Fusaric acid is produced by pathogenic fungi of the genus Fusarium, and is toxic to plants and rhizobacteria. Many fluorescent pseudomonads can prevent wilt diseases caused by these fungi. This study ...was undertaken to evaluate the effect of fusaric acid on P. protegens Pf-5 and elucidate the mechanisms that enable the bacterium to survive in the presence of the mycotoxin. The results confirm that fusaric acid negatively affects growth and motility of P. protegens. Moreover, a notable increase in secretion of the siderophore pyoverdine was observed when P. protegens was grown in the presence of fusaric acid. Concomitantly, levels of enzymes involved in the biosynthesis of pyoverdine and enantio-pyochelin, the second siderophore encoded by P. protegens, increased markedly. Moreover, while similar levels of resistance to fusaric acid were observed for P. protegens mutants unable to synthesize either pyoverdine or enanto-pyochelin and the wild type strain, a double mutant unable to synthesize both kinds of siderophores showed a dramatically reduced resistance to this compound. This reduced resistance was not observed when this mutant was grown under conditions of iron excess. Spectrophotometric titrations revealed that fusaric acid binds not only Fe2+ and Fe3+, but also Zn2+, Mn2+ and Cu2+, with high affinity. Our results demonstrate that iron sequestration accounts at least in part for the deleterious effect of the mycotoxin on P. protegens.
Pseudomonas protegens
synthesizes two major iron-chelating metabolites (siderophores): pyoverdine (Pvd) and enantio-pyochelin (E-Pch). Although iron sequestration and uptake seem to be the main ...biological role of these siderophores, other functions including metal homeostasis and antibiotic activity have been proposed. The aim of this study was to evaluate the contribution of Pvd and E-Pch to the survival of
P. protegens
in soil using wild type and isogenic mutant strains unable to produce Pvd, E-Pch or both siderophores. Survival of these strains in sterile soil microcosms, in soil microcosms containing the native microflora and in sterile soil microcosms containing fusaric acid (a mycotoxin able to chelate iron and other metals), was compared by determination of colony forming units (CFU) per gram dry soil over time. In sterile soil, cell densities of Pvd-producing strains were significantly higher than that of non-producers after 21 days of permanence in the microcosms. In non-sterile soil, viability of all strains declined faster than in sterile soil and Pvd producers showed higher CFU × (g dry weight soil)
−1
values than non-producers. The presence of fusaric acid negatively affected viability of strains unable to produce Pvd, while had no effect on the viability of strains able to produce Pvd. Altogether, these results show that the ability to produce Pvd increases survival of
P. protegens
in soil, while the ability to synthesize E-Pch does not, indicating that under the conditions which prevail in soil, iron scavenging via Pvd is more beneficial than via E-Pch.
Pseudomonas extremaustralis produces mainly polyhydroxybutyrate (PHB), a short chain length polyhydroxyalkanoate (sclPHA) infrequently found in Pseudomonas species. Previous studies with this strain ...demonstrated that PHB genes are located in a genomic island. In this work, the analysis of the genome of P. extremaustralis revealed the presence of another PHB cluster phbFPX, with high similarity to genes belonging to Burkholderiales, and also a cluster, phaC1ZC2D, coding for medium chain length PHA production (mclPHA). All mclPHA genes showed high similarity to genes from Pseudomonas species and interestingly, this cluster also showed a natural insertion of seven ORFs not related to mclPHA metabolism. Besides PHB, P. extremaustralis is able to produce mclPHA although in minor amounts. Complementation analysis demonstrated that both mclPHA synthases, PhaC1 and PhaC2, were functional. RT-qPCR analysis showed different levels of expression for the PHB synthase, phbC, and the mclPHA synthases. The expression level of phbC, was significantly higher than the obtained for phaC1 and phaC2, in late exponential phase cultures. The analysis of the proteins bound to the PHA granules showed the presence of PhbC and PhaC1, whilst PhaC2 could not be detected. In addition, two phasin like proteins (PhbP and PhaI) associated with the production of scl and mcl PHAs, respectively, were detected. The results of this work show the high efficiency of a foreign gene (phbC) in comparison with the mclPHA core genome genes (phaC1 and phaC2) indicating that the ability of P. extremaustralis to produce high amounts of PHB could be explained by the different expression levels of the genes encoding the scl and mcl PHA synthases.
Fusaric acid (FA) is an important virulence factor produced by several
species. These fungi are responsible for wilt and rot diseases in a diverse range of crops. FA is toxic for animals, humans and ...soil-borne microorganisms. This mycotoxin reduces the survival and competition abilities of bacterial species able to antagonize
spp., due to its negative effects on viability and the production of antibiotics effective against these fungi. FA biodegradation is not a common characteristic among bacteria, and the determinants of FA catabolism have not been identified so far in any microorganism. In this study, we identified genes, enzymes, and metabolic pathways involved in the degradation of FA in the soil bacterium
T16. Our results provide insights into the catabolism of a pyridine-derivative involved in plant pathogenesis by a rhizosphere bacterium.
