Brucella virulence is linked to components of the cell envelope
and tightly connected to the function ofthe BvrR/BvrS sensory-regul
atory system. To qu
antify the imp
act of BvrR/BvrS on cell envelope proteins,we performed
a l
abel-free m
ass spectrometry-b
ased proteomic
an
alysis of spont
aneously rele
asedouter membr
ane fr
agments from four str
ains of
Brucella abortus (wild type virulent,
avirulent
bvrR-and
bvrS- mut
ants
as well
as reconstituted virulent
bvrR+ (
bvrR-/p
bvrR+)). We identified 167 differenti
allyexpressed proteins, of which 25 were
assigned to the outer membr
ane. Approxim
ately h
alf of the outermembr
ane proteins decre
ased in
abund
ance, where
as h
alf incre
ased. Not
ably, expression of five Omp3f
amily proteins decre
ased where
as five lipoproteins incre
ased in the mut
ant str
ains. In the peripl
asmicsp
ace, by contr
ast,
approxim
ately 80% of the 60 differenti
ally expressed proteins were incre
ased in
atle
ast one
avirulent mut
ant. Peripl
asmic proteins
are prim
arily involved in substr
ate upt
ake
and tr
ansport,
and
a uniform incre
ase in this cl
ass m
ay indic
ate
a nutrition
al stress response, possibly
a consequenceof defective outer membr
ane function. Virtu
ally
all proteins reverted to wild type levels in thereconstituted virulent
bvrR+ str
ain. We propose th
at the wide ch
anges in cell envelope protein expressionrel
ate to the m
arkedly
avirulent phenotype of
bvrR- and
bvrS- mut
ants
and th
at
Brucella virulencedepends on regul
atory networks involving cell envelope
and met
abolism r
ather th
an on discretevirulence f
actors. This model m
ay be relev
ant to other
ages/gifch
ars/
alph
a.gif" BORDER=0>-
Proteobacteria h
arboring BvrR/BvrS orthologoussystems known to be essenti
al for p
ar
asitism or endosymbiosis.