الفهرس 
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Abstract
The role of bacteria in remediation of toxic compounds has
been documented over the years and would continue to be a dominant technology for the bioremediation.
In this study, three different polluted soil samples were collected from Ismailia Canal in front of Al Saad factory, Egypt, Ismailia Canal in front of Al Chenny Company, Egypt and Al Allam, Sallah Elddin governorate, Iraq.
Samples were enriched on LPM broth medium. Nine faint to dark blue molybdate reducing bacterial colonies were selected and purified on LPM solid medium.
The characteristic absorption peak maximum at 865 nm and a shoulder at 700 nm which indicated the formation of molybdenum blue from the reduction of molybdate.
Three bacterial isolates (Mo1, Mo4 and MoI) which shows higher production of Mo blue (0.767 ± 0.004, 0.511 ± 0.010 and 0.343 ± 0.048) respectively at 865 mM were selected for further characterization and assessment of different conditions affecting molybdate reduction.
These 3 isolates were identified by 16S rRNA gene into Raoultella ornithinolytica strain Mo1, Klebsiella aerogenes strain Mo4 and Raoultella planticola strain MoI. The nucleotide sequences were submitted to GenBank under accession number KY508302, KY508303 and MG786753 respectively.
The 3 novel isolates were recorded as a molybdate reducing bacteria for the first time in this study.
Factors influencing the bacterial reduction of molybdate were studied. These conditions included: different concentrations of electron donors (Glocose,Sucrose , Lactost, mannitole, Starch) separately, different concentrations of sodiume molybdate ((1,5,10,15,20,30,40,50,80,100,120,150,180,200,220,240,270 and 300mM),incubation periods (24, 48, 72, 96, 120, 144 and 168 h), pH (4, 6, 7, 8, 9 and11), inoculum sizes (0.1, 0.3, 0.5, 1 and 2 ml) and incubation temperatures (15, 25, 30, 37 and 45°C). Accordingly optimum conditions for molybdate reduction obtained from this study (type of electron donor, glocose; electron acceptor concentration, 20 mM; incubation period, 48h; pH, 6; inoculum size, 0.3 ml and incubation temperature, 30°C) were determined with maximum Mo- blue production reached to 0.998 ± 0.002, 0.899 ± 0.001 and 0.592 ± 0.002 for Raoultella ornithinolytica strain Mo1, Raoultella planticola strain MoI and Klebsiella aerogenes strain Mo4 respectively.
Molybdate treated and untreated bacterial cells were examined under The Scanning Electron Microscope (SEM) which recorded the difference in shape between treated and untreated cells.
For in vivo study, two groups of Oreochromis niloticus were used; control and treated groups. The water of treated group was supplied by1.5x107cfu/ml of K. aerogenes Mo4. The present results showed that K. aerogenes had negative impact on the behavior of O. niloticus, caused 34% mortality and caused histopathological signs to the gills and liver but not the kidneys. It is recommended that further studies on the use of bacterial enzymes rather than intact bacterial cells to treat molybdate polluted water need to be done. Or that the molybdate-polluted water would be treated by bacteria before adding the fish.