In situ Reactions and Microbial Communication

The discovery that bacteria are able to communicate with each other changed our general perception of many single, simple organisms inhabiting our world. Instead of language, bacteria use signaling molecules, which are released into the environment. A wide range of communication mechanisms have been described so far within bacteria, such as production of bacteriocins, pheromones, and signaling molecules (e.g. acyl-L-homoserine lactones). As well as releasing the signaling molecules, bacteria are also able to measure the number (concentration) of the molecules within a population. Today we use the term 'Quorum Sensing' (QS) to describe the phenomenon whereby the accumulation of signaling molecules enable a single cell to sense the number of bacteria (cell density) (Konaklieva and Plotkin 2006).

Quorum sensing enables bacteria to coordinate their behavior. Environmental conditions often change rapidly, and bacteria need to respond quickly to survive. These responses include adaptation to available nutrients, defense against other microorganisms - which may compete for the same nutrients - and avoiding toxic compounds that are potentially dangerous for the bacteria. Today, several QS systems are intensively studied in various organisms such as marine bacteria and some pathogenic bacteria. Quorum sensing is very important for pathogenic bacteria during infection of a host (e.g. humans, other animals or plants) to co-ordinate their virulence. Although little is still known on the role of QS in food ecosystems, it has recently been shown that this mechanism regulates the in situ phenotypic expression and population behavior of food spoilage bacteria (Gram, et al. 2002).

In response to the above needs, genetic methods based upon molecular biology have been developed recently to study microbial populations without cultivation and for the identification and sub-typing of cultivable bacteria. Today, a number of molecular techniques can provide outstanding tools for the detection, identification, and characterization of bacteria involved in fermented food processes (Giraffa 2004; Rantsiou and Cocolin 2006). In deciding to offer a routine service based upon one or more of these techniques - type-ability, reproducibility, discriminating power, ease of use, reliability, automation and cost - should all be taken into consideration.

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