Saad A. Alamri

Effect of nitrogen supply and Azospirillum brasilense Sp-248 on the response of wheat to seawater irrigation.

Response of wheat to Azospirillum brasilense Sp-248 inoculation with different N-fertilizer levels using seawater irrigation was investigated. All inoculated treatments increased plant height, shoot and root dry weight, and tiller number in compared with uninoculated treatments. Yield parameters measured were also increased due to the inoculation. In terms of the effect of saline irrigation, there were no significant differences in growth and yield parameters in plants treated with tap water and others irrigated with 8.0% seawater concentration. This would indicate a relatively high tolerance of A. brasilense to saline irrigation and its ability to reduce the deleterious effects of saline on growth by increasing the plants adaptation. However, increasing the seawater concentration in the irrigation water to 16.0% significantly decreased all tested parameters. Inoculation treatments generally increased NPKCa contents and decreased sodium ratio of the grains in compared with the uninoculated treatments. Overall results clearly revealed that the Azospirillum inoculation saved about 20 units of N-fertilizer and that saving was made economically feasible by decreasing the chemical fertilizers needed, improving the nitrogen content and counteracting the effects of salinity.

Selective inhibition of toxic cyanobacteria by β-carboline-containing bacterium Bacillus flexus isolated from Saudi freshwaters.

A bacterial strain SSZ01 isolated from a eutrophic lake in Saudi Arabia dominated by cyanobacterial blooms, showed an antialgal activity against cyanobacteria species. Based on the analysis of the 16S rDNA gene sequence, the isolated strain (SSZ01) most likely belonged to the genus Bacillus with a 99% similarity to Bacillus flexus strain EMGA5. The thin layer chromatography (TLC) analysis of the ethyl acetate extract of this bacterium revealed that this strain can produce harmine and norharmane compared to different β-carboline analog standards. Harmine and norharmane were also detected in considerable amounts in bacterial growth medium, indicating a potential excretion of these compounds into the aquatic environment. The crude extract of Bacillus flexus as well as pure materials of harmine and norharmane inhibited the growth of tested species of cyanobacteria. However, the bacterial crude extract has a higher toxicity against tested species of cyanobacteria than harmine and norharmane. In addition, harmine was more toxic to cyanobacteria than norharmane. On the other hand, neither pure compounds of harmine and norharmane nor crude bacterial extract showed any antialgal activity against tested species of green algae. The results of the present study suggest that B. flexus SSZ01 or its crude extract containing harmine and norharmane could be a candidate for the selective control of cyanobacterial blooms without affecting other algal species.

In vitro antifungal activity of Argemone ochroleuca Sweet latex against some pathogenic fungi

The in vitro antifungal activities of crude latex of Argemone ochroleuca Sweet against four clinical isolates of Candida (Candida albicans, Candida glabrata, Candida krusei and Candida tropicalis) and six isolates of plant pathogenic fungi (Alternaria alternate, Drechslera halodes, Fusarium oxysporum, Macrophomina phaseolina, Pythium ultimum and Rhizoctoina solani) were assessed using well diffusion method. The chemical compounds of the hexan extract of A. ochroleuca latex were investigated using Perkin-Elmer Gas chromatography-Mass spectrometry. The latex of A. ochroleuca showed antifungal activity against D. halodes (10.60 mm) and Candida spp. (15.06 to 20.16 mm). GC-MS analysis of the hexan extract of A. ochroleuca latex revealed that the latex contains diethyl phthalate (81.57%), 6-Nitro-imidazo(1,2-a)pyridine compound (8.833%), cyclohexasiloxane, dodecamethyl(5.607%), 4-(2,2-Dimethyl-6-methylenecyclohexylidene)-3-methylbutan-2-one compound (2.410%) and cycloheptasiloxane, tetradecamethyl- (1.574%). These findings indicate that the latex of A. ochroleuca could be a good source of antifungal agent against D. halodes and Candida spp. and the phytocomponents present in the latex could be used against fungal pathogens.

