# Indole Degradation in a Model System and in Poultry Manure by _Acinetobacter_ spp.
## 1 Introduction  
Indole is a common metabolite of tryptophan formed in the rumen and colon of monogastric animals [1; 2; 3; 4]. It is one of the major recalcitrant odorant compounds in livestock and poultry industries [5] that are considered environmental pollutants [6]. It is produced in animal intestines by tryptophan degradation [1; 2]. Indole is also industrially produced for various purposes such as pharmaceuticals, cosmetics, pesticides, disinfectants, agrochemicals, and dyestuffs [7; 8], and then released into the environment, where it is often found in waste water, costal logoons, and sediment. It is a typical nitrogen heterocyclic aromatic pollutant and extensively spread in industrial wastewater [9]. Indole contributes to the unpleasant odor of feces in mammals and birds, and are major pollutants affecting public health and livestock industries [10; 11]. It can be absorbed into the blood and hemolyze bovine erythrocytes [12], is toxic to many microorganisms, and has a fairly broad bacteriostatic effect [13]. Previous studies used different physico-chemical and biological methods to remove indole from animal manure and waste water [14; 15], however the challenge is still persistent and there is demand for an efficient and eco-friendly means of elimination. Microorganisms play a vital role in the removal of indole compounds and its derivatives under aerobic and anaerobic conditions [2; 3; 16; 17; 18]. [PERSON] et al. [19] reported that indole was degraded aerobically by a bacterium isolated from tap water. [PERSON] et al. [20] investigated aerobic degradation of indole using _Pseudomonas aeruginosa_ Gs isolated from mangrove sediment. Under aerobic conditions, indole metabolism was generally initiated by oxidation of indole followed by heterocyclic ring cleavage [21]. Under anaerobic conditions indole could be metabolized to form methane [22]. [PERSON] and [PERSON] [1] isolated a sulfate reducing bacterium, _Desulfobacterium indolicum_ from marine sediments which used indole as its sole carbon source. Bacterial consortia also degrade indole under anaerobic and denitfriying conditions [23; 24; 25]. [PERSON] and [PERSON] [26; 27] studied the degradation of indole and 3-methylindole by an indole degrading methanogenic consortium enriched from sewage sludge. Microorganisms either mineralized indole compounds completely [28] or transformed into other compounds in the presence of an additional carbon source [18; 29]. indole biotransformation has also been studied in different bacterial strains [30; 31]. For instance, two phenol-degrading strains, _Pseudomonas_ sp. PI1 and _Acinetobacter_ sp. PI2 isolated from activated sludge could biosynthesis indigo [32]. [PERSON] et al. [33] reported transformation of indole to indigo using a biphenyl dioxygenase enzyme cloned from _Dyella ginsengi_ L-4 and heterologously expressed in _Escherichia coli_ (DE3). Co-metabolism of indole in glucose and nitrate was also reported in the mold _Aspergillus niger_[2]. Aerobic degradation of organic pollutants using microbes is faster and more efficient compared with anaerobic methods [34]. Several bacteria degrading indole were isolated and studied, but only a few indole-degrading _Acinetobacter_ strains were reported. For instance, many _Acinetobacter_ have been reported in the degradation of n-alkane and long chain hydrocarbons [35; 36], and aromatic compounds such as phenol and chlorophenol [37; 38; 39; 40]. Recently indole degradation has been reported in genus _Acinetobacter_ by different researchers [41; 42; 43; 44]. Even though some work has been done on indole biodegradation by microorganisms from different environments such as marine and mangrove sediments, and others [20; 28; 45; 46], limited work has been done on the biodegradation of indole in the poultry industry. The strains of _Acinetobacter_ used in this experiment therefore degraded indole efficiently under aerobic conditions.