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MOLECULAR SYSTEMATICS
One of the main goals of taxonomy is to provide a hierarchical framework for identifying and
classifying diverse biological species. Modern classification systems have an additional goal,
beyond imposing order upon biological diversity: phylogenetic systems seek to infer
genealogical relationships, which reflect the evolutionary pathways followed during life
history. Close phylogenetic relationship implies not only phenotypic or genotypic similarity,
but common evolutionary history as well.
Until recently, microbial systematists have relied predominantly on morphological, nutritional
and biochemical criteria for taxonomic classification. Phenetic analyses have provided an
empirical framework for classifying and identifying physiologically diverse microbial types.
Their utility for the identification and characterization of microorganisms is unquestionable.
Taxonomic classifications based on phenetic analyses do not necessarily imply evolutionary
relationship, however. In addition, most phenetic analyses demand laboratory cultivation, a
requirement that may severely limit the range of naturally occurring microbes which can be
characterized. Furthermore, identifying common, homologous phenetic traits of evolutionarily
diverse taxa can be problematic. Current developments in molecular systematics are now
resolving some of these difficulties, and are providing insight into the evolutionary
relationships of the most diverse lineages known today (Fox et al., 1980; Woese, 1987; Iwabe
et aZ., 1989; Pace et aZ., 1986b; Woese et aZ., 1990).
Molecular approaches to systematics rely on sequence comparisons of informational
macromolecules (RNA, DNA, or protein). Comparative sequence analyses can provide a
quantitative and relatively unbiased assessment of evolutionary relatedness (Felsenstein, 1982;
Felsenstein, 1988; Olsen, 1988; Swofford and Olsen, 1990). In theory, gene sequences
provide more evolutionary information than is available from study of the phenotypic
properties of the expressed gene (Zuckerkandl and Pauling, 1965). Analyses of highly
conserved macromolecular sequences may provide insight about evolutionary relationships
over very wide phylogenetic ranges, supplementing phenotypic or morphological studies where
few characters are shared between distantly related taxa (Field et aZ., 1988). Since methods
for obtaining and analyzing nucleic acid and protein sequences are continually improving
MOLECULAR SYSTEMATICS
One of the main goals of taxonomy is to provide a hierarchical framework for identifying and
classifying diverse biological species. Modern classification systems have an additional goal,
beyond imposing order upon biological diversity: phylogenetic systems seek to infer
genealogical relationships, which reflect the evolutionary pathways followed during life
history. Close phylogenetic relationship implies not only phenotypic or genotypic similarity,
but common evolutionary history as well.
Until recently, microbial systematists have relied predominantly on morphological, nutritional
and biochemical criteria for taxonomic classification. Phenetic analyses have provided an
empirical framework for classifying and identifying physiologically diverse microbial types.
Their utility for the identification and characterization of microorganisms is unquestionable.
Taxonomic classifications based on phenetic analyses do not necessarily imply evolutionary
relationship, however. In addition, most phenetic analyses demand laboratory cultivation, a
requirement that may severely limit the range of naturally occurring microbes which can be
characterized. Furthermore, identifying common, homologous phenetic traits of evolutionarily
diverse taxa can be problematic. Current developments in molecular systematics are now
resolving some of these difficulties, and are providing insight into the evolutionary
relationships of the most diverse lineages known today (Fox et al., 1980; Woese, 1987; Iwabe
et aZ., 1989; Pace et aZ., 1986b; Woese et aZ., 1990).
Molecular approaches to systematics rely on sequence comparisons of informational
macromolecules (RNA, DNA, or protein). Comparative sequence analyses can provide a
quantitative and relatively unbiased assessment of evolutionary relatedness (Felsenstein, 1982;
Felsenstein, 1988; Olsen, 1988; Swofford and Olsen, 1990). In theory, gene sequences
provide more evolutionary information than is available from study of the phenotypic
properties of the expressed gene (Zuckerkandl and Pauling, 1965). Analyses of highly
conserved macromolecular sequences may provide insight about evolutionary relationships
over very wide phylogenetic ranges, supplementing phenotypic or morphological studies where
few characters are shared between distantly related taxa (Field et aZ., 1988). Since methods
for obtaining and analyzing nucleic acid and protein sequences are continually improving