• Journal of Microbiology and Biotechnology
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• v.24 no.5
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• pp.690-695
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• 2014

Bacterial 1-aminocyclopropane-1-carboxlyate (ACC) deaminase (AcdS) is an enzyme that cleaves ACC, a precursor of the plant hormone ethylene, into ${\alpha}$-ketobutyrate and ammonia. The acdS gene was cloned from Pseudomonas fluorescens, which was capable of improving the seedling of Chinese cabbage under salinity condition. The recombinant AcdS (rAcdS) exhibited optimal activity at pH 8.5 and $30^{\circ}C$. Strong activity was sustained at up to 100 mM NaCl. The polyclonal anti-P. fluorescens AcdS antibody was produced in a rabbit that had been immunized with the purified rAcdS. This antibody successfully recognized the homologous antigens derived from the total proteins of isolated plant growth-promoting microorganisms. A statistically significant correlation was observed between the intensity of hybridization signal and AcdS activity measured by a biochemical method, suggesting its application as a useful indicator for active deaminases.

• Journal of Microbiology and Biotechnology
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• v.11 no.5
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• pp.756-762
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• 2001

As a component for a recirculating aquaculture system, a new strain of denitrifying bacterium was isolated from municipal sewage. The isolate was motile by means of one polar flagellum, catalase-positive, and a Gram-negative rod-shaped cell measuring $0.5-0.6{\mu}m$ in width and $1.3-1.9{\mu}m$ in length. The isolate was identified as Pseudomonas fluorescens and produced dinitrogen gas via the reduction of nitrate. The optimal growth conditions (pH, temperature, carbon source, and C/N ratio) of the isolate were found to be 6.8, $30^{\circ}C$, malate, and 3, respectively. Under optimal growth conditions of P. fluorescens, dinitrogen gas was first detected in the exponential growth phase, then a small amount of nitrite was developed and converted to dinitrogen gas in the stationary phase. Pseudomonas fluorescens cells were immobilized in modified polyvinyl alcohol (PVA) gel beads, and the maximum denitrification rate was measured as $36.6 {\mu}lN_2h^-1$ per bead with an optimum cell loading of $20mg {\mu}l^-1$ and $2\%$ sodium alginate added to the PVA gel. The operating stability of the modified PVA gel beads remained unchanged for up to 43 repeated batches.

• The Plant Pathology Journal
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• v.20 no.1
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• pp.75-80
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• 2004

In an attempt to develop effective biocontrol system for management of stem rot disease in groundnut, 57 bacterial isolates and 13 isolates of Trichoderma spp. were evaluated for their antagonistic activity against Sclerotium rolfsii. The antagonists were selected based on their ability to inhibit the external growth of S. rolfsii from infected groundnut seeds. Four isolates of Pseudomonas fluorescens, GB 4, GB 8, GB 10 and GB 27, and T. viride pq 1 were identified as potent antagonists of S. rolfsii. T. viride pq 1 produced extracellular chitinase and parasitized the mycelium of S. rolfsii. Under controlled environment conditions, P. fluorescens GB 10, GB 27, T. viride pq 1 and the systemic fungicide Thiram(equation omitted) reduced the mortality of S. rolfsii inoculated to groundnut seedlings by 58.0％, 55.9％, 70.0％ and 25.9％, respectively compared to control. In vitro growth of P. fluorescens GB 10 and GB 27 was compatible with T. viride pq 1 and Thiram(equation omitted). Integrated use of these two bacterial isolates with T. viride pq 1 or Thiram(equation omitted) improved their biocontrol efficacy. Combined application of either GB 10 or GB 27 with T. viride pq 1 was significantly effective than that with Thiram(equation omitted) in protecting groundnut seedlings from stem rot infection.