Biocontrol of apple blue mould by new yeast strains: Cryptococcus albidus KKUY0017 and Wickerhamomyces anomalus KKUY0051 and their mode of action

Seeking new yeast strains having the ability to protect apple fruits against blue mould for a long time under different storage conditions was the main goal of this work. Based on the in vitro test, yeast strains KKUY0017 and KKUY0051 were selected as the most effective antagonists against Penicillium expansum. Sequencing of 26S rDNA of both yeasts confirmed that the identity of KKUY0017 and KKUY0051 was Cryptococcus albidus and Wickerhamomyces anomalus, respectively. The two strains protected the apple fruits from the blue mould disease under a wide range of temperature (5–30°C); however, W. anomalus KKUY0051 was more effective. At 25°C, W. anomalus KKUY0051 involved in the reduction of disease severity and disease incidence of blue mould by 56.49% and 57.78%, respectively. When either of the two yeasts was applied in concentration of 108 or 109 cells/mL, the maximum reduction in disease severity and disease incidence was achieved. Under cold storage (5°C), both yeast strains succeeded to protect the apple fruits free from the infection up to 24 days. Electron micrograph showed a fit attachment between the cells of C. albidus KKUY0017 and the fungal hyphae leading to the degrading of the hyphae; however, W. anomalus killed the fungal hyphae without direct attachment to them. Gas chromatography–mass spectrometry analysis of the cell-free extract of W. anomalus KKUY0051 revealed the presence of toxic compounds such as the nitrophenol derivatives. The results support the assumption that the main mode of action of this yeast is by killer toxins. We conclude that application of these yeasts under cold storage condition could keep the apple fruits free from blue mould infection for a long time.

Enhancing the efficiency of the bioagent Bacillus subtilis JF419701 against soil-borne phytopathogens by increasing the productivity of fungal cell wall degrading enzymes

This study was devoted to increasing the production of fungal cell wall degrading enzymes by Bacillus subtilis JF419701 to enhance its efficiency in the biological control process. In dual culture, B. subtilis JF419701 showed the highest antagonistic effect of the 256 bacterial strains tested against six soil-borne pathogens, Alternaria alternata, Exserohilum rostratum, Fusarium oxysporum, Macrophomina phaseolina, Pythium ultimum and Rhizoctonia solani. The production potentiality of the enzymes α-1,3-glucanase, β-1,3-glucanase, chitinase and protease by B. subtilis JF419701 was studied in vitro. Results proved that the maximum production of enzymes by this bacterium was achieved after a two-day incubation period at a slightly alkaline pH (8). The addition of colloidal chitin or S-glucan to the growth media enhanced the production of all the enzymes except protease, which was stimulated by casein. This study therefore recommends that to obtain an efficient and strong bioagent culture of B. subtilis JF419701, it is necessary to grow this micro-organism on a specific medium containing either chitin or its derivatives at pH 8 for two days.

Biodegradation and detoxification of aliphatic and aromatic hydrocarbons by new yeast strains

Seeking new efficient hydrocarbon-degrading yeast stains was the main goal of this study. Because microorganisms are greatly affected by the environmental factors, the biodegradation potentiality of the microorganisms varies from climatic area to another. This induces research to develop and optimize the endemic organisms in bioremediation technology. In this study, 67 yeast strains were tested for their growth potentiality on both aliphatic and aromatic hydrocarbons. The most efficient six strains were identified using sequence analysis of the variable D1/D2 domain of the large subunit 26S ribosomal DNA. The identity of these strains was confirmed as Yamadazyma mexicana KKUY-0160, Rhodotorula taiwanensis KKUY-0162, Pichia kluyveri KKUY-0163, Rhodotorula ingeniosa KKUY-0170, Candida pseudointermedia KKUY-0192 and Meyerozyma guilliermondii KKUY-0214. These species are approved for their ability to degrade both aliphatic and aromatic hydrocarbons for the first time in this study. Although, all of them were able to utilize and grow on both hydrocarbons, Rhodotorula taiwanensis KKUY-0162 emerged as the best degrader of octane, and Rhodotorula ingeniosa KKUY-170 was the best degrader of pyrene. GC-MS analysis approved the presence of many chemical compounds that could be transitional or secondary metabolites during the utilization of the hydrocarbons. Our results recommend the application of these yeast species on large scale to approve their efficiency in bioremediation of oil-contamination of the environment. Using these yeasts, either individually or in consortia, could offer a practical solution for aquatic or soil contamination with the crude oil and its derivatives in situ.

