Aims:  The goal of this work was to investigate the influence of DMSO, garlic extract and p‐coumaric acid on bacterial quorum sensing (QS). Methods and Results:  The decreases in the QS responses of QS reporter strains Escherichia coli pSB401 and pSB536, Agrobacterium tumefaciens NTL4, Chromobacterium violaceum 5999 and wt 494, Pseudomonas putida IsoF/gfp and environmental Pseudomonas chlororaphis were quantified in relation to growth inhibitory effects. DMSO showed no significant QS‐specific effects on the strains tested even at close‐to‐lethal concentrations. Garlic extracts antagonized the activity of QS receptors LuxR, AhyR and TraR, but were toxic at higher concentrations. P‐coumaric acid fully inhibited QS responses of 5999, NTL4 and P. chlororaphis, with no influence on cell viability. Conclusions:  The quorum sensing inhibition activity of garlic was extended to novel receptors, and p‐coumaric acid was found to possess previously undescribed QS antagonist properties. Significance and Impact of the Study:  The results suggest that p‐coumaric acid might act as QS inhibitor. Further studies are required to understand its role in the regulation of QS and investigate structurally related compounds.

No abstract

Nutrient pollution is one of worldwide most diffused, expensive and challenging environmental issues.The monitoring of nutrients in coastal areas is a complex task, due to the fact that the available methods reaching the required sensitivity are based on optical wet chemistry measurements. In order to be representative, a reliable water sample collection for further laboratory analysis requires a very strict protocol and sample handling. Because of this, most of the scientists agree in affirming that the best and practical solution is to measure nutrients directly on field. SYSTEA S.p.A. has been working in the last two decades to improve automated solutions for on-line nutrient monitoring. The micro Loop Flow Reactor (μLFR) technology was presented in 2009 in Oceans conference in Biloxi (USA) and is currently a consolidated technique allowing the field measurement of nutrients in different environmental conditions.Fast growing urbanization and industrialization of river basins and coastal areas in China are imposing the local Government to improve large water quality monitoring networks; during the last few years, around one hundred in-situ nutrient multi-parameter probes (NPA pro and WIZ) were installed and provided extensive long term data to support the environmental control and related decisions making policy.The WIZ probe is an advanced real time instrument to measure the nutrient concentrations in aquatic environments. In particular, it is the only portable and submersible equipment able to measure the total concentrations of both phosphorus and nitrogen. The uniqueness of this probe is given by the fact that the unit performing the sample digestion, required for the analysis of both total phosphorus and nitrogen, was downscaled to fit within the probe.The efficiency of NPA pro and WIZ probes in measuring the concentrations of ammonia, nitrate, phosphate and nitrite was evaluated on field deployments in coastal waters, in China and South Korea, respectively. Importantly, the probe results were found to be highly correlated with laboratory measurements.The μLFR technology was also applied to the design and manufacturing of μLFA modules, on-line nutrient analyzers integrated in Ferrybox systems for the measurement of ammonia and orthophosphates. In situ results obtained in Ferrybox installations were compared and correlated with laboratory analysis of grab samples.Finally, a number of practical solutions for the improvement of NPA pro and WIZ probes in terms of instrument robustness, data reproducibility, deployment life and reliability, were, for the first time, presented and discussed.The Alliance for Coastal Technologies (ACT) is a US partnership of research organizations, water stakeholders and private companies competent in the field of nutrient management which, by means of dedicated market surveys, were able to catalogue the most frequently requested specifications for nutrient analyzers. This record was used as a guide to assess the current performance level of μLFR-based probes and modules with resp...

A vast bibliography on nutrient effects on high-density cultures exists, while it has been overlooked that low densities of starving cells are often the rule in natural environments. By means of a novel sensitive ␤-galactosidase assay, we examined Escherichia coli transitions to minimal media when the cell concentration was 100 to 10,000 cells per ml. As in high-density cultures, the enzyme activity depended on amino acid availability and was subject to catabolite repression and stringent control. In all conditions tested, despite the presence of other nutrient sources, the relationship between ␤-galactosidase activity and the L-amino acid pool was hyperbolic. The affinity constant when the amino acid pool was the only nutrient source averaged 14 M after 90 min and increased up to 222 M after 4.5 h. While investigating the transition from lag phase to exponential phase, we observed that the cells did not enter into starvation mode in the presence of amino acids, even when the nutrient amount was insufficient to support full survival. Based on these premises, the switch from starvation to hunger was investigated in relation to the amino acid pools. A critical range of concentrations at which E. coli linearly synthesized ␤-galactosidase despite, at the same time, suffering a large decrease in cell viability was then recognized. Since both ␤-galactosidase production and the dilution rate were reduced by more than half in the absence of leucine, we examined the contribution of leucine to cell recovery capabilities.The natural state in which microorganisms conduct their lives oscillates between feast and famine (20). The growth rate in either soil or water is often not measurable, with duplication times in the order of days or weeks (16), because most bacteria are under starving conditions and only bacteria inhabiting "hot spots," such as the gut, rhizosphere soil, or sites around vegetable debris, have wide access to nutrients (7). Simulating environmental fluctuations of nutrient conditions via controlled nutritional shifts for Escherichia coli showed the activation/ deactivation of many different molecular systems coordinating the regulation of the cell metabolism by carbon, nitrogen, and amino acids, like the cyclic AMP (cAMP)-cAMP receptor protein modulon (34), the nitrogen-regulated response (31), and the stringent modulon (4, 9, 24). However, upon the complete exhaustion of an essential nutrient, cells were shown to enter into stationary phase through a general stress response controlled by the rpoS-encoded sigma-S subunit of the RNA polymerase (17). When nutrients were limited yet not completely absent, the cells exhibited the hunger response, which partly overlapped with the stress response (13). It has been thoroughly shown how nutrient downshifts or upshifts also influence the induction of ␤-galactosidase due to catabolite repression (22), stringent control (30), and stationary-phase control (14). On the other hand, the lack of suitable analytical approaches and the need to uniform experimental conditions ...

No abstract