Lipoxygenases (EC. 1.13.11.12) are a non-heme iron enzymes consisting of one polypeptide chain folded into two domains, the N-terminal domain and the catalytic moiety β-barrel domain. They catalyze the dioxygenation of 1Z,4Z-pentadiene moieties of polyunsaturated fatty acids obtaining hydroperoxy fatty acids. For years, the presence of lipoxygenases was considered a eukaryotic feature, present in mammals, plants, small marine invertebrates, and fungi, but now, some lipoxygenase sequences have been detected on prokaryotic organisms, changing the idea that lipoxygenases are exclusively a eukaryotic affair. Lipoxygenases are involved in different types of reactions on eukaryote organisms where the biological role and the structural characteristics of these enzymes are well studied. However, these aspects of the bacterial lipoxygenases have not yet been elucidated and are unknown. This revision discusses biochemical aspects, biological applications, and some characteristics of these enzymes and tries to determine the existence of a subfamily of bacterial lipoxygenases in the context of the phylogeny of prokaryotic lipoxygenases, supporting the results of phylogenetic analyzes with the comparison and discussion of structural information of the first prokaryotic lipoxygenase crystallized and other eukaryotic lipoxygenases structures.
Genetic diversity and genetic relationships among 42 Pseudomonas stutzeri strains belonging to several genomovars and isolated from different sources were investigated in an examination of 20 metabolic enzymes by multilocus enzyme electrophoresis analysis. Forty-two distinct allele profiles were identified, indicating that all multilocus genotypes were represented by a single strain. All 20 loci were exceptionally polymorphic, with an average of 15.9 alleles per locus. To the best of our knowledge, this P. stutzeri sample exhibited the highest mean genetic diversity (H ؍ 0.876) found to date in all bacterial species studied by multilocus enzyme electrophoresis. A high frequency of occurrence of null alleles was identified. The index of association (I A ) for the P. stutzeri strains analyzed was 1.10. The I A values were always significantly different from zero for all subgroups studied, including clinical and environmental isolates and strains classified as genomovar 1. These results suggest that the population structure of P. stutzeri is strongly clonal, indicating that there is no significant level of assortative recombination that might destroy linkage disequilibrium.Pseudomonas stutzeri was first isolated by Burri and Stutzer (6) as Bacillus denitrificans II and named P. stutzeri by Van Niel and Allen (47). It has an unusual colony shape and consistency when directly isolated, being described as wrinkly, dry, and tenaciously coherent. P. stutzeri, a gram-negative rod-shaped bacterium that is mobile by means of a single polar flagellum, is a nonpigmented denitrifier that liberates nitrogen gas from nitrate, is amylase positive and gelatinase negative, and is able to grow on maltose and starch (4, 43). P. stutzeri has a wide environmental distribution but is found mainly in soil and water. Many strains have been isolated from clinical specimens (20). The members of the species share physiological characteristics that make P. stutzeri of special interest in ecological studies. This species shows high metabolic versatility (35) including the degradation of environmental pollutants (1, 37) and high-molecular-weight polyethylene glycols (30). P. stutzeri serves as a model for the study of the biochemistry and genetics of denitrification and natural transformation processes.Pseudomonas species are grouped on the basis of rRNA-DNA hybridization studies (31). P. stutzeri is a nonfluorescent denitrifying species of the genus Pseudomonas included in the rRNA group I. P. stutzeri forms a homogeneous group within the genus Pseudomonas, with phenotypic traits that permit description to the species level. However, P. stutzeri is a heterogeneous species with respect to many phenotypic characteristics and DNA composition. Several studies have demonstrated that P. stutzeri consists of a complex collection of strains that might be distributed in more than one species (2, 25, 31, 35). DNA-DNA hybridization studies (35,43) have shown the existence of at least eight genomic groups, called genomovars.Confirmation of this syste...
