Effects of temperature on carbon and nitrogen metabolisms of porcelana microbial mat community: Rates, strategies and gene expression

The microbial mat community along the temperature gradient (66, 58 and 48°C) on the non-acidic hot spring of Porcelana (Northern Chilean Patagonia) was investigated by integrative approaches: DNA/RNA sequencing, isotopic labeled carbon (H13CO3) and nitrogen (15N2,15NH4Cl and K15NO3), and culture controlled conditions assays.

The Porcelana microbial mat composition reveals that phyla Chloroflexi (Roseiflexus sp. and Chloroflexus sp.) and Cyanobacteria (Mastigocladus spp.) were prevalent and dominant along the temperature gradient and co-occurring at intermediate temperatures. Three different pathways of carbon fixation were found and attributed to Cyanobacteria, Chloroflexi and Archaea members. Cyanobacteria have an important role in the incorporation of new nitrogen into the microbial mat.

Diversity of diazotrophic reveals the dominance of the genus Mastigocladus (between 69-38ºC). In situ nitrogenase activity, cellular uptake of 15N2, and nifH mRNA expression were light dependent and detected at temperatures ranging from 46 to 58°C but not at 66ºC. The contribution of N and C fixation was approximately 3 g N m-2 y-1 and 27 g C m-2 y-1, respectively, suggesting that these vital demands are fully met by the diazotrophic and photoautotrophic capacities of the Stigonematal cyanobacteria.

Strain CHP1 (isolated from Porcelana hot spring) was identified as Mastigocladus sp., with a thermophilic character. Mastigocladus sp. strain CHP1 has maximum nitrogenase activity in light independent of temperature. Also, has high affinity for nitrate instead of ammonium, showing certain plasticity to use different nitrogen sources. It is proposed that Mastigocladus sp. strain CHP1 represent major players in Porcelana hot spring contributing the most new nitrogen by biological nitrogen fixation.

• Nombre: María Estrella Alcamán Arias
• Laboratorio: Ecología Microbiana y Microbiología Ambiental
• Mención: Genética Molecular y Microbiología
• Director Tesis: Beatriz Díez