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Mannitol, a compatible solute synthesized by A cinetobacter baylyi in a two‐step pathway including a salt‐induced and salt‐dependent mannitol‐1‐phosphate dehydrogenase
Author(s) -
Sand Miriam,
Mingote Ana I.,
Santos Helena,
Müller Volker,
Averhoff Beate
Publication year - 2013
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/1462-2920.12090
Subject(s) - mannitol , biochemistry , dehydrogenase , biology , fructose , biosynthesis , enzyme , osmoprotectant , alcohol dehydrogenase , amino acid , proline
Summary The nutritionally versatile and naturally competent soil bacterium A cinetobacter baylyi copes with salt stress by the accumulation of compatible solutes. NMR analyses revealed that cells amassed glutamate and the rather unusual sugar alcohol mannitol upon an increase of the external NaCl concentration. To unravel the path of mannitol biosynthesis, the genome was inspected for genes potentially involved in its biosynthesis. A gene encoding a potential mannitol‐1‐phosphate dehydrogenase ( mtlD ) was identified in the genome of A . baylyi . Expression of mtlD was highly induced at high salinity. mtlD was overexpressed and the purified protein indeed produced mannitol‐1‐phosphate from fructose‐6‐phosphate. The enzyme preferred NADPH over NADH and the specific activity of fructose‐6‐phosphate reduction with NADPH was 130 U mg −1 . Enzymatic activity was strictly salt‐dependent. Deletion of mtlD resulted in a complete loss of salt‐dependent mannitol biosynthesis. We provide clear evidence that osmo‐induced synthesis of the compatible solute mannitol is by a two‐step pathway and that the mannitol‐1‐phosphate dehydrogenase mediating the first step of this pathway is regulated by salinity on the transcriptional as well as on the activity level.