Display omitted
Fusaric acid (FA) is a fungal metabolite produced by several Fusarium species responsible for wilts and root rot diseases of a great variety of plants. Bacillus spp. and Pseudomonas ...spp. have been considered as promising biocontrol agents against phytopathogenic Fusarium spp., however it has been demonstrated that FA negatively affects growth and production of some antibiotics in these bacteria. Thus, the capability to degrade FA would be a desirable characteristic in bacterial biocontrol agents of Fusarium wilt. Taking this into account, bacteria isolated from the rhizosphere of barley were screened for their ability to use FA as sole carbon and energy source. One strain that fulfilled this requirement was identified according to sequence analysis of 16S rRNA, gyrB and recA genes as Burkholderia ambifaria. This strain, designated T16, was able to grow with FA as sole carbon, nitrogen and energy source and also showed the ability to detoxify FA in barley seedlings. This bacterium also exhibited higher growth rate, higher cell densities, longer survival, higher levels of indole-3-acetic acid (IAA) production, enhanced biofilm formation and increased resistance to different antibiotics when cultivated in Luria Bertani medium at pH 5.3 compared to pH 7.3. Furthermore, B. ambifaria T16 showed distinctive plant growth-promoting features, such as siderophore production, phosphate-solubilization, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, in vitro antagonism against Fusarium spp. and improvement of grain yield when inoculated to barley plants grown under greenhouse conditions. This strain might serve as a new source of metabolites or genes for the development of novel FA-detoxification systems.
Bioprocesses conducted under conditions with restricted O2 supply are increasingly exploited for the synthesis of reduced biochemicals using different biocatalysts. The model facultative aerobe ...Escherichia coli, the microbial cell factory par excellence, has elaborate sensing and signal transduction mechanisms that respond to the availability of electron acceptors and alternative carbon sources in the surrounding environment. In particular, the ArcBA and CreBC two-component signal transduction systems are largely responsible for the metabolic regulation of redox control in response to O2 availability and carbon source utilization, respectively. Significant advances in the understanding of the biochemical, genetic, and physiological duties of these regulatory systems have been achieved in recent years. This situation allowed to rationally-design novel engineering approaches that ensure optimal carbon and energy flows within central metabolism, as well as to manipulate redox homeostasis, in order to optimize the production of industrially-relevant metabolites. In particular, metabolic flux analysis provided new clues to understand the metabolic regulation mediated by the ArcBA and CreBC systems. Genetic manipulation of these regulators proved useful for designing microbial cells factories tailored for the synthesis of reduced biochemicals with added value, such as poly(3-hydroxybutyrate), under conditions with restricted O2 supply. This network-wide strategy is in contrast with traditional metabolic engineering approaches, that entail direct modification of the pathway(s) at stake, and opens new avenues for the targeted modulation of central catabolic pathways at the transcriptional level.
Pseudomonas sp. 14-3, a strain that accumulates large quantities of polyhydroxybutyrate (PHB) when grown on octanoate, was isolated from Antarctic environments. This isolate was characterized on the ...basis of phenotypic features and partial sequencing of its 16S ribosomal RNA gene. Pseudomonas sp. 14-3 showed increased tolerance to both thermal and oxidative stress compared with three other Pseudomonas species. Stress tolerance of Pseudomonas sp. 14-3 was analyzed in polyhydroxyalkanoate accumulating and non-accumulating conditions, and increased levels of stress resistance were observed when PHB was produced. Pseudomonas sp. 14-3 was isolated from Antarctic regions, a habitat normally exposed to extreme conditions. An association between high PHB accumulation and high stress resistance in bacteria adapted to extreme environments is suggested.
Abstract
arcA codes for a central regulator in Escherichia coli that responds to redox conditions of growth. Mutations in this gene, originally named dye, confer sensitivity to toluidine blue and ...other redox dyes. However, the molecular basis for the dye-sensitive phenotype has not been elucidated. In this work, we show that toluidine blue redirects electrons to O2 and causes an increase in the generation of reactive O2 species (ROS). We also demonstrate that synthesis of poly (3-hydroxybutyrate) suppresses the Dye phenotype in E. coli recombinants, as the capacity to synthesize the polymer reduces sensitivity to toluidine blue, O2 consumption and ROS production levels.
Pseudomonas oleovorans GPo1 and its polyhydroxyalkanoic acid (PHA) depolymerization-minus mutant, GPo500 phaZ, residing in natural water microcosms, were utilized to asses the effect of PHA ...availability on survival and resistance to stress agents. The wild-type strain showed increased survival compared to the PHA depolymerase-minus strain. The appearance of a round cellular shape, characteristic of bacteria growing under starvation conditions, was delayed in the wild type in comparison to the mutant strain. Percent survival at the end of ethanol and heat challenges was always higher in GPo1 than in GPo500. Based on these results and on early experiments (H. Hippe, Arch. Mikrobiol. 56:248-277, 1967) that suggested an association of PHA utilization with respiration and oxidative phosphorylation, we investigated the association between PHA degradation and nucleotide accumulation. ATP and guanosine tetraphosphate (ppGpp) production was analyzed under culture conditions leading to PHA depolymerization. A rise in the ATP and ppGpp levels appeared concomitant with PHA degradation, while this phenomenon was not observed in the mutant strain unable to degrade the polymer. Complementation of the phaZ mutation restored the wild-type phenotype.
PDF
