Substrate mobilisation

The type of carrier that is involved in substrate mobilisation largely depends on the chemical and physical state of the substrate. It is generally agreed that most microorganisms rely on the presence of water-dissolved substrate molecules. This is because microbial cell walls exclude the uptake of molecules larger than about 600 g moL1 [3]. Furthermore, the activity and growth of most... 

The acquisition and assimilation of bioelements are the most fundamental processes in an organism s struggle for life. It is therefore obvious that in complex natural systems the competition between thousands of species for limited quantities of a small number of elements is a major evolutionary factor. However, the individual contributions of the physical and biochemical aspects of nutrition to the fitness of an organism are widely unknown. The frequent observation that biodegradation processes, e.g. in soil remediation, are limited by physical obstacles to substrate acquisition, rather than by biochemical incapacities, points at the importance of substrate mobilisation strategies. 

The subject of this chapter will be the most important mechanisms by which microorganisms mobilise substrates. We will thereby focus on the mobilisation of nonliving food molecules, and will not deal with living food organisms. Besides organic compounds, we will also treat the biological mechanisms to acquire iron as the least bioavailable inorganic nutrient in many environments. 

MOBILISATION OF HYDROPHOBIC ORGANIC SUBSTRATES USING BIOSURFACTANTS... 

Microbes were frequently found to synthesise surface-active molecules in order to mobilise hydrophobic organic substrates. These biosurfactants, which are either excreted by the producing organisms or remain bound to their cell surfaces, are composed of a hydrophilic part making them soluble in water and a lipophilic part making them accumulate at interfaces. With respect to their physical effects, one can distinguish two types of biosurfactants firstly, molecules that drastically reduce the surface and interfacial tensions of gas-liquid, liquid-liquid and liquid-solid systems, and, secondly, compounds that stabilise emulsions of nonaqueous phase liquids in water, often also referred to as bioemulsifiers. The former molecules are typically low-molar-mass... 

Mobilisation of Liquid, Solid or Sorbed Substrates by Solubilisation in Biosurfactant Micelles... 

The type Ilia /3-lactamase [141] can be mobilised on the R factor RPl [142] into strains of Ps. aeruginosa. The crypticity of the type Ilia /3-lactamase can then be determined against a number of substrates. That an efficient penetration barrier exists in these organisms between the substrate located outside the cell and the /8-lactamase located in the periplasmic space [141] can be seen from the following crypticity values for Ps. aeruginosa (1822 RPl) penicillin G, 80 ampicillin, 60 carbenicil-lin, 60 cephaloridine, 50. 

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