Role of Soil Amendment with Micronutrients in Suppression of Certain Soilborne Plant Fungal Diseases: A Review

Micronutrients might affect the resistance of plants to pathogens or disease tolerance. In addition, there are conflicting reports about the effect of micronutrients on plant diseases, and many features that impact this response are unclear. Soil is crucial for micronutrient storage such as Br, Mn, Zn, Cu, Fe and Cl, which can reduce the severity of plant disease by increasing disease tolerance and resistance of plants to pathogens. In particular, micronutrients have significant effects on controlling soilborne plant fungal diseases. Micronutrients can reduce disease to a satisfactory level or at least to a level at which further control by other conventional organic biocides or traditional practices is cheap and more fruitful. This review article recaps the latest information concerning the effect of micronutrients, such as Br, Mn, Zn, Cu, Fe, Cl and Mo, on disease resistance and tolerance and their use in sustainable agriculture. Here, our main focus is the critical analysis of various factors responsible for the suppression of certain plant fungal diseases due to micronutrients. In addition, we have identified efforts to determine key areas where sincere research efforts are still needed to develop strategies for manipulating micronutrient application in such a way that it could be more efficiently utilised in managing soilborne plant fungal diseases.

The efficiency of two new formulated biofungicides in the control of damping-off and root rot of cucumber and improving the plant defence system

The ability of Rhizoleen-T and Rhizoleen-B to suppress the roots’ diseases of cucumber caused by Fusarium oxysporum and Rhizoctonia solani and induction of the plant defence system was evaluated. The results showed a significant suppression in damping-off and root rot of cucumber when the two biofungicides were applied. They increased the surviving percentage of the treated plants to 98.0% and reduced the mean disease rating to 1.0. The biofungicides significantly enhanced the plant’s morphology and physiology when compared with either infected or non-infected control. The mechanism of action of the biofungicides is could be through the enhancement of the plant defences, in addition to their antifungal effect. They stimulated the defence of the plants by increasing the content of proline and phenols and induction the defensin genes. Biofungicides induced defence genes in the 50-day-old treated plants. The biofungicides are effective, cost effective and applicable in the control of root diseases of cucumber.

Application of fluorescence in situ hybridization (FISH) to the analysis of sulfate reducing bacterial community in an oily bench scale reactor

Advances in the field of genomics and meta-genomics have led to rapid and accurate strategies for the monitoring of microbial biodiversity and have revealed its potential for biotechnological applications. In this study, fluorescent in situ hybridization (FISH) as a culture-independent molecular approach using specific CY3-labelled oligonucleotide probes was used to study the dynamics of the sulfate reduction bacterial community (SRB) of the activated sludge from an oily wastewater treatment system. The relative abundance of members of the dominant bacteria in the oily water reactor was determined by FISH for 16S rRNA using EUB338 probes, for detecting general eubacteria, and SRB385 for targeting SRBs and major species of delta- proteobacteria sulfate reducers. The percentage of cells hybridizing with probe EUB338 for the dominant bacteria decreased from 25.85 to 6.25%, while with the SRB385 probe for SRB bacteria, it increased from 7.21 to 10.20% of total cells during the reactor process. These data show that SRB bacteria dominated the active microbial community in the system. It is interesting that delta-proteobacterial SRBs occupied a high percentage and took place in an oily biological system under aerobic conditions. Keywords: Sulfate reducing bacteria, fluorescence in situ hybridization, 16S rRNA oligonucleotide probes, microbial community, dynamics

Enhancing the Biocontrol Efficiency of Trichoderma harzianum JF419706 through Cell Wall Degrading Enzyme Production

The goal of this study was to enhance the biocontrol efficiency of Trichoderma harzianum JF419706 via its mycoparastic affinity as well as inducing the production of cell wall degrading enzymes. Different carbon and nitrogen sources were added to the growing medium of T. harzianum JF419706 to induce cell wall degrading enzymes. Production conditions of the target enzymes were optimized. The mycoparasitic affinity was induced by induction of the mutation of T. harzianum JF419706 by ethidium bromide and UV radiation. Results indicated that 4 days was appropriate to achieve the maximum production of the enzymes. The slight acidic pH (5.5‒6.0) was more favorable for production of enzymes. The results exposed that chitin was responsible for improvement in the productivity of all tested enzymes, except the protease that was improved only by casein. All enzymes exhibited a high level of activity in media supplemented with yeast extract. Ethidium bromide in concentration either 0.5 or 1.0 mg mL-1 enhanced the mycoparasitic affinity of T. harzianum JF419706 more than UV radiation. However, both treatments enhanced the mycoparasitic affinity of the biocontrol agent compared with the wild type. This observation was confirmed by RAPD-PCR technique using primers chitinase (C15) and R2 that succeeded to differentiate among the mutants and the wild isolate.