The history of Herpetomonas megaseliae:
Herpetomonas megaseliae
is a single-celled animal that lives naturally inside a tiny fly named Megaselia scalaris. In order to
understand why H. megaseliae is so
interesting, you have to appreciate the fly, M. scalaris. This fly is one of the truly obnoxious survivors, and
so, it turns out, is the parasite H.
megaseliae that lives inside it. Megaselia
scalaris lays its eggs in about any kind of organic material from the
rankest of garbage to the cleanest of sterile culture media, but generally it
prefers the rank garbage, or better yet, sewage-soaked soil and even feces.
Rotten fish that have been stored in formaldehyde are pretty attractive to this
fly. So anything that might have been thrown away, from bacterial Petri plates
to toad manure, is a magnet for M.
scalaris. This wide range of larval substrates is the reason why M. scalaris is such a survivor; it can
get by on all kinds of things other flies treat as garbage. Quite literally, M. sclaris has the ability to fall into
a pile of shit and come out smelling like a . . . . well, about like a very
healthy fly. Thus we have our basic metaphor: survivors are not very picky,
regardless of the organisms playing this role.
Among
the most remarkable demonstration of this survivorship ability involved a very
large and beautiful lizard, Basiliscus
plumifrons, that we had in the lab many years ago as part of a study of the
biogeography of parasites that infect reptiles. This lizard had food and water
dishes in its aquarium; the food was mainly meal worms and crickets, although
once in a while it would get a roach. A dish full of meal worms was also
attractive to Megaselia scalaris, and
before long there were fly larvae crawling around in the litter and food dish.
Naturally, B. plumifrons ate these fly
larvae (it would also try to eat your hand if you didn’t handle it carefully.)
But the fly larvae then ate their way out of the lizard’s stomach and through
the skin, leaving tiny holes. The lizard eventually died and we didn’t figure
out why until a grad student cultured a piece of muscle and discovered Herpetemonas megaseliae, a parasite that
could only have come from the fly larvae. The lizard and formaldehyde fish
provide a rather sobering lesson: environments intended to kill things can turn
out to be breeding grounds for survivors.
Herpetomonas megaseliae
is a member of the same family as numerous other parasites that cause untold
misery and enormous economic loss around the world. Some of the diseases caused
by these parasites include classical African sleeping sickness, nagana—the livestock disease that
prevents cattle from being raised profitably over a 4 million square mile
region of Africa, leishmaniasis (sometimes horribly disfiguring), and Chagas’
Disease, a devastating illness that occurs throughout much of Latin America and
which, according to data provided by molecular biologists, has occurred there
for thousands of years. So regardless of its fondness for garbage, H. megaseliae is a member of a
distinguished group of organisms.
Most
of H. megaseliae’s relatives can be
cultured, but they are fastidious pansies that must have rich, sterile, usually
blood-based environments, and the correct temperatures. Herpetomonas megaseliae, however, can grow in a lot of different environments.
One of its favorites at the time was called LPG, which stands for Locke’s
balanced salt solution (L) plus (P) Guinea pig shit (G). It also grew at
relatively high temperatures that would kill its pansy-ass relatives (“If you
can’t stand the heat, get out of the kitchen.”) Most of the world’s scientists
and doctors, especially those in armies, think that the pansy-ass relatives are
very important. If H. megaseliae
could talk, it would probably agree with the doctors. But among its kin, H. megaseliae is, like its fly host, a
survivor. Furthermore, it was quite cooperative, being easily manipulated to
develop into particular life cycle stages on a human schedule, so that a person
could do a set of experiments in the morning and be on the golf course by
mid-afternoon.
When
my students and I first decided to study H.
megaseliae, back in the late 1960s or early 1970s, that decision was based
on our sense that this parasite was simply a very interesting animal. As we
studied it for years, we realized that not only was it interesting from a
biologist’s perspective, but it was also interesting metaphorically because of
its survivorship qualities and its ability to perform under the most trying of
culture circumstances. All of the students who were attracted to H. megaseliae seemed to be people who
could, or would, do things that other students couldn’t, or wouldn’t, do, and
furthermore, those things seemed to advance the careers of people who could, or
would, do them. If you’re in academia, you know what those “things” are and how
such activities produce transferable skills by default.
About
this time in my career I was walking through a mall in Lincoln, NE, where a
bunch of artists had set up exhibits. One of these artists was making jewelry,
and just on a whim I asked her if she could make a bracelet with H. megaseliae on it. She said it would
be easy, so I drew her a picture, and a week or later I picked up this
bracelet. People, especially my departmental colleagues at UNL, probably
thought I was a jewelry jerk for having this bracelet made, and then wearing
it, but it was actually my statement that I thought the students in my lab who
could do anything under trying conditions were more admirable role models for
the next generation of young scientists than were my pansy-ass colleagues. I’ve
worn that bracelet now, pretty much every day, for the past 40+ years.
JJJr
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