Sorting underground microorganisms

　Finding underground microorganisms in sediment is no simple thing however. “Under the seafloor, there are only cell density of 1/10,000 compared to those on the earth’s surface. They can’t be found with the usual analysis techniques,” tells Yuki Morono, who with Inagaki makes study of the deep biosphere and analyses the core samples that were retrieved. To deal with this issue, sediment is grounded into fine powder, solved into two solutions of differing specific gravity, and the microorganisms are sorted from the minerals by their weight. “Even then, mineral fragments get mixed in, adding chemical compounds that bond with the genetic material of the microorganisms. As dyed cells produce flourescent under ultraviolet light, that can be used to seek them out with a microscope.” When Morono actually shows us, the microorganisms can only be seen as lonely green specks of light in the narrow field of the microscope. This detection work is also computerized, but on board the CHIKYU researchers do it sometimes with their own eyes.

　But this is not all. Since this is work done by people, using drilling fluid for the drilling, it is inevitable that drilling fluid, sea water or microorganisms surrounding people end up mixed into the retrieved core samples. Explains Morono, “When foreign microorganisms get mixed in, it means that they are contaminated. We use the samples with a low degree of contamination, and examine the genetic material of the microorganisms we find. If we find that they are close to microorganisms that live around people or in sea water, they have found their way in from somewhere. In this way we narrow them down to the deep biosphere microorganisms alone.”

　The Geomicrobiology Group which is lead by Inagaki and includes Morono have a technology at their disposal for the automatic extraction of individual microbial cells found in the core samples and are engaged in cutting edge bioscience research. Considering that long ago microorganisms were dealt with by culturing them in a petri dish and creating large colonies, this is dizzying progress.

The accuracy required by science

Mud gas analysis lab

　In scientific research, technology and accuracy are important. Inagaki explains the achievements that are underpinned by technology: “On board the CHIKYU we have a laboratory for proper real-time geochemical analysis of the subterranean gases from the drill hole and the circulating drilling fluid, and we have obtained important data for the exploration of the subseafloor environment. We have also been able to use several sensors to take stable stratum data of a high quality, because with the riser drilling system the borehole wall is stable, protected as it is with drilling fluid.” The retrieved samples are stored at the Kochi Institute for Core Sample Research, and arrangements have been made for samples to be sent on request to researchers worldwide. They are currently being analysed on a variety of aspects, such as sedimentology and biology, mainly by researchers who sailed on the CHIKYU.

　As Inagaki explains, there are also problems: “For the first time we applied the latest technology for direct acquisition of formation water in its original state, developed for oil drilling, to scientific drilling. It is the first sample that we were able to extract with its original pressure level intact. But a considerable amount of fluid apart from ground water was mixed in with it. In order to use this for scientific purposes, we need to further increase its purity. Technology development will need to be proposed from the side of science.”