A polyphasic study was performed to determine the taxonomic position of two Aeromonas strains, 665N and 868E T , isolated from bivalve molluscs, that could not be identified at the species level in a previous numerical taxonomy study. The DNA G+C content of these isolates was 62.3 and 62.6 mol%, respectively. Sequence analysis of the 16S rRNA gene showed that the two new strains were closely related to members of the genus Aeromonas. Fluorescence amplified fragment length polymorphism fingerprinting revealed that strains 665N and 868E T clustered together with a similarity of 78 % but did not cluster with any of the Aeromonas genomospecies. DNA-DNA hybridization experiments revealed a high level of relatedness between the two new isolates (76 %) but low levels of relatedness between these and phylogenetically most closely related Aeromonas genomospecies (30-44 %). Useful tests for the phenotypic differentiation of strains 665N and 868E T from other mesophilic Aeromonas species included those for gas from glucose, lysine decarboxylase, Voges-Proskauer reaction, acid from L-arabinose, hydrolysis of aesculin and utilization of L-lactate. On the basis of genotypic and phenotypic evidence, strains 665N and 868E T are considered to represent a novel species of the genus Aeromonas, for which the name Aeromonas bivalvium sp. nov. is proposed. The type strain is 868E T (=CECT 7113 T =LMG 23376 T ).Members of the genus Aeromonas, belonging to the class Gammaproteobacteria, are Gram-negative, non-spore-forming bacilli or coccobacilli, and are facultatively anaerobic, chemo-organotrophic, oxidase-and catalase-positive, resistant to the vibriostatic agent O/129 (2,4-diamino-6,7-diisopropylpteridine), generally motile by means of a single polar flagellum and are able to reduce nitrate to nitrite. Aeromonads are primarily aquatic, widespread in environmental habitats, frequently isolated from foods and often associated with aquatic animals, and some species are primary or opportunistic pathogens in invertebrates and vertebrates including humans (Martin-Carnahan & Joseph, 2005).At the time of writing, 17 Aeromonas species and 20 DNA-DNA hybridization groups (HGs) have been described: Aeromonas hydrophila (HG1), A. bestiarum (HG2), A. salmonicida (HG3), A. caviae (HG4), A. media (HG5), A. eucrenophila (HG6), A. sobria (HG7), A. veronii bv. Sobria (HG8/10), A. jandaei (HG9), A. veronii bv. Veronii (HG10/ 8), Aeromonas sp. HG11, A. schubertii (HG12), Aeromonas sp. group 501 (HG13), A. trota (HG14), A. allosaccharophila (HG15), A. encheleia (HG16), A. popoffii (HG17), A. culicicola (HG18), A. simiae (HG19) and A. molluscorum (HG20) (Pidiyar et al., 2002; Harf-Monteil et al., 2004; Miñana-Galbis et al., 2004;Martin-Carnahan & Joseph, 2005). In addition to the continuous description of novel species, the complexity of Aeromonas taxonomy results from the isolation of motile and non-motile, mesophilic and psychrophilic, pigmented and non-pigmented strains within several Aeromonas species (Altwegg et al., 1990;Martin-Carnahan & Joseph,...
An analysis of the universal target (UT) sequence from the cpn60 gene was performed in order to evaluate its usefulness in phylogenetic and taxonomic studies and as an identification marker for the genus Aeromonas. Sequences of 555 bp, corresponding to the UT region, were obtained from a collection of 35 strains representing all of the species and subspecies of Aeromonas. From the analysis of these sequences, a range of divergence of 0-23.3 % was obtained, with a mean of 11.2±0.9 %. Comparative analyses between cpn60 and gyrB, rpoD and 16S rRNA gene sequences were carried out from the same Aeromonas strain collection. Sequences of the cpn60 UT region showed similar discriminatory power to gyrB and rpoD sequences. The phylogenetic relationships inferred from cpn60 sequence distances indicated an excellent correlation with the present affiliation of Aeromonas species with the exception of Aeromonas hydrophila subsp. dhakensis, which appeared in a separate phylogenetic line, and Aeromonas sharmana, which exhibited a very loose phylogenetic relationship to the genus Aeromonas. Sequencing of cpn60 from 33 additional Aeromonas strains also allowed us to establish intra-and interspecific threshold values. Intraspecific divergence rates were ¡3.5 %, while interspecific divergence rates fell between 3.7 and 16.9 %, excluding A. sharmana. In this study, cpn60 UT sequencing was shown to be a universal, useful, simple and rapid method for the identification and phylogenetic affiliation of Aeromonas strains.
Five Aeromonas strains (848T T , 93M, 431E, 849T and 869N), which were isolated from bivalve molluscs and were recognized previously by numerical taxonomy as members of an unknown Aeromonas taxon, were subjected to a polyphasic taxonomic study. DNA-DNA hybridization experiments showed that DNA of strain 848TT was <70 % similar (27-45 %) to that of the type/reference strains of the current Aeromonas hybridization groups (HGs), but 93 % similar to that of strain 93M. The DNA G+C content of the five strains ranged from 59?0 to 59?4 mol%. 16S rRNA gene sequence analysis confirmed that the strains belonged to the genus Aeromonas and showed high similarity to Aeromonas encheleia. Amplified fragment length polymorphism fingerprinting clustered the novel strains in a homogeneous group with low genotypic relatedness to other Aeromonas species. Useful phenotypic features for differentiating the five isolates from other Aeromonas species include their negative reactions in tests for indole production, lysine decarboxylase, gas from glucose and starch hydrolysis.From the results of this study, the name Aeromonas molluscorum sp. nov. is proposed for these strains, with the type strain 848T T (=CECT 5864 T =LMG 22214 T ).
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