title: Discrete Responses to Limitation for Iron and Manganese in Agrobacterium tumefaciens: Influence on Attachment and Biofilm Formation.
abstract: Transition metals such as iron and manganese are crucial trace nutrients for the growth of most bacteria, functioning as catalytic cofactors for many essential enzymes. Dedicated uptake and regulatory systems have evolved to ensure their acquisition for growth, while preventing toxicity. Transcriptomic analysis of the iron- and manganese-responsive regulons of Agrobacterium tumefaciens revealed that there are discrete regulatory networks that respond to changes in iron and manganese levels. Complementing earlier studies, the iron-responsive gene network is quite large and includes many aspects of iron-dependent metabolism and the iron-sparing response. In contrast, the manganese-responsive network is restricted to a limited number of genes, many of which can be linked to transport and utilization of the transition metal. Several of the target genes predicted to drive manganese uptake are required for growth under manganese-limited conditions, and an A. tumefaciens mutant with a manganese transport deficiency is attenuated for plant virulence. Iron and manganese limitation independently inhibit biofilm formation by A. tumefaciens, and several candidate genes that could impact biofilm formation were identified in each regulon. The biofilm-inhibitory effects of iron and manganese do not rely on recognized metal-responsive transcriptional regulators, suggesting alternate mechanisms influencing biofilm formation. However, under low-manganese conditions the dcpA operon is upregulated, encoding a system that controls levels of the cyclic di-GMP second messenger. Mutation of this regulatory pathway dampens the effect of manganese limitation.
  
  
  OBJECTIVE
  Responses to changes in transition metal levels, such as those of manganese and iron, are important for normal metabolism and growth in bacteria. Our study used global gene expression profiling to understand the response of the plant pathogen Agrobacterium tumefaciens to changes of transition metal availability. Among the properties that are affected by both iron and manganese levels are those required for normal surface attachment and biofilm formation, but the requirement for each of these transition metals is mechanistically independent from the other.
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana, USA.
authors.forename: Jason E
authors.identifier: http://orcid.org/0000-0003-3919-8045
authors.initials: JE
authors.lastname: Heindl
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Hibbing
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Xu
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana, USA.
authors.forename: Ramya
authors.initials: R
authors.lastname: Natarajan
authors.affiliation: Center for Genomics and Bioinformatics, Indiana University, Bloomington, Indiana, USA.
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Buechlein
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana, USA cfuqua@indiana.edu.
authors.forename: Clay
authors.identifier: http://orcid.org/0000-0001-7051-1760
authors.initials: C
authors.lastname: Fuqua
mesh_terms: D016960:Agrobacterium tumefaciens / Q000187:drug effects / Q000502:physiology*; D001422:Bacterial Adhesion / Q000187:drug effects / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018441:Biofilms / Q000187:drug effects / Q000254:growth & development*; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000502:physiology; D007501:Iron / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology; D008345:Manganese / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology; D059467:Transcriptome
chemical_list: D001426:Bacterial Proteins; D008345:Manganese; D007501:Iron