What's the similarity between your gut and the bottom of the ocean? Well, they're both dark and oxygen-poor places. And full of bacteria. Now, a group of Japanese researchers has discovered that some of the nastiest germs thriving in the human intestine, triggering some severe diseases could have evolved from hardy ancestors living deep under the sea bottom.

The team said they had analyzed the DNA material of two well-known disease-producing gut bacteria and compared them to two closely related but inoffensive bacteria encountered deep on the ocean bed. The two types of bacteria appeared to share many similar common genes which made them able to thrive in extreme environments. They also possessed a low number of DNA repair genes, a fact that permitted them to experience frequent mutations and adapted quickly to continuously changing environment and to the immune activity of a symbiotic host. This is the weapon that allows the gut bacteria to "persist in infections," signaled the researchers.

"The researchers suggest that human pathogens (gut bugs) evolved from a deep-sea ancestor, and acquired further virulence factors while living in symbiosis with invertebrates," they added.

The two gut bugs analyzed by the Japanese researchers were the helicobacter, which causes ulcers and the campylobacter, which induces food-borne diarrhea.

The two proteobacteria, Sulfurovum litthotrophicum (that gets its energy from oxidizing sulfur and thiosulfate) and Nitratiruptor (two species that get their energy by nitrate reduction with hydrogen, forming free nitrogen) are encountered in very deep seas, inside the sea floor, in such a harsh environment that they are the only living things there and are classified as one of the hardiest micro-organisms. Recent technological advances permitted the researchers to culture these bacteria. These micro-organisms could tolerate temperatures ranging from 4 to 70 degrees Celsius (39 to 158 Fahrenheit).