Investigation of keratinase activity and feather degradation ability of immobilised Bacillus sp. Khayat in the presence of heavy metals in a semi continuous fermentation

Abstract

Tonnes of feathers generated from slaughterhouses and those that were being used for the removal of heavy metals in wastewaters are often contaminated with high heavy metals and other chemical agents. The toxic nature of these chemicals makes it difficult for feather degrading bacteria to degrade the feathers. An investigation was made on the effect of different concentration of heavy metals on the keratinase activity and feather degrading ability of immobilised cells of Bacillus sp khayat. PH 8, temperature 27�C, gellan gum concentration of 0.8% and 250 beads per 100 ml of heavy metals free media were the optimum conditions to achieve highest keratinase yield and complete feather degradation within 18 h. Immobilised cells were able to secrete higher keratinase enzyme in the presence of 30 ppm Ag, 20 ppm Co and 15 ppm Cu. While feather degradation and keratinase yield were inhibited by above 5 ppm of Hg, Pb and Zn, up to 10 ppm of As and Cd have no effect on the duo. Immobilised cells were successfully used to degrade 5 g/L of feathers in the presence of individual 30 ppm Ag, 20 ppm Co, 15 ppm Cu, and combination of 5 ppm each of Ag, As, Co, Cu and Ni for 10 and 6 consecutive cycles respectively in a semi-continuous mode of cultivation without desorption. The beads used to degrade feather in the presence of a particular heavy metals were successfully used to degrade other feather laden with other metals. Enhanced keratinase activities and 90-100% feather degradations by gellan gum entrapped Bacillus sp. khayat in the presence of various concentrations of chemically known toxic heavy metals showed that the Bacillus has a relatively high tolerance to heavy metals while still maintaining its feather degrading ability. This property makes the Bacillus a potential tool not only in the bioremediation and waste management of heavy metal laden feathers, but also in the production of keratinase protease for industrial usage.