Pseudomonas siderophores: A mechanism explaining disease-suppressive soils
TL;DR: These findings suggest that disease suppressiveness is caused in part by microbial siderophores which efficiently complex iron(III) in soils, making it unavailable to pathogens, thus inhibiting their growth.
Abstract: The addition of either fluorescentPseudomonas strain B10, isolated from a take-all suppressive soil, or its siderophore, pseudobactin, to bothFusarium-wilt and take-all conducive soils inoculated withFusarium oxysporum f. sp.lini orGaeumannomyces graminis var.tritici, respectively, rendered them disease suppressive. Our findings suggest that disease suppressiveness is caused in part by microbial siderophores which efficiently complex iron(III) in soils, making it unavailable to pathogens, thus inhibiting their growth. Amendment of exogenous iron(III) to disease-suppressive soils converted them to conductive soils presumably by repressing siderophore production.
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TL;DR: Biocontrol strains of fluorescent pseudomonads produce antifungal antibiotics, elicit induced systemic resistance in the host plant or interfere specifically with fungal pathogenicity factors during root colonization.
Abstract: Particular bacterial strains in certain natural environments prevent infectious diseases of plant roots. How these bacteria achieve this protection from pathogenic fungi has been analysed in detail in biocontrol strains of fluorescent pseudomonads. During root colonization, these bacteria produce antifungal antibiotics, elicit induced systemic resistance in the host plant or interfere specifically with fungal pathogenicity factors. Before engaging in these activities, biocontrol bacteria go through several regulatory processes at the transcriptional and post-transcriptional levels.
2,263 citations
TL;DR: The microbial basis of specific suppression to four diseases, Fusarium wilts, potato scab, apple replant disease, and take-all, is discussed and the microbial composition and complex interactions in suppressive soils are dissected.
Abstract: ▪ Abstract Agricultural soils suppressive to soilborne plant pathogens occur worldwide, and for several of these soils the biological basis of suppressiveness has been described. Two classical types of suppressiveness are known. General suppression owes its activity to the total microbial biomass in soil and is not transferable between soils. Specific suppression owes its activity to the effects of individual or select groups of microorganisms and is transferable. The microbial basis of specific suppression to four diseases, Fusarium wilts, potato scab, apple replant disease, and take-all, is discussed. One of the best-described examples occurs in take-all decline soils. In Washington State, take-all decline results from the buildup of fluorescent Pseudomonas spp. that produce the antifungal metabolite 2,4-diacetylphloroglucinol. Producers of this metabolite may have a broader role in disease-suppressive soils worldwide. By coupling molecular technologies with traditional approaches used in plant patholog...
1,573 citations
TL;DR: Resistance-inducing and antagonistic rhizobacteria might be useful in formulating new inoculants with combinations of different mechanisms of action, leading to a more efficient use for biocontrol strategies to improve cropping systems.
Abstract: Bacteria that colonize plant roots and promote plant growth are referred to as plant growth-promoting rhizobacteria (PGPR). PGPR are highly diverse and in this review we focus on rhizobacteria as biocontrol agents. Their effects can occur via local antagonism to soil-borne pathogens or by induction of systemic resistance against pathogens throughout the entire plant. Several substances produced by antagonistic rhizobacteria have been related to pathogen control and indirect promotion of growth in many plants, such as siderophores and antibiotics. Induced systemic resistance (ISR) in plants resembles pathogen-induced systemic acquired resistance (SAR) under conditions where the inducing bacteria and the challenging pathogen remain spatially separated. Both types of induced resistance render uninfected plant parts more resistant to pathogens in several plant species. Rhizobacteria induce resistance through the salicylic acid-dependent SAR pathway, or require jasmonic acid and ethylene perception from the plant for ISR. Rhizobacteria belonging to the genera Pseudomonas and Bacillus are well known for their antagonistic effects and their ability to trigger ISR. Resistance-inducing and antagonistic rhizobacteria might be useful in formulating new inoculants with combinations of different mechanisms of action, leading to a more efficient use for biocontrol strategies to improve cropping systems.
1,011 citations
Cites background from "Pseudomonas siderophores: A mechani..."
...…siderophore produced by P. putida B10 strain was also able to suppress Fusarium oxysporum in soil deficient in iron; this suppression was lost when the soil was replenished with iron, a condition that represses the production of iron chelators by microorganisms (Kloepper et al., 1980b)....
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...The potent siderophore, pyoverdin, for example, can inhibit the growth of bacteria and fungi that present less potent siderophores in iron-depleted media in vitro (Kloepper et al. 1980a)....
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TL;DR: Some pest management researchers have focused their efforts on developing alternative inputs to synthetic chemicals for controlling pests and diseases, among these alternatives are those referred to as biological controls.
