Mohamed Cherif - Academia.edu (original) (raw)
Papers by Mohamed Cherif
Phytopathologia Mediterranea, 2003
The interaction of Fusarium roseum var. sambucinum, the causal agent of potato dry rot, with two ... more The interaction of Fusarium roseum var. sambucinum, the causal agent of potato dry rot, with two antagonistic bacteria, Bacillus cereus X16 and B. thuringiensis 55T, was studied on wounded potato tubers using light and electron microscopy. Application of B. cereus X16 or B. thuringiensis 55T to potato wounds before challenge with the pathogen suppressed dry rot and restricted fungal growth in plant tissues to the first few cell layers beneath the site of inoculation. Both bacterial antagonists penetrated into potato tissues and established themselves through intercellular and intracellular proliferation. The extent of Fusarium colonization was appreciably reduced in the bacterized tubers, and most fungal cells in these tubers were severely damaged, with appreciable morphological and structural changes. In potato tubers bacterized by B. thuringiensis 55T, Fusarium invasion of the host tissues did not stimulate structural host reactions, and direct parasitism, which operates by degrad...
Journal of Plant Pathology, 2001
SUMMARY A total of 83 spore-forming bacteria belonging to the genus Bacillus was isolated from Tu... more SUMMARY A total of 83 spore-forming bacteria belonging to the genus Bacillus was isolated from Tunisian salty soils. These isolates as well as five additional strains of Bacillus thuringiensis, previously selected for their efficiency against insects, were tested in vitro and in vivo against Fusarium roseum var. sambucinum, the causal agent of dry rot of potato tubers. Results of the in vitro dual culture screening revealed that more than 50% of Bacillus spp. isolated from salty soils inhibited the growth of the pathogen in vitro. By contrast, all five B. thuringiensis strains failed to inhibit the growth of the pathogen in vitro. On wounded potato tubers, the most effective isolates obtained from salty soils were X7, X9, X16, I32 and G7, with a percentage of dry rot reduction ranging from 66 to 89%. These effective Bacillus isolates were identified as belonging to one of the species B. cereus (X9, X16 and G7), B. lentimorbus (X7) or B. licheniformis (I32). Although ineffective in v...
This report presents a survey of previous and more recent ultrastructural and cytochemical invest... more This report presents a survey of previous and more recent ultrastructural and cytochemical investigations of disease development in elm, caused by Ophiostoma novo-ulmi, with results of some comparative studies of other wilt diseases caused by f.spp., of Fusarium oxysporum and of Verticillium sp. For cytochemical studies, probes complexed to colloidal gold to detect cellulose, pectin, chitin, and DNA were used. Thus, the formation of tyloses, pit membrane alterations, and the disease effect on parenchyma cells in mature as well as in young tissue were characterized. Vessel lumina in these plants, in diverse situations, contained heterogeneous matter, among which occurred masses of opaque matter and in certain instances pectin fibrils secreted by parenchyma cells and tyloses. Numerous globoid, opaque bodies of regular sizes, which have been mostly overlooked previously, abounded in vessel elements of U. americana and U. glabra, including trees injected with glucose solutions prior to ...
Phytoprotection, 2006
Various cell reactions occurred in staghorn sumac plants inoculated with Fusarium oxysporum f. sp... more Various cell reactions occurred in staghorn sumac plants inoculated with Fusarium oxysporum f. sp. callistephi. Light and transmission electron microscopy observations and results of cytochemical tests showed: 1) increased laticifers and latex production in the phloem; 2) tylosis formation; 3) host cell wall modifications, including appositions or other cell wall thickenings; and 4) unusual cross wall formation in some cells, and cell hypertrophy and hyperplasia. Tylosis walls labelled for pectin and cellulose and many displayed inner suberin-like layers. These layers were also noted in cells of the medullary sheath and in many cells with dense content and thickened walls in the barrier zones that had formed. These zones also contained fibres with newly-formed gelatinous-like layers. In the vicinity of these cells, host cell walls were frequently altered, associated with opaque matter. Many small particles present in chains also occurred in some of these cells, which contained only ...
