that environment.
DGGE can give you a community profile: what OTU are in the samples and it is pretty useful comparing samples e.g. different depths in a river. You can cut and sequence bands and then perform FISH for exact numbers
And many more, search for microbial ecology techniques or microbial population analysis.... there is a lot of information
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