<Emphasis Type="Italic">Azospirillum brasilense</Emphasis> siderophores with antifungal activity against <Emphasis Type="Italic">Colletotrichum acutatum</Emphasis>

Anthracnose, caused by the fungus Colletotrichum acutatum is one of the most important diseases in strawberry crop. Due to environmental pollution and resistance produced by chemical fungicides, nowadays biological control is considered a good alternative for crop protection. Among biocontrol agents, there are plant growth-promoting bacteria, such as members of the genus Azospirillum. In this work, we demonstrate that under iron limiting conditions different strains of A. brasilense produce siderophores, exhibiting different yields and rates of production according to their origin. Chemical assays revealed that strains REC2 and REC3 secrete catechol type siderophores, including salicylic acid, detected by thin layer chromatography coupled with fluorescence spectroscopy and gas chromatography–mass spectrometry analysis. Siderophores produced by them showed in vitro antifungal activity against C. acutatum M11. Furthermore, this latter coincided with results obtained from phytopathological tests performed in planta, where a reduction of anthracnose symptoms on strawberry plants previously inoculated with A. brasilense was observed. These outcomes suggest that some strains of A. brasilense could act as biocontrol agent preventing anthracnose disease in strawberry.     

Interaction of <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> and <Emphasis Type="Italic">Glomus intrarradix</Emphasis> in Sugar Cane Roots

Fifteen-day-old variety NA 56-79 sugar cane seedlings were inoculated with Azospirillum brasilense and Glomus intrarradix. This article aims at examining changes in sugar cane root seedlings inoculated with Glomus intrarradix and Azospirillum brasilense, the increase in microbial biomass and the acetylene reduction process as well. The internal root colonization was studied 20 days after inoculation using scanning and a transmission electron microscope. Both microorganisms entered the sugar cane root through the emergent lateral roots. The microorganisms were capable of coexisting both intra and intercellularly, producing changes in the cell wall, thus allowing colonization and interaction between the organisms. These changes increased the number of microorganisms inside the root as well as acetylene nitrogen reduction. Sugar cane plant biomass increased with joint-inoculation. The number of endophytic microorganisms and nitrogen fixing activity increased when they were colonized by Azospirillum and Glomus together.     

Study of immunochemical heterogeneity of <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> lipopolysaccharides

A comparative immunochemical analysis of lipopolysaccharides (LPS) in Azospirillum brasilense model strains Sp7 and Sp245 and in mutants with altered somatic antigens has been performed. According to the results of a complex of various immunochemical methods, including studies with polyclonal antibodies against the LPS these bacteria, their LPS consist of an assembly of macromolecules with different antigenic characteristics. Two types of O-specific polysaccharides (O-PS) are present in the LPS of every strain of A. brasilense under study. The major difference between the two O-PS is the antigenic heterogeneity of one of them. This heterogeneous O-PS has been shown to possess at least two O-factors (antigenic determinants) different in their structure. Meanwhile, according to all the tests performed, the other O-PS in every strain is immunochemically homogeneous and identical to one of the determinants revealed in the more diversified O-PS. The LPS heterogeneity among the given strains may be due to the pattern of O-specific polysaccharide synthesis, one of the O-PS being an intermediate in the synthesis of the other.     

Phenol Oxidase Activity of <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> Sp245 Mutants with Modified Motility and <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> Sp7 Phase Variants with Different Plasmid Composition

Herein, we reveal the alteration in phenol oxidase enzymes complex production from Azospirillum brasilense Sp245 omegon mutants with polar and lateral flagella dysfunction and from A. brasilense Sp7 phase variants with different plasmid composition. The enzymatic activities for various laccases, tyrosinases, Mnperoxidases, and lignin peroxidases as well as the isomorphic composition of intracellular laccases and tyrosinases were estimated for the studied variants and the parent strains. It was noted that various genetic events correlating with phenotypic heterogeneity in A. brasilense populations affect their phenol oxidase activity level.     

