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Biomedical subjects

H Antoun

Publications and source records attributed to H Antoun.

26 records · Page 2Linked to original sources
PubMed1996

Root colonization of maize and lettuce by bioluminescent Rhizobium leguminosarum biovar phaseoli.

Two strains of Rhizobium leguminosarum bv. phaseoli and three other plant growth-promoting rhizobacteria (PGPR) were examined for the potential of maize and lettuce root colonization. All of these strains were selected in vitro for their phosphate-solubilizing abilities. Maize and lettuce seeds were treated with derivatives of all strains marked with lux genes for bioluminescence and resistance to kanamycin and rifampin prior to planting in nonsterile Promix and natural soil. The introduced bacterial strains were quantified on roots by dilution plating on antibiotic media together with observation of bioluminescence. Rhizobia were superior colonizers compared with other tested bacteria; rhizobial root populations averaged log 4.1 CFU/g (fresh weight) on maize roots 4 weeks after seeding and log 3.7 CFU/g (fresh weight) on lettuce roots 5 weeks after seeding. The average populations of the recovered PGPR strains were log 3.5 and log 3.0 CFU/g (fresh weight) on maize and lettuce roots, respectively. One of the three PGPR was not recovered later than the first week after seeding in Promix. Bioluminescence also permitted visualization of in situ root colonization in rhizoboxes and demonstrated the efficiency of rhizobial strains to colonize and survive on maize and lettuce roots.

Lactuca↗
PubMed1995

Effect of compost on rhizosphere microflora of the tomato and on the incidence of plant growth-promoting rhizobacteria.

Four commercial composts were added to soil to study their effect on plant growth, total rhizosphere microflora, and incidence of plant growth-promoting rhizobacteria (PGPR) in the rhizosphere of tomato plants. Three of the compost treatments significantly improved plant growth, while one compost treatment significantly depressed it. Compost amendments caused only small variations in the total numbers of bacteria, actinomycetes, and fungi in the rhizosphere of tomato plants. A total of 709 bacteria were isolated from the four compost treatments and the soil control to determine the percentage of PGPR in each treatment. The PGPR tests measured antagonism to soilborne root pathogens, production of indoleacetic acid, cyanide, and siderophores, phosphate solubilization, and intrinsic resistance to antibiotics. Our results show that the addition of some composts to soil increased the incidence in the tomato rhizosphere of bacteria exhibiting antagonism towards Fusarium oxysporum f. sp. radicis-lycopersici, Pyrenochaeta lycopersici, Pythium ultimum, and Rhizoctonia solani. The antagonistic effects observed were associated with marked increases in the percentage of siderophore producers. No significant differences were observed in the percentage of cyanogens, whereas the percentages of phosphate solubilizers and indoleacetic acid producers were affected, respectively, by one and two compost treatments. Intrinsic resistance to antibiotics was only marginally different among the rhizobacterial populations. Our results suggest that compost may stimulate the proliferation of antagonists in the rhizosphere and confirm previous reports indicating that the use of composts in container media has the potential to protect plants from soilborne root pathogens.

Journal Article↗
PubMed1992

Heat and cold shock protein synthesis in arctic and temperate strains of rhizobia.

