Welcome to The Penczykowski Lab!

Q1:  What is the BIG PICTURE of your research?
A1:  Parasites are infamous for causing great harm – and sometimes even death – to their hosts. Understanding risks and consequences of infection is therefore critically important for public health, wildlife management, and agriculture. One aim of our research is to better understand how ecological context (including physical and chemical features of the environment as well as the community of organisms living there) affects the risk of infection and consequences of disease for hosts. This is a particularly important area of research because human-driven changes in climate, land use, and biodiversity are altering the ecological context in which host–parasite interactions occur.

Effects of parasites can also extend beyond host populations. Changes in the density or traits of infected hosts may affect other members of the ecological community, and alter flows of energy and nutrients through food webs. Thus, another aim of our research is to uncover how parasites influence the communities and ecosystems in which they occur.

Q2:  What is your approach to research?
A2:  We use a combination of observational (field), experimental (field + lab), and theoretical (mathematical modelling) approaches.

Q3:  What host–parasite systems do you work on, and where are your field sites?
A3:  Several of us in the lab are currently focusing on the interaction between Plantago species and their powdery mildew pathogens along a large latitudinal gradient in the central USA, as well as locally in the St. Louis area. Visit the Research page for details.


Leaf of Plantago lanceolata infected with powdery mildew.

Q4:  In A1 above, you use the word “parasite“, and then in A3 you use the word “pathogen.” Do those words mean the same thing?
A4:  Excellent question! Short answer: in our lab, we typically use those words interchangeably to mean the same thing.

Longer answer: in our lab, we use the word “parasite” in a broad sense, to mean an organism that lives in or on an organism of another species (its host) and benefits by deriving nutrients at the other’s expense. We include both macroparasites (helminths and parasitic arthropods) and microparasites (protozoa, fungi, bacteria, and even viruses) in that definition (click here for a blog post on the biology and epidemiology of macroparasites vs. microparasites; see also Lafferty & Kuris 2002 for a framework that classifies multiple types of parasitism and predation; and note that Carl Zimmer uses the broad definition of parasites in the book Parasite Rex). The word “pathogen” is usually defined as a microorganism that causes disease (i.e., a microparasite).

Some examples to illustrate how these terms are used (and why this gets confusing):

  • Powdery mildews are fungi (Phylum: Ascomycota, Class: Leotiomycetes, Order: Erysiphales) that are obligate parasites of plants (they only grow by extracting nutrients from living plant tissue). They are microscopic and multiply on their plant host, so they meet the definition of microparasites. Because powdery mildews are microorganisms that cause disease in their hosts, they are called pathogens.
  • The fungus Metschnikowia bicuspidata (Phylum: Ascomycota, Class: Saccharomycetes, Order: Saccharomycetales) is a microparasite of Daphnia (small freshwater crustaceans). Simply out of habit and/or semantic preference, researchers in the DaphniaMetschnikowia system typically just use the word parasite to describe this fungus, even though it could also be called a pathogen
  • Nematode (helminth) parasites in the intestines of a buffalo are macroparasites, and would typically only be called parasites, not pathogens (though macroparasites can cause “pathology”, and macroparasites can also affect the success of co-infecting microparasites, i.e., pathogens!).

Distinguishing between macroparasites and microparasites (and/or between other aspects of organisms’ biology, including life history strategies) can be really important! There is also a long legacy of taxonomic divides in infectious disease research, including different terminology used by researchers in plant pathology, veterinary & human medicine, and ecology & evolutionary biology. Thus, we think it’s essential to read and think broadly and inclusively across different host and parasite systems, but also to clearly define how we use terms like parasite and pathogen.

Click here or here for Twitter conversations about the definitions of the words parasite and pathogen!

Q5: Does everyone in the Penczykowski Lab focus on Plantago and powdery mildew?
A5: Nope! Graduate students in our group are all studying some aspect of plant-microbe interactions, but not all are focusing on the Plantago-mildew system.