Biocontrol of Rhizoctonia solani, the causal agent of bean damping-off by fluorescent pseudomonads

Rhizosphere bacteria belonging to the fluorescent pseudomonads are receiving increasing attention for the protection of plants against soil-borne fungal pathogens. Among these pathogens, Rhizoctonia solani, the causal agent of bean damping- off is very important in bean fields of Iran. In this study, the antagonistic activity of 46 isolates of fluorescent pseudomonads (isolated from different area of Iran) and Pseudomonas fluorescens strain CHA0 investigated against one isolate of R. solani. About 64% of isolates revealed antagonistic activity against R. solani. Production of antifungal metabolites such as HCN, siderophore and protease was evaluated. The results showed that 97.8%, 17% and 78% of isolates produced siderophore, HCN and protease respectively. There was no significant correlation between antagonistic activity and production of these metabolites. Isolates P-5, P-10 and P-32 with strain CHA0 were selected in order to investigate involvement of siderophore, volatile metabolites (HCN), and non-volatile metabolites in reducing mycelial growth of R. olani. Isolate P-5 showed much more inhibitory effect by production of volatile metabolites and siderophore. Non-volatile metabolites in isolates P-32 and P-5 completely inhibited mycelial growth of the fungus. After the primary labrotory tests, isolates P-14, P-35, P-30, P-5 and strain CHA0 were selected for in vivo experiments. These selected isolates with benomyl fungicide were used as seed coating and soil drenching in sterile soil under greenhouse condition. The result indicated that in seed treatment method, isolates P-30 by 66% had the most effect in disease reduction while in soil treatment method, strain CHAO by 60% had the most effect, such that this two isolates showed significant differences in comparison with plants inoculated with R. solani inoculums.

Effect of fluorescent pseudomonades and Trichoderma sp. and their combination with two chemicals on Penicillium digitatum caused agent of citrus green mold

Citrus green mold (Penicillium digitatum) causes economic losses. Chemical fungicides such as imazalil provide the primary means for controlling green mold decay of citrus fruits. Continuous use of fungicides has faced two major obstacles- increasing public concern regarding contamination of perishables with fungicidal residues, and proliferation of resistance in the pathogen populations. The aim of this research was to determine if the attacks of green mold on orange could be reduced by usage of biocontrol agent alone or in combination with low dosage of imazalil or sodium bicarbonate. Pseudomonas fluorescens isolate PN, P. fluorescens isolate PS and Trichoderma virens isolate TE were evaluated as potential biological agents for control of green mold of oranges caused by P. digitatum. Increasing concentration of SB decreased spore germination of P. digitatum. In laboratory tests, a cell suspension (10(8) cells per ml.) of bacterial strains reduced the incidence of green mold. On fruits surface biocontrol activity of antagonistic isolates was significantly increased when combined with low dosage of imazalil (500ppm) or sodium carbonate (5%). Effect of Trichoderma virens on controlling P. digitatum was better than others with or without these chemicals.

Growth and survival of immature Heamatobia irritans (Diptera; Muscidae) is influenced by bacterial isolated from cattle manure and conspecific larvae

Twenty species of bacteria were isolated from cattle manure and seven species were isolated from the gut of larval horn fly Hematobia irritans (L.). Bacteria in manure belonged to the Bacillaceae, Pseudomonadaceae, Micrococcaceae, Corynebacteriaceae, Enterobacteriaceae, Microbacteriaceae, and two unassigned genera. Gut bacteria belonged to the Enterobacteriaceae, Bacillaceae, Neisseriaceae, and Pseudomonadaceae. H. irritans larval survival and growth on the various bacterial species were evaluated by rearing larvae in sterilized cattle manure that was inoculated with single bacterial isolates. H. irritans larvae failed to develop in sterilized, uninoculated manure, indicating that bacteria are necessary for larval development. Survival averaged 74% in nonsterilized manure and ranged from 4 to 53% in manure with individual isolates. Survival was highest when larvae were reared on manure inoculated with Pseudomonadaceae, Corynebacteriaceae, Micrococcaceae, and Bacillaceae and was lowest when reared in manure inoculated with Enterobacteriaceae and Microbacteriaceae. Pupal weights were heaviest when reared on the Flavobacteria, followed by the Pseudomonadaceae and Corynebacteriaceae. Pupae averaged 4.9 +/- 0.08 mg when reared on gram-negative isolates, compared with 3.6 +/- 0.09 mg when reared on gram-positive isolates. Pupal weights were not significantly correlated with larval survival, indicating that bacteria that promote growth do not necessarily promote survival. A reproductive index was used as a measure of fitness and was highest for larvae reared in the nonsterile control, followed most closely by Pseudomonadaceae and Corynebacteriaceae. These groups appeared to best meet the nutritional requirements of larvae and may be used in further experiments to define an artificial rearing media for H. irritans.

