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J. Bacteriol., Nov 1995, 6276-6281, Vol 177, No. 21
HP Spaink, AH Wijfjes and BJ Lugtenberg
Thin-layer chromatographic analysis of extracts of D-[1-14C]glucosamine-
labelled rhizobia was used to analyze the effects of nodI, nodJ, and nodT
on secretion of lipochitin oligosaccharide (LCO) signal molecules.
Secretion was analyzed by comparing quantities of radiolabelled LCOs
present in the cellular and spent growth medium fractions. A second rapid
and sensitive method was introduced to estimate the secreted LCO fractions
by using D-[1-14C]glucosamine-labelled cells grown in medium supplemented
with chitinase. At various times after induction of LCO synthesis, the
quantity of degradation products of LCOs was compared with the amount of
nondegraded LCOs. In wild-type strains of Rhizobium leguminosarum biovars
viciae and trifolii the nodI and nodJ genes (but not the nodT gene)
strongly enhance the secretion of LCOs during the first 5 h after the
induction of LCO synthesis. In LCO-overproducing strains the enhancement of
secretion was observed only during the first 3 h after induction. At times
later than 5 h after induction, a significant influence of the presence of
the nodI and nodJ genes on LCO secretion was detectable neither in the wild
type nor in LCO- overproducing strains. By using plasmids in which the nodI
and nodJ genes are cloned separately under control of a flavonoid-inducible
promoter, it was shown that both genes are needed for a wild-type level of
LCO secretion. Therefore, these results demonstrate that nodI and nodJ play
a role in determining the efficiency of LCO secretion.
Copyright © 1995, American Society for Microbiology
Rhizobium NodI and NodJ proteins play a role in the efficiency of secretion of lipochitin oligosaccharides
Clusius Laboratory, Institute of Plant Molecular Biology, Leiden University, The Netherlands.
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