Biological substrates catalyze the nucleation and growth of sparingly soluble salts however, the underlying mechanism is largely unknown. In the present study, the growth of calcium carbonate (CaCO₃), on Acutodesmus obliquus (AO) microalgae was investigated. The test microalgae favored the growth of CaCO₃ from solutions supersaturated with respect to calcite (7.94 < SR_calcite < 104.71). The precipitation of calcite on AO was not preceded by measurable induction times, and the rates of calcite crystal growth were higher for higher microalgae cell concentrations. The presence of the microalgae cultivation medium and illumination of the supersaturated solutions accelerated the precipitation of CaCO₃, increasing the rate by 75% in comparison with the respective value in its absence. AO cultures, air dried at 25 °C yielded higher precipitation rates, in comparison with the respective rates in the presence of active AO cultures. At 70 °C, nucleation and growth were suppressed, due to the destruction of the molecular structure of the microalgae. The CaCO₃ precipitation rates on calcite precipitated on air-dried AO culture, were doubled in comparison with the respective rates obtained with the respective quantities of each component of the composite substrate.

Acinetobacter baumannii is a typically short, almost round, rod-shaped (coccobacillus) Gram-negative bacterium. It can be an opportunistic pathogen in humans, affecting people with compromised immune systems, and it is becoming increasingly important as a hospital-associated (nosocomial) infection. It has also been isolated from environmental soil and water samples. In this work, unlike conventional medical methods like antibiotics, the influence of atmospheric-pressure cold plasma on this bacterium is evaluated by means of a colony count technique and scanning electron microscopy. The plasma used here refers to streamers axially propagating into a helium channel penetrating the atmospheric air. The plasma is probed with high resolution optical emission spectroscopy and copious reactive species are unveiled under low-temperature conditions. Based on the experimental results, post-treatment (delayed) biochemical effects on Acinetobacter baumannii and morphological modifications appear dominant, leading to complete deactivation of this bacterium.