Soil salinization and desertification due to climate change are the most relevant challenges for the agriculture of the 21st century. Soil compost amendment and plant growth promoting rhizobacteria (PGP-R) are valuable tools to mitigate salinization and desertification impacts on agricultural soils. Selection of novel halo/thermo-tolerant bacteria from the rhizosphere of glicophytes and halophytes, grown on soil compost amended and watered with 150/300 mM NaCl, was the main objective of our study. Beneficial effects on the biomass, well-being and resilience, exerted on the assayed crops (maize, tomato, sunflower and quinoa), were clearly observable when soils were amended with 20% compost despite the very high soil electric conductivity (EC). Soil compost amendment not only was able to increase crop growth and biomass, but also their resilience to the stress caused by very high soil EC (up to 20 dS m⁻¹). Moreover, compost amendment has proved itself a valuable source of highly halo-(4.0 M NaCl)/thermo tolerant rhizobacteria (55 °C), showing typical PGP features. Among the 13 rhizobacterial isolates, molecularly and biochemically characterized, two bacterial strains showed several biochemical PGP features. The use of compost is growing all around the world reducing considerably for farmers soil fertilization costs. In fact, only in Italy its utilization has ensured, in the last years, a saving of 650 million euro for the farmers, without taking into account the environment and human health benefits. Furthermore, the isolation of halo/thermo-tolerant PGPR strains and their use will allow the recovery and cultivation of hundreds of thousands of hectares of saline and arid soils now unproductive, making agriculture more respectful of agro-ecosystems also in view of upcoming climate change.

Soil salinity, due to natural phenomena or human activities, alters the water potential, which in turn affects plant growth, negatively influencing their nutrient and water uptake. Plant-growth-promoting rhizobacteria (PGPR) can be used to counteract these negative effects, especially in glycophytes. The aim of our study was to characterize physiologically, genetically, and biochemically the novel halotolerant/halophilic bacteria isolated in our previous work. We evaluated the plant-growth-promoting (PGP) features and NaCl regulation’s roles in them. In this regard, analysis based on 16S rDNA sequences confirmed that our isolates are distinct bacterial strains, probably belonging to new species, which we named Bacillus sp. M21 and M23 and Halomonas sp. QH23 and QH24. In literature, it is known that many species of Halomonas and Bacillus genera produce factors regulating plant development, such as indole-3-acetic acid (IAA), ammonium, and siderophores; and their efficiency in promoting plant growth and productivity was also demonstrated in vivo. We demonstrated that the newly isolated strains exhibit different PGP activities, highlighting how the latter are regulated by NaCl and in a strain-dependent manner. In particular, the main results showed that NaCl negatively affects the production of IAA in QH23, M21 and M23, whereas it promotes it in QH24, where it is strictly salt-dependent. Both Halomonas strains produce ammonium only in the presence of NaCl, directly correlated to its concentration. The opposite occurs in Bacillus strains, where salt reduces its production up to ten times. Overall, the results underline how halotolerance is a preferable, but not sufficient, condition for considering a PGPR potentially useful in applications aimed at improving the tolerance and productivity of crops in saline soils.

Antibiotic resistance (AR) is a critical global health issue with significant clinical and economic implications. AR occurs when microorganisms develop mechanisms to withstand the effects of antibiotics, reducing treatment efficacy and increasing the risk of mortality and healthcare costs. While the connection between antibiotic use in clinical and agricultural settings and the emergence of AR is well-established, the role of urban soils as reservoirs and spreaders of AR is underexplored. This review examines the complex dynamics of AR in urban soils, highlighting the various sources of antibiotics, including domestic wastewater, industrial effluents, urban agricultural practices, but also microplastics and domestic animal excrements. The selective pressure exerted by these anthropogenic sources promotes the proliferation of antibiotic-resistant bacteria, particularly through horizontal gene transfer, which facilitates the transmission of resistance genes among soil microorganisms in urban environments. About that, the presence of antibiotics in urban soils poses a significant threat to public health by potentially transferring resistance genes to human pathogens through multiple pathways, including direct contact, food consumption, and water ingestion. Furthermore, AR in urban soils disrupts microbial community dynamics, impacting soil fertility, plant growth, and overall environmental quality. Therefore, this review aims to address gaps in understanding AR in urban soils, offering insights into its implications for human health and ecosystem integrity. By identifying these gaps and suggesting evidence-based strategies, this review proposes valid and sustainable solutions to mitigate and counteract the spread of AR in urban environments.

