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Robin J Rowbury

Publications and source records attributed to Robin J Rowbury.

11 recordsLinked to original sources
PubMed2005

Extracellular sensors and extracellular alarmones, which permit cross-talk between organisms, determine the levels of alkali tolerance and trigger alkaliinduced acid sensitivity in Escherichia coli.

For several stress responses in Escherichia coli, switching on involves conversion by the stress of an extracellular stress sensor (an extracellular sensing component, ESC) to an extracellular induction component (EIC), the latter functioning as an alarmone and inducing the response. The aim of this study was to establish whether alkali tolerance induction at pH 9.0, alkali sensitisation induced at pH 5.5 and the acid sensitisation induced at pH 9.0 involve sensing of pH changes by ESCs. The techniques involved made use of studies with cell-free culture filtrates. With respect to the inducible responses under test, these filtrates were prepared either from induced or uninduced cultures and filtrates from uninduced cultures were also activated in vitro, by the pH stress, in the absence of bacteria. Tests were then made to examine whether EICs (known to be needed for all these systems) are formed by activation, at the appropriate pH values, of filtrates from pH 7.0-grown cultures (i.e. uninduced culture filtrates); appearance of an EIC on activation would indicate the presence in the uninduced culture filtrate of an ESC. The studies showed that all three systems use ESCs to detect pH changes. Tests involving attempted enzymic and physical inactivation of the ESCs, and attempted removal of the ESCs by dialysis, showed that the ESC involved in alkali sensitisation is a small very heat-resistant protein. Strikingly, protease only partially inactivated the ESCs needed for alkali tolerance induction and for acid sensitisation; each system may be complex, involving both protein and non-protein (RNA?) ESCs, although other explanations are possible. It was also established that appropriate killed cultures can induce all three responses when incubated with pH 7.0-grown living cultures. The occurrence of ESC/EIC pairs for these three responses has led to the evolution of early warning systems for each, the diffusibility of the EICs, and their interaction with non-producers, allowing them to act pheromonally, inducing sensitive organisms to stress tolerance, prior to exposure to stressor.

Acids↗
PubMed2005

Intracellular and extracellular components as bacterial thermometers, and early warning against thermal stress.

Responses induced by cold or heat are triggered following detection of temperature changes by specific sensing molecules, complexes or structures. Low temperature responses are often induced following sensing of cold-induced falls in membrane fluidity, such changes turning-on or -off enzymic activities in membrane proteins, although ribosomes and DNA may also function in cold perception. Many thermal sensors are components of structures damaged by the heat, with sensing involving changes to ribosomes, DNA, intracellular proteins and, less commonly, membrane fluidity. Additionally, secreted proteins (extracellular sensing components, ESCs) detect temperature increases i.e. act as thermometers, with ESC activation in the medium, by the stimulus, converting such sensors to extracellular signalling molecules, the extracellular induction components (EICs), which induce thermal responses. Several ESC/EIC pairs trigger thermal responses, and have the unique property of giving early warning of the stress by diffusing to regions (and organisms) not yet exposed to elevated temperatures.

Bacteria↗
PubMed2004

Enterobacterial responses to external protons, including responses that involve early warning against stress and the functioning of extracellular pheromones, alarmones and varisensors.

Several striking findings, related to biological effects of external acidity, are reviewed here. The first of these relates to the role of PhoE in the penetration of H+ and protonated metabolites into the cell. PhoE is an anion pore and would not be expected to take up protons. The work reviewed here, however, shows that the loss or repression of PhoE leads to poor H+ passage through the outer membrane (OM), whilst derepression of PhoE leads to facilitated passage. It is now believed that H+ crosses through the PhoE pore in association possibly with oligopeptides, and that other protonated molecules, such as the acid tolerance EIC, use the same means to cross the OM. Additionally, several processes that form early warning systems against acidity are reviewed here. First, the properties of the acid tolerance EIC alarmones allow them to diffuse to regions not yet facing acid stress, and there give early warning and induce sensitive organisms to tolerance. Second, some agents, such as glucose, induce acid tolerance in organisms, long before these organisms are exposed to catabolically-produced acidity, preparing them, in advance, to resist this impending acid challenge. Third, the occurrence of multiple forms of ESCs (i.e. of varisensors) ensures that where organisms have been grown under conditions that sensitise them to acid stress, the ESCs formed are modified so as to be activated at much higher pH values, ensuring that lethality by acid is reduced or abolished. Fourthly, normally only EICs induce tolerance. Strikingly, however, pH 8.5 or 9.0-grown cells are induced to tolerance by ESC formed at pH 6.5. This is believed to provide another early warning system, protecting alkali-grown cells against sudden acidification of media. Two other finding reviewed here should be emphasised. First, the hydrophobic antibiotic novobiocin is ineffective against enterobacteria, due to its failure to penetrate the OM barrier. This only applies to cultures in pH 7.0 media, however, cells growing at pH 5.0 being exquisitely sensitive to novobiocin, due to a conformational change to the antibiotic at acidic pH, which allows ready penetration through the OM. Second, acidic pHs affect the synthesis and effects of another antibiotic, namely colicin V. Thus pH 5.0 prevents both synthesis of this agent and its effects on sensitive cells. Exposure to external acidity leads to numerous other effects, including those that influence growth, cell division, plasmid transfer and chemotaxis; these have also been reviewed here.