Bioresource Technology, 1998
Bacteria were isolated from different naturally polluted environments. Metal-resistant bacteria w... more Bacteria were isolated from different naturally polluted environments. Metal-resistant bacteria were selected and minimal inhibitory concentrations of heavy metals (MICs) for each isolate were determined. In addition, the mobility of the most important metallic cations (Cu, Zn, Cr, Cd, Co, Hg) was evaluated by comparing results obtained by two tests of toxicity in solid and liquid media. Results of the test of toxicity in solid media agreed with those in liquid, however, inhibitory concentrations in solid media were much higher than those in liquid. The range of metal concentrations tolerated in solid and liquid media yielded information on the capacity of adsorption and complexation of the metals. Mercury, and to a lesser degree copper, seemed to have a good capacity for adsorption and complexation and, consequently, had a limited diffusion in different naturally polluted environments. The presence of metals in the growth medium allowed us to maintain the tolerance of bacteria at a comparable level with that observed in naturally polluted environments. Cu and Cr were the best tolerated metals. Hg was the most toxic component for all bacteria, followed by Co and Cd. Pseudomonas aeruginosa (strain $6), with a relatively high MIC for metals and a large spectrum of antibiotic resistance appears to be a bacterial model for eco-toxicological studies.
Bioresource Technology, 1998
The biosorption of the heavy metals most frequently found in polluted environments by Pseudomonas... more The biosorption of the heavy metals most frequently found in polluted environments by Pseudomonas aeruginosa and Bacillus thuringiensis was studied.
Using two cultivars (the susceptible ILC482 and the moderately resistant INRAT 87/1) of chickpea ... more Using two cultivars (the susceptible ILC482 and the moderately resistant INRAT 87/1) of chickpea (Cicer arietinum), the antagonistic activities of 21 Rhizobium isolates were tested in vitro in dual culture, and in vivo under greenhouse and field conditions against Fusarium oxysporum f.sp. ciceris (Foc) race 0, the causal agent of Fusarium wilt of chickpea. In dual culture, 14 isolates inhibited the mycelial growth of the pathogen more than 30% and the most effective were Rh8, Rh11, Rh16 and PchSOM, which inhibited fungal growth more than 50%. Among the 14 Rhizobium isolates tested for volatiles, cyanide production and phosphate solubilisation, 8 significantly inhibited fungal growth by producing volatiles, 6 were positive for cyanide production and only three were able to solubilise phosphate. Isolate Rh8 produced the highest levels of volatiles, giving more than 10.7% fungal inhibition, and was the only one positive for both cyanide production and phosphate solubilisation. Greenhouse experiments on the same 14 isolates revealed the effectiveness of five: PchDMS, Pch 121, Rh5, Rh17 and Pch43. These reduced the percentage of wilted plants in both susceptible and moderately resistant cultivars. These percentages ranged from 12.5 to 54.6% in the susceptible cultivar ILC482 and from 8.3 to 29.1% in the moderately resistant cultivar INRAT 87/1. The best disease control was achieved by isolate PchDMS. Despite its effectiveness in vitro, isolate Rh8 was ineffective under greenhouse conditions. Field experiments showed that none of the 14 Rhizobium isolates significantly reduced the percentage of wilted plants of the susceptible cultivar ILC482, although with the moderately resistant cultivar INRAT 87/1 eight of the isolates significantly reduced wilt incidence. Inoculation of seeds with these isolates reduced the percentage of diseased plants from more than 48.6% in infected control plants to less than 20.3% in plants inoculated with the bacteria and infected with the pathogen.
Bioresource Technology, 1998
This paper deals with the evaluation of the availability of mineral nitrogen in soil amended with... more This paper deals with the evaluation of the availability of mineral nitrogen in soil amended with different organic wastes (sewage sludges, farm manure, and compost of municipal solid wastes) and the impact of an additional amount of Cu, Zn and Cd on N-mineralization. ...
