Aims The aim of this study was investigation of the response of R. leguminosarum bv. trifolii wild-type and its two rosR and pssA mutant strains impaired in exopolysaccharide (EPS) synthesis to oxidative stress conditions caused by two prooxidants: a superoxide anion generator-menadione (MQ) and hydrogen peroxide (H 2 O 2 ). Methods The levels of enzymatic (catalase, superoxide dismutase, pectinase and β-glucosidase) and nonenzymatic (superoxide anion generator, formaldehyde, phenolic compounds) biomarkers were monitored using biochemical methods in both the supernatants and rhizobial cells after treatment with 0.3mM MQ and 1.5mM H 2 O 2 . The viability of bacterial cells was estimated using fluorescent dyes and confocal laser scanning microscopy. In addition, the effect of prooxidants on symbiosis of the R. leguminosarum bv. trifolii strains with clover was established. Results The tested stress factors significantly changed enzymatic patterns of the rhizobial strains, and the wildtype strain proved to be more resistant to these prooxidants than both pssA and rosR mutants. Significantly higher activities of both catalase and superoxide dismutase have been detected in these mutants in comparison to the wildtype strain. H 2 O 2 and MQ also increased the levels of pectinase and β-glucosidase activities in the tested strains. Moreover, pre-incubation of R. leguminosarum bv. trifolii strains with the prooxidants negatively affected the viability of bacterial cells and the number of nodules elicited on clover plants. Conclusions EPS produced in large amounts by R. leguminosarum bv. trifolii plays a significant protective role as a barrier against oxidative stress factors and during symbiotic interactions with clover plants.
Storing waste in concrete instead of landfills is environmentally friendly and also might make concrete more sustainable if some part is replaced with cement. This article presents a new way of valorising hazardous waste, namely ilmenite MUD from the production of titanium dioxide, which is used as a reactive additive to concrete. In fact, there are currently no articles presenting the way of valorisation that is presented in this paper. The global annual production of MUD is estimated to be about 0.7 million tons. Valorisation is possible due to the additional rinsing and filtering in the factory, which also confirms the novelty of this article. In this operation, the most hazardous compounds are returned back to the factory process. Rinsed mud (RMUD) is a pozzolanic reactive material with the potential use as a substitute of a part of Portland cement in concrete and other cementitious binders, like siliceous fly ash (FA). The level of RMUD pozzolanic activity is as high as the activity of siliceous fly ash. Comparative tests of concretes containing RMUD and fly ash, such as compressive strength, bending strength and shrinkage, were conducted. The concrete containing RMUD reached almost 90% of compressive and 108% of bending strength after 28 days of curing, compared to FA concrete. The results presented in this article are very promising and might point to a new way of valorising ilmenite mud waste.
The repairs of building structures are inevitable and indispensable. Repairs are used to restore or maintain the usability of existing facilities, often contributing to the extension of their expected service life, increasing the sustainability of building resources. Given that conservation rules are observed, repairs are also used to save monuments. The concept of repair durability brings to the foreground the durability of the repaired structure (after repair): what service life has been obtained/recovered as a result of the repair. Based on the available data (limited set), a generalised distribution function of repair durability was developed, with a disappointing course. This, however, applies (necessarily) to the past. Significant progress was shown to have been achieved in the theoretical and technical fundamentals of technical repair measures. In this situation, a prognostic distribution function was also designed for future repairs according to EN 1504. A rule of thumb called estimating concrete repair durability, CRD was proposed. The risk associated with estimating the durability of repairs was indicated. A reason for optimism is that proactive monitoring of the condition of the structure and, consequently, management of the repair strategy allows to reach the designed life of the structure.
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