We compared heat shock proteins (HSPs) and cold shock proteins (CSPs) produced by different species of Rhizobium having different growth temperature ranges. Several HSPs and CSPs were induced when cells of three arctic (psychrotrophic) and three temperate (mesophilic) strains of rhizobia were shifted from their optimal growth temperatures (arctic, 25 degrees C; temperate, 30 degrees C) to shock temperatures outside their growth temperature ranges. At heat shock temperatures, three major HSPs of high molecular weight (106,900, 83,100, and 59,500) were present in all strains for all shock treatments (29, 32, 36.4, 38.4, 40.7, 41.4, and 46.4 degrees C), with the exception of temperate strains exposed to 46.4 degrees C, in which no protein synthesis was detected. Cell survival of arctic and temperate strains decreased markedly with the increase of shock temperature and was only 1% at 46.4 degrees C. Under cold shock conditions, five proteins (52.0, 38.0, 23.4, 22.7, and 11.1 kDa) were always present for all treatments (-2, -5, and -10 degrees C) in arctic strains. Among temperate strains, five CSPs (56.1, 37.1, 34.4, 17.3, and 11.1 kDa) were present at temperatures down to 0 degrees C. The 34.4- and the 11.1-kDa components were present in all temperate strains at -5 degrees C and in one strain at -10 degrees C. Survival of all strains decreased with cold shock temperatures but was always higher than 50%. These results show that rhizobia can synthesize proteins at temperatures not permissive for growth. In all shock treatments, no correspondence between the number of HSPs or CSPs produced and rhizobial survival was found.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Biological↗
PubMed1992

Ice Nucleation Activity in Fusarium acuminatum and Fusarium avenaceum.

Twenty fungal genera, including 14 Fusarium species, were examined for ice nucleation activity at -5.0 degrees C, and this activity was found only in Fusarium acuminatum and Fusarium avenaceum. This characteristic is unique to these two species. Ice nucleation activity of F. avenaceum was compared with ice nucleation activity of a Pseudomonas sp. strain. Cumulative nucleus spectra are similar for both microorganisms, while the maximum temperatures of ice nucleation were -2.5 degrees C for F. avenaceum and -1.0 degrees C for the bacteria. Ice nucleation activity of F. avenaceum was stable at pH levels from 1 to 13 and tolerated temperature treatments up to 60 degrees C, suggesting that these ice nuclei are more similar to lichen ice nuclei than to bacterial ones. Ice nuclei of F. avenaceum, unlike bacterial ice nuclei, pass through a 0.22-mum-pore-size filter. Fusarial nuclei share some characteristics with the so-called leaf-derived nuclei with which they might be identified: they are cell free and stable up to 60 degrees C, and they are found in the same kinds of environment. Highly stable ice nuclei produced by fast-growing microorganisms have potential applications in biotechnology. This is the first report of ice nucleation activity in free-living fungi.

Journal Article↗
PubMed1990

Fungal catabolism of crown gall opines.

This study was conducted to determine the capacities of 37 fungi to utilize various crown gall opines as their sole carbon and nitrogen source. One strain of Fusarium solani, two of Cylindrocarpon destructans, and six of Cylindrocarpon heteronema catabolized octopine, mannopine, octopinic acid, succinamopine, or a combination of these opines. One C. heteronema and one Fusarium dimerum strain grew only on succinamopine. None of the fungal isolates had the ability to grow on nopaline. The catabolism of opines by fungi was confirmed by the disappearance of the opine from the growth medium and by an increase in final mycelial dry weight with rising initial concentration of test substrate. This study thus shows that the catabolism of opines is not restricted to bacteria.

Journal Article↗
PubMed1978

[Actinomycetes antagonistic to fungi and not affecting Rhizobium meliloti].

The effects of 481 actinomycetes isolated from agricultural soils supporting good growth of alfalfa or clover on two efficient strains of Rhizobium meliloti A2 and S14 were studied. Strain A2 was inhibited by 28% of the isolates and strain S14 was inhibited by 31% of them. No significant difference was found between the resistance of both actinomycete strains. The effects of the 288 isolates not affecting R. meliloti on six fungi were also studied. The most sensitive fungus was Stemphylium sarcinaeforme inhibited by 20% of the isolates, while Fusarium culmorum was the most resistant fungus and was inhibited by only 6% of the isolates. Thirteen isolates inhibited four to six fungi. In an autoclaved greenhouse soil, isolate 181 which inhibited the six fungi tested significantly reduced the population of the phytopathogenic fungus F. oxysporum f. sp. medicaginis and eliminated the inhibitory effect showed by this fungus on strain A2 of R. meliloti.

Actinomycetales↗