Introduction
The natural environment provides microorganisms with different conditions compared to well-established laboratory cultivation systems. In microbial habitats, carbon is typically present at very low concentrations and as a mixture of several substrates .For example, the content of dissolved organic carbon in ground-water can range from 75 to 180 M Additionally, under extreme conditions, such as the deep biosphere, microorganisms are exposed to a very low supply of organic carbon but bacteria are still able to survive under such oligotrophic conditions .Therefore, the question arises of how microorganisms with slow bacterial growth utilize carbon under environmental conditions of low substrate concentrations. One strategy would be to increase the amounts of transporters of limiting substrates . Additionally,to be able to react quickly to changing conditions, microorganisms may express various catabolic proteins that are not involved in the degradation of available substrates . Various substrate transport systems not present in growth medium have been found to be expressed in carbon-limited chemostats, not only by the model microorganism Escherichia coli but also by the environmentally relevant toluene-degrading bacterium Aromatoleum aromaticum EbN1