An Agrobacterium tumefaciens type I secretion system is involved in iron metabolism

HAURIGOT, L; FERELLA, M; DOWNIE JA; ZORREGUIETA A

Mar del Plata

Congreso; 43th Annual Meeting SAIB; 2007

SAIB

Type I secretion systems (TISSs) deliver proteins to the extracellular media in gram-negative bacteria. The PrsDE TISS of Rhizobium leguminosarum secretes NodO, several adhesins and the glycanases PlyA and PlyB. We have previously identified a TISS of Agrobacterium tumefaciens (AspDE) which restored protein secretion in the prsDE mutant. An extracellular protein encoded by an upstream gene of aspDE (hla) was overproduced when the hla aspDE locus cloned into pIJ7760 was expressed in R. leguminosarum. However, Hla was not detected in the extracellular medium of A. tumefaciens even in the presence of pIJ7760. Analysis of Hla showed no significant homology with known proteins. To investigate the function of both Hla and AspDE in Agrobacterium ecophysiology, we constructed an aspD mutant. This mutant showed increased cell clumping when it is grown at low iron concentration. In addition, we detected in the wild type strain a surface associated protein with a molecular weight similar to Hla that was absent in the aspD mutant. The mutant was also defective in the secretion of a 40 kDa-surface protein that is present in the wild type when hemoglobin was the iron source. Genomic analysis of the hla aspDE context suggests that this locus might be involved in iron acquisition. Taking together, our observations suggest that Hla and AspDE may be involved in the iron uptake.