Klasson lab

Collaborators

• Kostas Bourtzis, University of Western Greece, Greece
• Siv Andersson, Uppsala University, Sweden
• Wolfgang Miller, Medical University of Vienna, Austria
• Yuval Gottlieb-Dror, The Hebrew University of Jerusalem, Israel
• Olle Terenius, Swedish University of Agricultural Sciences, Sweden
• Julie Dunning-Hotopp, IGS, University of Maryland School of Medicine, USA

Popular science presentation

Microorganisms that cannot be grown in pure cultures make up a large part of the biomass and genetic diversity on earth, but because of the difficulties in studying them much of their unique properties and their genetic diversity has remained unknown. Among these are symbiotic microorganisms associated with eukaryotes, many of which have a large impact on both disease and health of their hosts and where the interactions have lead to intriguing and important evolutionary novelties and adaptations for the organisms involved.

Arthropods are one of the most species rich of all eukaryotic phylum’s and part of the explanation for their success comes from the ability to exploit new niches, by for example adapting to unusual and nutrient low dietary regimes, such as vertebrate blood and plant sap. In order to do so, many insect species have developed tight symbiotic relationships with microorganisms such as bacteria and fungi. Some of these symbionts are therefore necessary for the host to survive, but many are not strictly required for host survival and the reason for their presence is not well understood.

Most of our work is focused on the symbiotic bacterium Wolbachia that lives inside the cells of many different arthropod species and often affects their reproduction. Wolbachia can for example change males into females, selectively kill male embryos and induce asexual reproduction so that only female offspring are produced. Why? Because Wolbachia is transmitted from mothers directly to the offspring via the egg, and hence Wolbachia needs to infect females in order to spread. In order to prevent uninfected offspring from being produced, Wolbachia can also sterilize infected males if they try to mate with an uninfected female. This sterility effect is referred to as cytoplasmic incompatibility (CI), and is the focus of much of our research as we one of our goals is to find out which Wolbachia genes are responsible for causing it.

To reach this goal and to learn more about the natural diversity of symbiotic bacteria, we sequence the genomes of many different Wolbachia strains as well as other bacteria that live in symbiosis with insects and arthropods and compare them to each other. Using this method we can learn more about how they have adapted to a symbiotic lifestyle and hopefully also how they affect their hosts

Research projects

Bacteria that cannot be grown in pure cultures make up a large part of the biomass and genetic diversity on earth and play an important role in many system, for example in the many symbiotic associations with eukaryotes.

My research focuses on symbiotic bacteria that cannot live outside of a eukaryotic host cell. My main interests are in finding out how these tight associations affect genome evolution, determining genetic factors involved in host interactions and exploring the diversity of symbiotic bacteria in nature. I mostly use genome sequencing and comparative genomics to try to answer these questions.

Wolbachia

Wolbachia is a bacterial genus consisting of only one recognized species, Wolbachia pipientis, with several divergent supergroups. All members are intracellular endosymbionts of invertebrates, and it has been estimated that as many as 15-70% of all insect species on earth are infected by Wolbachia. The infection is transferred maternally from mother to offspring and Wolbachia has evolved at least four different ways to manipulate the host reproduction in order to increase the number of infected females in a population. The most commonly expressed phenotype is cytoplasmic incompatibility (CI) that results in embryonic death in crosses between uninfected females and infected males. The infected females hereby achieve a reproductive advantage over the uninfected females in a population and CI can thus result in spread of the Wolbachia infection throughout a population that was previously uninfected. Additionally, bidirectional CI can occur if the male and female are infected with different Wolbachia strains and has been implicated as a cause of host speciation and is also being exploited as a method for biocontrol of insect disease vectors. As of yet, the underlying molecular mechanism of CI and the genetic factors of Wolbachia that are involved are unknown.

I am currently involved in several genome sequencing projects of Wolbachia strains infecting different Drosophila species with the aim of determining the evolutionary mechanisms involved inshaping their genomes and determining the genetic factors in phenotypic expression. I am also working on the effect of Wolbachia on the host gene expression by using RNAseq.

Diversity of Insect Endosymbionts

Arthropoda is the most species rich of all eukaryotic phylum’s and part of the explanation for their success comes from the ability to exploit new niches, by adapting to unusual and nutrient low dietary regimes, such as vertebrate blood and plant sap. In order to do so, many insect species have developed very tight symbiotic relationships with microorganisms such as bacteria and fungi that provide them with the nutrients that are lacking in their diet. Apart from these nutritional interactions, many insects carry additional symbiotic bacteria of which we currently know quite little, but that in some insects have been shown to provide adaptation for specific conditions.

I have a workflow where we go from collecting single insects to genome sequencing of their bacterial symbionts, using simple lab methods and whole genome amplification. This method allows us to go out and sample the endosymbiotic diversity from many different insect species and from rare or dissected material. The overall goal is to study the diversity and genome evolution of symbionts, and if possible, get an understanding for what they are doing.

For this purpose, I am looking for collaborators who have either interesting symbionts they want to sequence, or who would like to collect insects for screening and sequencing.