from time to time I’ll find myself singing the famous Folgers Coffee jingle: “The best part of waking up is Folgers in your cup!”
Well, it looks like some bacteria have taken these ads to heart. A researcher from the University of Iowa has discovered a strain of bacteria called Pseudomonas putida CBB5 that appears to have evolved the capability to live off caffeine.1 This strain possesses three enzymes—called N-demethylases—that remove the three methyl groups from caffeine (see figure 1). The resulting product is then converted to xanthine, a common metabolite found in all organisms. Once this compound is formed, it can be further broken down using existing metabolic pathways.
Figure 1. Chemical structure of caffeine
Image source: http://en.wikipedia.org/wiki/File:Caffeine.svg
As humans have made widespread use of caffeine, this stimulant has “leaked” into the environment as a “pollutant.” Caffeine is made up of carbon, hydrogen, nitrogen, and oxygen, four elements that all life-forms need to survive. Given caffeine’sabundance in the environment, it is not surprising that P. putida would have acquired the ability to make use of caffeine as a food source.
For many people, discoveries like this convince them that biological evolution must be a fact. After all, seeing is believing and we are observing evolution happening right before our eyes.
But is evidence for the evolution of novel metabolic activity in bacteria evidence for biological evolution? A careful understanding of the various meanings associated with the term evolution as well as insight into the nature of the evolutionary changes taking place in P. putida help address this question.
The Ambiguity of Biological Evolution
The term “evolution” can take on a variety of meanings. Each one reflects a different type of biological transformation (or presumed transformation).
It is true that organisms can change as their environment changes. This occurs through mutations to the genetic material. In rare circumstances, these mutations can create new biochemical and biological traits. If these new traits impart to the organism a greater ability to survive, it will reproduce more effectively than organisms lacking the trait. Over time, this new trait will take hold in the population, causing a transformation of the species.
Evolutionary biologists have proposed that biological changes can take place at three distinct levels. The first is referred to as microevolution. This involves evolutionary variation within a species in response to selection pressures and genetic drift. Examples include the changes in wing color observed for the peppered moth.
The second level of evolutionary change is speciation. In this case, one species evolves to give rise to a closely related sister species. A well-known example is the finches of the Galapagos Islands that evolved from an ancestral species. The primeval finch species made its way to the Islands and then diversified into closely related species that vary in size and beak shape in response to the different ecological niches on the different islands.
Evolutionary biologists and most creationists agree that an abundance of evidence exists for microevolutionary changes and speciation. Biological evolution at these two levels is a fact and is largely noncontroversial.
The controversy centers largely on macroevolution, evolutionary modifications with the creative potential to generate large-scale biological changes. Evolutionary biologists argue that over vast periods of time the processes that generate microevolutionary changes and speciation can yield major transformations (like whales from a raccoon-like creature or birds from dinosaurs).
Creationists and some Intelligent Design proponents disagree. I include myself among those who are skeptical of macroevolution. I argue that organisms have the capacity to adapt to changing environments and other selective pressures, but they cannot evolve in dramatic ways. In other words, a Creator must be responsible for life’s origin and history and that biological and biochemical systems must be intelligently designed.
There is another type of biological evolution that doesn’t fit into any of these three categories: namely, microbial evolution. These types of transformations involve changes in viruses, bacteria, archaea, and single-celled eukaryotes. Such changes include the acquisition of antibiotic resistance in bacteria, the ability of viruses to hop from one host to another ( e.g., SARS and HIV), and the emergence of drug-resistant strains of the malaria parasites.
Microbial evolution also includes horizontal gene transfer between microbes, which accounts for the evolution of pathogenic bacteria from non-pathogenic strains like E. coli O157:H7. I don’t find microbial evolution particularly controversial. A preponderance of evidence exists for it. In a sense, it is not surprising that—given their extremely large population sizes and capacity to take up large pieces of DNA from their surroundings and incorporate it into their genomes—single-celled microbes and viruses can evolve .
The evolution of P. putida’s caffeine-consuming capability represents another example of microbial evolution. In that respect, it is nothing remarkable.
It is also not remarkable given that N-demethylase activity has been reported in a number of bacteria. More than likely it already existed in P. putida, and through microevolutionary changes, the N-demethylases adapted to remove methyl groups from caffeine.
It is also worth noting that caffeine is a natural product produced by plants as an insect repellent. As with humans, caffeine stimulates insects’ nervous systems. But unlike in humans, caffeine stimulation leads to insects’ deaths. (Watch the below video for a description of how caffeine stimulates the nervous system.)
In other words, caffeine was present well before humans began “polluting” the environment with caffeine. It could even be that P. putida has been waking up to it well before humans discovered the early morning benefits of a cup of joe.
For a detailed discussion of this discovery listen to the May 26 edition of Science News Flash.