Abstract: Plant diseases need to be controlled to maintain the quality and abundance of food, feed, and fiber produced by growers around the world. Different approaches may be used to prevent, mitigate or control plant diseases. Beyond good agronomic and horticultural practices, growers often rely heavily on chemical fertilizers and pesticides. Such inputs to agriculture have contributed significantly to the spectacular improvements in crop productivity and quality over the past 100 years. However, the environmental pollution caused by excessive use and misuse of agrochemicals, as well as fear-mongering by some opponents of pesticides, has led to considerable changes in people’s attitudes towards the use of pesticides in agriculture. Today, there are strict regulations on chemical pesticide use, and there is political pressure to remove the most hazardous chemicals from the market. Additionally, the spread of plant diseases in natural ecosystems may preclude successful application of chemicals, because of the scale to which such applications might have to be applied. Consequently, some pest management researchers have focused their efforts on developing alternative inputs to synthetic chemicals for controlling pests and diseases. Among these alternatives are those referred to as biological controls.
958 citations
Cites background from "Pseudomonas siderophores: A mechani..."
...Kloepper et al. (1980) were the first to demonstrate the importance of siderophore production as a mechanism of biological control of Erwinia carotovora by several plant-growthpromoting Pseudomonas fluorescens strains A1, BK1, TL3B1 and B10....
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...American Phytopathological Society, St. Paul, MN....
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TL;DR: This review presents recent advances in understanding of antibiotic production by bacterial biocontrol agents and their role in microbial interactions.
Abstract: Interest in biological control of plant pathogens has been stimulated in recent years by trends in agriculture towards greater sustainability and public concern about the use of hazardous pesticides There is now unequivocal evidence that antibiotics play a key role in the suppression of various soilborne plant pathogens by antagonistic microorganisms The significance of antibiotics in biocontrol, and more generally in microbial interactions, often has been questioned because of the indirect nature of the supporting evidence and the perceived constraints to antibiotic production in rhizosphere environments Reporter gene systems and bio-analytical techniques have clearly demonstrated that antibiotics are produced in the spermosphere and rhizosphere of a variety of host plants Several abiotic factors such as oxygen, temperature, specific carbon and nitrogen sources, and microelements have been identified to influence antibiotic production by bacteria biocontrol agents Among the biotic factors that may play a determinative role in antibiotic production are the plant host, the pathogen, the indigenous microflora, and the cell density of the producing strain This review presents recent advances in our understanding of antibiotic production by bacterial biocontrol agents and their role in microbial interactions
867 citations
References
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TL;DR: Two simple media for the enhancement of pigment production by certain organisms of the Pseudomonas genus are described and the results of comparative studies employing these media, certain synthetic broths, and some commonly used dehydrated preparations are reported.
5,006 citations
TL;DR: Evidence is presented that PGPR exert their plant growth-promoting activity by depriving native microflora of iron by producing extracellular siderophores (microbial iron transport agents) which efficiently complex environmental iron, making it less available to certain nativemicroflora.
Abstract: Specific strains of the Pseudomonas fluorescens-putida group have recently been used as seed inoculants on crop plants to promote growth and increase yields. These pseudomonads, termed plant growth-promoting rhizobacteria (PGPR), rapidly colonize plant roots of potato, sugar beet and radish, and cause statistically significant yield increases up to 144% in field tests1–5. These results prompted us to investigate the mechanism by which plant growth was enhanced. A previous study indicated that PGPR increase plant growth by antagonism to potentially deleterious rhizoplane fungi and bacteria, but the nature of this antagonism was not determined6. We now present evidence that PGPR exert their plant growth-promoting activity by depriving native microflora of iron. PGPR produce extracellular siderophores (microbial iron transport agents)7 which efficiently complex environmental iron, making it less available to certain native microflora.
1,492 citations
"Pseudomonas siderophores: A mechani..." refers background or methods in this paper
...PGPR exert their plant growth-promothag activity in part by depriving native microflora of iron [6], PGPR produce extraceUular siderophores (microbial iron transport agents [9]) which elficiently complex environmental iron, making it less available to certain native microflora and thus inhibiting their growth....
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...TASS, or its siderophore, pseudobactin [6]~ to the conducive soil....
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...Pseudobactin and ferric pseudobactin were isolated from Pseudomonas B I0 and were purified to homogeneity as described previously [6]....
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608 citations
TL;DR: Increases in growth and yield of various crop plants is presented and the results of a study on the effect of specific inoculated with A. chroococcum in five of 19 greenhouse rhizosphere pseudomonads on potato plant growth and trials and two of 13 cases in the field are presented.
