A Florida A&M professor grapples with an age-old problem–how to classify the creatures among us
The taxonomy of living things isn’t nearly as rigid as it’s made out to be in grade school. Scientists discover about 15,000 new species each year, some of them hiding right beneath our feet. George W. Bush, Dick Cheney, and Donald Rumsfeld have beetles named after them. Barack Obama has a namesake spider. The list goes on. And if you’ve been paying close attention to the work of Florida A&M’s Henry Williams over the past decade, you know what it looks like to see a taxonomical family fall apart at the seams.
The drama began around 2000, when Williams and his colleagues compared the genetic codes of several species in the genus Bdellovibrio. In the taxonomical world, closely related species are grouped into a genus, and related genuses are grouped into a family; Bdellovibrio is the largest of the three genuses in the family Bdellovibrionaceae, whose members all hew to the same, macabre modus operandi: They wriggle into their prey–usually E. coli or some other microorganism–and then feast on its innards.
Williams and company found that two members of the genus Bdellovibrio, starii and stolpii, had DNA that looked quite different from the others. Up to then, biologists had been treating those two species as siblings of the other Bdellovibrios. According to the 2000 study, they were more like first cousins.
Later studies revealed other dubious branches on the Bdellovibrionaceae family tree. In 2004, biologists found that the sea-dwelling members of the family were genetically similar to starii and stolpii, which live in soil, but different from the freshwater species. They grouped starii, stolpii, and the sea-dwellers into a new genus, Bacteriovorax. Then, other researchers found that the sea dwellers had genetic mutations not seen in starii, stolpii, or any of the land-based and freshwater species of Bdellovibrionaceae.
In 2008, Williams and coauthors from the University of Maryland decided that the entire family needed a split. They put the original outcasts, stolpii and starii, into a family called Peredibacteraceae, and the sea-dwellers went into the Bacteriovoracaceae family. (The suffix aceae, as you might have guessed, is latin for family.)
But the split wasn’t clean. In reassigning the families, the group broke a hallowed rule of the bacteriological code (and, yes, the bacteriological code is actually a thing): They had moved stolpii, previously designated the “type” species of the genus bacteriovorax, into a new genus and family. In other words, they were saying that the prototypical Bacteriovorax was no longer a Bacteriovorax, a big taxonomical no-no.
In their new paper, Williams and his collaborators clean up the mess. They return stolpii to the genus Bacteriovorax and the family bacteriovoracacae, and they create a new family, halobacteriovoracacae, made up of the saltwater species. Bdellovibrionaceae, once a tight-knit clan of vampire parasites, has now been split into four.
Like the creatures it aims to organize, taxonomy evolves. Sometimes, it’s because someone looked where no one else had before. In other cases, new species evolve before our eyes. Still other cases resemble the saga of the Bdellovibrionaceae family: We knew the little critters were there, we just didn’t know what to call them.