Microbial Ecology, 2001
The aim of this study was to characterize the impact of heavy metals on phenotypical markers of P... more The aim of this study was to characterize the impact of heavy metals on phenotypical markers of Pseudomonas aeruginosa. Twenty-two isolates of P. aeruginosa, either clinical (20) or secondary treated wasterwater (2), were used to inoculate micro-ecosystems of sterile distilled water or secondary waste effluent in the presence of subminimal inhibitory concentrations of a variety of heavy metals commonly encountered in the aquatic naturally habitat (Ca2+, Co2+, Cr3+, Cu2+, Hg2+, Ni2+, Zn2+). Micro-ecosystems were exposed to visible light at laboratory temperature and individual strains were reisolated after a 1-, 3-, or 6-month period. The re-isolates (129) were characterized using hierarchical classification analysis in order to define affinities among variants of P. aeruginosa. Subsequently, discriminant analysis was used to detect eventual relationships among the different phenotypical markers studied. Results of the hierarchical classification, based on qualitative or quantitative approaches, showed clearly that incubation of P. aeruginosa in the presence of heavy metals altered the studied phenotypical markers, namely serotype, phage type, MIC of metals, and pyocin type. Discriminant analysis showed that the studied phenotypical markers could be classified into four clusters: C1 (L1 and L2 phage types, Hg tolerance and/or resistance, S2 serotype), C2 (P2 pyocin type, Cd tolerance and/or resistance, S1 serotype), C3 (Co and Cr tolerance and/or resistance) and C4 (P1 pyocin type, Ni, Zn, and Cu tolerance and/or resistance).
Environmental and Experimental Botany, 2007
Twenty-one isolates of microorganisms, including Bacillus spp., Rhizobium spp., Ulocladium atrum,... more Twenty-one isolates of microorganisms, including Bacillus spp., Rhizobium spp., Ulocladium atrum, Candida guilliermondii, Pseudomonas sp., Rahnella aquatilis and other bacteria not yet identified, were tested to determine their effects on the mycelial growth and the sporulation of Fusarium oxysporum f.sp. albedinis (Foa), the causal agent of bayoud on date palm. The potential of these antagonists in the induction of defense reactions in date palm seedlings was also studied. Four bacteria, B. pumilus W1, R. aquatilis W2, B. cereus X16 and n.d. S1, have exhibited a high inhibition toward mycelial growth of Foa (70-77%), and its sporulation (80-95% of the control). Moreover, cytological alterations have been detected in the Foa mycelium grown in the inhibition zone. Application of these antagonists into date palm seedlings has led to trigger defense reactions with an accumulation of non-constitutive hydroxycinnamic acid derivatives, such as the sinapic derivative I2, known to play a crucial role in resistance of date palm to Foa. This reaction was more pronounced in resistant cultivar (BSTN) than in susceptible (JHL). The combined effects of direct and indirect actions of Foa antagonists are discussed in the hope of providing a biocontrol strategy against bayoud.
Plant Physiology and Biochemistry, 2007
Differential expression of phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) and isoflav... more Differential expression of phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) and isoflavone reductase (IFR) genes involved in phenylpropanoids metabolism was investigated using Northern blot analyses in chickpea seedlings bacterized with Rhizobium isolates (PchDMS and Pch43) and further challenged with Fusarium oxysporum f. sp. ciceris (Foc) race 0. Gene activation patterns in the moderately resistant accession INRAT87/1 were compared with those exhibited by the susceptible accession ILC482 at various time intervals after inoculation with Foc, to determine whether differences in levels or timing of transcript accumulation could be correlated with differences in the susceptibility of chickpea accessions to Foc. Gene activation was higher in the moderately resistant accession INRAT87/1 than in the susceptible ILC482. Pre-treatment of chickpea seedlings with Rhizobium isolates before inoculation with the pathogen enhanced the accumulation of the three genes' mRNA transcripts. In parallel, changes in the soluble phenolic pool produced through pathways involving these enzymes were analyzed in chickpea roots. A strong accumulation of these compounds was revealed at 72 hpi in both accessions. After that time, these high levels of phenolic compounds were maintained until the end of the experiment in the moderately resistant accession, while they have significantly declined in the susceptible accession. HPLC analyses revealed a very high accumulation of the constitutive isoflavones, formononetin and biochanin A and their glycoside conjugates in chickpea roots inoculated with Rhizobium isolates and/or challenged with Foc, as compared to the controls. Our results suggest that the increased accumulation of phenolic compounds, observed in chickpea seedlings inoculated with Foc, can be attributed to increased expression of genes in the phenylpropanoid pathway and that such gene expression is enhanced by pre-treatment with Rhizobium isolates.
