ABSTRACT
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In the previous chapters, we have learned that the traditional culture-dependent
methods to study soil microorganisms often quite poorly represent the
microbial diversity extant in soil. Thus, advanced culture-independent
methods to unravel soil microbial diversity, on the basis of molecular
markers that are present in the DNA, have already demonstrated the existence
in soil of an enormous diversity of microorganisms. Many of these organisms
have no known cultured representatives to date. The use of DNA:DNA
hybridization as well as of the RNApresent in the small subunit of the ribosome
as a universal molecular marker (see Chapter 2) have suggested that there
are commonly thousands of microbial species per Gram of soil [1]. Depending
on the soil type, as little as 1% of the microbial numbers present has been
amenable to study through cultivation, leaving up to 99% of the total
community unaccessed [2]. A possible remedy to the lack of information on
the array of functional genes present in this “silent majority” of soil micro-
organisms would be to access and unlock the collective genomes of the
microbial community as a whole, i.e. address the so-called soil community
metagenome. The soil metagenome is thought to contain vastly more genetic
information than that present in the culturable subset of organisms, and
therefore provides an enormous and novel gene pool for ecological
and evolutionary studies, as well as for biotechnological exploration and
exploitation.
