Composition of bacterial biofilms on insect-associated Laboulbeniomycetes fungi


Bacterial biofilms are a complex system consisting of a consortium of bacteria lodged in a three-dimensional extracellular matrix and have been described as a “city for microbes”. This matrix protects the bacteria from environmental, chemical, and mechanical stresses, and organisms embedded in a biofilm possess a high rate of survival and persistence compared to planktonic bacteria. Biofilms are ubiquitous and can be found in almost any non-sterile environment, but the species composition can be specific to a particular surface.

Fungi of the class Laboulbeniomycetes (Ascomycota) are obligate associates of arthropod hosts. Most taxa in this class are microfungi that form three-dimensional fruiting bodies—named thalli—instead of mycelia. These microfungi, with about 2400 described species in 147 genera, form the most diverse fungal assemblage associated with representatives of the Phylum Arthropoda, predominantly insects. Laboulbeniomycetes are an understudied group, with most research focusing on taxonomy. Very little is known about their associations with other organisms, including bacteria.


It was recently discovered that the thalli of some Laboulbeniomycetes are covered with a biofilm consisting of rod-shaped bacteria. These include thalli of taxa in the genera Herpomyces associated with cockroaches (Blattodea), Hesperomyces, associated with ladybirds (Coccinellidae), and Laboulbenia, associated with a large number of arthropod groups. There are only descriptions of the observation of these biofilms (by scanning electron microscopy); the species composition of the biofilms is unknown, as is anything regarding interactions between the fungi and their biofilms.


The aim of this project is to gain a better understanding of the species composition of bacterial biofilms on thallus-producing Laboulbeniomycetes. As biofilms do not persist in ethanol (often used to preserve arthropods), experiments will need to be done with living hosts. Host specimens will be collected through fieldwork as well as by ordering insects online (from pet stores, e.g., cockroaches). The hosts will then be screened for fungal thalli, and the presence of biofilms on thalli will be confirmed by scanning electron microscopy (SEM). A literature study will be done on how previous studies have dealt with the identification of species composition of biofilms. DNA will be extracted from the biofilms and the species composition will be determined by sequencing the 16S rRNA gene region. Statistical analyses may be performed to compare biofilm communities among different host species. The student will become familiar with a variety of research methods, including entomological fieldwork, light and electron microscopy, DNA extraction, PCR amplification, and sequencing.


Haelewaters D, Blackwell M, Pfister DH. 2021. Laboulbeniomycetes: Intimate fungal associates of arthropods. Annual Review of Entomology 66: 257-276. [pdf]

Hogan DA, Wargo MJ, Beck N. 2007. Bacterial biofilms on fungal surfaces. pp. 235–245. In: Kjelleberg S, Givskov M (eds.) The Biofilm Mode of Life: Mechanisms and Adaptations. Horizon Scientific Press, Norfolk. [pdf]

Lubbers M, Lamers GEM, De Kesel A, Nedvěd O, Schilthuizen M, Haelewaters D. 2022. Bacterial biofilms on thalli of Laboulbeniales: a community uncovered. Sydowia 74: 335-342. [pdf]