Review Received: 6 March 2012 Revised: 5 July 2012 Accepted: 18 July 2012 Published online in Wiley Online Library: (wileyonlinelibrary.com) DOI 10.1002/jsfa.5860 Halophilic hydrolases as a new tool for the biotechnological industries Mariana Delgado-Garc´ ıa, Blanca Valdivia-Urdiales, Crist ´ obal Noe Aguilar-Gonz ´ alez, Juan Carlos Contreras-Esquivel and Ra ´ ul Rodr´ ıguez-Herrera * Abstract Halophilic micro-organisms are able to survive in high salt concentrations because they have developed diverse biochemical, structural and physiological modifications, allowing the catalytic synthesis of proteins with interesting physicochemical and structural properties. The main characteristic of halophilic enzymes that allows them to be considered as a novel alternative for use in the biotechnological industries is their polyextremophilicity, i.e. they have the capacity to be thermostable, tolerate a wide range of pH, withstand denaturation and tolerate high salt concentrations. However, there have been relatively few studies on halophilic enzymes, with some being based on their isolation and others on their characterisation. These enzymes are scarcely researched because attention has been focused on other extremophile micro-organisms. Only a few industrial applications of halophilic enzymes, principally in the fermented food, textile, pharmaceutical and leather industries, have been reported. However, it is important to investigate applications of these enzymes in more biotechnological processes at both the chemical and the molecular level. This review discusses the modifications of these enzymes, their industrial applications and research perspectives in different biotechnological areas. c  2012 Society of Chemical Industry Keywords: halophilic micro-organisms; halophilic enzymes; industry; biochemical characteristics INTRODUCTION Microbial enzymes are widely used in various industrial fields. Some micro-organisms can grow easily on low-cost substrates, generally producing non-toxic derivatives. The principal function of microbial enzymes is to act as biocatalysts; in this way, energy consumption is low and they are able to perform their functions in non-aqueous culture media, especially in conditions where solubility is limited. 1 This has led to more efficient processes with better industry profitability, but above all to cleaner processes. 2 Worldwide, there is a huge annual expenditure on enzymes. In 2011, BCC Research noted that the enzyme market, particularly in terms of industrial applications, had increased in the past year to US$3.3 billion, and it is expected that this market will reach US$4.4 billion by 2015. Such demand has generated the search for new enzymes able to support the aggressive conditions of some industrial processes. Today, most enzymes do not show the same performance when they are exposed to extreme conditions such as high temperatures, acid or alkaline pH levels, denaturing, etc. 3,4 This situation has led to extremophile micro-organism research to understand the metabolic adaptation of these micro- organisms necessary for them to survive extreme conditions; these modifications are based on diverse enzymatic changes. 5 Among extremophile micro-organisms, a major group of interest has emerged, namely halophilic micro-organisms. In particular, these micro-organisms are able to survive in media with high salt concentrations, because their cellular metabolism has special characteristics. 6 In the last 10 years, halophilic enzymes, especially halophilic hydrolases, have been studied worldwide. These enzymes can perform in different salt concentrations; also, some of them are thermostable and tolerant to a wide range of pH. 7–9 These properties make halophilic enzymes an option for new enzymatic processes, mainly because they are tolerant to aggressive conditions, being candidates for use in various industrial fields (pharmaceuticals, foods, textiles, chemicals, etc). The objective of this review is to present the advances in halophilic enzyme knowledge, their industrial applications and their biotechnological potential. GENERAL COMMENTS ON HALOPHILIC MICRO-ORGANISMS Halophilic micro-organisms can live in hypersaline environments. They are considered as extremophiles owing to their complex system of adaptation enabling them to survive in high salt concentrations. 5 There is a wide diversity of halophilic micro- organisms, including prokaryotes, eukaryotes and archaea. How- ever, not all halophilic micro-organisms require the same salt concentration for growth. They are classified according to their salt requirement 5 as follows: (1) extreme halophile – grows in a medium with 3.5 – 5 mol L −1 NaCl; (2) moderate halophile – grows in a medium with 0.5 – 3.5 mol L −1 NaCl; (3) weak halophile – grows ∗ Correspondence to: Ra´ ul Rodr´ ıguez-Herrera, Food Research Department, School of Chemistry, Universidad Aut´ onoma de Coahuila, Blvd Venustiano Car- ranza, 25280 Saltillo, Coahuila, Mexico. E-mail: raul.rodriguez@uadec.edu.mx Food Research Department, School of Chemistry, Universidad Aut´ onoma de Coahuila, Blvd Venustiano Carranza, 25280 Saltillo, Coahuila, Mexico J Sci Food Agric (2012) www.soci.org c  2012 Society of Chemical Industry