Bioresource Technology, 2000
Eciency of UV disinfection of un®ltered and ®ltered secondary wastewater euent, using a large-sca... more Eciency of UV disinfection of un®ltered and ®ltered secondary wastewater euent, using a large-scale pilot system, and the inactivation of six bacterial species in a laboratory UV-device have been studied. Pilot plant studies revealed low levels of coliforms and streptococci (3 logarithmic units reduction) when a wastewater UV transmission of 45% and an average eective UV dose of 100 mW s cm À2 were used. By contrast, removal of Pseudomonas aeruginosa appeared insucient (<1.1 logarithmic units). Laboratory investigations, using the six bacterial species as reference, showed that the kinetics of bacterial removal agreed with the model of Chick±Watson, which is formulated by the equation dN adt Àk H C n N . It also appeared, that according to the UV dose applied, two types of inactivation prevailed: a high rate of inactivation, with weak UV doses, and a low rate of inactivation with relatively high doses. Each examined strain was characterised by two K coecients, (K 1 and K 2 ). Lower the K value, more the bacterial resistance to UV. Hierarchical classi®cation of bacteria, based on the values of kinetic constants, revealed three groups of dierent sensitivity to UV. A resistant group, represented by the two strains of P. aeruginosa ATCC 15442 and Bacillus subtilis 6633, and a sensitive group, with the strain of Escherichia coli ATCC 11229. A medium group was represented by Enterococcus faecalis ATCC 19433, Serratia marcescens ATCC 8100 and P. aeruginosa S21. Kinetic studies revealed that the ®rst instants of exposure (2±10 s) to a UV intensity of 5±8 mW cm À2 appeared as deciding factors in the disinfection with UV irradiation. The importance of cumulative UV dose was only secondary. Photoreactivation of micro-organisms following UV disinfection was observed with all bacterial strains studied here, except for P. aeruginosa ATCC 15442, P. aeruginosa ATCC 15442 mutant m1 and Enterococcus hirae ATCC 10541. Ó
Bioresource Technology, 2001
Phytopathologia Mediterranea, 2003
The interaction of Fusarium roseum var. sambucinum, the causal agent of potato dry rot, with two ... more The interaction of Fusarium roseum var. sambucinum, the causal agent of potato dry rot, with two antagonistic bacteria, Bacillus cereus X16 and B. thuringiensis 55T, was studied on wounded potato tubers using light and electron microscopy. Application of B. cereus X16 or B. thuringiensis 55T to potato wounds before challenge with the pathogen suppressed dry rot and restricted fungal growth in plant tissues to the first few cell layers beneath the site of inoculation. Both bacterial antagonists penetrated into potato tissues and established themselves through intercellular and intracellular proliferation. The extent of Fusarium colonization was appreciably reduced in the bacterized tubers, and most fungal cells in these tubers were severely damaged, with appreciable morphological and structural changes. In potato tubers bacterized by B. thuringiensis 55T, Fusarium invasion of the host tissues did not stimulate structural host reactions, and direct parasitism, which operates by degrad...
Journal of Plant Pathology, 2001
SUMMARY A total of 83 spore-forming bacteria belonging to the genus Bacillus was isolated from Tu... more SUMMARY A total of 83 spore-forming bacteria belonging to the genus Bacillus was isolated from Tunisian salty soils. These isolates as well as five additional strains of Bacillus thuringiensis, previously selected for their efficiency against insects, were tested in vitro and in vivo against Fusarium roseum var. sambucinum, the causal agent of dry rot of potato tubers. Results of the in vitro dual culture screening revealed that more than 50% of Bacillus spp. isolated from salty soils inhibited the growth of the pathogen in vitro. By contrast, all five B. thuringiensis strains failed to inhibit the growth of the pathogen in vitro. On wounded potato tubers, the most effective isolates obtained from salty soils were X7, X9, X16, I32 and G7, with a percentage of dry rot reduction ranging from 66 to 89%. These effective Bacillus isolates were identified as belonging to one of the species B. cereus (X9, X16 and G7), B. lentimorbus (X7) or B. licheniformis (I32). Although ineffective in v...
