Bacterial Growth Physiology in the Human Gut
The human gut is populated by trillions of bacterial cells. Over the last decade, meta-genomic sequencing studies have established the tremendous importance of the human gut microbiota for human physiology and health. However, the underlying physiological and physical factors shaping the intestine's microbial ecosystem are still largely unexplored. I aim to understand the specific role of such factors, like fluid flow and bacterial growth, on the composition and size of the microbiota. To obtain a quantitive and comprehensive understanding, I employ a combined approach of experimental measurements and theoretical modelling. Experiments are performed in controlled in-vitro setups with conditions mimicking the intestine. In such setups, the growth of different gut bacterial strains is investigated and parameters for further theoretical studies can be inferred. One particularly interesting question which can thereby be tackled is related to the bacterial density in the gut: This density is particularly high at the beginning of the large intestine even though net flow is large enough to drag bacteria down the intestine quicker than they can proliferate. One factor to prevent this could be peristaltic mixing by active contractions of the intestinal wall. To study the interplay between bacterial growth, flow, and peristaltic mixing by contractions of the large intestine we employ a new mechano-fluidic channel that allowed us to grow and monitor E. coli cells while emulating peristaltic mixing by controlled wall-deformations.
Physiological Conditions Triggering Biofilm Formation
Biofilm formation is a crucial part of the bacterial life-cycle and has been confirmed to exist in many bacterial species. While thereby induced increased stress resistance and other increases in viability are thought to lead to substantial fitness advantage, the expression of biofilm genes comes with a heavy cost: Exopolysacherides and amyloids, crucial componentes of an intact biofilm, take metabolic ressources which otherwise could be invested into faster proliferation. Crucial for an optimized fitness is thus an optimized regulation of biofilm formation where biofilms are expressed only when needed. To gain understanding into this regulation process, I study biofilm formation in Escherichia coli. I quantify biofilm formation and the activity of important biofilm genes for different physiological conditions spanning a range of different ‘stress-levels’.
Emergence and Stability of Cooperative Behavior
Cooperative behavior where individuals are providing benefits to others, related to a cost to themselves, is ubiquitous in nature. This observation is tackling from an evolutionary point of few since non-cooperating free-riders or cheaters can spare the costs while still benefiting from the benefit. A lot of research has been performed to understand the general principles which overcome this dilemma of cooperation and lead to evolutionary stable cooperative behavior - often within the frameworks of group- and kin-selection. However, the underlying pathways leading to cooperation are often unclear. In my work I consider ecological conditions which are often faced by microbial populations. I study the role of growth-dynamics and population bottlenecks and how these can lead to not only the stability of cooperative behavior but how these can also allow the onset of cooperation from a single cooperative mutant.