Three nifty unicellular organisms

August 8, 2019 3:06 PM

The extremophile Thermus scotoductus, previously known from hot springs and hydrothermal vents, is nearly ubiquitous in household water heaters. (Wilpiszeski, R.L., Zhang, Z. & House, C.H. Extremophiles (2019) 23: 119. https://doi.org/10.1007/s00792-018-1066-z).

Prometheoarchaeum syntrophicum was brought up from deep-sea mud and was very hard to grow in the lab. 2000 days of fiddly incubation. It's interesting both because it may be very like the Archaean ancestor of eukaryotes (us!), and also because of its syntrophy. Summary; preprint ( Isolation of an archaeon at the prokaryote-eukaryote interface.
Hiroyuki Imachi, Masaru K Nobu, Nozomi Nakahara, Yuki Morono, Miyuki Ogawara, Yoshihiro Takaki, Yoshinori Takano, Katsuyuki Uematsu, Tetsuro Ikuta, Motoo Ito, Yohei Matsui, Masayuki Miyazaki, Kazuyoshi Murata, Yumi Saito, Sanae Sakai, Chihong Song, Eiji Tasumi, Yuko Yamanaka, Takashi Yamaguchi, Yoichi Kamagata, Hideyuki Tamaki, Ken Takai
bioRxiv 726976; doi: https://doi.org/10.1101/726976).

Beautiful pictures of Acetebularia, a giant among single-celled creatures -- nearly a centimeter across! -- dwelling in reefs and estuaries and inland ponds.

posted by clew (8 comments total)

Can't read due to the paywall.

I'm assuming this lab is an extremophile lab? And that they totally sterilized everything in Not-An-Autoclave (0.5N-10N hydroxide) prior to inoculation?

Because I vaguely recall another "X is ubiquitous!" paper from at least a decade ago that ended up being a case study in cross contamination.
posted by Slackermagee at 3:53 PM on August 8, 2019 [3 favorites]

Is it the abstract or the whole paper that's paywalled for you?
posted by clew at 4:26 PM on August 8, 2019

I will be happy to send a copy of the PDF for the purposes of the academic discussion here. Send me a memail if you'd like it.

I'm not a microbiologist but the authors are based at Penn State University and Oak Ridge National Lab, so I would assume they're following standard microbiological procedures to avoid contamination.
posted by biogeo at 7:06 PM on August 8, 2019 [1 favorite]

I think Slackermagee is pointing out that standard microbiological cleaning might not eliminate thermophiles. If you memail me the PDF, biogeo, I will summarize the methods section.
posted by clew at 7:25 PM on August 8, 2019

Sorry for the delay, I've just sent it along!
posted by biogeo at 9:58 PM on August 8, 2019

Does the article list where the 101 water heaters referenced in the abstract are? (Is the conclusion really that some Pennsylvania water heaters contain extremophiles?) Neat-sounding result. (Paywalled for me, too.)
posted by leahwrenn at 10:18 PM on August 8, 2019

The paper indicates the water heaters were located in all 50 US states:

To better understand the biogeography of thermophilic microorganisms in the built environment, we conducted a citizen-science survey of organisms colonizing household water heaters across the United States. Citizen-scientists were recruited from all 50 states to sample hot water from their households. Participants filtered water to collect cells and inoculated sterile media to grow enrichment cultures of thermophilic species. DNA sequences from both the filtered cells and enrichment cultures provided a broad view of the biogeography of thermophilic microorganisms living in household hot water systems. [...] At least two non-scientist households in each state were recruited to collect samples from their home water heaters.

Later they also mention that Puerto Rico was included in their samples. The first figure is a map of the US with dots showing where they received samples from. Though I admit it's a little confusing in that it doesn't quite add up to "two non-scientist households in each state", as there's clearly more than two dots in some states and only one in others. Also, they say that while the obtained 101 samples, only 36 of them successfully cultured anything, though those 36 seem reasonably well distributed across the continental US and Alaska. So at least the conclusions are broader than just Pennsylvania.

Also, regarding the collection of samples:

Participants were asked to sterilize a faucet using an alcohol wipe, run hot water through the faucet for 5 min, and then collect hot water in a clean mug. Whole-community samples were collected by filtering 600 mL hot tap water through sterile 0.22-μm Sterivex(TM) flters to collect microbial cells. Enrichment cultures were inoculated with 5 mL hot tap water in 15 mL sterile growth media and pre-incubated at 160 °F (70 °C) for 3 h in a household oven to select for thermophilic organisms. Colorimetric strips were used to record water temperature, pH, and chlorine concentrations (Fig. S1). Participants self-reported information about the local water source (well or municipal), temperature setting, age of water heater, make and model, household size, environment (rural or urban), and household water treatment systems. Estimates of the maximum daily temperature at the time each sample was collected were determined using the Weather Underground Historical Weather tool (wunderground.com/history) based on zip code. All samples were shipped to the Pennsylvania State University. Upon receipt, filter samples were stored at −80 °C prior to extraction. Inoculated growth media samples were immediately incubated to promote cell growth.

At least at quick glance I don't see any greater detail on how the sample tubes and culture media were sterilized, so I don't know if that really addresses the question of whether the representation of T. scotoductus could have been caused by contamination from the lab. Certainly the practices at the citizen-scientist end are not exactly high sterility, but that probably doesn't matter as much for just getting a representative sample of the biogeography of thermophiles in water heaters.

I get the strong impression from the paper that the idea that thermophiles can be found in water heaters is already well established in their field; for example, they reference previous findings in industrial heaters and in Icelandic tap water. They seem more focused on demonstrating that they are common/ubiquitous, and that T. scotoductus specifically is found in all their samples, and shows no evidence of geographic variation. Their discussion includes a couple of paragraphs on this point, in which they note that populations of Thermus species found in natural environments in the US (e.g., the thermal vents of Yellowstone) exhibit genetic signatures of local isolation and speciation, and populations that are geographically close together are genetically more similar than those that are far apart. This however doesn't seem to be true of the Thermus scotoductus populations they sampled in water heaters, which apparently are genetically very similar and exhibit little or no relationship between geographic and genetic distance. They say this indicates two important things: first, that environmental selective pressures, rather than evolutionary history, are the primary factor in determining what species and strains of thermophiles are found in water heaters; and second, that the physically isolated nature of water heaters does not serve as a barrier to thermophile dispersal.

Since I'm not a microbiologist or an expert in biogeography (despite my username) I'm not really equipped to evaluate the work in any detail, so the above is just my read of what the authors seem to be saying are the important findings in their discussion/conclusion.
posted by biogeo at 1:20 AM on August 9, 2019 [4 favorites]

THanks for sending the paper *and* doing the summary, biogeo!

I wonder how many water heater manufacturers there are, and if the tanks arrive at domestic locations pre-inoculated.
posted by clew at 9:15 PM on August 12, 2019 [1 favorite]