This report presents a survey of previous and more recent ultrastructural and cytochemical invest... more This report presents a survey of previous and more recent ultrastructural and cytochemical investigations of disease development in elm, caused by Ophiostoma novo-ulmi, with results of some comparative studies of other wilt diseases caused by f.spp., of Fusarium oxysporum and of Verticillium sp. For cytochemical studies, probes complexed to colloidal gold to detect cellulose, pectin, chitin, and DNA were used. Thus, the formation of tyloses, pit membrane alterations, and the disease effect on parenchyma cells in mature as well as in young tissue were characterized. Vessel lumina in these plants, in diverse situations, contained heterogeneous matter, among which occurred masses of opaque matter and in certain instances pectin fibrils secreted by parenchyma cells and tyloses. Numerous globoid, opaque bodies of regular sizes, which have been mostly overlooked previously, abounded in vessel elements of U. americana and U. glabra, including trees injected with glucose solutions prior to ...
Phytoprotection, 2006
Various cell reactions occurred in staghorn sumac plants inoculated with Fusarium oxysporum f. sp... more Various cell reactions occurred in staghorn sumac plants inoculated with Fusarium oxysporum f. sp. callistephi. Light and transmission electron microscopy observations and results of cytochemical tests showed: 1) increased laticifers and latex production in the phloem; 2) tylosis formation; 3) host cell wall modifications, including appositions or other cell wall thickenings; and 4) unusual cross wall formation in some cells, and cell hypertrophy and hyperplasia. Tylosis walls labelled for pectin and cellulose and many displayed inner suberin-like layers. These layers were also noted in cells of the medullary sheath and in many cells with dense content and thickened walls in the barrier zones that had formed. These zones also contained fibres with newly-formed gelatinous-like layers. In the vicinity of these cells, host cell walls were frequently altered, associated with opaque matter. Many small particles present in chains also occurred in some of these cells, which contained only ...
Bioresource Technology, 1998
Bacteria were isolated from different naturally polluted environments. Metal-resistant bacteria w... more Bacteria were isolated from different naturally polluted environments. Metal-resistant bacteria were selected and minimal inhibitory concentrations of heavy metals (MICs) for each isolate were determined. In addition, the mobility of the most important metallic cations (Cu, Zn, Cr, Cd, Co, Hg) was evaluated by comparing results obtained by two tests of toxicity in solid and liquid media. Results of the test of toxicity in solid media agreed with those in liquid, however, inhibitory concentrations in solid media were much higher than those in liquid. The range of metal concentrations tolerated in solid and liquid media yielded information on the capacity of adsorption and complexation of the metals. Mercury, and to a lesser degree copper, seemed to have a good capacity for adsorption and complexation and, consequently, had a limited diffusion in different naturally polluted environments. The presence of metals in the growth medium allowed us to maintain the tolerance of bacteria at a comparable level with that observed in naturally polluted environments. Cu and Cr were the best tolerated metals. Hg was the most toxic component for all bacteria, followed by Co and Cd. Pseudomonas aeruginosa (strain $6), with a relatively high MIC for metals and a large spectrum of antibiotic resistance appears to be a bacterial model for eco-toxicological studies.
Bioresource Technology, 1998
The biosorption of the heavy metals most frequently found in polluted environments by Pseudomonas... more The biosorption of the heavy metals most frequently found in polluted environments by Pseudomonas aeruginosa and Bacillus thuringiensis was studied.
