No abstract

Bioremediation is a biological process to remove or neutralize environmental pollutants. This study was carried out to investing at the efficacy of arsenic resistant endophytic bacteria isolated from Pteris vittata, Pityrogramma calomelanos, Blenchum orientale, and Nephrolepis exaltata, which grow in a highly arsenic (As) contamination mining site in Vietnam. Their segmented roots, stems, and leaves were homogenized separately and inoculated on LB agar plates containing 5mM As(III) and As(V). A total of 31 arsenic resistant endophytic strains were selected, in which strain R2.5.2 isolated from the root of P. calomelanos had the highest arsenic resistant capability. Strain R2.5.2 tolerated up to 320 mM and 160 mM of arsenate and arsenite, respectively. The strain developed well on a media of 0.1 5% NaCl, at 20-40ºC and pH 5 9, and actively utilized most of the sugar sources. It had a high IAA biosynthesis capacity with an average concentration of 19.14 mg/L, tolerated to 0.5-16 mM concentration of Ag+, Hg2+, Co2+, Ni2+, Cu2+, Cr4+, and reduced As(V). Based on 16s rDNA, R2.5.2 was identified as Priestia megaterium. The ars C gene coding for arsenate reductase catalyzing reduction of As(V) was successfully amplified in P. megaterium R2.5.2.  The selected strain may have potential use for bioremediation practice.

Endophytic actinomycetes colonize in living plant tissues without causing harm to the host plant. In fact, they are regarded as effective bio-control agents and plant growth promoters due to their ability to activate plant self-immunity and produce biologically active secondary metabolites. Recent studies reported higher rates in finding new strains and antimicrobial substances among endophytes than actinomycetes from soil and plant surface. In this work, endophytic actinomycetes were isolated from Ham Yen orange trees, a famous specialty of Tuyen Quang province, and screened for antimicrobial activity against plant pathogenic bacteria and fungi. The isolate TQR8-14, showing strong activity, was studied with regard to its biological and taxonomical characteristics and production of antimicrobial substance. Based on the mycelial morphology, this isolate was placed in yellow group of streptomycetes. The isolate developed milky to yellow aerial mycelia on all test media and long straight spore chains bearing smooth cylinder spores. The isolate could grow at wide range of temperature 15 to 45oC, of pH 4 to 10; on substrates such as carboxy methyl cellulose, starch, protein and chitin; and tolerated up to 3% salinity. Its 16S rDNA nucleotide sequence (1,404 bp) shared 99% similarity to Streptomyces parvus. Therefore, the isolate was named as Streptomyces parvus TQR8-14. The highest antimicrobial activity was achieved in culture on medium AH4 containing soybean meal and glucose, at 30oC and pH 7.0.

Penicillium digitatum is a major pathogen of post-harvest decay on orange fruits. In Vietnam, the control of P. digitatum is usually done mostly with use of chemicals which advertly affect on local environment and human health. Recently, nanomaterials show significant effectiveness in treating pathogenic fungi without harming the environment and human health. Therefore, nanomaterials are regarded as promising agents in plant protection and post-harvest processing. In this study, a fungus labeled as N11 causing green mould disease was isolated from decayed orange fruits of Tuyen Quang province and identified as Penicillium digitatum N11. The fungus was subjected to treatment with silver and copper nanoparticles and nano composites to evaluate the effectiveness of those materials on inhibition of fungal growth. Various concentrations of the nanoparticles were tested for different growth stages of the fungus. For silver and copper nanoparticles, the inhibition of fungal growth up to 50% was observed after 21 days of inoculation at the concentrations of 200-400 ppm and 250 ppm, respectively. At 500 ppm, copper nanoparticles completely inhibited the growth of P. digitatum N11. Nano composite Ag-silica (AgS) showed stronger inhibition of fungal growth than Ag-Bentonite (AgB) nano composite. In the treatment of fungal spores, inhibition of germination up to 90% for three days was observed at the concentrations of 1000 ppm for Cu, over 200 ppm for Ag nanoparticles, over 2000 ppm of AgS nano composite and 4000 ppm of AgB nano composite.

Soybean is a high valuable crop of Vietnam and many other countries. The ability of soybean plants in nitrogen fixation and soil improvement is attributed to their symbiosis with different rhizobia in the root nodules. It has been well documented that members of genus Rhizobium are the most effective in nodulation and nitrogen fixation in legumes. Recently, in oder to minimize undesired accumulation of agro-chemicals and metal salts in soil, nanotechnology products have been intensively studied and applied as nanofertilizers. In this report, the effect of nanoparticles of iron, cobalt and copper on the in vitro growth of nitrogen fixing bacterium Sinorhizobium fredii T14 and nodulation in the root of soybean DT26 was studied. In the cultures of S. fredii T14, nano Fe at the final concentrations of 2, 5, 10, 25 and 50 ppm did not affect the growth, but the latter was reduced of 20, 35 and 46% at 100, 250 and 500 ppm, respectively. No growth inhibition was observed at nano Co concentrations below 10 ppm, while it was reduced of 73% at 500 ppm. Nano Cu seemed to have significant adverse effect on S. fredii T14, showing growth inhibition of 23, 68 and 100% at the concentrations of 5, 25 ppm and 50 ppm, respectively. The production of extracellular polysaccharide by S. fredii T14 was not affected at the concentrations of nano Fe and Co below 250 ppm, while drastic decrease occurred at the presence of nano Cu. Laboratory experiments showed that nanoparticles of all three studied metals at extremely low concentration of 2 ppm significantly increased the number of effective nodules in the roots of soybean DT26 and enhanced the plant growth.