The activity of nitrifying microorganisms in a high-altitude Andean wetland.

High-altitude wetland holds freshwater springs, evaporitic ponds and lagoon with variable salinity and nutrients, potentially influencing the ecology of nitrifying communities. In this study, nitrifying microorganisms in Salar de Huasco (Chile) were surveyed to determine bacterial and archaeal contribution to ammonium (AO), nitrite oxidation (NO), ammonium uptake (AU) during wet and dry seasons. The activity signals from these groups were assessed by specific amoA-qPCR transcription, 15N tracer studies and addition of group specific inhibitor experiments for nitrifying microorganisms (N1-guanyl-1, 7-diaminoheptane [GC7]-archaeal specific and allylthiourea [ATU]-bacterial specific). Nitrifying communities, i.e. Nitrosopumilus, Nitrosospira, Nitrosomonas, Kuenenia and Nitrospira, were more frequent (∼0.25% of 16S rRNA sequences) at low salinity sites. Bacterial amoA-qPCR transcripts also increased at low salinity and along in situ ammonium increase observed between wet/dry seasons. Nutrient changes through time and 15N tracer experiments results showed that AO and NO were detected and peaked mainly at low salinity-high ammonium sites (<37 000 µS cm-1 and >0.3 µM), whereas AU was predominant at evaporitic sites. Our results indicate that salinity and ammonium affect the nitrifying communities that are potentially more active at low-salinity sites but persistent at saltier evaporitic areas of the wetland when ammonium is available.

Titanium uptake and incorporation into silica nanostructures by the diatom Pinnularia sp. (Bacillariophyceae).

Diatoms are an ecologically successful group within the phytoplankton, and their special feature is a biofabricated silica cell encasement called a frustule. These frustules attract interest in material technology, and one potential application is to use them in solar cell technology. The silica frustule with its nanoscaled pattern is interesting per se, but the utility is enhanced if we succeed in incorporating other elements. Titanium is an interesting element because its oxide is a semi-conductor with a high band gap. However, doping with relevant elements through bioincorporation is challenging, and it is necessary to understand the biology involved in element uptake and incorporation. Here we present data on bioincorporation of Ti into the silica frustules of the pennate diatom Pinnularia sp. (Ehrenberg) and show that the distribution of the incorporated Ti is inhomogeneous both between and within valves. More than a tenfold increase of Ti in newly synthesised valves was achieved, and increased Ti around the pores was confirmed by both EDS and EELS analyses. HAADF STEM spectroscopy revealed a grainy surface with amorphous silica particles of 4 to 5 nm in size. These observations are explained by what is known from the physico-chemical processes involved in biosilification and frustule formation, looking into it from a biological point of view.