Growth and phosphorus removal by <Emphasis Type="Italic">Synechococcus elongatus</Emphasis> co-immobilized in alginate beads with <Emphasis Type="Italic">Azospirillum brasilense</Emphasis>

This study examined the co-immobilization of the cyanobacterium Synechococcus elongatus with the plant growth-promoting bacterium Azospirillum brasilense in alginate beads and its potential application for the removal of phosphorus from aquaculture wastewater. Co-immobilization of both microorganisms significantly increased the cell density of S. elongatus (2852.5?×?10⁴ cells mL^?1) compared with that of immobilization of cyanobacteria alone (1325.2?×?10⁴ cells mL^?1). Chlorophyll a content was similar in co-immobilized (11.1?±?3.5 pg cell^?1) and immobilized S. elongatus (14.5?±?4.9 pg cell^?1). Azospirillum brasilense showed continuous growth until day 2, after which its cell concentration declined until the end of the assay. Co-immobilized S. elongatus removed more phosphorus (44.8 %) than immobilized cyanobacteria cells alone (32.0 %). In conclusion, phosphate removal was greater with free cells of S. elongatus but overlapped with the values that were obtained with the treatment of co-immobilization of cells. Our results demonstrate that A. brasilense enhances the growth of S. elongatus and improves its removal of phosphorus when they are co-immobilized in alginate beads compared with only immobilization of cyanobacteria cells alone.     

Detection of a sheath on <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> polar flagellum

The presence of a polysaccharide sheath on the surface of the polar flagellum of Azospirillum brasilense was revelted by immunoelectron microscopy and immunodiffusion analysis with strain-specific antibodies to lipopolysaccharides (LPS). The antigenic identity of A. brasilense Sp245 sheath material and one of the two O-specific polysaccharides of its somatic LPS was demonstrated. The screening effect of the sheath in respect to flagellin was determined by agglutination tests and by the inhibition of azospirilla motility in liquid and semisolid agarized media caused by strain-specific antibodies to LPS; no pronounced effect of genus-specific antibodies to flagellin was observed.     

The Electron Transfer Flavoprotein <Emphasis Type="Italic">fixABCX</Emphasis> Gene Products from <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> Show a NifA-Dependent Promoter Regulation

The complete nucleotide sequence of the A. brasilense fixA, fixB, fixC, and fixX genes is reported here. Sequence similarities between the protein sequences deduced from fixABCX genes and many electron transfer flavoproteins (ETFs) have been noted. Comparison of the amino acid sequences of both subunits of ETF with the A. brasilense fixA and fixB gene products exhibits an identity of 30%. The amino acid sequence of the other two genes, fixC and fixX, revealed similarity with the membrane-bound electron transfer flavoprotein ubiquinone oxidoreductase (ETF-QO). Using site-directed mutagenesis, mutations were introduced in the fixA promoter element of the A. brasilense fixABCX operon and chimeric pfixA-lacZ reporter gene fusions were constructed. The activation of the fixA promoter of A. brasilense is dependent upon the presence of the NifA protein being approximately 7 times less active than the A. brasilense nifH promoter. These results indicate that NifA from Klebsiella pneumoniae activates the fix promoter of A. brasilense and provide further evidence in support of the regulatory model of NifA activation in A. brasilense. Although no specific function has been assigned to the fixABCX gene products they are apparently required for symbiotic nitrogen fixation. An electron-transferring capacity in the nitrogen fixation pathway has been suggested for the fix gene products based on sequence homologies to the ETFs and ETF-QO proteins and by the absence of orthologous electron transfer proteins NifJ and NifF in A. brasilense.     

Characterization of <Emphasis Type="Italic">chsA,</Emphasis> a new gene controlling the chemotactic response in <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> Sp7

We report, here, the characterization of a mutant strain of Azospirillum brasilense Sp7 impaired in surface motility and chemotactic response. Presence of flagella in the mutant strain was confirmed by western blot analysis, using antisera raised against the polar and lateral flagellins, and by electron microscopy. Genetic complementation and nucleotide sequencing led to the identification of a new gene, named chsA. The deduced translation product, ChsA protein, contained a PAS sensory domain and an EAL domain. As ChsA displayed characteristic signaling protein architecture, it is thought that this protein is a component of the signaling pathway controlling chemotaxis in Azospirillum.     

The plant growth promoting bacterium <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> is vertically transmitted in <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> (common bean)

Bactrocera dorsalis (Diptera: Tephritidae) is a serious menace to agricultural production worldwide. In order to prevent further damage, it is of paramount important that cost-effective strategies should be developed for their management. Gut bacteria has established diverse relationships with their insect hosts, which could be exploited in pest management programs to improve on control efficiency. In this study, gut bacteria isolates identified by culture dependent technique were incorporated into larval diets in an attempt to understand the roles they play in the development and survival of oriental fruit fly. From our results, the isolated bacteria belonged to four different phyla including the Firmicutes, Proteobacteria, Bacteroidetes and Actinobacteria. The response of the fly to different gut isolates varied greatly. Diets enriched with Enterococcus phoeniculicola had lower larval developmental duration, higher pupal weight, and an increased percentage survival. On the other hand, diets supplemented with Lactobacillus lactis had negative effects on B. dorsalis development. This study provides clues on how symbiotic bacteria could be exploited in mass rearing for an efficient implementation of the Sterile Insect Technique (SIT) in pest management programs.     

