Jakob Herschend:
Unravelling the mechanisms of bacterial interactions in model communities

Date: 15-02-2017    Supervisor: Mette Burmølle & Søren J. Sørensen

Microbial communities, such as microbial biofilms, are dynamic structural communities. The architecture and function of these communities is shaped by the interaction with the surrounding environment and by the interactions between community members. In most natural and manmade environments, microbial communities host a plethora of different species. The community is a heterogeneous structure with pH, oxygen and nutrient gradients creating suitable niches for a diversity of life. Manuscript IV shows how different environments create unique niches for different microbial communities, and that bacteria in different niches have different potential for interacting.

Understanding the development of microbial communities is indispensable as microbial communities, such as biofilms, are highly associated with chronic infections, colonization of catheters and implants. Biofilms have also been associated with crop promotion and pathogenicity and contamination of food products with spoilage and potential pathogenic strains. Additionally, the use of microbial communities for bioremediation, wastewater treatment and bioenergy could provide environmentally friendly and lowcost alternatives to current technologies.

Unravelling the mechanisms influencing community development is not simple, as the community is often the result of a range of mechanism all acting simultane ously. By studying simpler model communities it is possible to restrict the diversity of acting mechanisms, and study them individually. Using this approach, we show how a range of mechanisms can influence community development of mixed species. In Manuscript I we present how metabolic interplay can cause pH stabilization of the environment, which in turn enhances community growth.

Manuscript II identifies cross feeding on amino acids as a potential driver for community development, while emphasizing that competition for limited resources also affect community development. Manuscript V shows how facilitation of surface attachment can promote community formation and how sharing of public goods can promote community protection. Finally Manuscript III shows how individual mechanisms can affect each other over time, and select for unique phenotypes in the community.