H alorhabdus tiamatea: proteogenomics and glycosidase activity measurements identify the first cultivated euryarchaeon from a deep‐sea anoxic brine lake as potential polysaccharide degrader

Abstract

Summary Euryarchaea from the genus H alorhabdus have been found in hypersaline habitats worldwide, yet are represented by only two isolates: H alorhabdus utahensis AX ‐2 T from the shallow G reat S alt L ake of U tah, and H alorhabdus tiamatea SARL 4 B T from the S haban deep‐sea hypersaline anoxic lake ( DHAL ) in the R ed S ea. We sequenced the H . tiamatea genome to elucidate its niche adaptations. Among sequenced archaea, H . tiamatea features the highest number of glycoside hydrolases, the majority of which were expressed in proteome experiments. Annotations and glycosidase activity measurements suggested an adaptation towards recalcitrant algal and plant‐derived hemicelluloses. Glycosidase activities were higher at 2% than at 0% or 5% oxygen, supporting a preference for low‐oxygen conditions. Likewise, proteomics indicated quinone‐mediated electron transport at 2% oxygen, but a notable stress response at 5% oxygen. H alorhabdus tiamatea furthermore encodes proteins characteristic for thermophiles and light‐dependent enzymes (e.g. bacteriorhodopsin), suggesting that H . tiamatea evolution was mostly not governed by a cold, dark, anoxic deep‐sea habitat. Using enrichment and metagenomics, we could demonstrate presence of similar glycoside hydrolase‐rich H alorhabdus members in the M editerranean DHAL M edee, which supports that H alorhabdus species can occupy a distinct niche as polysaccharide degraders in hypersaline environments.

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