## 1 Introduction  
Unsymmetrical dimethylhydrazine (1,1-Dimethylhydrazine, UDMH) is an important liquid propellant for space rockets and missiles. At present, countries such as Russia, India, and China still use UDMH, which is a relatively inexpensive fuel also named \"heptyl\", as a heavy cargo carrier rockets propellant [1]. UDMH is proven to be an highly toxic, carcinogenic, and mutagenic substance [2] that could induce lung and liver tumors [3, 4], and digestive system, skin, and mucous membranes could also be damaged at the same time [5]. Several governments have developed comprehensive regulations applied to the hazards of this compound from production, transport, and storage to disposal. In the USA, UDMH was classified as a Group 2B carcinogenic substance [6]. In Russia, the maximum allowable concentration is 0.02 mg\(\cdot\) L\({}^{-1}\) in water and 0.1 mg\(\cdot\) kg\({}^{-1}\) in soil [7, 8]. In China, UDMH was listed in the highly toxic chemical index in 2003, and the discharge standard (GB14734) of UDMH in water was set to control its environmental toxicity early in 1993 [9]. Although UDMH hasmany flaws, it is still likely to stay in use for the next 25-50 years because it has unique physico-chemical characteristics such as high energy and specific impulse [8].  
Because of the water solubility and widespread use of UDMH, the opportunity for spills during storage or transportation creates a potential for environmental contamination [10]. On 1 February 1988, in a railway cargo train near the city of Yaroslavl, three tank cars containing UDMH left the tracks and approximately 740 L was spilled from one overturned tank [7]. In Kazakhstan, the fall of the first stages of rocket-carriers launched from the Baikonur Cosmodrome is accompanied by the spill of 0.6 to 4 tons of unburned propellant, of which 10-30 kg reach the ground and are subsequently spread into the soil and water [11]. It is estimated that the negative influence of space activities influences thousands of square kilometers (more than 7,700,000 km\({}^{2}\)) with a fragile and unique ecosystem [12; 13]. According to studies of soil samples from fall regions of rockets, UDMH and its transformation products can exist for 30 years after landing [14].  
Nowadays, some new treatment technology appear, including oxidation over heterogeneous catalysts [15], catalytic oxidation with dioxygen and hydrogen peroxide over Cu- and Fe-containing catalysts [16], catalytic detoxification in heterogeneous Fenton system [17], reduction with Raney nickel [18], photocatalytic oxidation on TiO\({}_{2}\)[19], oxidation in a microstructured catalytic reactor [20], and so on. They are mainly the target of wastewater treatment, and these methods cannot be used for the environmental remediation of the UDMH spills. Currently, the popular method for the spill of UDMH was using hypochlorite [21]. Information about the bioremediation of UDMH is limited. Although the U.S. Air Force had performed correlative research 30 years ago, little success was achieved in the area of providing a tolerant microbe and revealing the biological mechanisms. Until now, few biotechnologies had been used to dispose of UDMH fuel. Actually, bioremediation, which involves the capabilities of microorganisms in the removal of pollutants, is the most promising, relatively efficient, and cost-effective technology, and is widely used in the soil and water remediation of toxic compounds [22]. Thus it is essential to find out whether biotechnology is able to reverse the environmental contamination of UDMH.  
The purpose of this study is to isolate the bacterial strains capable of degrading UDMH and characterize their degradative potential in water and soil. The transformation products of UDMH and the biodegradation pathway were also discussed. This study attempted to provide a fundamental practical way for the bioremediation of soil and water contaminated by UDMH spills at ambient temperature.