Enhancement of thiamine release during synthetic mutualism between <Emphasis Type="Italic">Chlorella sorokiniana</Emphasis> and <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> growing under stress conditions

Thiamine release during synthetic mutualism between Chlorella sorokiniana co-immobilized in alginate beads with the microalgae growth-promoting bacterium Azospirillum brasilense was measured under stress conditions of pH, light intensity, and nitrogen starvation in short-term experiments. Thiamine release in the co-immobilized treatment was significantly higher at acidic pH compared to thiamine released by either microorganism alone. Under slightly alkaline pH, C. sorokiniana released the highest amount of thiamine. At stressful pH 6, the co-immobilized treatment released a higher quantity of thiamine than the sum of thiamine released by either microorganisms when immobilized separately. Release of thiamine by C. sorokiniana alone or co-immobilized was light intensity dependent; with higher the light intensity, more thiamine was released. Extreme light intensity negatively affected growth of the microalgae and release of thiamine. Nitrogen starvation during the first 24 h of culturing negatively affected release of thiamine by both microorganisms, where C. sorokiniana was more severely affected. Partial or continuous nitrogen starvation had similar negative effects on C. sorokiniana, but co-immobilization improved thiamine release. These results indicate that thiamine is released during synthetic mutualism between C. sorokiniana and A. brasilense, and this happens specifically during the alleviation of pH stress in the microalgae.     

<Emphasis Type="Italic">Ty</Emphasis>1<Emphasis Type="Italic">/copia</Emphasis>- and <Emphasis Type="Italic">Ty</Emphasis>3<Emphasis Type="Italic">/gypsy</Emphasis>-like DNA sequences in <Emphasis Type="Italic">Helianthus </Emphasis>species

Two repeated DNA sequences isolated from a partial genomic DNA library of Helianthus annuus, p HaS13 and p HaS211, were shown to represent portions of the int gene of a Ty3 /gypsy retroelement and of the RNase-Hgene of a Ty1 /copia retroelement, respectively. Southern blotting patterns obtained by hybridizing the two probes to BglII- or DraI-digested genomic DNA from different Helianthus species showed p HaS13 and p HaS211 were parts of dispersed repeats at least 8 and 7 kb in length, respectively, that were conserved in all species studied. Comparable hybridization patterns were obtained in all species with p HaS13. By contrast, the patterns obtained by hybridizing p HaS211 clearly differentiated annual species from perennials. The frequencies of p HaS13- and p HaS211-related sequences in different species were 4.3x10(4)-1.3x10(5) copies and 9.9x10(2)-8.1x10(3) copies per picogram of DNA, respectively. The frequency of p HaS13-related sequences varied widely within annual species, while no significant difference was observed among perennial species. Conversely, the frequency variation of p HaS211-related sequences was as large within annual species as within perennials. Sequences of both families were found to be dispersed along the length of all chromosomes in all species studied. However, Ty3 /gypsy-like sequences were localized preferentially at the centromeric regions, whereas Ty1/ copia-like sequences were less represented or absent around the centromeres and plentiful at the chromosome ends. These findings suggest that the two sequence families played a role in Helianthusgenome evolution and species divergence, evolved independently in the same genomic backgrounds and in annual or perennial species, and acquired different possible functions in the host genomes.     

