## 1 Introduction  
Isoflavones, one of the most abundant phytochemicals in leguminous plants, have attracted attention because of their activity against cancer [1], cardiovascular disease [2], osteoporosis [3], and menopausal symptoms [4]. The biological activity of isoflavones is improved by their deglycosylation into aglycones, which are more quickly absorbed in the gut because of their lower molecular weight and better hydrophobicity [5, 6]. However, isoflavone aglycones exist at low concentrations in leguminous plants. Therefore, many studies have focused on the biotransformation of isoflavone glycosides such as daidzin, genistin, and glycitin into their corresponding isoflavone aglycones; daidzein, genistein, and glycitin. These isoflavone aglycones have been obtained through the hydrolytic activity of microorganisms, including _Bacillus subtilis_, _Enterococcus durans_, _Lactobacillus parplantarum_, _Rrizopus oligosporus_, _Streptococcus salivarius_, and _Weissella confusa_[7, 8, 9]. However,microbial hydrolysis has several disadvantages, including low productivity, poor yield, and the production of by-products. Therefore, enzymes have been commonly used for the hydrolysis of isoflavone glycosides because of their high specificity, productivity, and yield. Although various microbial and plant-derived glycosidases have been used, thermostable glycosidases from thermophilic microorganisms, including _Dictyogolomus turgidum_[10], _Microbulbifer thermotolerans_[11], _Neesatorya fischeri_[12], _Pyrococcus furious_[13], _Sulfolbus solftatricus_[14], _Talaromyces leyctetanus_[15], _Thermogilum pendens_[16], and _Thermogolar nitima_[17] have exhibited high hydrolytic activity toward isoflavone glycosides. In order to use thermostable glycosidases from thermophilic microorganisms, it is more efficient to use recombinant enzymes expressed in _E. coli_ through cloning, because the growth conditions of thermophilic microorganisms are generally harsh.  
The extreme thermophile _Thermogroleus azoniensis_ is a rod-shaped archaebacterium found in hot springs and soil of the Uzon caldera (SW of Kamchatka pen.) [18]. Glycosidase from this strain is a powerful candidate for application in the hydrolysis of isoflavone glycosides because it showed high hydrolytic activity on ginsengides (ginseng saponins) in a previous study [19]. However, this enzyme has not yet been characterized.  
Soybean (_Glycine max_ (L.) Merr.), a representative leguminous plant, contains a high abundance of isoflavones. However, significant differences have been noted in the total isoflavone content of soybean depending on the country or region of cultivation [20]. Wild soybean (_Glycine soja_ Siebold & Zucc.), the ancestor of the domesticated soybean, was found to harbor a high level of genetic diversity that was abolished during the process of domestication [21]. Therefore, it has been previously suggested that the isoflavone content of domesticated soybean is not as high as that of wild soybean due to unintentional selection [22] and Korean wild soybeans have been reported to contain a high amount of isoflavones [23; 24; 25].  
The global Crop Wild Relatives (CWR) project, launched in 2011, aims to adapt agriculture to climate change. The wild relatives of crops, which have evolved to survive tough conditions, can often contain useful traits, the analysis of which could help develop crops that are more resilient to climate change. Soybeans are one of the main target species for this project and wild soybean is an important CWR of soybean. Thus, considering the global importance of the soybean crop, the enzymatic conversion of isoflavones in wild soybeans to their aglycones is of great interest.  
In this study, we cloned a thermostable \(\beta\)-galactosidaseose from _T. azoniensis_ and characterized its properties, such as molecular weight, pH, temperature, thermostability, and substrate specificity. The enzyme was used to produce daizein and genistein from daidzin and genistin in the seed and root extracts of Korean wild soybeans.