Bacterial Physiological Phenomena↗
PubMed2003

UV radiation-induced enterobacterial responses, other processes that influence UV tolerance and likely environmental significance.

The ability of enterobacteria to become UV-tolerant is important because such tolerance may enable organisms to resist irradiation in the environment, in water treatment, in shell-fish, in stages of food processing, and at locations in the domestic, commercial and hospital environment The mechanism for regulation of tolerance induction and SOS response induction has been studied for many years, and is well understood, except for the early stages of induction. Such early stages, namely sensing of the stimulus (UV irradiation) and the way in which such sensing leads to signal production, have until now been poorly understood. The claim has been made that DNA is the sensor and that either damage to DNA or production of SS regions in DNA (following interaction of UV with DNA) triggers the signal that sets in train RecA activation and other stages of tolerance induction. This claimed induction mechanism is a "classical" one in the sense that it involves intracellular sensing (by DNA) of the stressing stimulus (UV), and production of an intracellular signalling molecule. It is not, however, firmly established as the mechanism for initiation of UV tolerance induction and SOS response induction. The results reviewed here give firm evidence for a different and unique mechanism for sensing of UV and production of the signal. These results establish without doubt that, for UV tolerance induction, the UV sensor is an extracellular protein, which is a UV tolerance-specific extracellular sensing component (ESC). This component is formed by unstressed cells and on interacting with the stimulus (UV) in the medium, is converted to the tolerance induction signalling molecule, which is a UV tolerance-specific extracellular induction component (EIC). It is this extracellular signal which interacts with the sensitive organisms and triggers tolerance induction. This pair of extracellular components (ECs) may offer the only means of switching-on such tolerance induction; certainly they offer the only known way for early warning to be given of impending UV challenge. Thus, the EIC can diffuse from a region of UV stress to a stress-free region and there warn organisms of impending stress and prepare them to resist it. As indicated here, UV irradiation not only induces UV tolerance, but also switches-on acid tolerance, alkali tolerance and thermotolerance responses. The fact that all three responses involve ESC/EIC pairs strongly supports the view that functioning of such EC pairs form the major, if not the only, means for UV tolerance induction. The UV tolerance-specific ESC can detect other stresses and becomes activated, leading to cross-tolerance responses. Of particular interest, this ESC acts as a biological thermometer, detecting increases in temperature, such increases leading to gradually increasing formation of the EIC and, accordingly, gradual increases in UV tolerance. This UV tolerance-specific ESC can also detect other stresses e.g. acting as a pH sensor. In all cases, on activation, the EIC formed (from this specific ESC) only induces UV tolerance. It is proposed that the interaction of EICs with stress-sensitive organisms should be examined, and it is suggested that such EICs may, directly or indirectly, interact with and activate the same stress response regulators as are used to detect internal stressors and which, on activation, also trigger the switching-on of stress responses. For example, EICs either a in a protonated or oxidised state (formed by activation of ESCs by H+ or H2O2) or b produced by irradiation, may lead to protonation or oxidation or other forms of activation of the appropriate regulator (e.g. Fur or OxyR or RecA etc), leading to response induction.

DNA Damage↗
PubMed2003

How killed enterobacterial cultures can activate living organisms to resist lethal agents or conditions.

