Heavy metal pollution due to excessive use of chemical fertilizers (CF) causes a major damage to the environment. Microbial consortia, closely associated with the rhizosphere are able to remediate heavy metal-contaminated soil by reducing plant toxicity. Thus, this study was undertaken to examine the remedial effects of microbial bio lms against contaminated heavy metals. Fungi and bacteria isolated from soil were screened for their tolerance against Cd 2+ , Pb 2+ and Zn 2+ . Fungal-bacterial bio lms (FBBs) were developed with the highest tolerant isolates and were further screened for their bioremediation capabilities against heavy metals. The best bio lm was evaluated for its rhizoremediation capability with different CF combinations using a pot experiment conducted under greenhouse conditions with potato. Three bacterial and two fungal isolates were selected to develop FBBs upon the tolerance index (TI) percentage. Signi cantly (P < 0.05) the highest metal removal percentage was observed in Trichoderma harzianum and Bacillus subtilis bio lm under in situ condition. The bio lm with 50% of recommended CF (50CB) signi cantly (P < 0.05) reduced the soil available Pb 2+ by 77%, Cd 2+ by 78% and Zn 2+ by 62% compared to 100% recommended CF (100C). In comparison to initial soil, it was 73%, 76% and 57% lower of Pb 2+ , Cd 2+ and Zn 2+ , respectively. In addition, 50CB treatment signi cantly (P < 0.05) reduced the metal penetration into the tuber tissues in comparison with 100C. Thus, it is concluded that T. harzianum-B. subtilis bio lm is an ideal combination to remediate soil contaminated with Cd 2+ , Pb 2+ and Zn 2+ .

Drying is an important method for preserving phytochemicals in plant materials though the stability is altered with the type of drying method. This study aimed at evaluating the effectiveness of different drying methods on antioxidant activity and phytochemical availability in leaf ethanolic extracts of Costus speciosus, Coccinia grandis, and Gymnema sylvestre. Plant leaves of the selected species were subjected to shade drying at room temperature (25 + 5℃), oven drying at 45 ℃ and freeze-drying methods. The extracts were obtained by a maceration method with 95% ethanol. Obtained ethanolic extracts were analyzed for antioxidant activity in terms of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, 2,2-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical scavenging activity, total reducing power and total antioxidant capacity. Phytochemical availability was determined qualitatively and quantitatively in the extracts. All the plant species and drying methods had a significant difference (p<0.05) for the tested antioxidant activities. Among the drying techniques, the freeze-drying method was more effective to preserve the antioxidant compounds and phytochemicals compared to oven drying and shade drying. The lowest antioxidant activity and phytochemical availability were shown by the leaves subjected to oven drying at 45 ℃. The freeze-dried leaves of C. speciosus ethanolic extract demonstrated the best radical scavenging activity for DPPH and ABTS assays with IC50 values of 57.27 + 2.08 μg/ml, 21.86+ 3.55 μg/ml respectively. Furthermore, the highest content of total phenolics (82.88+2.31 mg GAE/g), tannins (9.58 +2.71mg TAE/ g), terpenoids (45.10+3.46 %), and alkaloids (19.37+3.54%) were recorded in C. speciosus among all dried leaves from the selected species. It can be concluded that the freeze-dried leaves of all plant species showed a higher value of antioxidant activity and phytochemical availability and that can be potentially used for the production of pharmaceuticals and novel functional foods.

No abstract