Snap Shots of Bacterial Adaptation

Adaptation to changing environmental conditions is necessary for the survival of all living organisms. The research described in this PhD thesis was aimed at understanding adaptive responses mounted by two different bacterial species to challenges that they have to face regularly in their environment. A major part of this PhD thesis focuses on adaptive processes of the soil bacterium Bacillus subtilis when exposed to an environment with low salinity, a condition that occurs upon rain and flooding. This revealed the importance of the so-called Tat pathway for protein transport across the bacterial membrane to prevent oxidative membrane damage. Additionally, it was discovered that a system for iron uptake, which requires the Tat pathway for its assembly, is regulated by a small RNA molecule named S313. More importantly, the studies on the S313 molecule highlighted the global impact that a small regulatory RNA molecule can have on different cellular processes, ranging from iron uptake to the bacterial resistance to antibiotics. Another part of the studies described in this PhD thesis addresses adaptive responses shown by methicillin resistant Staphylococcus aureus (MRSA) upon exposure to the clinically relevant antibiotic ciprofloxacin. This revealed that exposure of clinical MRSA isolates to subinhibitory concentrations of ciprofloxacin may lead both to mutations that cause resistance to antibiotics, and to activation of bacterial viruses (phages) that may transfer the resulting resistance genes into other bacteria. Altogether, this PhD research has put a spotlight on the importance of investigating adaptive responses of bacteria to environmental changes and insults.