Researchers estimate 9 million bacterial genes in the human gut 
While estimates of the number of genes in the human genome is said to be around 20,000, new research estimates that if you take into account our microbiota there may be as many as 9 million genes in the human gut.
"A new concept is to consider human as a super-organism containing those microbes in or on human body as well [7]. There are more than 100 trillion bacterial cells in human gut, which are about 10 times more than cells in human itself [8]. Those bacteria can help digest food and harvest nutrition and energy that otherwise cannot be collected by the human body directly [9]–[11], i.e., human has obtained many genes needed for itself though these genes did not evolve in human genome."
"By combining completed genomes currently available and culture-independent sequencing data, we built a model to estimate the number of genes in human gut bacterial community. The total number of genes is estimated to be about 9 million. Although this number is huge, we believe it is underestimated. This is an initial step to tackle this gene counting problem for the human super-organism. It will still be an open problem in the near future."
"A new concept is to consider human as a super-organism containing those microbes in or on human body as well [7]. There are more than 100 trillion bacterial cells in human gut, which are about 10 times more than cells in human itself [8]. Those bacteria can help digest food and harvest nutrition and energy that otherwise cannot be collected by the human body directly [9]–[11], i.e., human has obtained many genes needed for itself though these genes did not evolve in human genome."
"By combining completed genomes currently available and culture-independent sequencing data, we built a model to estimate the number of genes in human gut bacterial community. The total number of genes is estimated to be about 9 million. Although this number is huge, we believe it is underestimated. This is an initial step to tackle this gene counting problem for the human super-organism. It will still be an open problem in the near future."
