Plant growth promoting rhizobacteria produce chemical compounds with different benefits for the plant. Among them, HCN is recognized as a biocontrol agent, based on its ascribed toxicity against plant pathogens. Based on several past studies questioning the validity of this hypothesis, we have re-addressed the issue by designing a new set of in vitro experiments, to test if HCN-producing rhizobacteria could inhibit the growth of phytopathogens. The level of HCN produced by the rhizobacteria in vitro does not correlate with the observed biocontrol effects, thus disproving the biocontrol hypothesis. We developed a new concept, in which HCN does not act as a biocontrol agent, but rather is involved in geochemical processes in the substrate (e.g., chelation of metals), indirectly increasing the availability of phosphate. Since this scenario can be important for the pioneer plants living in oligotrophic alpine environments, we inoculated HCN producing bacteria into sterile mineral sand together with germinating plants and showed that the growth of the pioneer plant French sorrel was increased on granite-based substrate. No such effect could be observed for maize, where plantlets depend on the nutrients stored in the endosperm. To support our concept, we used KCN and mineral sand and showed that mineral mobilization and phosphate release could be caused by cyanide in vitro. We propose that in oligotrophic alpine environments, and possibly elsewhere, the main contribution of HCN is in the sequestration of metals and the consequential indirect increase of nutrient availability, which is beneficial for the rhizobacteria and their plant hosts.
COBISS.SI-ID: 29936167
In this study the development of stable polyelectrolyte-surfactant complex nanoparticles composed of alginate and cetylpyridinium chloride (CPC), with and without ZnCl2, for therapeutic use, is investigated. The mechanism of CPC binding by alginate was analyzed using a cetylpyridinium cation (CP+) selective membrane electrode. The cooperative nature of the interaction between CP+ and alginate was underlined by the sigmoidal shape of the binding isotherms. The presence of salts was shown to weaken interactions and, moreover, ZnCl2 reduced the cooperativity of binding. The CP+ cations in the form of micellar associates acted as multivalent crosslinkers of the alginate chains where stable dispersions of CP-alginate nanoparticles were formed in water at CP+/alginate charge ratios from 0.2 to 0.8. Characterization of the nanoparticles showed hydrodynamic diameters from 140 to 200 nm, a polydispersity index below 0.2, a negative zeta potential and spherical morphology. The entrapment efficiency of CPC was -94%, the loading capacity more than 50% and prolonged release over 7 days were shown. The formulations with noted charge ratios resulted in stable CP-alginate nanoparticles with a potential of treating periodontal disease.
COBISS.SI-ID: 4132465
Aminobacter sp. MSH1 immobilized in an alginate matrix in porous stones was tested in a pilot system as an alternative inoculation strategy to the use of free suspended cells for biological removal of micropollutant concentrations of 2,6-dichlorobenzamide (BAM) in drinking water treatment plants (DWTPs). BAM removal rates and MSH1 cell numbers were recorded during operation and assessed with specific BAM degradation rates obtained in lab conditions using either freshly grown cells or starved cells to explain reactor performance. Both reactors inoculated with either suspended or immobilized cells showed immediate BAM removal under the threshold of 0.1 μg/L, but the duration of sufficient BAM removal was 2-fold (44 days) longer for immobilized cells. The longer sufficient BAM removal in case of immobilized cells compared to suspended cells was mainly explained by a lower initial loss of MSH1 cells at operational start due to volume replacement and shear. Overall loss of activity in the reactors though was due to starvation, and final removal rates did not differ between reactors inoculated with immobilized and suspended cells. Management of assimilable organic carbon, in addition to cell immobilization, appears crucial for guaranteeing long-term BAM degradation activity of MSH1 in DWTP units.
COBISS.SI-ID: 30114087