Abstract

Roxarsone (ROX) (3-nitro-4-hydroxybenzene arsenic acid), an arsenic (As) containing compound is widely used as a food additive in the production of broiler chickens to control coccidial intestinal parasites and to favour rapid growth. Broiler chickens receiving ROX in their diet (between 23 and 45 g ton-1 food) excrete it untransformed in manure. This manure is commonly used as fertilizer, polluting farming fields. However, several soil bacteria can degrade ROX, releasing inorganic As. The results of this work demonstrated that a bacterial consortium, isolated from chicken manure and cultured under anaerobic conditions, was mainly composed by bacilli. DGGE analysis of the 16s rDNA sequences demonstrated that Firmicutes, which has been reported as main components in soils, sediments and animal faeces under anaerobic conditions, was the predominant tax a present in the studied consortium. The growth kinetics of the consortium was higher in the presence of ROX than in its absence, suggesting that ROX could be used as carbon source by the consortium. ROX was degraded by the consortium producing inorganic As, mainly arsenite (As(III)). Concomitantly with ROX biotransformation, the consortium produced As free methane. These results provide the first evidence that an anaerobic bacteria consortium isolated from chicken manure can rapidly biotras form ROX to inorganic arsenic and produce arsenic free biogas.