• Journal of Microbiology and Biotechnology
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• v.14 no.4
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• pp.653-657
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• 2004

The cold resistant mutants of P. fluorescens strain $PRS_{9}$ and ATCC13525 were developed which could grow equally well at $28^{\circ}C$ and $10^{\circ}C$. All the mutants were tested for siderophore production, of which $CRPF_9$ (ATCC13525 mutant) was selected, as there was a 16.8-fold increase when compared to its wild-type. Under in vitro conditions, $CRPF_9$ showed better growth promotion both in wheat (29.1% increase in root length) and mung bean (51.5% increase in root length) at $10^{\circ}C$. Greenhouse trials showed a significant increase in root (13.84cm) and shoot (15.0cm) length of $CRPF_9$-treated mung bean seeds, indicating increased rhizocompetence of the mutant. Ferric citrate was a better iron source than ferric hydroxide for plant growth.

• Mycobiology
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• v.32 no.1
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• pp.47-53
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• 2004

Pseudomonas fluorescens 1-94 induced systemic resistance in chickpea against Fusarium wilt of chickpea caused by Fusarium oxysporum f. sp. ciceri by the synthesis and accumulation of phenolic compounds, phenylalanine ammonia lyase(PAL) and pathogenesis related(PR) proteins(chitinase, $\beta$-1,3-glucanase and peroxidase). Time-course accumulation of these enzymes in chickpea plants inoculated with P. fluorescens was significantly(LSD, P=0.05) higher than control. Maximum activities of PR-proteins were recorded at 3 days after inoculation in all induced plants; thereafter, the activity decreased progressively. Five PR peroxidases detected in induced chickpea plants. Molecular mass of these purified peroxidases was 20, 29, 43, 66 and 97 kDa. Purified peroxidases showed antifungal activity against plant pathogenic fungi.

• Mycobiology
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• v.32 no.3
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• pp.139-147
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• 2004

A severe damping-off disease of bush okra caused by Pythium aphanidermatum, was diagnosed in plastic houses in Der Attia village, 15 km southwest of El-Minia city, Egypt, during the winter of 2001. Bush okra seedlings showed low emergence with bare patches inside the plastic houses. Seedlings that escaped pre-emergence damping-off showed poor growth, stunting and eventually collapsed. Examination of the infected tissues confirmed only Pythium aphanidermatum, showing its typical intercalary antheridia, and lobulate zoosporangia. P. aphanidermatum was shown to be pathogenic on bush okra under pot and field experiments. Bacteria making inhibition zones against the damping-off fungus P. aphanidermatum were selected. Agar discs from rhizosphere soil of bush okra containing colonies were transferred onto agar plate culture of P. aphanidermatum. After 2 days of incubation, colonies producing clear zones of non-Pythium growth were readily detected. The two bacteria with the largest inhibition zones were identified as Pseudomonas fluorescens. Bush okra emergence(%) in both pot and plastic houses experiments indicated that disease control could be obtained by applying P. fluorescens to the soil or coating the bacteria to the bush okra seeds before sowing. In the plastic houses, application of the bacteria onto Pythium-infested soil and sowing bush okra seeds dressed with bacteria gave 100% emergence. In addition, This was the first reported disease of bush okra by this oomycete in Egypt.

• The Plant Pathology Journal
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• v.22 no.3
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• pp.289-294
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• 2006

Two isolates of mucous bacteria, mc75 and pc78, were isolated from fungal culture plate as culture contaminants with an interesting swarming motility. Both isolates were identified as Pseudomonas fluorescens based on microscopy, biochemical analysis, Biolog test and DNA sequence analysis of the 16S rRNA gene. Both strains have the exactly the same 16S rRNA gene sequences, and yet their biological control activity were not identical each other. In vitro analysis of antagonistic activity of two isolates against several plant pathogenic fungi indicated that both produced diffusible and volatile antifungal compounds of unknown identities. Treatment of the bacterial culture of P. fluorescens pc78 and its culture filtrate exhibited a strong biological control activity against rice sheath blight in vivo among six plant diseases tested. More effective disease control activity was obtained from treatment of bacterial culture than that of culture filtrate. Therefore, in addition to antifungal compound and siderophore production, other traits such as biofilm formation and swarming motility on plant surface may contribute to the biological control activity of P.fluorescens pc78 and mc75.

