Siv Andersson lab

The research in Siv Andersson´s group aims at understanding how intracellular bacteria and organelles evolve. Knowledge about host-adapted bacterial genomes is important for our understanding of the interplay between bacteria and higher organisms. Which gene functions are required for life within and outside already existing cells? How should these genes be organized and embedded inside the cell to provide beneficial functions for the host? A long-term goal is to have such a deep knowledge of these processes that we can design bacterial genomes with new, host-beneficial functions.

Popular science presentation

The eukaryotic cell has a complex structure consisting of intracellular membranes and a nuclear membrane that surrounds the genetic material while prokaryotic cells (bacteria and archaea) have neither intracellular membranes nor a nuclear membrane. Most eukaryotic cells also have energy-producing organelles, mitochondria, which are thought to have originated from bacteria that lived in a symbiotic relationship with an ancestor of the eukaryotic cell.

We have studied bacteria that live in symbioses with insects or that are transmitted between vertebrates (including humans) with the aid of insects. We have also studied the origin and evolution of mitochondria. Currently, we study lactic acid bacteria that live in symbioses with honeybees and which we believe protect the honeybee food sources from infection with bacteria that kill the honeybee larvae.

The overall goal of our studies is to understand how cellular complexity evolves and learn more about the forces that drive the evolution of different types of cells. It was previously considered impossible for a simple bacterial cell to develop a more complex intracellular structure. But surprisingly, bacterial cells with intracellular membrane structures have been found. Some of these have an extraordinary internal structure consisting of a large energy-producing organelle while others are able to eat other bacterial cells, which was previously considered impossible. The discovery of these bacterial cells challenges our previous knowledge about the differences between prokaryotic and eukaryotic cells.

 

Research projects

Evolution of host-adapted bacteria

The research in Siv Andersson´s group aims at understanding how intracellular bacteria and organelles evolve. A long-term goal is to design novel intracellular bacterial genomes with beneficial functions using synthetic biology. To achieve this goal we need a basic understanding of the interplay between bacteria and hosts, and why organelles and mutualistic bacteria need a distinct genome. Below are a few examples of ongoing projects.

Why do some organisms need bacteria?

Many host-adapted bacterial populations produce nutrients that the host cannot get from its diet. Others produce antimicrobials to defend the host against pathogens and other invading microbes. The secreted compounds benefit the whole bacterial population and/or the host, but are costly to make for the individual bacterial cell. Hence there is a risk that cheaters arise that benefit from the secreted compounds without contributing to their production. In this project, we use bacteria adapted to mammals and insects as model systems to study how the production of the public good is organized and how cheaters are avoided in the bacterial population.

Why do some cells need internal compartments?

Eukaryotic cells contain several membrane-bound compartments, such as for example mitochondria. Bacterial cells do not normally contain internal membranes. But there are exceptions. To understand why and how complex cellular architectures arise we study bacterial cells that contain a network of internal membranes and connected vesicles. In this project, we use comparative, functional and ecological genomics to learn more about cellular compartmentalization.

Why do some compartments need a genome?

We have recently published results that support the hypothesis that mitochondria need a genome to avoid that the encoded proteins are transported to the Endoplasmatic Reticulum. Transporting proteins between compartments inside the cell requires a multitude of signals to ensure that each protein reaches its final destination. In this project, we use bioinformatics and experimental methods to learn more about why mitochondria need a distinct genome.

This work is supported by the Knut and Alice Wallenberg Foundation (KAW).

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