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Biofilms constitute the predominant microbial style of life in natural and engineered ecosystems. Facing harsh environmental conditions, microorganisms accumulate reactive oxygen species (ROS), potentially encountering a dangerous condition called oxidative stress. While high levels of oxidative stress are toxic, low levels act as a cue, triggering bacteria to activate effective scavenging mechanisms or to shift metabolic pathways. Although a complex and fragmentary picture results from current knowledge of the pathways activated in response to oxidative stress, three main responses are shown to be central: the existence of common regulators, the production of extracellular polymeric substances, and biofilm heterogeneity. An investigation into the mechanisms activated by biofilms in response to different oxidative stress levels could have important consequences from ecological and economic points of view, and could be exploited to propose alternative strategies to control microbial virulence and deterioration.

Summary The host range of phages is a key to understand their impact on bacterial ecology and evolution. Because of the complexity of phage–host interactions, the variables that determine the breadth of a phage host range remain poorly understood. Here, we propose a novel holistic approach to identify the host range determinants of a new collection of phages infecting Salmonella, isolated from animal, environmental and wastewater samples that were able to infect 58 of the 71 Salmonella strains in our collection. By using a set of statistic approaches (non‐metric dimensional scaling, Bray–Curtis distance, PERMANOVA), we analysed phenotypic (host range on wild‐type and receptor mutants) and genetic data (taxonomic assignment and receptor binding proteins) to evaluate the impact of isolation strain and niche, phage receptor and genus on the host range. Statistical analysis revealed that two phage characteristics influence the host range by explaining the most variance: the receptor by 45% and the genus by 51%. Interestingly, phage genus and receptor in combination explained 79% of the variance, establishing these characteristics as the major determinants of the host range. This study demonstrates the power and the novelty of applying statistical approaches to phenotypic and genetic data to investigate the ecology of phage–host interactions.

Application of phages as alternative antimicrobials to combat pathogenic bacteria and their association to a healthy gut microbiome has prompted a need for precise methods for detection and enumeration of phage particles. There are many applicable methods, but care should be taken considering the measured object (infectious phage, whole phage particle or nucleic acid and proteins) and the concept behind the technique to avoid misinterpretations. While molecular methods cannot discriminate between viable and non-infectious phages, the traditional techniques for counting infectious phages can be time consuming and poorly reproducible. Here, we describe the methods currently used for phage detection and enumeration and highlight their advantages as well as their limitations. Finally, we provide insight on how to deal with complex samples, as well as future prospects in the field of phage quantification.

This work showed that perturbations of the physiological steady-state level of reactive oxygen species (ROS) affected biofilm genesis and the characteristics of the model bacterium Azotobacter vinelandii. To get a continuous endogenous source of ROS, a strain exposed to chronic sub-lethal oxidative stress was deprived of the gene coding for the antioxidant rhodanese-like protein RhdA (MV474). In this study MV474 biofilm showed (i) a seven-fold higher growth rate, (ii) induction of catalase and alkyl-hydroxyl-peroxidase enzymes, (iii) higher average thicknesses due to increased production of a polysaccharide-rich extracellular matrix and (iv) less susceptibility to hydrogen peroxide than the wild-type strain (UW136). MV474 showed increased swimming and swarming activity and the swarming colonies experienced a higher level of oxidative stress compared to UW136. A continuous exogenous source of ROS increased biofilm formation in UW136. Overall, chronic sub-lethal oxidative events promoted sessile behavior in A. vinelandii.

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A protocol for a simple and reliable dot-blot immunoassay was developed and optimized to test work of art samples for the presence of specific proteinaceus material (i.e. ovalbumin-based). The analytical protocol has been extensively set up with respect, among the other, to protein extraction conditions, to densitometric analysis and to the colorimetric reaction conditions. Feasibility evaluation demonstrated that a commercial scanner and a free image analysis software can be used for the data acquisition and elaboration, thus facilitating the application of the proposed protocol to commonly equipped laboratories and to laboratories of museums and conservation centres. The introduction of method of standard additions in the analysis of fresh and artificially aged laboratory-prepared samples, containing egg white and various pigments, allowed us to evaluate the matrix effect and the effect of sample aging and to generate threshold density values useful for the detection of ovalbumin in samples from ancient works of art. The efficacy of the developed dot-blot immunoassay was proved testing microsamples from 13th-16th century mural paintings of Saint Francesco Church in Lodi (Italy). Despite the aging, the altered conditions of conservation, the complex matrix, and the micro-size of samples, the presence of ovalbumin was detected in all those mural painting samples where mass-spectrometry-based proteomic analysis unambiguously detected ovalbumin peptides.

Re-direction of gene expression, linked to selective toxicity, suggests a strong impact of Ag-NPs on soil bacterial communities.