Diurnal Changes in Active Carbon and Nitrogen Pathways Along the Temperature Gradient in Porcelana Hot Spring Microbial Mat

Abstract

Composition, carbon and nitrogen uptake, and gene transcription of microbial mat communities in Porcelana neutral hot spring (Northern Chilean Patagonia) were analyzed using metagenomics, metatranscriptomics and isotopically labeled carbon (H13CO3) and nitrogen (15NH4Cl and K15NO3) assimilation rates. The microbial mat community included 31 phyla, of which only Cyanobacteria and Chloroflexi were dominant. At 58°C both phyla co-occurred, with similar contributions in relative abundances in metagenomes and total transcriptional activity. At 66°C, filamentous anoxygenic phototrophic Chloroflexi were >90% responsible for the total transcriptional activity recovered, while Cyanobacteria contributed most metagenomics and metatranscriptomics reads at 48°C. According to such reads, phototrophy was carried out both through oxygenic photosynthesis by Cyanobacteria (mostly Mastigocladus) and anoxygenic phototrophy due mainly to Chloroflexi. Inorganic carbon assimilation through the Calvin–Benson cycle was almost exclusively due to Mastigocladus, which was the main primary producer at lower temperatures. Two other CO2 fixation pathways were active at certain times and temperatures as indicated by transcripts: 3-hydroxypropionate (3-HP) bi-cycle due to Chloroflexi and 3-hydroxypropionate-4-hydroxybutyrate (HH) cycle carried out by Thaumarchaeota. The active transcription of the genes involved in these C-fixation pathways correlated with high in situ determined carbon fixation rates. In situ measurements of ammonia assimilation and nitrogen fixation (exclusively attributed to Cyanobacteria and mostly to Mastigocladus sp.) showed these were the most important nitrogen acquisition pathways at 58 and 48°C. At 66°C ammonia oxidation genes were actively transcribed (mostly due to Thaumarchaeota). Reads indicated that denitrification was present as a nitrogen sink at all temperatures and that dissimilatory nitrate reduction to ammonia (DNRA) contributed very little. The combination of metagenomic and metatranscriptomic analysis with in situ assimilation rates, allowed the reconstruction of day and night carbon and nitrogen assimilation pathways together with the contribution of keystone microorganisms in this natural hot spring microbial mat.

Biomarker Profiling of Microbial Mats in the Geothermal Band of Cerro Caliente, Deception Island (Antarctica): Life at the Edge of Heat and Cold

“…For instance, the relatively enriched δ 13 C ratio observed in Mat-1 suggests CO 2 fixation pathways mostly related to the reductive tricarboxylic acid (rTCA) cycle (Preuß et al , 1989) and/or the 3-hydroxypropionate (3HP) bicycle (Van Der Meer et al , 2001). This is consistent with the detection of Chloroflexi , Armatimonadetes , Nitrospirae , and Aquificae (this one at relative abundance <0.5%) (Herter et al , 2002; Hügler et al , 2007; Hügler and Sievert, 2011; Lee et al , 2014; Alcamán-Arias et al , 2018). The dominance of rTCA or 3HP processes also suggests the lower oxygen availability prevailing under the surface of Mat-1, which is consistent with the generally more oxygen depletion in high-temperature habitats (Hügler and Sievert, 2011) and the presence of facultative/strict anaerobes, such as Gemmatimonadales ( e.g.…”

Temperature impacts community structure and function of phototrophic Chloroflexi and Cyanobacteria in two alkaline hot springs in Yellowstone National Park

“…As expected based on previous studies of alkaline hot springs, more than 50% of the OTUs were classified as either Chloroflexi or Cyanobacteria (Fig. 1) (Brock, 1978;Bateson and Ward, 1988;Nübel et al, 2002;Bhaya et al, 2007;Miller et al, 2009;Rozanov et al, 2017;Alcamán-Arias et al, 2018, reviewed in Thiel et al, 2018Hamilton et al, 2019). Chloroflexi richness (OTUs per sample) did not show a linear trend with temperature ( Fig.…”

Anoxygenic Phototrophs Span Geochemical Gradients and Diverse Morphologies in Terrestrial Geothermal Springs

“…High abundance of bchY transcripts in ocean surface waters suggests anoxygenic phototrophs in this environment are of ecological importance (55). In circumneutral hot springs, transcripts of Bchl biosynthesis genes have been reported, but peak transcript abundance varies by site, taxonomy, or time of day (18, 56, 57). Given high abundance of bchY transcripts in alkaline sites reported here, our data suggest anoxygenic phototrophs are ecologically relevant, particularly in alkaline hot springs.…”