Isolation of Hexavalent chromium tolerant fungal species from urban vegetable farm soil and effluent waste in Addis Ababa& Rift valley, Ethiopia

Abstract

Hexavalent chromium is resistant to degradation and harmful toxic substance to environment and community health. Physicochemical treatment methods are demanding high cost, used large quantities of chemicals & energy, release large amount of secondary toxic degradants. Mycoremediation is an eco-friendly alternative treatment method. The main objective of this research is to isolate and characterize chrome (VI) tolerant fungi from farm soil & industry effluent for mycoremedation purpose. The screening and isolation of yeast was carried out on potato dextrose agar media. PDA and broth assay test for fungi tolerance to hexavalent chromium at different concentration, temperature and pH was evaluated. Fungi species was identified biochemically using Biolog Microstation depending on carbon utilization and chemical sensitivity test. The result revealed that 10 yeast species was identified with full ID from effluent waste and farm soil based on their probability ≥ 75% and similarity index ≥ 0.5 as well as their Cr (VI) tolerance ability up to 2500ppm. These are Yarrowia lipolytica (100%, 0.7), Cryptococcus luteolus(100%, 0.64), Rhodotorula aurantiaca A(100%, 0.62), Ustilago maydis(100%, 0.58) Trichosporon beigelii B (100%, 0.51), Cryptococcus terreus A (100%, 0.62), Zygosaccharomyces bailii (98%, 0.65), Nadsoniafulvenscens (90%, 0.62), Schizoblastosporonstarkeyihenricii (89%, 0.56), Endomycopsis vivi (84%, 0.62), Rhodotorula pustula (Sim, 0.59). Two yeast species Yarrowia lipolytica and Nadsoniafulvenscens show the highest growth mean Optical density (OD) measure 0.74 ± 0.2& 0.60 ± 0.2 respectively at pH 7 & 25°C. The highest tolerance index (mm) was recorded by Schizoblastosporon starkey henricii 0.3067 ± 0.152. Cr (VI)-tolerance ability of these yeast strains used in the development of chromium-bioremediation technologies provide an alternative option for chromium sequestration after HPLC analysis& molecular characterization.