“HLA secreted by the ASPDE system, belongs to an iron responsive operon in A.tumefaciens”

HAURIGOT, L; FERELLA, M; RUSSO, D. M.; DOWNIE JA; ZORREGUIETA A

Villa Carlos Paz, Córdoba

Congreso; XLIV Reunión Anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular; 2008

SAIB

We have previously identified a locus encoding a Type I Secretion System in A. tumefaciens (AspDE), which restored protein secretion in the prsDE mutant of R. leguminosarum. An extracellular protein (Hla) encoded by an aspDE upstream gene cloned into the pIJ7760 cosmid was overproduced when expressed in R. leguminosarum A34. However, Hla is not detected in the extracellular medium of Agrobacterium.  A34 turned out to behave as an iron responsive mutant. We noted that other genes encoded by pIJ7760 (including hla) may be iron responsive since their products are also overproduced in A34. Analysis of the region cloned in pIJ7760 supports the hypothesis that the hla aspDE locus belongs to an operon that is involved in iron acquisition. Furthermore this operon contains an upstream RirA regulatory sequence. Analysis of the Hla showed no homology with known proteins but the hla gene is syntenic with the HasA hemophore gene from S. marcescens. An aspD mutant showed increased cell clumping and reduced growth rate compared with the WT. Under low iron conditions, the aspD mutant showed increased motility, which was restored by normal iron. The secretion of several proteins encoded by the iron-responsive operon in A. tumefaciens was induced by hemoglobin and dependent on a functional AspDE system. AspDE might be involved in heme uptake through Hla, influencing other physiological functions.