The pattern of evolutionary change in bacteria

The Leeuwenhoek Lecture, 1992 Bacterial evolution and the nitrogen-fixing plant

Biological nitrogen fixation is fundamental to the economy of the biosphere, yet it is restricted to a few dozen bacterial species. Why have plants not acquired it during evolution? No serious physiological or genetic obstacles seem to exist. Has a relatively late emergence, among genomically flexible prokaryotes, effectively precluded appropriate seletion pressure?

Metabolic pathways in Paracoccus denitrificans and closely related bacteria in relation to the phylogeny of prokaryotes

Denitrification and methylotrophy in Paracoccus denitrificans are discussed. The properties of the enzymes of denitrification: the nitrate-nitrite antiporter, nitrate reductase, nitrite reductase, nitric oxide reductase and nitrous oxide reductase are described. The genes for none of these proteins have yet been cloned and sequenced from P. denitrificans. A number of sequences are available for enzymes from Escherichia coli, Pseudomonas stutzeri and Pseudomonas aeruginosa. It is concluded that pathway specific c-type cytochromes are involved in denitrification. At least 40 genes are involved in denitrification. In methanol oxidation at least 20 genes are involved. In this case too pathway specific c-type cytochromes are involved. The sequence homology between the quinoproteins methanol dehydrogenase, alcoholde-hydrogenase and glucose dehydrogenase is discussed. This superfamily of proteins is believed to be derived from a common ancestor. The moxFJGI operon determines the structural components of methanol dehydrogenase and the associated c-type cytochrome. Upstream of this operon 3 regulatory proteins were found. The moxY protein shows the general features of a sensor protein and the moxX protein those of a regulatory protein. Thus a two component regulatory system is involved in both denitrification and methylotrophy. The phylogeny of prokaryotes based on 16S rRNA sequence is discussed. It is remarkable that the 16S rRNA of Thiosphaera pantotropha is identical to that of P. denitrificans. Still these bacteria show a number of differences. T. pantotropha is able to denitrify under aerobic circumstances and it shows heterotrophic nitrification. Nitrification and heterotrophic nitrification are found in species belonging to the beta-and gamma-subdivisions of purple non-sulfur bacteria. Thus the occurrence of heterotrophic nitrification in T. pantotropha, which belongs to the alpha-subdivision of purple non-sulfur bacteria is a remarkable property. Furthermore T. pantotropha contains two nitrate reductases of which the periplasmic one is supposed to be involved in aerobic denitrification. The nitrite reductase is of the Cu-type and not of the cytochrome cd1 type as in P. denitrificans. Also the cytochrome b of the Qbc complex of T. pantotropha is highly similar to its counterpart in P. denitrificans. It is hypothesized that the differences between these two organisms which both contain large megaplasmids is due to a combination of loss of genetic information and plasmid-coded properties. The distribution of a number of complex metabolic systems in eubacteria and in a number of species belonging to the alpha-group of purple non sulphur bacteria is reviewed.(ABSTRACT TRUNCATED AT 400 WORDS)

Evolution of alkaline phosphatase in marine species of Vibrio

The evolution of alkaline phosphatase was studied in marine species of Vibrio. Two antisera prepared against purified alkaline phosphatases from Vibrio splendidus and Vibrio harveyi were used to estimate the amino acid sequence divergence of this enzyme in 51 strains belonging to nine species. The methods used were the quantitative microcomplement fixation technique and the Ouchterlony double-diffusion procedure. There was a high degree of congruence between the measurement of the amino acid sequence divergence of alkaline phosphatase and the percentage of deoxyribonucleic acid homology of the different organisms relative to both reference strains (correlation coefficient of -0.89) as well as between the amino acid sequence divergence of alkaline phosphatase and superoxide dismutase (correlation coefficient of 0.92) relative to V. splendidus. These findings supported the view that the evolution of marine species of Vibrio is primarily vertical and that horizontal evolution (involving genetic exchange between species), if significant, is restricted to a minor fraction of the bacterial genome.

Arginine gene cluster of Serratia marcescens

Biochemical and genetic studies on the arginine-requiring auxotrophs derived from a Serratia marcescens strain were carried out. The arg mutants were classified into seven biochemical groups based on their growth response to five precursors of arginine biosynthesis and enzyme deficiency. Reciprocal transduction tests among these arg mutants divided them into three linkage groups, and the fine mapping in each of the groups by two- or three-point crosses revealed the following arrangement of loci. (1) arg44-thy11-lys1; (2) met1-glt2-argE-(arg19-arg51)-arg120-argG-argH; (3) arg33-pyr4. Five of the seven biochemically distinct arg mutants belonged to the second linkage group, and they constituted an agr-gene cluster. A characteristic feature of the arg-gene cluster of S. marcescens is that it involves argG, which was previously reported only in the Proteus group of Enterobacteriaceae.