Special Issue: Quorum Sensing and Chemical Communication between Species

Abstract

Living organisms on earth are seldom alone. Most often they exist as dynamic collections of species from different kingdoms of life, coexisting and even collaborating to function successfully as 'superorganisms'. While the overall dynamics between populations of species and their regulation within such a superorganism are still poorly understood, more and more specific interactions between individual species (e.g., human-fungal, human-bacterial, bacterial-fungal, bacterial-bacterial) are being uncovered, yielding a wealth of information about important processes that govern the delicate balancing act enabeling such forms of coexistence. Bacteria secrete small molecules that enable synchronization of a population, and a coordinated upregulation of virulence, as function of its population density, in a process termed quorum sensing (QS). Such molecules, also termed autoinducers, can reach high local concentrations, and in recent years it has become clear that these signaling molecules can often perform dual or multiple functions and play important roles in guiding the interactions between bacteria and their hosts, as well as with various bacterial competitors. In recent years important advances in our understanding of microbial quorum sensing as well as interspecies crosstalk have been achieved. This special issue contains contributions that summarize the state of the art in our understanding of various types of chemical communication between bacteria and between different species. A general overview of the different types of systems that regulate QS within various bacteria is presented by Bloom-Ackerman, Ganin and Kolodkin-Gal, while the effects of specific bacterial QS molecules on other species (both prokaryotes and eukaryotes) are described by Clinton and Rumbaugh. A prime example of a dynamic environment that contains hundreds of different bacterial species is the oral cavity, and Steinberg presents an overview of the important roles of chemical communication in guiding the interactions between species and formation of complex biofilms in this habitat. In-depth overviews of the roles of specific QS molecules on bacterial and fungal cooperation are presented by Dow et al. (the diffusible signal factor, DSF), by Sams et al. (the Pseudomonas quinolone signal, PQS) and by Krom et al. (the fungal signal farnesol). Many species appear to have evolved tools to interfere with QS systems of competitors, and an overview of the diverse array of natural QS inhibitors is presented by Delago et al. Finally, as an example of the largely untapped rich vocabulary of QS signals in marine habitats, Saurav et al. report the discovery of previously unknown QS systems in a bacterial symbiont of a Mediterranean sponge. I thank Ehud Keinan (Editor, IJC), Charles Diesendruck (Associate Editor, IJC), and Brian Johnson (Publisher, Wiley-VCH) for their kind cooperation and support, and Dr. Rambabu Dandela and Shimrit David for their assistance in preparing the cover graphic. 1 Michael M. Meijler Ben Gurion University of the Negev, Be'er Sheva Guest Editor