Bacillus subtilis at near-zero specific growth rates: adaptations to extreme caloric restriction

Bacillus subtilis is an important soil-dwelling bacteria species that is used for the production of e.g. vitamins, enzymes and medicines. In both the natural and industrial environment the availability of energy sources can be limited. In contrary to a situation of complete ‘nutrient depletion’, many microbial communities live under conditions of ‘hunger’, because the concentration of available energy sources usually is not completely zero. Consequently, in these circumstances microorganisms grow with an extremely low growth rate, especially in comparison with laboratory cultivation. To better understand microbial life, the study of adaption to such conditions is necessary.
In this thesis the study is described of B. subtilis at near-zero growth rates. These extremely low growth rates are achieved by extreme caloric restriction in a so-called retentostat system. Despite these harsh conditions nearly all bacteria remained viable. Calculations showed that almost all the available energy was used for cellular processes that were related to maintenance of the cell, and not for growth. Analysis of gene expression levels revealed that cells reprogram their gene expression to increase their chance of survival. This response to ‘hunger’ has similarities with the response to complete nutrient depletion, but differs in some areas.
Additionally, this thesis describes i.e. the study and upgrade of the Green Fluorescent Protein ‘toolbox’ for B. subtilis, Lactococcus lactis and Streptococcus pneumoniae. Green Fluorescent Protein (GFP) is an important tool in molecular biology to visualize gene expression and protein localisation.