ABSTRACT
References ................................................................................................... 207
In the previous chapters, we have seen that soil generally offers quite varied and
fluctuating conditions to its inhabitants. Due to the heterogeneous nature of
soil, the occurrence of spatial and temporal gradients of many compounds of
quite different nature, be they in the gaseous or liquid phases, is the rule rather
than the exception. Hence, the microbes that have successfully adapted to soil
must have developed specific “skills” to cope with all of its vagaries. A key
aspect that determines the fitness of microorganisms in soil is obviously the
capacity of the microbial cells to interact appropriately with their immediate
abiotic and/or biotic environments. In addition to the physiological adaptation
strategies of microbial cells (discussed in Chapter 4), soil microorganisms
must have evolved strategies that allow them to sense, and interact with, their
immediate surroundings, in order to “fine-tune” their cellular metabolism to
locally-determined conditions. The basic conjecture here is this environmental
sensing is based on the perception of a range of chemical compounds in soil,
and, in this respect, it is irrelevant whether the environmental stimuli are
abiotic or biotic in origin. In fact, most environmental sensing is based on
the perception of gradients in the concentrations of specific compounds,
whether these are of abiotic (e.g. specific substrates that may serve as nutrients,
volatiles, protons) or biotic (e.g. signaling compounds) origin. Here, we will
discuss the interactions of microorganisms in their microhabitats in soil, in
particular in relation to other microorganisms that are present. The focus will
be on the molecular mechanisms that are used in the perception of the neigh-
boring organisms, and the strategies employed to communicate with them,
i.e. by sending out and/or receiving signals of different kinds.
