Extinction of chlorophyll fluorescence emission in the <i>A</i>. <i>lobatus</i> cells treated with AgNP concentrations.

<p>The digital images were captured every hour/day of the experiment using the Leica TCS SP8 Confocal Laser Microscope.</p

The photosynthetic activity inhibition ratio (RIA^ph) and the growth inhibition ratio (RI^g) of the <i>A</i>. <i>lobatus</i> cells treated with AgNP concentrations at every hour/day of the experiment and the concurrent chlorophyll fluorescence intensity (^chlFI) and biomass (B) of the control cells; the statistical significance at the 0.05 level.

<p>The photosynthetic activity inhibition ratio (RIA^ph) and the growth inhibition ratio (RI^g) of the <i>A</i>. <i>lobatus</i> cells treated with AgNP concentrations at every hour/day of the experiment and the concurrent chlorophyll fluorescence intensity (^chlFI) and biomass (B) of the control cells; the statistical significance at the 0.05 level.</p

Silver nanoparticles as a control agent against facades coated by aerial algae—A model study of <i>Apatococcus lobatus</i> (green algae)

<div><p>Aerial algae are an important biological factor causing the biodegradation of building materials and facades. Conservation procedures aimed at the protection of historic and utility materials must be properly designed to avoid an increase of the degradation rate. The aim of the present study was to investigate the effect of silver nanoparticles (AgNP) synthetized with features contributing to the accessibility and toxicity (spherical shape, small size) on the most frequently occurring species of green algae in aerial biofilms and thus, the most common biodegradation factor–<i>Apatococcus lobatus</i>. Changes in the chloroplasts structure and the photosynthetic activity of the cells under AgNP exposure were made using confocal laser microscopy and digital image analysis and the estimation of growth inhibition rate was made using a biomass assay. In the majority of cases, treatment with AgNP caused a time and dose dependant degradation of chloroplasts and decrease in the photosynthetic activity of cells leading to the inhibition of aerial algae growth. However, some cases revealed an adaptive response of the cells. The response was induced by either a too low, or—after a short time—too high concentration of AgNP. Taken together, the data suggest that AgNP may be used as a biocide against aerial algal coatings; however, with a proper caution related to the concentration of the nanoparticles.</p></div

Percentage of the growing inhibition rate and the biocidal effect of AgNP against aerophytic algal cells after 14 days of AgNP exposure.

<p>Percentage of the growing inhibition rate and the biocidal effect of AgNP against aerophytic algal cells after 14 days of AgNP exposure.</p

Electrodynamic and hydrodynamic characteristics of AgNP.

<p>a) Zeta potential of AgNP at different pH; b) DLS of AgNP.</p

The biomass of <i>A</i>. <i>lobatus</i> cells under AgNP exposure; the biomass was expressed using chl <i>a</i> concentration.

<p>The biomass of <i>A</i>. <i>lobatus</i> cells under AgNP exposure; the biomass was expressed using chl <i>a</i> concentration.</p

Digital imaging of the changes in <i>A</i>. <i>lobatus</i> chloroplasts under AgNP exposure (20 ppm); cross-sections in 3-D were performed using the Leica TCS SP8 Confocal Laser Microscope and the LAS-AF 3.3.0.10134 software.

<p>a) control samples; b) chloroplasts after 1 hour of AgNP exposure; c) chloroplasts after 24 hours of AgNP exposure; d) chloroplasts after 1 week of AgNP exposure.</p

The range of chlorophyll fluorescence intensity of <i>A</i>. <i>lobatus</i> cells under AgNP exposure; the fluorescence was measured using the Leica TCS SP8 Confocal Laser Microscope equipped with WLL of 488 nm.

<p>The range of chlorophyll fluorescence intensity of <i>A</i>. <i>lobatus</i> cells under AgNP exposure; the fluorescence was measured using the Leica TCS SP8 Confocal Laser Microscope equipped with WLL of 488 nm.</p

Effective L-Tyrosine Hydroxylation by Native and Immobilized Tyrosinase

<div><p>Hydroxylation of L-tyrosine to 3,4-dihydroxyphenylalanine (L-DOPA) by immobilized tyrosinase in the presence of ascorbic acid (AH₂), which reduces DOPA-quinone to L-DOPA, is characterized by low reaction yields that are mainly caused by the suicide inactivation of tyrosinase by L-DOPA and AH₂. The main aim of this work was to compare processes with native and immobilized tyrosinase to identify the conditions that limit suicide inactivation and produce substrate conversions to L-DOPA of above 50% using HPLC analysis. It was shown that immobilized tyrosinase does not suffer from partitioning and diffusion effects, allowing a direct comparison of the reactions performed with both forms of the enzyme. In typical processes, additional aeration was applied and boron ions to produce the L-DOPA and AH₂ complex and hydroxylamine to close the cycle of enzyme active center transformations. It was shown that the commonly used pH 9 buffer increased enzyme stability, with concomitant reduced reactivity of 76%, and that under these conditions, the maximal substrate conversion was approximately 25 (native) to 30% (immobilized enzyme). To increase reaction yield, the pH of the reaction mixture was reduced to 8 and 7, producing L-DOPA yields of approximately 95% (native enzyme) and 70% (immobilized). A three-fold increase in the bound enzyme load achieved 95% conversion in two successive runs, but in the third one, tyrosinase lost its activity due to strong suicide inactivation caused by L-DOPA processing. In this case, the cost of the immobilized enzyme preparation is not overcome by its reuse over time, and native tyrosinase may be more economically feasible for a single use in L-DOPA production. The practical importance of the obtained results is that highly efficient hydroxylation of monophenols by tyrosinase can be obtained by selecting the proper reaction pH and is a compromise between complexation and enzyme reactivity.</p></div

Stability of Tyrosinase in Reaction Mixture Components and Examples of Oxygen Consumption in Reaction Systems.

<p>(A) Relative activity of native (black) and immobilized tyrosinase (gray) after a 1 h incubation at 30°C in 0.1 M phosphate buffer, pH 7 (Control) containing 1 mM L-tyrosine (L-tyr), 1 mM L-DOPA, or 2 mM ascorbic acid (AH₂). (B) An example of the effect of 1 mM L-tyrosine hydroxylation (gray lines) or 2 mM ascorbic acid oxidation (black lines) by native tyrosinase over time on the oxygen concentration in non-aerated (solid lines) and aerated (dashed or dotted lines) reaction mixtures. Red lines represents control experiments with 2 mM ascorbic acid whereas blue lines with 1 mM L-tyrosine, both without tyrosinase. Reaction conditions: 0.1 M phosphate buffer, pH 7; 30°C; and 20 rpm. (C) Relative initial reaction rates of immobilized tyrosinase in three consecutive 1 h processes in the batch reactor. Bars: black–measured from the increase in the L-DOPA concentration or white–measured from the decrease in the L-tyrosine concentration. Reaction conditions: 1 mM L-tyrosine and 2 mM ascorbic acid in 0.1 M phosphate buffer, pH 7; 0.133–0.235 O₂; 30°C; and 120 rpm.</p