What is the Second Genome and how does it affect us?

Did you know that there are fewer human cells in our body than bacterial cells?

For the human body to contain anything other than our own cells has always caused controversy; however, the idea of a second genome has been around for a while. Since 1972, scientists held the opinion there was a ratio of 10:1 microbe (single celled organisms)-to-human cells in our body, making us only 10% our own cells! This was shocking and incredibly controversial at the time. However, recent research has found the ratio to be closer to 1:1, or more specifically only 43% of the cells in our body are our own, the rest is a mixture of bacteria and archaea and other microbes. These microbes, mainly found in the gut, have been nicknamed the ‘second genome’ from the idea humans have two genomes. The native human genome, and the more diverse set of genomes carried by the human microbiota.

The Effect of the Second Genome

Overall, the microbiome plays a very important role in all areas of life: from digestion, the immune system, manufacturing vital vitamins and even mental health, working very similar to human cells. Some produce enzymes to digest foods, others will produce electrical stimuli to send signals to the brain (this is especially important when understanding the link between mental health and microbes). However, within one’s gut there is a diverse mix of microbes (roughly 2-20 million total), some benefitting health and some if present in too high of a concentration adversely affecting health. For example, a high concentration of bacteria from the ​Acamancia ​genus digests fats, whilst the phylum of bacteria, ​Firmicutes, ​absorb fat and hence people with higher concentrations will gain weight more readily. However, some microbes have both positive and negative consequences; an interesting example being ​Blautia obeum ​as it contributes to inflammation as the bacteria favours that environment, but it is also important in the recovery process when infected with certain pathogens​. ​ Therefore, a diverse mix of microbes is preferable, especially as some may not have obvious functions.