Using two cultivars (the susceptible ILC482 and the moderately resistant INRAT 87/1) of chickpea ... more Using two cultivars (the susceptible ILC482 and the moderately resistant INRAT 87/1) of chickpea (Cicer arietinum), the antagonistic activities of 21 Rhizobium isolates were tested in vitro in dual culture, and in vivo under greenhouse and field conditions against Fusarium oxysporum f.sp. ciceris (Foc) race 0, the causal agent of Fusarium wilt of chickpea. In dual culture, 14 isolates inhibited the mycelial growth of the pathogen more than 30% and the most effective were Rh8, Rh11, Rh16 and PchSOM, which inhibited fungal growth more than 50%. Among the 14 Rhizobium isolates tested for volatiles, cyanide production and phosphate solubilisation, 8 significantly inhibited fungal growth by producing volatiles, 6 were positive for cyanide production and only three were able to solubilise phosphate. Isolate Rh8 produced the highest levels of volatiles, giving more than 10.7% fungal inhibition, and was the only one positive for both cyanide production and phosphate solubilisation. Greenhouse experiments on the same 14 isolates revealed the effectiveness of five: PchDMS, Pch 121, Rh5, Rh17 and Pch43. These reduced the percentage of wilted plants in both susceptible and moderately resistant cultivars. These percentages ranged from 12.5 to 54.6% in the susceptible cultivar ILC482 and from 8.3 to 29.1% in the moderately resistant cultivar INRAT 87/1. The best disease control was achieved by isolate PchDMS. Despite its effectiveness in vitro, isolate Rh8 was ineffective under greenhouse conditions. Field experiments showed that none of the 14 Rhizobium isolates significantly reduced the percentage of wilted plants of the susceptible cultivar ILC482, although with the moderately resistant cultivar INRAT 87/1 eight of the isolates significantly reduced wilt incidence. Inoculation of seeds with these isolates reduced the percentage of diseased plants from more than 48.6% in infected control plants to less than 20.3% in plants inoculated with the bacteria and infected with the pathogen.
Bioresource Technology, 1998
This paper deals with the evaluation of the availability of mineral nitrogen in soil amended with... more This paper deals with the evaluation of the availability of mineral nitrogen in soil amended with different organic wastes (sewage sludges, farm manure, and compost of municipal solid wastes) and the impact of an additional amount of Cu, Zn and Cd on N-mineralization. ...
Microbial Ecology, 2001
The aim of this study was to characterize the impact of heavy metals on phenotypical markers of P... more The aim of this study was to characterize the impact of heavy metals on phenotypical markers of Pseudomonas aeruginosa. Twenty-two isolates of P. aeruginosa, either clinical (20) or secondary treated wasterwater (2), were used to inoculate micro-ecosystems of sterile distilled water or secondary waste effluent in the presence of subminimal inhibitory concentrations of a variety of heavy metals commonly encountered in the aquatic naturally habitat (Ca2+, Co2+, Cr3+, Cu2+, Hg2+, Ni2+, Zn2+). Micro-ecosystems were exposed to visible light at laboratory temperature and individual strains were reisolated after a 1-, 3-, or 6-month period. The re-isolates (129) were characterized using hierarchical classification analysis in order to define affinities among variants of P. aeruginosa. Subsequently, discriminant analysis was used to detect eventual relationships among the different phenotypical markers studied. Results of the hierarchical classification, based on qualitative or quantitative approaches, showed clearly that incubation of P. aeruginosa in the presence of heavy metals altered the studied phenotypical markers, namely serotype, phage type, MIC of metals, and pyocin type. Discriminant analysis showed that the studied phenotypical markers could be classified into four clusters: C1 (L1 and L2 phage types, Hg tolerance and/or resistance, S2 serotype), C2 (P2 pyocin type, Cd tolerance and/or resistance, S1 serotype), C3 (Co and Cr tolerance and/or resistance) and C4 (P1 pyocin type, Ni, Zn, and Cu tolerance and/or resistance).
Environmental and Experimental Botany, 2007
Twenty-one isolates of microorganisms, including Bacillus spp., Rhizobium spp., Ulocladium atrum,... more Twenty-one isolates of microorganisms, including Bacillus spp., Rhizobium spp., Ulocladium atrum, Candida guilliermondii, Pseudomonas sp., Rahnella aquatilis and other bacteria not yet identified, were tested to determine their effects on the mycelial growth and the sporulation of Fusarium oxysporum f.sp. albedinis (Foa), the causal agent of bayoud on date palm. The potential of these antagonists in the induction of defense reactions in date palm seedlings was also studied. Four bacteria, B. pumilus W1, R. aquatilis W2, B. cereus X16 and n.d. S1, have exhibited a high inhibition toward mycelial growth of Foa (70-77%), and its sporulation (80-95% of the control). Moreover, cytological alterations have been detected in the Foa mycelium grown in the inhibition zone. Application of these antagonists into date palm seedlings has led to trigger defense reactions with an accumulation of non-constitutive hydroxycinnamic acid derivatives, such as the sinapic derivative I2, known to play a crucial role in resistance of date palm to Foa. This reaction was more pronounced in resistant cultivar (BSTN) than in susceptible (JHL). The combined effects of direct and indirect actions of Foa antagonists are discussed in the hope of providing a biocontrol strategy against bayoud.
