LAUSR

Simple Summary Amylases are a group of enzymes that degrade starch into simple sugars. These proteins are produced by a wide variety of organisms and are supposed to be one of the most valuable industrial enzymes. However, the extreme conditions required for many industrial operations limit the applicability of most amylases found in nature. In this context, halophilic archaea entail an excellent source of novel proteins that tolerate harsh conditions, as they live in environments with high salt concentration and temperature. In this work, a screening of haloarchaea, isolated from Odiel salterns in the southwest of Spain, was carried out to select a new strain with a high amylase activity. This microorganism was identified as Haloarcula sp. HS and showed amylase activities in both, the cellular and the extracellular extracts. Both amylase activities were poly-extremotolerant, as their optimal yields were achieved at 60 °C and 25% NaCl. Additionally, the study of the protein sequences from Haloarcula sp. HS allowed the identification of three different amylases, which conserved the typical structure of the alpha-amylase family. Finally, the applicability of the extracellular amylase to treat bakery wastes under high salinity conditions was demonstrated. Abstract Alpha-amylases are a large family of α,1-4-endo-glycosyl hydrolases distributed in all kingdoms of life. The need for poly-extremotolerant amylases encouraged their search in extreme environments, where archaea become ideal candidates to provide new enzymes that are able to work in the harsh conditions demanded in many industrial applications. In this study, a collection of haloarchaea isolated from Odiel saltern ponds in the southwest of Spain was screened for their amylase activity. The strain that exhibited the highest activity was selected and identified as Haloarcula sp. HS. We demonstrated the existence in both, cellular and extracellular extracts of the new strain, of functional α-amylase activities, which showed to be moderately thermotolerant (optimum around 60 °C), extremely halotolerant (optimum over 25% NaCl), and calcium-dependent. The tryptic digestion followed by HPLC-MS/MS analysis of the partially purified cellular and extracellular extracts allowed to identify the sequence of three alpha-amylases, which despite sharing a low sequence identity, exhibited high three-dimensional structure homology, conserving the typical domains and most of the key consensus residues of α-amylases. Moreover, we proved the potential of the extracellular α-amylase from Haloarcula sp. HS to treat bakery wastes under high salinity conditions.