Original Article

Subject Category: Integrated genomics and post-genomics approaches in microbial ecology

The ISME Journal (2014) 8, 636–649; doi:10.1038/ismej.2013.165; published online 19 September 2013

Trehalose/2-sulfotrehalose biosynthesis and glycine-betaine uptake are widely spread mechanisms for osmoadaptation in the Halobacteriales

Noha H Youssef1, Kristen N Savage-Ashlock1,3, Alexandra L McCully1,4, Brandon Luedtke1,5, Edward I Shaw1, Wouter D Hoff1,2 and Mostafa S Elshahed1

  1. 1Department of Microbiology and Molecular Genetics, Oklahoma State University, Stillwater, OK, USA
  2. 2Department of Chemistry, Oklahoma State University, Stillwater, OK, USA

Correspondence: MS Elshahed, Oklahoma State University, Department of Microbiology and Molecular Genetics, 1110 S Innovation Way, Stillwater, OK 74074, USA. E-mail: Mostafa@okstate.edu

3Present address: Department of Biology, Georgia State University, Atlanta, Georgia.

4Present address: Department of Biology, Indiana University, Bloomington IN.

5Present address: US Department of Agriculture, Agricultural Research Service, Roman L. Hruska Meat Animal Research Center, Clay Center, NE 68933-0166.

Received 15 July 2013; Revised 16 August 2013; Accepted 21 August 2013
Advance online publication 19 September 2013

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Abstract

We investigated the mechanisms of osmoadaptation in the order Halobacteriales, with special emphasis on Haladaptatus paucihalophilus, known for its ability to survive in low salinities. H. paucihalophilus genome contained genes for trehalose synthesis (trehalose-6-phosphate synthase/trehalose-6-phosphatase (OtsAB pathway) and trehalose glycosyl-transferring synthase pathway), as well as for glycine betaine uptake (BCCT family of secondary transporters and QAT family of ABC transporters). H. paucihalophilus cells synthesized and accumulated ~1.97–3.72μmol per mg protein of trehalose in a defined medium, with its levels decreasing with increasing salinities. When exogenously supplied, glycine betaine accumulated intracellularly with its levels increasing at higher salinities. RT-PCR analysis strongly suggested that H. paucihalophilus utilizes the OtsAB pathway for trehalose synthesis. Out of 83 Halobacteriales genomes publicly available, genes encoding the OtsAB pathway and glycine betaine BCCT family transporters were identified in 38 and 60 genomes, respectively. Trehalose (or its sulfonated derivative) production and glycine betaine uptake, or lack thereof, were experimentally verified in 17 different Halobacteriales species. Phylogenetic analysis suggested that trehalose synthesis is an ancestral trait within the Halobacteriales, with its absence in specific lineages reflecting the occurrence of gene loss events during Halobacteriales evolution. Analysis of multiple culture-independent survey data sets demonstrated the preference of trehalose-producing genera to saline and low salinity habitats, and the dominance of genera lacking trehalose production capabilities in permanently hypersaline habitats. This study demonstrates that, contrary to current assumptions, compatible solutes production and uptake represent a common mechanism of osmoadaptation within the Halobacteriales.

Keywords:

Halobacteriales; osmoadaptation; trehalose