Abstract: BURR, T. J., M. N. SCHROTH, and T. SUSLOW. 1978. Increased potato yields by treatment of seedpieces with specific strains of Pseudomonas fluorescens and P. putida. Phytopathology 68:1377-1383. Significant increases in growth and yield of potato plants seedpieces planted in field soils in the greenhouse resulted in were achieved by treating seedpieces with suspensions of two lip to 100% increase in fresh weight of shoot and root systems Pseudomonas spp. at 109 colony-forming units (cfu)/ml in a 4-wk period. Statistically significant increases in yield prior to planting. The pseudomonads were selected from over ranged from 14 to 33% in five of nine field plots in California 100 strains that were isolated from the surface of potato and Idaho. The pseudomonads had no effect on plant growth tubers and also exhibited antibiosis against Erwinia or tuber yield when seedpieces were planted in peat soil, or in carotovora var. carotovora in vitro. The isolates were soil that was relatively dry. Both Pseudomonas spp. were identified as strains of Pseudomonas fluorescens and P. compatible with fungicides that were commonly used to treat putida. These strains survived for at least I mo on treated seedpieces, except for manganese ethylenebisdithioseedpieces planted in loamy sand field soil at populations carbamate zinc salt (mancozeb). The mechanism by which of -10" cfu/0.785 cm. Also, they colonized developing these bacteria enhance plant growth and tuber yield may be potato roots and were the predominant bacteria in the associated with changes in the composition of rhizosphere rhizospheres up to 2 mo after planting. Bacterization of bacterial flora. There are numerous instances in which bacteria the bacteria could not be responsible for the yield inoculated onto plant seeds and roots (a process called increases that sometimes were obtained. Furthermore, bacterization) have been reported to enhance plant they implied that these bacteria may not be rhizosphere growth (4, 7, 13, 14, 17, 18, 19, 21,25). Most of these have organisms (9, 12, 16), but opinions vary on this aspect (11, concerned bacteria in the genera Azotobacter, Bacillus, 21). Pseudomonas, and Clostridium. Results from these We became interested in the phenomenon of studies have been highly variable, however, and the bacterization upon noting increased root and foliar average yield data generally have not differed growth with several plants, such as potato, sugarbeet, and significantly from those of the nonbacterized controls. lettuce, when seeds or seedpieces were treated with Brown et al. (5), for example, obtained significant. specific bacterial strains prior to planting. This report increases in growth and yield of various crop plants presents the results of a study on the effect of specific inoculated with A. chroococcum in five of 19 greenhouse rhizosphere pseudomonads on potato plant growth and trials and two of 13 cases in the field. Increases in yield tuber yield. ranged from 3 to 11%, but replicate variance was great and differences usually were not significant even at P = MATERIALS AND METHODS 0. 10. The results of Merriman et al. also were inconsistent for both greenhouse (18) and field experiments (19). Initial selection of antagonists.---Bacteria were isolated Most experimental and commercial bacterization from the surface of freshly dug healthy potato tubers and efforts in Russia have been conducted with preparations arbitrarily selected for inhibition of Erwinia carotovora of A. chroococcum (called "azotobacterin") and Bacillus var. carotovora (Ecc) in vitro. Isolations were made from megaterium (called "phosphobacterin"). Azotobacterin is potato cultivars White Rose and Russet Burbank. Each considered to act as a nitrogen fertilizer by the fixation of tuber was washed in 100-ml sterile distilled water for 10 atmospheric nitrogen, and phosphobacterin supposedly min. Dilutions then were made from the wash water, improves the phosphorus nutrition of the plant by plated on King's Medium B (KB), and incubated at 28 C mineralization of organic phosphorus and making it for 24 hr. Then plates were sprayed with a 24-hr-old more available to the plant. However, researchers (6, 20) culture of Ecc and incubated an additional 24 hr at which have concluded that the amounts of nitrogen fixed and time inhibition zones were apparent about antagonistic phosphorus made available to the plants by the action of colonies. Colonies that exhibited antibiosis were 00032-949X/78/000 25o0o3.o0/0 restreaked, examined for purity, and stored. The strains Copyright © 1978 The American Phytopathological Society, 3340 were subsequently checked for antibiosis against Ecc, E. Pilot Knob Road, St. Paul, MN 55121. All rights reserved. carotovora var. atroseptica (Eca), and the Erwinia sp.
313 citations
"Pseudomonas siderophores: A mechani..." refers background in this paper
...The techniques for applying high numbers of viable pseudomonads to field crops in commercial fields have been extensively and successfully tested with plant growth-promoting rhizobacteria [2,7,13]....
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TL;DR: Both types of antagonism are probably operative in long-term wheat growing areas of the Pacific Northwest U.S.A. where take-all is virtually nonexistent and in much of the southern Australian wheat belt, where some general but rarely specific antagonism is apparently operative.
Abstract: The suppression of Gaeumannomyces graminis var. tritici by certain soils or following certain soil treatments is considered to be an expression of either specific or general antagonism sensu Gerlagh (1968). Specific antagonism is effective in dilutions as high as 1 in 1,000, can be transferred from soil to soil, operates near or on wheat roots, is destroyed by 60°C moist heat for 30 min. or desiccation, is fostered by wheat monoculture but may be lost from a soil by fallow or rotation with certain crops, especially legume hay or pasture crops. Strains of Pseudomonas fluorescens may be involved. General antagonism is a soil property which cannot be transferred and is resistant to 80°C moist heat for 30 min, to methyl bromide and chloropicrin, but not to autoclaving. Take-all control by organic amendments, minimum tillage, or a soil temperature of 28°C may be expressions of increased general antagonism. In much of the southern Australian wheat belt, where take-all can cause heavy crop losses, some general but rarely specific antagonism is apparently operative. Both types of antagonism are probably operative in long-term wheat growing areas of the Pacific Northwest U.S.A. where take-all is virtually nonexistent.
259 citations
"Pseudomonas siderophores: A mechani..." refers background in this paper
...Various microorganisms including a pseudomonad [10] have also been implicated in both TASS and FWSS [3,11,12]....
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