Less than 1% of the bacterial species, about 4500, can be cultivated in the lab. Most of the research on bacteria has therefore been done on a tiny fraction of the bacteria. Slava Epstein, at Northeastern University in the US, has been able to cultivate about 30% of the bacteria from a particular coastal area by keeping cultures in their environment, separated by membranes. This indicates that the overwhelming majority of bacteria are parts of functioning communities and simply cannot live alone. Bacteria make communal decisions by adding up chemical signals. If the concentration of a signal becomes high enough from all the individual contributions, then some communal action will be taken. This is called quorum sensing. They also pass signals with the same ions, sodium and potassium, as are used for signaling in our own brains.
Interpreting these communications is thus far limited to very specific bacterial communities, such as the bacteria that produce light in the bobtail squid light organ. A complex interaction of three chemical signals between the bacteria and the squid host has been uncovered but has not been deciphered. Considering then, the scale of the bacterial community of the ocean, we can see that our understanding of this community is in very early days.
There is a layer of “ooze” that covers much of the ocean bottom. It turns out to be a layered community of different bacteria, each of which work with what other bacteria excrete. Nanowires have been seen in this ooze that carry electrons between bacteria for more than a foot. That is equivalent to a human-scaled electrical grid system that spans a continent. As small as these microbes are, there are no natural limits to their community: the whole ocean bottom is connected. It is also connected to the bacteria at the surface via a continual rain of organic detritus, and also by ocean currents. The ocean community is connected to the continent-spanning soil community in a wide variety of ways. The only natural boundary for this interconnected set of environments is Earth itself.
We see much evidence of this worldwide community, but does it function as a whole in some way? This question is addressed in the next chapter.