ORIGINAL ARTICLE In silico characterization of a novel dehalogenase (DehHX) from the halophile Pseudomonas halophila HX isolated from Tuz Gölü Lake, Turkey: insights into a hypersaline-adapted dehalogenase Mohamed Faraj Edbeib 1 & Roswanira Abdul Wahab 2 & Yilmaz Kaya 3 & Fahrul Huyop 1 Received: 6 October 2016 /Accepted: 7 April 2017 # Springer-Verlag Berlin Heidelberg and the University of Milan 2017 Abstract Halogenated compounds represent potential long- term threats to human well-being and health and, therefore, the quest for microorganisms capable of degrading these haz- ardous substances merits urgent consideration. We have iso- lated a novel dehalogenase-producing bacterium from the hy- persaline environment of Tuz Gölü Lake, Turkey and subse- quently identified this isolate as Pseudomonas halophila HX. Under optimal culture conditions (pH 8.0, 15% NaCl, 30 °C, 200 rpm, 96 h culture time), the strain almost completely de- graded (99.3%) 2,2-dichloropropionic acid (20 mM). The dehalogenase gene (dehHX) of the bacterium was amplified by PCR, and the deduced amino acid sequence of the DehHX was found to belong to a Group I dehalogenase and to share an 82% sequence identity to the dehalogenase DehI of Pseudomonas putida strain PP3. Interestingly, the pI of DehHX was more acidic (pI 3.89) than those of the non- halophilic dehalogenases (average measured pI 5.95). Homology-based structural modeling revealed that the surface of DehHX was unusually negatively charged due to the higher presence of acidic residues, which accounts for the uncom- monly low pI seen in DehHX and explains the mechanism of adaptation that contributes to the exceptional halotolerance of the enzyme. The excess surface acidic residues were beneficial in enhancing the water-binding capacity, a crucial feature for preserving the stability and solubility of DehHX in highly sa- line conditions. In summary, we suggest that bio-prospecting for halogenated compound-degrading microorganisms in high- ly saline environments is a practical and safe strategy for the bioremediation of contaminated coastal areas. Keywords Biodegradation . 2,2-Dichloropropionic acid . Pseudomonas halophila . Halostable dehalogenase Introduction Halogenated compounds liberated by natural and/or industrial processes generally contain high concentrations of four ha- lides, i.e., fluoride (F - ), chloride (Cl - ), bromide (Br - ), and iodide (I - ), all of which are well-known environmental pollut- ants (Slater et al. 1995). While there are more than 5000 types of naturally occurring halogenated hydrocarbons (Gribble 2009), the ever increasing number of manufacturing activities and cases of illegal dumping of halogenated compounds into water bodies (Oren et al. 1992) further increase their presence in the environment. An estimated 5% of the highly halogenat- ed industrial effluents released into the environment enter sa- line or hypersaline water systems (Lefebvre et al. 2012), with 2,2-dichloropropionic acid (2,2-DCP) (also known as Dalapon), a highly toxic and recalcitrant biocide, being one of the commonly found contaminants (Häggblom et al. 2000; Van Pée and Unversucht 2003). Most worrying is the persis- tence of 2,2-DCP in the environment, suggesting that this compound has the potential to pose long-term risks to both Electronic supplementary material The online version of this article (doi:10.1007/s13213-017-1266-2) contains supplementary material, which is available to authorized users. * Roswanira Abdul Wahab roswanira@kimia.fs.utm.my * Fahrul Huyop fahrul@utm.my 1 Department of Biotechnology and Medical Engineering, Faculty of Biosciences and Medical Engineering, Universiti Teknologi Malaysia (UTM), 81310 Johor Bahru, Malaysia 2 Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia (UTM), 81310 Johor Bahru, Malaysia 3 Agricultural Biotechnology Department, Faculty of Agriculture, Ondokuz Mayis University, Samsun, Turkey Ann Microbiol DOI 10.1007/s13213-017-1266-2