A major aim in many areas of microbiology is to ensure sterility, and even where this is impossible, to reduce the number of viable organisms occurring in particular environments to an absolute minimum. This applies in the aquatic environment, where e.g. water treatment must ensure as complete absence of viable microbes as possible. It is also crucial in food processing and production; many food constituents contain appreciable numbers of viable organisms, even potential pathogens, and the number must be greatly reduced and in many situations, the presence of viable organisms totally abolished. Cleaning of food production components and surfaces must also kill associated microbes. In domestic, hospital and commercial situations, similar disinfection is critical. Ultimately, the aim is to ensure, if possible, sterility, with the assurance that microbial problems cannot occur if organisms are absent. Additionally, however, it has been implicitly assumed that killed organisms and even killed cultures cannot (except in minor and trivial ways) influence the behaviour of living organisms that later enter the environment. The work reviewed here challenges that view and in fact disproves it. The findings described show that killed enterobacterial cultures, which prior to killing had phenotypically gained the ability to resist potentially lethal stresses, can pass on such ability to living organisms that later enter their environment i.e. that such killed cultures can convey a baleful legacy to living ones. This phenomenon is so widespread that it is clear that it has significance for enterobacterial survival in natural waters, in foods and in food production, in the domestic, commercial and hospital situation, and in the animal and human body. In fact, in this last area, the likely effect of killed cultures appears to be of appreciable public health importance. Here, the ability of appropriate killed cultures to transfer tolerance to acidity, alkalinity and thermal stress is described, as well as their ability to pass on sensitisation to acid and alkali. Other work reviewed suggests that killed cultures can almost certainly transfer the ability to tolerate hydrogen peroxide, ultraviolet irradiation and metal ions. The serious implications of this phenomenon are further emphasised by the fact that numerous killing methods produce cultures effective in tolerance response transfer. All the evidence suggests that it is extracellular components (extracellular sensing components, ESCs, and extracellular induction components, EICs), in the killed cultures which are involved in stress response transfer, and that the actual stress response induction process depends on interaction of living organisms with EICs from the killed cultures. It is of note that ESCs and EICs survive in killed cultures because of their extreme resistance to irreversible inactivation by lethal levels of stressing agents and conditions. This is in contrast to the fact that EC activation, namely the conversion of ESC to EIC occurs on exposure to very low levels of stressors. Not only is this the case, but in fact high levels of stressors (e.g. those that kill organisms) generally fail to convert ESC to EIC.

Bacterial Physiological Phenomena↗
PubMed2003

Extracellular proteins as enterobacterial thermometers.

Biological thermometers are cellular components or structures which sense increasing temperatures, interaction of the thermometer and the thermal stress bringing about the switching-on of inducible responses, with gradually enhanced levels of response induction following gradually increasing temperatures. In enterobacteria, for studies of such thermometers, generally induction of heat shock protein (HSP) synthesis has been examined, with experimental studies aiming to establish (often indirectly) how the temperature changes which initiate HSP synthesis are sensed; numerous other processes and responses show graded induction as temperature is increased, and how the temperature changes which induce these are sensed is also of interest. Several classes of intracellular component and structure have been proposed as enterobacterial thermometers, with the ribosome and the DnaK chaperone being the most favoured, although for many of the proposed intracellular thermometers, most of the evidence for their functioning in this way is indirect. In contrast to the above, the studies reviewed here firmly establish that for four distinct stress responses, which are switched-on gradually as temperature increases, temperature changes are sensed by extracellular components (extracellular sensing components, ESCs) i.e. there is firm and direct evidence for the occurrence of extracellular thermometers. All four thermometers described here are proteins, which appear to be distinct and different from each other, and on sensing thermal stress are activated by it to four distinct extracellular induction components (EICs), which interact with receptors on the surface of organisms to induce the appropriate responses. It is predicted that many other temperature-induced processes, including the synthesis of HSPs, will be switched-on following the activation of similar extracellular thermometers by thermal stimuli.

Adaptation, Physiological↗
PubMed2003

Morphological changes to Escherichia coli O157:H7, commensal E. coli and Salmonella spp in response to marginal growth conditions, with special reference to mildly stressing temperatures.

Certain rod-shaped bacteria have been reported to form elongated filamentous cells when exposed to marginal growth conditions, including refrigeration temperatures. To expand upon these observations, the filamentation of commensal Escherichia coli, E. coli O157:H7 and Salmonella spp was investigated, following exposure to certain, mildly stressing, levels of temperature, pH or water activity (aw), with levels of cellular protein being monitored during cell elongation, in some experiments. Our studies indicated that cellular filamentation could be demonstrated in all 15 strains of the above organisms tested, following exposure to marginal conditions achieved by incubation at high or low temperatures, high or low pH values and low aw. The level of environmental stress causing filamentation tended to be specific to the particular organisms. For example, Salmonella spp formed filamentous cells at 44 degrees C, whereas E. coli strains, including O157, grew by binary fission at that temperature, but formed filamentous cells at 46 degrees C. In addition, plate count techniques to enumerate bacteria during filamentation, failed to reflect the increase in cell biomass that was occurring, whereas measurements of protein concentration demonstrated the increase quite strikingly. These findings have important implications for our understanding of the ability of food-borne pathogens to cause disease, since the infectious dose of a microorganism implicated in an outbreak of such disease is typically determined by a viable count method, which could underestimate the number of potential infectious units present in a food that had been stored in such a way as to provide marginal growth conditions.

Colony Count, Microbial↗