Chemical Communication Among Bacteria

Summarizes the science and recent research developments of chemical communication among bacteria

Quorum sensing (QS) describes a chemical communication behavior that is nearly universal among bacteria. Individual cells release a diffusible small molecule (an autoinducer) into their environment. A high concentration of this autoinducer serves as a signal of high population density, triggering new patterns of gene expression throughout the population. However QS is often much more complex than this simple census-taking behavior. Many QS bacteria produce and detect multiple autoinducers, which generate quorum signal cross talk with each other and with other bacterial species. QS gene regulatory networks respond to a range of physiological and environmental inputs in addition to autoinducer signals. While a host of individual QS systems have been characterized in great molecular and chemical detail, quorum communication raises many fundamental quantitative problems which are increasingly attracting the attention of physical scientists and mathematicians. Key questions include: What kinds of information can a bacterium gather about its environment through QS? What physical principles ultimately constrain the efficacy of diffusion-based communication? How do QS regulatory networks maximize information throughput while minimizing undesirable noise and cross talk? How does QS function in complex, spatially structured environments such as biofilms? Previous books and reviews have focused on the microbiology and biochemistry of QS. With contributions by leading scientists and mathematicians working in the field of physical biology, this volume examines the interplay of diffusion and signaling, collective and coupled dynamics of gene regulation, and spatiotemporal QS phenomena. Chapters will describe experimental studies of QS in natural and engineered or microfabricated bacterial environments, as well as modeling of QS on length scales spanning from the molecular to macroscopic. The book aims to educate physical scientists and quantitative-oriented biologists on the application of physics-based experiment and analysis, together with appropriate modeling, in the understanding and interpretation of the pervasive phenomenon of microbial quorum communication.

Microbial extracellular polymeric substances (EPS) are the key components for the aggregation of microorganisms in biofilms, flocs and sludge. They are composed of polysaccharides, proteins, nucleic acids, lipids and other biological macromolecules. EPS provide a highly hydrated gel matrix in which microbial cells can establish stable synergistic consortia. Cohesion and adhesion as well as morphology, structure, biological function and other properties such as mechanical stability, diffusion, sorption and optical properties of microbial aggregates are determined by the EPS matrix. Also, the protection of biofilm organisms against biocides is attributed to the EPS. Their matrix allows phase separation in biofiltration and is also important for the degradation of particulate material which is of great importance for the self purification processes in surface waters and for waste water treatment.

