Responses to Chemical, Physical and Biological Stresses: Involvement of Extracellular Alarmones, Pheromones and Varisensors

Introduction The first article in this special issue (1) seems at first slightly out of place, in that it considers the synthesis, properties and roles of the ribosome modulation factor (RMF) and related agents. In fact, this article is firmly related to stress effects of potentially lethal agents and conditions and on responses to these, with the author reviewing particularly RMF effects on responses to stationary-phase stress and to thermal and acid stresses. First, the group of agents El-Sharoud considers interact with ribosomes allowing bacteria to survive stresses in the stationary-phase. These agents do more than this, however, in that they both protect organisms from potentially lethal chemical stress agents in the stationary-phase, but also from the same and other agents in exponential phase. RMF has two major properties namely: (1) leading to ribosome dimerisation, the active 70S particles dimerising to form inactive 100S ones, whilst (2) this ribosome binding component also influences rRNA degradation. It appears that the latter property is more important as a means of protecting organisms from stress. Of interest is the finding that ppGpp controls RMF synthesis, probably explaining why this component, which is not influenced by the sigma factor, RpoS, nonetheless increases in level in stationary-phase. It has become clear that responses to oxidative stress are of critical importance to bacteria, because bacteria face numerous oxidative agents in many situations. Some of us may be familiar with the fact that certain oxidative components (e.g. [H.sub.2][O.sub.2]) are frequently used in water purification, shell-fish disinfection and in sterilisation of production areas and containers in food microbiology, but many such agents are also involved in phagocytic killing in the human and animal body. Marquis, however, in his article (2) deals with some aspects of the above, but mainly concentrates on the striking role of these components in influencing the growth and survival of oral microbes, as well as considering how these agents influence the nature of the oral microbiota. This article is of considerable significance not only because so many of us have infections by oral microbes, but also because some oral microbes escape to other sites in the body, and on occasions, cause very serious disease there. One area considered relates to the structure and properties of dental plaque. Marquis points out that this layer is not, as often believed, highly anaerobic, but that [O.sub. 2] can readily permeate into it, and give rise by metabolism to reactive oxygen species (ROS). He also describes how fluoride acts; we find (2) that its level in plaque is much more than in saliva, and that because plaque pH is generally acidic, substantial HF is present. Whereas F poorly crosses membranes, HF readily does so, and following dissociation leads to enzyme inhibition. Bacteriophages are considered in Martin Day's article (3). Whilst many phages are normal constituents of natural waters, others enter from sources such as sewage and other domestic waste, from agricultural inputs and from hospital and commercial effluents, and these latter are pollutants of these waters, just as lethal agents entering from factory or mining wastes are. The effects of phages on bacteria in natural waters will depend on whether nutrient levels permit effective attachment to the microbial surfaces and efficient multiplication in the cells. For polluting phages the problem may well be that temperatures are too low for attachment and for phage multiplication. Whereas naturally occurring phages will [unction well at temperatures in the 10-20[degrees]C range, this will not be true for polluting phages which have entered natural waters from animals. The final article (4) considers effects of and responses to inorganic acids. Such agents can enter environmental waters from chemical works, agricultural slurries and mine wastes and tailings, but also arise following atmospheric pollution, acidity resulting from the precipitation of acid rain or snow. …