• Journal of Microbiology and Biotechnology
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• v.12 no.2
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• pp.249-257
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• 2002

Pseudomonas fluorescens GL20 is a plant growth-promoting rhizobacterium that produces a large amount of hydroxamate siderophore under iron-limited conditions. The strain GL20 considerably inhibited the spore germination and hyphal growth of a plant pathogenic fungus, Fusarium solani, when iron was limited, significantly suppressed the root-rot disease on beans caused by F. solani, and enhanced the plant growth. The mechanism for the beneficial effect of strain GL20 on the disease suppression was due to the siderophore production, evidenced by mutant strains derived from the strain. Analysis of the outer membrane protein profile revealed that the growth of strain GL20 induced the synthesis of specific iron-regulated outer membrane proteins with molecular masses of 85- and 90 kDa as the high-affinity receptors for the ferric siderophore. In addition, a cross-feeding assay revealed the presence of multiple inducible receptors for heterologous siderophores in the strain. In order to induce increased efficacy and potential in biological control of plant disease, a siderophore-overproducing mutant, GL20-S207, was prepared by NTG mutagenesis. The mutant GL20-S207 produced nearly 2.3 times more siderophore than the parent strain. In pot trials of beans with F. solani, the mutant increased plant growth up to 1.5 times compared with that of the parent strain. These results suggest that the plant growth-promoting P. fluorescens GL20 and the genetically bred P. fluorescens GL20-S207 can play an important role in the biological control of soil-borne plant diseases in the rhizosphere.

• Journal of Soil and Groundwater Environment
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• v.12 no.2
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• pp.1-8
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• 2007

A series of batch and column experiments were conducted for the development of biobarrier technology which can be applied to containment and reduction of contaminants in soil and ground waters. The growth kinetic constants of Pseudomonas fluorescens on glucose or molasses were determined using batch experiments. The maximum specific growth rate (Vmax) of P. fluorescens at $23^{\circ}C$ on glucose or molasses were $0.246\;hr^{-1}$ and $0.073\;hr^{-1}$, respectively. However, molasses was selected as carbon source due largely to the absence of lag phase of P. fluorescens growth on molasses and economic reason. In constant head column experiments, the hydraulic conductivity of the column soil reduced by $6.8{\times}10^{-3}$ times from $4.1{\times}10^{-2}cm/sec$ to $2.8{\times}10^{-4}cm/sec$ after the inoculation of P. fluorescens and administration of carbon source and nutrients. The biomass concentration was observed highest in the column inlet. Measurements of carbon source and electron accepter (dissolved oxygen) concentration showed that the growth of P. fluorescence, which is the main reason for hydraulic conductivity reduction, was limited not by the concentration of carbon source but by the concentration of electron acceptor.

• Journal of Food Hygiene and Safety
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• v.16 no.3
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• pp.232-240
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• 2001

One hundred twenty five bacterial isolates were obtained from the brown blotch-diseased oyster mushrooms collected from markets. Among them, 45 were determined as pathogenic bacteria and white line forming organisms(WLFO) were 6 strains and white line reaction organisms (WLRO) were 6 strains. All of the white line forming isolates were identified as Pseudomonas tolaasii which is a known pathogen of brown blotch disease of oyster mushroom by GC-MIS(Gas chromatography-microbial identification system). Six of the white line reacting organisms were identified as P. chlomraphis, P. fluorescens biotype A and type C. The rest of them were P gingeri, P. agarici, P. fluorescens biotype B, P. chloroyaphis, non-pathogenic P. tolaasii, P. putida biotype A and B etc. For spectrum of activity of tolaasin, culture filtrates from pathogenic isolates were examined by browning of mushroom tissue and pitting of mushroom caps. The weak pathogenic bacteria didn't induce browning or pitting of mushroom tissue. On the other hand, strong pathogenic isolates showed browning and pitting reaction on mushroom. An extracellular toxin produced by P. tolaasii, was investigated. The hemolysis activity test of 6 strains identified as P. tolaasii were 0.8∼0.9 at 600 nm and 3 strains of WLRO were 0.9∼1.0 and Pseudomonas app. were 1.0∼1.2. Observation of fresh mushroom tissue using confocal laser scanning microscopy was carried out for images of optical sectioning and vertical sectioning. Also images of brown blotch diseased oyster mushroom tissue after contamination P. tolaasii was obtained by CLSM.