Investigation of soil property changes and olive tree stress as caused by excessive sewage-sludge application

This study was undertaken to assess the impact of a single excessive sludge application (300 Mg ha-1) on the soil surface of an olive orchard several years after the event. Selected soil properties were compared in two soil profiles, one in the sludge-amended field and another in an adjacent unamended field of naturally growing trees. Leaf analysis included macronutrients [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg)], trace elements [copper (Cu), zinc (Zn), manganese (Mn), iron (Fe), nickel (Ni), boron (B)], and isotopic composition (δ 15N and δ 13C). Soil pH and other chemical properties were increased in the surface soil and the root zone of the sludge-treated profile in comparison to those of the untreated control. The multifold increase of Bray P and nitrates indicated a serious risk for dissolved phosphates in runoff and nitrate contamination of groundwater. Trace-element content also increased, but not greater than the critical soil concentration. Olive trees responded to excessive sludge application by increased N uptake as evidenced by increased leaf N content and elevated 15N signal. The increased leaf δ 13C signal of the leaves further indicated tree stress in the sludge-amended field during the summer growing season in comparison to the naturally growing control trees. Isotopic composition, leaf nutrient, and trace element concentration did not reveal the causes of leaf tip burning in half of the trees of the sludge-amended field. Copyright © Taylor & Francis Group, LLC

Transcriptomic analysis of pseudomonas aeruginosa response to pine honey via rna sequencing indicates multiple mechanisms of antibacterial activity

Pine honey is a unique type of honeydew honey produced exclusively in Eastern Mediterranean countries like Greece and Turkey. Although the antioxidant and anti-inflammatory properties of pine honey are well documented, few studies have investigated so far its antibacterial activity. This study investigates the antibacterial effects of pine honey against P. aeruginosa PA14 at the molecular level using a global transcriptome approach via RNA-sequencing. Pine honey treatment was applied at sub-inhibitory concentration and short exposure time (0.5× of minimum inhibitory concentration –MIC-for 45 min). Pine honey induced the differential expression (>two-fold change and p ≤ 0.05) of 463 genes, with 274 of them being down-regulated and 189 being up-regulated. Gene ontology (GO) analysis revealed that pine honey affected a wide range of biological processes (BP). The most affected down-regulated BP GO terms were oxidation-reduction process, transmembrane transport, proteolysis, signal transduction, biosynthetic process, phenazine biosynthetic process, bacterial chemotaxis, and antibiotic biosynthetic process. The up-regulated BP terms, affected by pine honey treatment, were those related to the regulation of DNA-templated transcription, siderophore transport, and phosphorylation. Pathway analysis revealed that pine honey treatment significantly affected two-component regulatory systems, ABC transporter systems, quorum sensing, bacterial chemotaxis, biofilm formation and SOS response. These data collectively indicate that multiple mechanisms of action are implicated in antibacterial activity exerted by pine honey against P. aeruginosa. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Physicochemical Characterization and Biological Properties of Pine Honey Produced across Greece

Pine honey is a honeydew honey produced in the East Mediterranean region (Greece and Turkey) from the secretions of the plant sucking insect Marchalina hellenica (Gennadius) (Coccoidea: Marchalini-dae) feeding on living parts of Pinus species. Nowadays, honeydew honey has attracted great attention due to its biological activities. The aim of this study was to study unifloral pine honey samples produced in Greece regarding their physicochemical parameters and antioxidant and antibacterial activity against five nosocomial and foodborne pathogens. These honeys showed physicochemical and microscopic characteristics within the legal limits, except for diastase activity, a parameter known to be highly variable, depending on various factors. Substantially higher levels of H2 O2 were estimated compared to other types of honeydew honey, whereas protein content was similar. The total phenolic content was 451.38 ± 120.38 mg GAE/kg and antiradical activity ranged from 42.43 to 79.33%, while FRAP values (1.87 to 9.43 mmol Fe+2 /kg) were in general higher than those reported in the literature. Various correlations could be identified among these parameters. This is the first attempt to investigate in depth the antibacterial activity of pine honey from Greece and correlate it with honey quality parameters. All tested honeys exerted variable but significant antibacterial activity, expressed as MIC and MBC values, comparable or even superior to manuka honey for some tested samples. Although honey antibacterial activity is mainly attributed to hydrogen peroxide and proteins in some cases (demonstrated by elevated MICs after catalase and Proteinase K treatment, respectively), no strong correlation between the antibacterial activity and hydrogen peroxide concentration or total protein content was demonstrated in this study. However, there was a statistically significant correlation of moisture, antioxidant and antibacterial activity against Klebsiella pneuomoniae, as well as antioxidant and antibacterial activity against Salmonella ser. Typhimurium. Interestingly, a statistically significant negative correlation has been observed between. © 2022 by the authors. Licensee MDPI, Basel, Switzerland