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. IMPORTANCEResponses 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.

A central role for the transcriptional regulator VtlR in small RNA-mediated gene regulation in Agrobacterium tumefaciens

“…In A. tumefaciens ∆vtlR, divK is over-expressed, suggesting the possibility of divK dysregulation could alter biofilm formation. While no other genes from the ∆vtlR RNA-seq analysis have been linked directly to biofilm formation, several genes have been speculated to be necessary for biofilm production (e.g., glcF and gguB) 40 .…”

Insights on the Functions and Ecophysiological Relevance of the Diverse Carbonic Anhydrases in Microalgae

“…Response to Mn 2+ availability at the genetic level has been studied in several organisms. In the bacterium Agrobacterium tumefaciens, 55 genes were differentially expressed in manganese-limited cells, and the cells showed a reduction in biofilm formation [137]. Furthermore, the Mn-sensing transcriptional regulator MtsR controls the expression of genes related to Mn 2+ uptake as well as genes controlling Streptococcus pyrogenes virulence [138].…”

Overview on the Bacterial Iron-Riboflavin Metabolic Axis

“…This consists in the downregulation of non-essential iron-dependent enzymes in order to prioritize iron for fundamental functions. For example, iron-starving Mycobacterium tuberculosis and Bacillus subtilis downregulate aconitase and succinate dehydrogenase ( Janagama et al, 2010 ; Smaldone et al, 2012 ), while Agrobacterium tumefaciens downregulates a system encoding a multicopper oxidase, cytochrome c 556 and a NAD-dependent formate dehydrogenase complex, all of them needing iron as cofactor ( Heindl et al, 2015 ). Strikingly, the iron-sparing response may also include the replacement of iron-cofactored enzymes by flavin-dependent enzymes.…”