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Smalls in the deep mudAugust 20, 2012

Good morning! It is 4 a.m. and almost time for lunch.

As Ms. Marcella Purkey stated in her report, we have two work shifts since the “Chikyu” is under operation 24 hours a day. I, a night shift guy, have been sleepy during this early morning time period because of “jet [not actually jet] lag”, though I’m now gradually getting used to it.

By the way, today’s report is about subseafloor microbiology. Seafloor lies more than a kilometer away from our feet at current site, and below the seafloor, that is the world where we are looking at.

What do you imagine when you see the word “microbe”? Ticks? Water fleas? While these organisms are in the small size range of 0.01 to 0.1 mm, that is still “large” for us microbiologists, and we don’t usually see such big guys in subseafloor sediments.

Our target microbes have a size of around 0.001 mm, like the lactic acid bacterium that produces yogurt by fermenting milk. Microbes tend to have a bad reputation for rotting stuff or causing diseases, however, microbes also produce antibiotics to keep you healthy and help you digest your food. It is not an exaggeration to say that we cannot live our life without microbes.

Subseafloor microbes (green dots) viewed through a microscope look like stars in the night sky.

Only microbes are able to live in the subseafloor. We estimate that there are about 10^30 cells (1000 billion billion billion cells!!) per cubic centimeter living deep down below the Earth’s surface.


(Additional comment) Through the previous counts of subseafloor microbes, now we know that there are 1000 to billions of the cells per cubic centimeter below the seafloor By extrapolating this number to the whole subseafloor on the Earth, Whitmann et al. got an estimation of 10^30 microbial cells in subseafloor realm.

In this expedition, one of our missions is to find microbes in the deepest subseafloor core samples ever drilled. Are there microbes that deep? No one knows yet. Like the Mars rover Curiosity’s mission to explore for signs of life on Mars, we are going to look for life deep into the Earth.

DiCE (discriminative cell enumeration) system for automated microbial counting

Since microbes are so tiny (about 0.001 mm), we cannot see them with the naked eye. We have to use microscopes to see and count them. These microbes are also very different from the ones on the Earth surface we can easily grow in a lab, so we have to find ways to study them directly from the sediment where they live. This can make cell counting very difficult because we have to distinguish between what is a sediment particle and what is a microbe. We sometimes miss small cells and have to take frequent breaks. So we decided to give this work to a computer named “DiCE”, shown in the picture above.

It doesn't need breaks and can tell the difference between cells and sediment automatically. All the analyses are recorded as pictures, so that we can come back later if we find some weird stuff that needs to be looked at again. This means we can constantly produce professional cell counting data throughout our expedition.

What microbes are living there? How are they making a living? How harsh of conditions they can stand? There are many mysteries in the subseafloor biosphere. Counting cells is just the beginning, but a very important step on the journey to understand the world below our feet.

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