A two‐partner secretion system is involved in seed and root colonization and iron uptake by Pseudomonas putida KT2440

Abstract

We describe the first two-partner secretion system known to play a role in mutualistic plant-bacterial interactions, identified in the soil and rhizosphere-colonizing bacterium Pseudomonas putida KT2440. The genes coding for the two components of the system are organized in an operon, which we have named hlpBA. HlpA is a secreted protein that has similarities with iron-regulated haemolysins, while HlpB would be responsible for the activation and transport of HlpA across the outer membrane. Mutations in this novel two-partner secretion system result in reduced capacity to colonize corn seeds. When introduced in the rhizosphere, hlpA and hlpB mutants show no competitive disadvantage, but the number of cells attached to the root surface is reduced with respect to the wild type, suggesting this protein plays a role directly in the bacterial cell-root surface interaction. Under iron-limiting conditions, the presence of a truncated HlpA causes reduced viability and high levels of siderophore release. These data further strengthen our previous observations indicating the importance of iron acquisition for attachment of P. putida KT2440 to plant surfaces.

Pumping iron to keep fit: modulation of siderophore secretion helps efficient aromatic utilization in Pseudomonas putida KT2440

“…Apart from aromatic utilization, iron has been shown to play a significant role in various physiological attributes of P. putida, including root/seed colonization, motility, biofilm formation, biocontrol and pollutant degradation (Dinkla & Janssen, 2003;Dinkla et al, 2001;Fernández-Piñar et al, 2011;Molina et al, 2005Molina et al, , 2006. Therefore, one can presume that accelerated siderophore secretion will have multidimensionally positive impacts on the survival and proliferation of P. putida in its natural environment.…”

Characterization of a Novel Two-Partner Secretion System in Escherichia coli O157:H7

“…One group of TPS exoproteins, which includes Serratia marcescens ShlA, Proteus mirabilis HpmA, Photorhabdus luminescens PhlA, Haemophilus ducreyi HhdA, and Edwardsiella tarda EthA, have hemolytic/cytolytic activities and share extensive sequence homology (3,4,16,28,40,45). A hemolysin-like protein from Pseudomonas putida (HlpA) has recently been shown to affect root colonization and iron uptake and may also be a member of this family (25). A second family of TPS proteins, which includes enterotoxigenic Escherichia coli EtpA, Bordetella pertussis FHA, and Haemophilus influenzae HMW1 and HMW2, function as adhesins (10,37,46).…”

“…TPS exoproteins are large proteins that range in size from 100 kDa to more than 500 kDa (2,4,5,10,20,25). They usually contain typical N-terminal signal peptides that target them for translocation across the inner membrane via the Sec pathway (20).…”

A Two-Component Regulatory System Integrates Redox State and Population Density Sensing in Pseudomonas putida

“…To rule out DNA contamination, a negative control was included whereby the mixture was heated for 5 min at 94°C to inactivate reverse transcriptase before the PCR amplification step. As positive controls, primers corresponding to the hlpBA operon (23) or to the rpoB gene were used. A list of the oligonucleotides used is included as Table S1 in the supplemental material.…”