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Biofilms are complex bacterial assemblages with a defined three-dimensional architecture, attached to solid surfaces, and surrounded by a self-produced matrix generally composed of exopolysaccharides, proteins, lipids and extracellular DNA. Biofilm formation has evolved as an adaptive strategy of bacteria to cope with harsh environmental conditions as well as to establish antagonistic or beneficial interactions with their host. Plant-associated bacteria attach and form biofilms on different tissues including leaves, stems, vasculature, seeds and roots. In this review, we examine the formation of biofilms from the plant-associated bacterial perspective and detail the recently-described mechanisms of genetic regulation used by these organisms to orchestrate biofilm formation on plant surfaces. In addition, we describe plant host signals that bacterial pathogens recognize to activate the transition from a planktonic lifestyle to multicellular behavior., (© 2015 Institute of Botany, Chinese Academy of Sciences.)

Fire blight is a devastating plant disease caused by the bacterium Erwinia amylovora, and its control is frequently based on the use of copper-based compounds whose mechanisms of action are not well known. Consequently, in this article, we investigate the response of E. amylovora to copper shock by a whole-genome microarray approach. Transcriptional analyses showed that, in the presence of copper, 23 genes were increased in expression; these genes were classified mainly into the transport and stress functional categories. Among them, the copA gene was strongly induced and regulated in a finely tuned manner by copper. Mutation of copA, soxS, arcB, yjcE, ygcF, yhhQ, galF and EAM_3469 genes revealed that tolerance to copper in E. amylovora can be achieved by complex physiological mechanisms, including: (i) the control of copper homeostasis through, at least, the extrusion of Cu(I) by a P-type ATPase efflux pump CopA; and (ii) the overcoming of copper toxicity caused by oxidative stress by the expression of several reactive oxygen species (ROS)-related genes, including the two major transcriptional factors SoxS and ArcB. Furthermore, complementation analyses demonstrated the important role of copA for copper tolerance in E. amylovora, not only in vitro, but also in inoculated pear shoots. [ABSTRACT FROM AUTHOR]