Assembly and function of type III secretory systems

Type III secretion systems allow Yersinia spp., Salmonella spp., Shigella spp., Bordetella spp., and Pseudomonas aeruginosa and enteropathogenic Escherichia coli adhering at the surface of a eukaryotic cell to inject bacterial proteins across the two bacterial membranes and the eukaryotic cell membrane to destroy or subvert the target cell. These systems consist of a secretion apparatus, made of approximately 25 proteins, and an array of proteins released by this apparatus. Some of these released proteins are "effectors," which are delivered into the cytosol of the target cell, whereas the others are "translocators," which help the effectors to cross the membrane of the eukaryotic cell. Most of the effectors act on the cytoskeleton or on intracellular-signaling cascades. A protein injected by the enteropathogenic E. coli serves as a membrane receptor for the docking of the bacterium itself at the surface of the cell. Type III secretion systems also occur in plant pathogens where they are involved both in causing disease in susceptible hosts and in eliciting the so-called hypersensitive response in resistant or nonhost plants. They consist of 15-20 Hrp proteins building a secretion apparatus and two groups of effectors: harpins and avirulence proteins. Harpins are presumably secreted in the extracellular compartment, whereas avirulence proteins are thought to be targeted into plant cells. Although a coherent picture is clearly emerging, basic questions remain to be answered. In particular, little is known about how the type III apparatus fits together to deliver proteins in animal cells. It is even more mysterious for plant cells where a thick wall has to be crossed. In spite of these haunting questions, type III secretion appears as a fascinating trans-kingdom communication device.

The genome sequence of the plant pathogen Xylella fastidiosa. The Xylella fastidiosa Consortium of the Organization for Nucleotide Sequencing and Analysis

Xylella fastidiosa is a fastidious, xylem-limited bacterium that causes a range of economically important plant diseases. Here we report the complete genome sequence of X. fastidiosa clone 9a5c, which causes citrus variegated chlorosis--a serious disease of orange trees. The genome comprises a 52.7% GC-rich 2,679,305-base-pair (bp) circular chromosome and two plasmids of 51,158 bp and 1,285 bp. We can assign putative functions to 47% of the 2,904 predicted coding regions. Efficient metabolic functions are predicted, with sugars as the principal energy and carbon source, supporting existence in the nutrient-poor xylem sap. The mechanisms associated with pathogenicity and virulence involve toxins, antibiotics and ion sequestration systems, as well as bacterium-bacterium and bacterium-host interactions mediated by a range of proteins. Orthologues of some of these proteins have only been identified in animal and human pathogens; their presence in X. fastidiosa indicates that the molecular basis for bacterial pathogenicity is both conserved and independent of host. At least 83 genes are bacteriophage-derived and include virulence-associated genes from other bacteria, providing direct evidence of phage-mediated horizontal gene transfer.