Starting from the Industrial Revolution in the 18th century to date, urban areas have faced increasing environmental challenges due to the diffusion of harmful substances, resulting from vehicular traffic, the activities of different industries, waste, and building construction, etc. These pollutants are dangerous, since they pose a threat to both the environment and human health. Phytoremediation is an environmentally friendly and low-cost technique that uses plants and their associated microorganisms to clean-up contaminated sites. In this review, we explore its main applications in urban settings. Specifically, we investigate how phytoremediation works, highlighting the most effective plants for its success in a city context. Moreover, we also describe the main factors influencing its effectiveness, such as soil, climate, and pollutants. In this regard, several case studies, conducted worldwide, have reported on how phytoremediation can successfully reclaim contaminated areas, transforming them into reusable city green spaces, with reduced costs compared to traditional remediation techniques (e.g., soil replacement, soil washing, etc.). Moreover, by integrating it into urban planning, cities can address environmental pollution, while promoting biodiversity, enhancing the landscape, and increasing its social acceptance. This nature-based solution offers a practical path toward more sustainable and resilient urban environments, especially in regard to the climate change framework.

The effects of solar photo-Fenton (SPF) process mediated by the iron chelate Fe³⁺ imminodisuccinic acid (Fe:IDS) on both the inactivation of seven relevant pathogens and the potential for antibiotic resistance transfer (degradation of antibiotic resistance genes (ARGs) and after treatment regrowth), in real secondary treated urban wastewater, were investigated for the first time. A comparison with results obtained by sunlight/H₂O₂ process and Fe³⁺ ethylenediaminedisuccinic acid (Fe:EDDS) SPF was also carried out. ARGs were quantified by polymerase chain reaction (PCR) in samples before and after (3 h) the treatment. The persistence of the selected pathogens and ARGs was also evaluated in regrowth tests (72 h) under environmentally mimicking conditions. Fe:IDS SPF resulted to be more effective (from 1.4 log removal for Staphylococcus spp. to 4.3 log removal for Escherichia coli) than Fe:EDDS SPF (from 0.8 log removal for Pseudomonas aeruginosa to 2.0 log removal for Total coliphages) and sunlight/H₂O₂ (from 1.2 log removal for Clostridium perfringens to 3.3 log removal for E. coli) processes for the seven pathogens investigated. Potential pathogens regrowth was also severely affected, as no substantial regrowth was observed, both in presence and absence of catalase. A similar trend was observed for ARGs removal too (until 0.001 fold change expression for qnrS after 3 h). However, a poor effect and a slight increase in fold change was observed after treatment especially for gyrA, mefA and intl1. Overall, the effect of the investigated processes on ARGs was found to be ARG dependent. Noteworthy, coliphages can regrow after sunlight/H₂O₂ treatment unlike SPF processes, increasing the risk of antibiotic resistance transfer by transduction mechanism. In conclusion, Fe:IDS SPF is an attractive solution for tertiary treatment of urban wastewater in small wastewater treatment plants as it can provide effective disinfection and a higher protection against antibiotic resistance transfer than the other investigated processes.

Biodeterioration of paintings, caused by microorganisms interacting with the organic/inorganic compounds of the canvas, represents a serious problem for preserving cultural heritage. In our study, the microbial degradation caused on an eighteenth century painting “Sant’Anna, San Gioacchino e la Vergine Bambina” was investigated. Seventeen bacterial and six fungal strains on the altered parts of the canvas were identified, and their deteriorating ability were evaluated on two pictorial pigments: the yellow ochre and the ivory black. We recognized that microorganisms interacted with these pigments and modified their chromatic features. Furthermore, we adopted an eco-friendly antimicrobial treatment based on natural plant extracts (thymus, rosemary, and garlic) as an alternative to conventional biocides and highlighted how rosemary ( Salvia rosmarinus ) extract was the best and inhibited 74% of the isolated bacterial strains. When the extract was applied on the contaminated canvas, it reduced bacterial colonization by ~ 75% in only 48 h and eliminated the fungi within 7 days. The extract application was optimized, to minimize potential alterations of the painting caused by the extract, by adopting different strategies: (i) direct nebulization, (ii) Evolon® tissue (an innovative technical polyester-polyamide textile), and (iii) pretreatment with cyclomethicone D5. Finally, we also verified that it did not cause chromatic variations on the canvas confirming its suitability for conservation purposes. Our study provides new insights on the role of microorganisms in the deterioration of cultural heritage and highlights the potentiality of plant-based antimicrobials as sustainable, non-invasive, and alternative to traditional methods for the artwork preservation. Future research should focus on long-term efficacy assessments and formulation optimization to enhance applicability in heritage conservation practices. Key points: • Identification of 17 bacteria and 6 fungi from a deteriorate canvas painting • Microorganisms altered yellow ochre and ivory black, causing chromatic changes • Rosemary extract applied on canvas reduced microbial colonization