Effect of the molybdate reducing bacteria, Klebsiella aerogenes strain Mo4, on the health of the Nile tilapia, Oreochromis niloticus.

Abstract

Bioremediation is an effective technique currently used to reduce or eliminate heavy metals hazards, so the present study aimed to investigate the potential effect of Klebsiella aerogenes in molybdate bioremediation and to evaluate its effect on the health of Oreochromis niloticus. A molybdate reducing bacterium was isolated from polluted soil sample that was obtained from Ismailia Canal, Cairo, Egypt. The bacterium was identified by 16S-rRNA gene sequencing as K. aerogenes strain Mo4 and was submitted to GenBank (accession number KY508303). Molybdate was optimally reduced to molybdenum blue by using glucose as an electron donor, 20 mmol l-1 molybdate, pH 6 and 30°C incubation temperature. For in vivo study, two groups of O. niloticus were used; control and treated groups. The water of treated group was supplied by 0.46 ×102 cfu/ml of K. aerogenes. Although K. aerogenes showed efficient results in molybdate reduction, the consequences of using this bacterium as a bioremediation agent on fish health were negative. The mortality rate was 34% and the gills and liver showed histopathological alterations. The present results recommend that further studies on the use of bacterial enzymes rather than intact bacterial cells to treat molybdate polluted water need to be done.