Biological activity of Burkholderia (Pseudomonas) cepacia lipopolysaccharide

Burkholderia cepacia has emerged as an important multiresistant pathogen in cystic fibrosis (CF), associated in 20% of colonised patients with a rapid and fatal decline in lung function. Although knowledge of B. cepacia epidemiology has improved, the mechanisms involved in pathogenesis remain obscure. In this study, B. cepacia lipopolysaccharide (LPS) was assessed for endotoxic potential and the capacity to induce tumour necrosis factor (TNF). LPS preparations from clinical and environmental isolates of B. cepacia and from the closely related species Burkholderia gladioli exhibited a higher endotoxic activity and more pronounced cytokine response in vitro compared to preparations from the major CF pathogen Pseudomonas aeruginosa. This study help to explain the vicious host immune response observed during pulmonary exacerbations in CF patients colonised by B. cepacia and lead to therapeutic advances in clinical management.

Nonhost resistance genes and race-specific resistance

Apart from physical barriers, plants have two major types of defense against potential pathogens. In 'race-specific' resistance, plants match single mendelian resistance genes with the 'avirulence' genes possessed by races of a pathogen. Plants also employ the more complex and evolutionarily more robust system of 'nonhost resistance' against a broad range of pathogenic species. In peas, both types of resistance are associated with the expression of a common group of 'resistance response' genes.

Safety evaluation of Protaminobacter rubrum: intravenous pathogenicity and toxigenicity study in rabbits and mice

The iv pathogenicity and toxigenicity of Protaminobacter rubrum was studied in New Zealand White rabbits and CF1 BR mice. Following a probe study, nine groups of six rabbits each were injected iv with; 1 ml of viable-cell suspension (VCS) at concentrations of 2.23 x 10(8), 10(6), 10(4) and 10(2) organisms/ml; the cell-free supernatant (CFS; in which the test organism had been cultured to a concentration of approximately 3 x 10(10) cells/ml) at dilutions of 1:100, 1:10,000 and 1:1,000,000 in phosphate buffered saline (PBS); uninoculated culture medium; or uninoculated PBS. Rabbits were observed daily for 14 days and body weights were recorded on days 0, 7 and 14. Body temperatures were recorded in two rabbits per group until 18 hr after dosing. On day 14, each rabbit was killed. Blood samples, sections of liver and spleen, and any tissues presenting lesions possibly indicating an infection were excised and cultured for P. rubrum. Deaths occurred in the probe study following 1 ml iv injection of VCS at a concentration of 2.5 x 10(10) organisms/ml or of undiluted CFS in which P. rubrum had been grown to a concentration of approximately 2.5 x 10(10) organisms/ml. Blood and tissue samples obtained less than 24 hr after treatment from rabbits in the VCS group tested positive for P. rubrum, which would be expected after iv administration of such a high concentration of cells. No deaths occurred, no adverse effects on body-weight gain were seen, and in no instance was P. rubrum recovered from blood or tissue cultures in the definitive study. Overt signs of infection or toxinosis were limited to transient reduced activity in the highest two VCS concentration groups, and the highest CFS group. Modestly elevated body temperatures were also recorded for rabbits that received the highest two concentrations of either VCS or CFS. A similar 14-day study was carried out in mice. Four groups of 20 Crl: COBS CF1 BR mice received a single iv injection of 0.1 ml of VCS (2.5 x 10(10) organisms/ml), CFS in which the test organism was cultured to approximately 2.5 x 10(10) cells/ml, uninoculated culture medium or uninoculated PBS. The mice were observed daily and body weights were recorded on days 0, 7 and 14. On day 14, each mouse was killed and blood samples as well as liver and spleen sections were obtained and cultured. In this study no deaths occurred, and signs of infection or toxinosis were limited to reduced activity and ptosis for all mice in the VCS and CFS groups.(ABSTRACT TRUNCATED AT 400 WORDS)

[Biological properties of opportunistic enterobacteria isolated from the blood of patients]

The comparative study of the signs of pathogenicity in enterobacteria (119 strains) isolated from the blood of 145 patients with the clinical symptoms of sepsis and from the feces of healthy persons (560 strains from 220 persons) has demonstrated that the same species of opportunistic microorganisms may essentially differ in the formation of DNase, RNase, as well as in their capacity for the positive reaction with Congo red. The possibility of using the above-mentioned signs of pathogenicity for diagnostic purposes as additional signs for the differentiation of virulent cultures of opportunistic enterobacteria from avirulent ones is suggested.