In situ hydrogen dynamics in a hot spring microbial mat during a diel cycle

© 2016, American Society for Microbiology. Microbes can produce molecular hydrogen (H2) via fermentation, dinitrogen fixation, or direct photolysis, yet the H2 dynamics in cyanobacterial communities has only been explored in a few natural systems and mostly in the laboratory. In this study, we investigated the diel in situ H2 dynamics in a hot spring microbial mat, where various ecotypes of unicellular cyanobacteria (Synechococcus sp.) are the only oxygenic phototrophs. In the evening, H2 accumulated rapidly after the onset of darkness, reaching peak values of up to 30 μmol H2 liter-1 at about 1-mm depth below the mat surface, slowly decreasing to about 11 μmol H2 liter-1 just before sunrise. Another pulse of H2 production, reaching a peak concentration of 46 μmol H2 liter-1, was found in the early morning under dim light conditions too low to induce accumulation of O2 in the mat. The light stimulation of H2 accumulation indicated that nitrogenase activity was an important source of H2 during the morning. This is in accordance with earlier findings of a distinct early morning peak in N2 fixation and expression of Synechococcus nitrogenase genes in mat samples from the same location. Fermentation might have contributed to the formation of H2 during the night, where accumulation of other fermentation products lowered the pH in the mat to less than pH 6 compared to a spring source pH of 8.3

Substantial near-infrared radiation-driven photosynthesis of chlorophyll f-containing cyanobacteria in a natural habitat

© Kühl et al. Far-red absorbing chlorophylls are constitutively present as chlorophyll (Chl) d in the cyanobacterium Acaryochloris marina, or dynamically expressed by synthesis of Chl f, red-shifted phycobiliproteins and minor amounts of Chl d via far-red light photoacclimation in a range of cyanobacteria, which enables them to use near-infrared-radiation (NIR) for oxygenic photosynthesis. While the biochemistry and molecular physiology of Chl f-containing cyanobacteria has been unraveled in culture studies, their ecological significance remains unexplored and no data on their in situ activity exist. With a novel combination of hyperspectral imaging, confocal laser scanning microscopy, and nanoparticle-based O2 imaging, we demonstrate substantial NIR-driven oxygenic photosynthesis by endolithic, Chl f-containing cyanobacteria within natural beachrock biofilms that are widespread on (sub)tropical coastlines. This indicates an important role of NIR-driven oxygenic photosynthesis in primary production of endolithic and other shaded habitats

Разработка метода формирования износостойких поверхностных слоев в технически чистом алюминии

Объектом исследования является технически чистый алюминий марки А7, подвергнутый азотированию в плазме несамостоятельного частотно-импульсного тлеющего разряда с полым катодом при низком давлении. Цель работы – разработка метода формирования износостойких поверхностных слоев в технически чистом алюминии. Проведены исследования механических и трибологических свойств материала (микротвердость, коэффициент износа, коэффициент трения). В результате исследования выявлен режим азотирования, позволяющий кратно повысить трибологические и механических характеристики технически чистого алюминия марки А7.The subject of the study is technically pure aluminum of the A7, subjected to nitriding in the plasma of a frequency-pulse non-self-sustained glow discharge with a hollow cathode at low pressure. The aim of the work is to development of a method for the formation of wear-resistant surface layers in technically pure aluminum. Mechanical and tribological properties of the material (microhardness, wear coefficient, coefficient of friction) are studied. As a result of the study, the nitriding mode was revealed, which allows to increase the tribological and mechanical characteristics of technically pure aluminum of the A7