Glutamine synthetase of the rhizobacterium <Emphasis Type="Italic">Azospirillum brasilense</Emphasis>: Specific features of catalysis and regulation

Data on glutamine synthetase (GS) of Azospirillum brasilense, a plant growth-promoting rhizobacterium, have been reviewed. GS of the azospirillum is a type α₁₂ dodecamer with oligomer and monomer having molecular weights of 630 and 52 kDa, respectively. Glutamine synthesis is performed in 12 active sites of the enzyme, depending, first and foremost, on the extent of GS adenylylation and, secondarily, on the exact bivalent metal cations involved in the catalysis. Structural characteristics and catalytic properties of the completely unadenylylated and moderately adenylated forms of GS of A. brasilense have been studied. The enzyme appears as a highly structured protein, with α helices and β structures accounting for about 70% of the polypeptide chain length. Binding of Mg²⁺, Co²⁺, and Mn²⁺ to the protein globule changes both the secondary structure and the catalytic properties of the enzyme. The use of nuclear gamma resonance emission spectroscopy demonstrates that the active center of GS of the azospirillum has two metal-binding sites differing in their affinity for Co²⁺. The activity and biosynthesis of GS of the azospirillum is regulated by wheat lectin (a molecular signal of the host plant), in addition to other means of regulation described for GSs.     

<Emphasis Type="Italic">Galleria</Emphasis><Emphasis Type="Italic">mellonella</Emphasis> are Resistant to <Emphasis Type="Italic">Pneumocystis</Emphasis><Emphasis Type="Italic">murina</Emphasis> Infection

Studying Pneumocystis has proven to be a challenge from the perspective of propagating a significant amount of the pathogen in a facile manner. The study of several fungal pathogens has been aided by the use of invertebrate model hosts. Our efforts to infect the invertebrate larvae Galleria mellonella with Pneumocystis proved futile since P. murina neither caused disease nor was able to proliferate within G. mellonella. It did, however, show that the pathogen could be rapidly cleared from the host.     

Immunoelectron microscopy investigation of the cell surface of <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> strains

The genus-specific surface protein antigens of Azospirillum brasilense strains were visualized immunochemically. The procedure used for cell sample preparation was optimized to ensure that the surface protein structures were detected on cells in situ. Gold and gold-silver nanoparticles were conjugated to antibodies raised against the flagellin of A. brasilense type strain Sp7, against the lipopolysaccharide of A. brasilense Sp245, and against the genus-specific protein determinants of A. brasilense Sp7. Electron microscopic analysis using nanoparticle-labeled antibodies revealed antigenic determinants of the polar flagellum on the A. brasilense Sp245 cell surface, which in these bacteria are normally screened from the surroundings by a lipopolysaccharide sheath. Pili-like structures were detected on the Sp245 wild-type strain and on its Fla^– Swa^– Omegon-Km mutant SK048, which are presumably involved in microcolonial spreading in these bacteria.     

Changes in cell surface properties and biofilm formation efficiency in <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> Sp245 mutants in the putative genes of lipid metabolism <Emphasis Type="Italic">mmsB1</Emphasis> and <Emphasis Type="Italic">fabG1</Emphasis>

The previously obtained insertion mutants of Azospirillum brasilense Sp245 in the genes mmsB1 and fabG1 (strains SK039 and Sp245.1610, respectively) were characterized by impaired flagellation and motility. The putative products of expression of these genes are 3-hydroxyisobutyrate dehydrogenase and 3-oxoacyl-[acyl-carrier protein] reductase, respectively. In the present work, A. brasilense strains Sp245, SK039, and Sp245.1610 were found to have differences in the content of 3-hydroxyhexadecanoic, hexadecanoic, 3-hydroxytetradecanoic, hexadecenoic, octadecenoic, and nonadecanoic acids in their lipopolysaccharide preparations, as well as in cell hydrophobicity and hemagglutination activity and dynamics of cell aggregation, in biomass amount, and in the relative content of lipopolysaccharide antigens in mature biofilms formed on hydrophilic or hydrophobic surfaces.     

<Emphasis Type="Italic">Ent</Emphasis>-kaurenoic acid oxidase genes in wheat

Ent-kaurenoic acid oxidase (KAO) catalysis three steps in the gibberellin (GA) biosynthesis pathway, which yields a large hormone family affecting plant growth and development. In the current study, we performed partial gene cloning and comparative structural and mapping analysis among three Kao genes in bread wheat (Triticum aestivum L.). Molecular-marker-based mapping demonstrated that the Kao loci map to the distal ends of the chromosome arms 7AS, 4AL and 7DS, corresponding to the 7BS/4AL translocation region. Co-linearity of the chromosomal regions carrying the Kao genes was shown. It was concluded that the Kao genes we mapped represent a homoeoloci set, therefore the genes were designated Kao-A1 (chromosome 7AS), Kao-B1 (4AL), and Kao-D1 (7DS). It was found that exonic sequences of the three homoeologues differ from each other mainly by silent mutations, and each homoeologue is expressed.