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Appl. Environ. Microbiol., Mar 1995, 1045-1053, Vol 61, No. 3
MW Breedveld, AJ Benesi, ML Marco and KJ Miller
Rhizobium meliloti and Agrobacterium tumefaciens synthesize periplasmic
cyclic (beta)-(1,2)-glucans during adaptation to hypoosmotic environments.
It also appears that these glucans provide important functions during the
interactions of these bacteria with plant hosts. A large fraction of these
glucans may become modified with anionic substituents such as
phosphoglycerol or succinic acid; however, the role(s) of these
substituents is unknown. In this study, we show that growth of these
bacteria in phosphate-limited media leads to a dramatic reduction in the
levels of phosphoglycerol substituents present on the periplasmic cyclic
(beta)-(1,2)-glucans. Under these growth conditions, R. meliloti 1021 was
found to synthesize anionic cyclic (beta)-(1,2)-glucans containing only
succinic acid substituents. Similar results were obtained with R. meliloti
7154 (an exoH mutant which lacks the ability to succinylate its
high-molecular-weight exopolysaccharide), revealing that succinylation of
the cyclic (beta)-(1,2)-glucans is mediated by an enzyme system distinct
from that involved in the succinylation of exopolysaccharide. In contrast,
when A. tumefaciens C58 was grown in a phosphate-limited medium, it was
found to synthesize only neutral cyclic (beta)-(1,2)-glucans.
Copyright © 1995, American Society for Microbiology
Effect of Phosphate Limitation on Synthesis of Periplasmic Cyclic (beta)-(1,2)-Glucans
Departments of Food Science and Chemistry and Graduate Programs in Plant Physiology and Genetics, The Pennsylvania State University, University Park, Pennsylvania 16802
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