It is generally assumed that microorganisms synthesize, release, detect and respond to small signaling hormone-like molecules. These molecules are used for a process termed “quorum sensing” (QS), a phenomenon that enables bacteria to sense when the minimal number of cells, or “quorum,” is achieved for a concerted response to be initiated. Words such as “language” and “behavior” are frequently used to depict QS in the literature. More simply put, language and cross-talk between bacteria, and between bacteria and animal or plant hosts, determines the behavior (e.g., beneficial or pathogenic effects) of bacteria. Currently, the major concern is to understand and decode this language. Overall, bacterial cross-talk was mainly studied on environmental, plant, and human pathogenic bacteria. Few studies considered food-related lactic acid bacteria. The cross-talk between bacteria influences the behavior and, in turn, the environmental adaptation and phenotypes. Therefore, it is understood that bacterial cross-talk has important applicative repercussions. The language spoken between bacteria populating the same food ecosystem may condition the phenotypic traits of starter lactic acid bacteria and, consequently, their performance. This Brief aims to define the basis of cell-to-cell signalling in food fermentation and will highlight: (i) microbiology, nutritional, chemical and functional aspects; (ii) functional properties due to microbial adaptation to the gastrointestinal tract; (iii) principal phenotypes under control of QS circuitries; (iv) quorum quenching. This Brief will be the first reference on this topic and it will highlight the main results for a more productive industrial application. Draft content 1. Signals of food related Gram-negative and Gram-positive bacteria The chapter will describe the different signaling languages used by Gram-negative bacteria (N-acyl-L-homoserine lactones) and Gram-positive bacteria (based on the synthesis of post-translationally modified peptides) and the universal chemical lexicon, shared by both Gram-positive and -negative bacteria (autoinducer-2 through the activity of the LuxS enzyme). 2. Phenotypes related to quorum sensing The chapter will describe the bacterial phenotypes, such as virulence, biofilm maturation, bacteriocin synthesis, and secondary metabolite production under control of QS circuitries. 3. Cell-to-cell signalling in fermented food: sourdough The chapter will describe the language spoken between bacteria populating the same food ecosystem (sourdough) and will provide an overview of the conditioned phenotypic traits of starter lactic acid bacteria and, consequently, their performance. 4. Cell-to-cell signalling in fermented food: yoghurt The chapter will describe the language spoken between bacteria populating the same food ecosystem (yoghurt) and will provide an overview of the conditioned phenotypic traits of starter lactic acid bacteria and, consequently, their performance. 5. Probiotic message at the intra-, inter-species and inter-kingdom level The chapter will describe the mechanisms that regulate the interaction between microorganism and host, and the capacity of the microorganism to adapt to environment. Particular reference will also be made to: (i) pathogen inhibition and restoration of microbial homeostasis through microbe-microbe interactions; (ii) enhancement of epithelial barrier function; and (iii) modulation of immune responses. 6. New Perspectives of quorum sensing This chapter will provide an overview of the future perspective regarding quorum sensing, showing that bacterial cross-talk may have important applicative repercussions. It will highlight the interference on the language of QS, which is defined as quorum quenching (QQ). Increasing translation of the bacterial cross-talk has shown that in some environmental circumstances, quenching of the language may occur.

Intraspecific communication involves the activation of chemoreceptors and subsequent activation of different central areas that coordinate the responses of the entire organism—ranging from behavioral modification to modulation of hormones release. Animals emit intraspecific chemical signals, often referred to as pheromones, to advertise their presence to members of the same species and to regulate interactions aimed at establishing and regulating social and reproductive bonds. In the last two decades, scientists have developed a greater understanding of the neural processing of these chemical signals. Neurobiology of Chemical Communication explores the role of the chemical senses in mediating intraspecific communication. Providing an up-to-date outline of the most recent advances in the field, it presents data from laboratory and wild species, ranging from invertebrates to vertebrates, from insects to humans. The book examines the structure, anatomy, electrophysiology, and molecular biology of pheromones. It discusses how chemical signals work on different mammalian and non-mammalian species and includes chapters on insects, Drosophila, honey bees, amphibians, mice, tigers, and cattle. It also explores the controversial topic of human pheromones. An essential reference for students and researchers in the field of pheromones, this is also an ideal resource for those working on behavioral phenotyping of animal models and persons interested in the biology/ecology of wild and domestic species.

The crustaceans are ecologically and economically important organisms. They constitute one of the dominant invertebrate groups on earth, particularly within the aquatic realm. Crustaceans include some of the preferred scientific model organism, profitable aquaculture specimen, but also invasive nuisance species threatening native animal communities throughout the world. Chemoreception is the most important sensory modality of crustaceans, acquiring important information about their environment and picking up the chemical signals that mediate communication with conspecifics. Significant advances have been made in our understanding of crustacean chemical communication during the past decade. This includes knowledge about the identity, production, transfer, reception and behavioral function of chemical signals in selected crustacean groups. While it is well known that chemical communication is an integral part of the behavioral ecology of most living organisms, the intricate ways in which organisms allocate chemicals in communication remains enigmatic. How does the environment influence the evolution of chemical communication? What are the environmental cues that induce production or release of chemicals? How do individuals economize production and utilization of chemicals? What is the importance of molecule specificity or mix of a molecule cocktail in chemical communication? What is the role of chemical cues in multimodal communication? How does the ontogenetic stage, the sex or the physiological status of an individual affect its reaction to chemical cues? Many of these questions still represent important challenges to biologists.

This series presents critical reviews of the present position and future trends in modern chemical research.