A[BillionBillionBillion]undant Prochlorococcus
August 11, 2021 12:14 AM   Subscribe

Penny Chisholm won the 2019 Crafoord Prize for her 1985 discovery of the most abundant living thing on the blue dot. Obligatory TED talk.

Exec summary. Maybe Procholorococcus qualifies for "weird forms of life"? In 1985 Penny Chisholm and Rob Olsen took a flow cytometer out to sea looking for something else and found an abundant [105/ml] small [0.6μm] ubiquitous photosynthetic bacterium. Back of an envelope says that Procholorococcus marinus is the most a[BillionBillionBilllio]undant = 1027 indivs organism we know about. They tiny, we big; so the biomass is about the same.

Finding so many so tiny photosynthetic organisms in the ocean made us radically re-think our view of the carbon cycle, which up until then had been focused, with a sense of awe, on tropical rain-forest which includes some of the largest living things on the planet. The annual amount 5 Gtonnes of carbon fixed by Prochlorococcus is in the same ball-park as the excess 6 Gtonnes we are adding to the atmosphere by burning fossils fuels. Our carbon footprint is still increasing but the density of Prochlorococcus is remarkably stable year after year, despite doubling about once a day, so we must conclude that half of each day's reproductive bounty is promptly scarfed up by something else for dinner.

Small as it is, Chisholm discovered it shipping fluid-filled vesicles out from the surface membrane for purposes intriguing but not yet fully understood. These vesicles contain DNA, RNA and proteins and could be regarded as mobile workshops spreading out from the minuscule mother-ship. It seems that Prochlorococcus lives in a complex commensal relationship with other bacteria that have only a tenuous physical connexion - it's really dilute in the sea. These other bacteria are able to scavenge the limiting elements, mainly nitrogen, phosphorus and iron, in a marine environment. It's almost as if Prochlorococcus is paying its taxes in fixed carbon and receiving the key N, P, Fe building blocks for making more DNA and protein as it doubles its numbers every day.

Be extremely skeptical of people, even 'scientists' who propose that, by seeding the ocean with iron or one of the other limiting elements we can boost the carbon-holding capacity of oceanic life. That reductionist single-factor analysis is likely mad bad and dangerous to implement because it will boost some unknown and unculturable microbes at the expense of others and upset the equilibrium of the n-dimensional [Fe, P, N, pH, salinity, conductivity, day-length, light intensity, depth, unknown-but-important-1, unmeasurable-but-important-2, intangible-but-vital-3 etc.] hyperspace that is an ecological niche. That niche is occupied by just one species characterised for what we can measure. But an ecosystem is an interlocked set of niches involving thousands of interacting and inter-dependent species. To the nearest whole number, the best estimate of how much we know about how an ecosystem works is . . . nothing. More? Prof Chisholm talks about it for an hour [starting at 7mins]
posted by BobTheScientist (3 comments total) 16 users marked this as a favorite
It's my bedtime so I am not able to absorb all this information and comment on it. I will only say that I knew nothing about this whatsoever, which means I am delighted that you have posted this. Thank you, BobTheScientist!
posted by Bella Donna at 1:56 PM on August 11 [1 favorite]

I was just wondering yesterday whatever happened to the whole "we'll dump a shipload of rust into the ocean, problem solved!" thing. Glad we didn't...uh...do that?
posted by mittens at 2:03 PM on August 11

Wow, really eye-opening. Thanks for posting this, BobTheScientist.
posted by mpark at 10:59 PM on August 11

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