Azomonas

Abstract: Chromosomal DNA from group I Pseudomonas species, Azotobacter vinelandii, Azomonas macrocytogens, Xanthomonas campestris, Serpens flexibilis, and three enteric bacteria was screened for sequences homologous to four Pseudomonas aeruginosa alginate (alg) genes (algA, pmm, algD, and algR1) All the group I Pseudomonas species tested (including alginate producers and nonproducers) contained sequences homologous to all the P aeruginosa alg genes used as probes, with the exception of P stutzeri, which lacked algD Azotobacter vinelandii also contained sequences homologous to all the alg gene probes tested, while Azomonas macrocytogenes DNA showed homology to all but algD X campestris contained sequences homologous to pmm and algR1 but not to algA or algD The helical bacterium S flexibilis showed homology to the algR1 gene, suggesting that an environmentally responsive regulatory gene similar to algR1 exists in S flexibilis Escherichia coli showed homology to the algD and algR1 genes, while Salmonella typhimurium and Klebsiella pneumoniae failed to show homology with any of the P aeruginosa alg genes Since all the organisms tested are superfamily B procaryotes, these results suggest that within superfamily B, the alginate genes are distributed throughout the Pseudomonas group I-Azotobacter-Azomonas lineage, while only some alg genes have been retained in the Pseudomonas group V (Xanthomonas) and enteric lineages

Abstract: The relationships of the genus Azotobacter, Azomonas macrocytogenes and the genus Pseudomonas were revealed by comparative analysis of partial 16S rRNA and atpD, carA and recA gene sequences and as concatenated nucleotide and peptide sequences. Sequence similarities of Azotobacter species and Azomonas macrocytogenes indicated that these may be considered to be synonyms at the molecular level. In addition, these species show an intimate relationship with species of Pseudomonas, especially P. aeruginosa (the type species of the genus). In terms of the current circumscription of the genus Pseudomonas, Azotobacter and Azomonas macrocytogenes should be considered for amalgamation with Pseudomonas. Azotobacter and Azomonas comprise nitrogen-fixing strains with large pleomorphic cells that form cysts, and peritrichous flagella insertion; characteristics not included in the current circumscription of Pseudomonas. The data are discussed in the light of whether lateral transfer of genes could be involved in the determination of significant morphological characteristics, thus leading to a problem that may be encountered more frequently: how to resolve classification of taxa based on conserved sequences with those based on their phenotype. More fundamentally, the results illuminate problems that will increasingly be encountered: by what criteria can taxa be delineated, what are the most appropriate methods for classification, and what are the proper assumptions of bacterial classification?

Abstract: Six species of free-living nitrogen fixing bacteria, Azomonas agilis, Azospirillum brasilense, Azospirillum lipoferum, Azotobacter chroococcum, Azotobacter vinelandii, and Beijerinckia mobilis, were surveyed for their ability to grow and fix N2 using aromatic compounds as sole carbon and energy source. All six species grew and expressed nitrogenase activity on benzoate, catechol, 4-hydroxybenzoate, naphthalene, protocatechuate, and 4-toluate. In many cases, growth rates on one or more aromatic compounds were comparable to or greater than those on the non-aromatic substrates routinely used for cultivation of the organisms. Specific activity of nitrogenase in extracts of aromatic-grown cells often exceeded that in cells grown on non-aromatic substrates. All six species growing on substrates typically converted to catechol expressed inducible catechol 1,2-dioxygenase and/or catechol 2,3-dioxygenase. When grown on substrates typically converted to protocatechuate, inducible protocatechuate 3,4-dioxygenase and/or protocatechuate 4,5-dioxygenase was expressed. A. chroococcum expressed only ortho cleavage dioxygenases during growth on naphthalene and 4-toluate and only meta cleavage dioxygenases on the other aromatics. B. mobilis expressed only ortho cleavage dioxygenases. The other four species examined expressed both ortho and meta cleavage enzymes.

Abstract: Publisher Summary The genus Pseudomonas is usually divided into five rRNA-homology groups, one of which comprises the so-called “fluorescents.” When grown under iron deficiency, they excrete yellow-greenishly fluorescing substances into the culture medium. Originally these were called bacterial fluoresc(e)ins, but today they are referred to as pseudobactins or more commonly as pyoverdins. The genera Azotobacter and Azomonas produce the same type of siderophores. Over the years, it was suggested that they are flavins, pyrrol derivatives, or pteridines, and it was not before 1981 that the structure of the first member of this class was established by chemical degradation, nuclear magnetic resonance (NMR), and X-ray studies. So far, 17 complete or fairly complete pyoverdin structures have been elucidated. Usually, several pyoverdins are excreted together, which possess the same peptide chain, but differ in the nature of the dicarboxylic acid bound to the chromophore. The peptide chain of pyoverdins has a two-fold function. It provides two of the ligands for Fe3+ in the correct position for complexation and it is responsible for the recognition of the complex at the cell surface.