الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
anotechnology provides a valid tool to give effect enhancing and toxicity
reducing of many chemo-preventive compounds that naturally occurring,
like elemental selenium. The synthesis of nanoparticles which have sizes less
than 100 nm in at least one dimension with unique chemical, physical and
biological properties that dissimilar from those of the bulk materials. Chemical
and physical production of SeNPs are expensive, contamination arises from
chemical precursors and products, high toxicity of the used solvents and in many
cases demand specialized equipment.
Biological methods of nanoparticles synthesis are considered to be safe and
called ”green chemistry” as they tend to be an environmentally friendly method
for production of SeNPs because they include natural processes that happen in
living systems. Microorganisms play a major role in the biogeochemical cycle of
selenium in the environment including aerobic and anaerobic selenite reducing
bacteria. However, these methods also have some drawbacks, this limitation has
been overcome by optimizing the growth condition for the microorganisms
through the adjustment of factors such as the pH, incubation time, temperature
and metal salt concentrations. Metal ions are often absorbed into the cells,
reduced and deposited in intracellular space of microorganisms to form NPs.
Not only intracellular but also extracellular elemental selenium formation was
detected, although accumulation of SeNPs was mainly observed inside the
bacterial cell.
Forty-nine samples were collected from different places inside Menoufia
governorate. The samples vary between soil and wastewater samples. Only one
sample was from outside the governorate, a salted water sample, was collected
from Wadi Al-Natrun. These samples were collected due to the presence of
selenium in these environments and thus the presence of microorganisms that
can reduce it and form selenium nanoparticles.
Seventy-four isolates were obtained had the ability to reduce selenium from
the enriched cultures. These isolates were screened for extracellular reduction of
selenium. As some members of bacteria can reduce it extracellular by secreting
some metabolites that enables bacteria to use selenium ion as terminal electron
acceptor and reduce soluble selenite to insoluble elemental selenium or through
either detoxification or redox homeostasis.
Eighteen isolate was obtained had the ability to reduce selenium
extracellular. Those were a source not only of bio reducing microorganisms, but
also of bioactive substances with potential use for controlling reduction activity
and size control of the produced nanoparticles. In our study, the effect of
different concentrations of sodium selenite, highlight the best isolates that can
tolerate high concentrations of oxyanions over the others. Three isolates had the
ability to reduce it at 7 g/l. The reduction is due to the ability of bacteria to
secrete metabolic materials act as electron donors to selenium ion and turn it
into an atom. Also the high concentrations of selenium activate detoxication
processes, which transform selenite to elemental selenium (Se0).
The selected isolates were identified following Bergey’s manual of
systematic Bacteriology (1989) and genotypic characterization indicated that
that the isolates belonged to Streptococcus pyogenes, Streptococcus salivarius
and Bacillus pumilus. These were the strains, which gave the best bioreduction
rate.
Different media were used to test the reduction activity of the three selected
strains. As a result of this, the highest reduction activities were obtained in the case of Bennet medium for Streptococcus pyogenes strain AOS20,
Streptococcus salivarius strain AOS38 and on Nutrient broth medium for
Bacillus pumilus strain AOS68.
The phytochemical studies of crude extracts obtained from fermentation of
reducing bacteria in different culture media was evaluated to determine active
compounds that act as good electron donors for selenium reduction. The highest
reduction rate was on Bennet medium for Streptococcus pyogenes strain
AOS20, Streptococcus salivarius strain AOS38 and on Nutrient broth medium
for Bacillus pumilus strain AOS68 compared to other media as these media
enabled the bacterial strains to secrete active metabolites such as phenolic and
avonoid compounds that hold an aromatic ring bearing at least one hydroxyl
group and they are good electron donors because their hydroxyl groups can
directly contribute to antioxidant action.
After bacterial growth on all carbon sources which diverse among
monosaccharides, disaccharides and polysaccharides and obtaining the
supernatant free from bacterial cells and inoculating it with a solution of sodium
selenite, after incubation, it was found that dextrose was the best carbon source
for bacterial growth and reduction activity for Streptococcus pyogenes strain
AOS20, Streptococcus salivarius strain AOS38 and beef extract for Bacillus
pumilus strain AOS68.
Physical parameters are important in microbial growth, that affect on the
growth of microorganisms and their production of active metabolites that help in
selenium reduction rapidly with high efficiency.
Selenium reduction was affected by pH range, where in acidic pH, the
reduction activity was very low and it increased in slightly alkaline medium.
The optimum pH for selenium reduction was pH 8.0 for Streptococcus pyogenes
strain AOS20, Bacillus pumilus strain AOS68 and pH 9.0 for Streptococcus
salivarius strain AOS38.
Microbial growth is sensitive to temperature where the temperature affect
on the microorganisms growth and physiological activities inside the microbial
cells. In this study the isolates were applied to grow on the temperature range
from 15°C up to 50°C. The optimum temperature for selenium reduction was
30°C.
The produced selenium nanoparticles were characterized using TEM,
XRD, EDAX, FTIR and UV/VIS spectrophometer techniques. The
characterization technology confirmed producing selenium with nano-properties
(15-30 nm with spherical shape). The antibacterial activity of the produced
nano-selenium was evaluated against several bacterial pathogens such as
Escherichia coli, MRSA, Bacillus subtilis, Serratia and Klebsiella penumoniae
by well diffusion method and the MIC was calculated. The produced nanoselenium
has high activity and low MIC with the most tested pathogens. So that,
it can be applied as antibacterial agent for controlling the pathogens in hospital,
agricultural fields and municipal wastewater treatment units.
The aim of this study was production of selenium nanoparticles by ecofriendly
and cost-effective method using natural source such as bacteria isolated
from Egyptian environments.