Osmoregulation in Bacillus subtilis: synthesis of the osmoprotectant glycine betaine from exogenously provided choline

Abstract

Exogenously provided glycine betaine functions as an efficient osmoprotectant for Bacillus subtilis in high-osmolarity environments. This gram-positive soil organism is not able to increase the intracellular level of glycine betaine through de novo synthesis in defined medium (A. M. Whatmore, J. A. Chudek, and R. H. Reed, J. Gen. Microbiol. 136:2527Microbiol. 136: -2535Microbiol. 136: , 1990 Exogenously provided choline significantly increased the growth rate ofB. subtUis in high-osmolarity media and permitted its proliferation under conditions that are otherwise strongly inhibitory for its growth. Choline and glycine betaine were not used as sole sources of carbon or nitrogen, consistent with their functional role in the process of adaptation of B. subtilis to high-osmolarity stress.

Synthesis of the osmoprotectant glycine betaine in Bacillus subtilis: characterization of the gbsAB genes

“…For the selection of kanamycin-resistant B. subtilis strains, a final concentration of 5 g of the antibiotic per ml was used. Radiolabelled [methyl-14 C]glycine betaine was synthesized as described previously (4).…”

“…The induction of the general stress regulon, the uptake of potassium, and increased proline biosynthesis are, however, insufficient to ensure the growth of B. subtilis in harsh highosmolarity environments (4). A more effective defense against these growth conditions is the accumulation of large amounts of osmoprotectants which can be amassed to high intracellular levels without disturbing essential functions of the cell (8,35).…”

“…In addition to directly acquiring glycine betaine from the environment, B. subtilis can also accumulate this osmoprotective compound through synthesis (4). Synthesis requires the presence of the precursor choline or glycine betaine aldehyde in the growth medium (4).…”

“…Synthesis requires the presence of the precursor choline or glycine betaine aldehyde in the growth medium (4). Production of glycine betaine from choline is a two-step oxidation process with glycine betaine aldehyde as the intermediate.…”

“…Uptake of the precursor molecules for glycine betaine synthesis is mediated by an efficient transport system that is osmotically regulated at the level of transport activity and the expression of its structural gene(s). In contrast, the systems mediating the enzymatic conversion of choline into glycine betaine are only marginally stimulated by an increase in medium osmolarity (4). B. subtilis shares the ability to oxidize choline to glycine betaine for osmoprotective purposes with a number of gram-negative and gram-positive bacteria (8,15,35).…”