Plant Physiology and Biochemistry, 2007
Differential expression of phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) and isoflav... more Differential expression of phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) and isoflavone reductase (IFR) genes involved in phenylpropanoids metabolism was investigated using Northern blot analyses in chickpea seedlings bacterized with Rhizobium isolates (PchDMS and Pch43) and further challenged with Fusarium oxysporum f. sp. ciceris (Foc) race 0. Gene activation patterns in the moderately resistant accession INRAT87/1 were compared with those exhibited by the susceptible accession ILC482 at various time intervals after inoculation with Foc, to determine whether differences in levels or timing of transcript accumulation could be correlated with differences in the susceptibility of chickpea accessions to Foc. Gene activation was higher in the moderately resistant accession INRAT87/1 than in the susceptible ILC482. Pre-treatment of chickpea seedlings with Rhizobium isolates before inoculation with the pathogen enhanced the accumulation of the three genes' mRNA transcripts. In parallel, changes in the soluble phenolic pool produced through pathways involving these enzymes were analyzed in chickpea roots. A strong accumulation of these compounds was revealed at 72 hpi in both accessions. After that time, these high levels of phenolic compounds were maintained until the end of the experiment in the moderately resistant accession, while they have significantly declined in the susceptible accession. HPLC analyses revealed a very high accumulation of the constitutive isoflavones, formononetin and biochanin A and their glycoside conjugates in chickpea roots inoculated with Rhizobium isolates and/or challenged with Foc, as compared to the controls. Our results suggest that the increased accumulation of phenolic compounds, observed in chickpea seedlings inoculated with Foc, can be attributed to increased expression of genes in the phenylpropanoid pathway and that such gene expression is enhanced by pre-treatment with Rhizobium isolates.
Bioresource Technology, 2000
Eciency of UV disinfection of un®ltered and ®ltered secondary wastewater euent, using a large-sca... more Eciency of UV disinfection of un®ltered and ®ltered secondary wastewater euent, using a large-scale pilot system, and the inactivation of six bacterial species in a laboratory UV-device have been studied. Pilot plant studies revealed low levels of coliforms and streptococci (3 logarithmic units reduction) when a wastewater UV transmission of 45% and an average eective UV dose of 100 mW s cm À2 were used. By contrast, removal of Pseudomonas aeruginosa appeared insucient (<1.1 logarithmic units). Laboratory investigations, using the six bacterial species as reference, showed that the kinetics of bacterial removal agreed with the model of Chick±Watson, which is formulated by the equation dN adt Àk H C n N . It also appeared, that according to the UV dose applied, two types of inactivation prevailed: a high rate of inactivation, with weak UV doses, and a low rate of inactivation with relatively high doses. Each examined strain was characterised by two K coecients, (K 1 and K 2 ). Lower the K value, more the bacterial resistance to UV. Hierarchical classi®cation of bacteria, based on the values of kinetic constants, revealed three groups of dierent sensitivity to UV. A resistant group, represented by the two strains of P. aeruginosa ATCC 15442 and Bacillus subtilis 6633, and a sensitive group, with the strain of Escherichia coli ATCC 11229. A medium group was represented by Enterococcus faecalis ATCC 19433, Serratia marcescens ATCC 8100 and P. aeruginosa S21. Kinetic studies revealed that the ®rst instants of exposure (2±10 s) to a UV intensity of 5±8 mW cm À2 appeared as deciding factors in the disinfection with UV irradiation. The importance of cumulative UV dose was only secondary. Photoreactivation of micro-organisms following UV disinfection was observed with all bacterial strains studied here, except for P. aeruginosa ATCC 15442, P. aeruginosa ATCC 15442 mutant m1 and Enterococcus hirae ATCC 10541. Ó
Bioresource Technology, 2001