Effect of sulfate on low-temperature anaerobic digestion

The effect of sulfate addition on the stability of, and microbial community behavior in, low-temperature anaerobic expanded granular sludge bed-based bioreactors was investigated at 15 degrees C. Efficient bioreactor performance was observed, with chemical oxygen demand (COD) removal efficiencies of >90%, and a mean SO42- removal rate of 98.3%. In situ methanogensis appeared unaffected at a COD: SO42- influent ratio of 8:1, and subsequently of 3:1, and was impacted marginally only when the COD: SO42- ratio was 1:2. Specific methanogenic activity assays indicated a complex set of interactions between sulfate-reducing bacteria (SRB), methanogens and homoacetogenic bacteria. SO42- addition resulted in predominantly acetoclastic, rather than hydrogenotrophic, methanogenesis until >600 days of SO42--influenced bioreactor operation. Temporal microbial community development was monitored by denaturation gradient gel electrophoresis (DGGE) of 16S rRNA genes. Fluorescence in situ hybridizations (FISH), qPCR and microsensor analysis were combined to investigate the distribution of microbial groups, and particularly SRB and methanogens, along the structure of granular biofilms. qPCR data indicated that sulfidogenic genes were present in methanogenic and sulfidogenic biofilms, indicating the potential for sulfate reduction even in bioreactors not exposed to SO42-. Although the architecture of methanogenic and sulfidogenic granules was similar, indicating the presence of SRB even in methanogenic systems, FISH with rRNA targets found that the SRB were more abundant in the sulfidogenic biofilms. Methanosaeta species were the predominant, keystone members of the archaeal community, with the complete absence of the Methanosarcina species in the experimental bioreactor by trial conclusion. Microsensor data suggested the ordered distribution of sulfate reduction and sulfide accumulation, even in methanogenic granules.Pádhraig Madden was supported by a scholarship from the Irish Research Council. Gavin Collins is supported by a European Research Council (ERC) Starting Grant (‘3C-BIOTECH’; project no. 261330). Profs. Michael Böttcher and Tim Ferdelman, and Dr. Raeid Abed, are thanked for their insightful conversations.peer-reviewe

Community structure and activity of a highly dynamic and nutrient-limited hypersaline microbial mat in Um Alhool Sabkha, Qatar.

The Um Alhool area in Qatar is a dynamic evaporative ecosystem that receives seawater from below as it is surrounded by sand dunes. We investigated the chemical composition, the microbial activity and biodiversity of the four main layers (L1-L4) in the photosynthetic mats. Chlorophyll a (Chl a) concentration and distribution (measured by HPLC and hyperspectral imaging, respectively), the phycocyanin distribution (scanned with hyperspectral imaging), oxygenic photosynthesis (determined by microsensor), and the abundance of photosynthetic microorganisms (from 16S and 18S rRNA sequencing) decreased with depth in the euphotic layer (L1). Incident irradiance exponentially attenuated in the same zone reaching 1% at 1.7-mm depth. Proteobacteria dominated all layers of the mat (24%-42% of the identified bacteria). Anoxygenic photosynthetic bacteria (dominated by Chloroflexus) were most abundant in the third red layer of the mat (L3), evidenced by the spectral signature of Bacteriochlorophyll as well as by sequencing. The deep, black layer (L4) was dominated by sulfate reducing bacteria belonging to the Deltaproteobacteria, which were responsible for high sulfate reduction rates (measured using 35S tracer). Members of Halobacteria were the dominant Archaea in all layers of the mat (92%-97%), whereas Nematodes were the main Eukaryotes (up to 87%). Primary productivity rates of Um Alhool mat were similar to those of other hypersaline microbial mats. However, sulfate reduction rates were relatively low, indicating that oxygenic respiration contributes more to organic material degradation than sulfate reduction, because of bioturbation. Although Um Alhool hypersaline mat is a nutrient-limited ecosystem, it is interestingly dynamic and phylogenetically highly diverse. All its components work in a highly efficient and synchronized way to compensate for the lack of nutrient supply provided during regular inundation periods

Effect of sulfate on low-temperature anaerobic digestion

The effect of sulfate addition on the stability of, and microbial community behavior in, low-temperature anaerobic expanded granular sludge bed-based bioreactors was investigated at 15 degrees C. Efficient bioreactor performance was observed, with chemical oxygen demand (COD) removal efficiencies of >90%, and a mean SO42- removal rate of 98.3%. In situ methanogensis appeared unaffected at a COD: SO42- influent ratio of 8:1, and subsequently of 3:1, and was impacted marginally only when the COD: SO42- ratio was 1:2. Specific methanogenic activity assays indicated a complex set of interactions between sulfate-reducing bacteria (SRB), methanogens and homoacetogenic bacteria. SO42- addition resulted in predominantly acetoclastic, rather than hydrogenotrophic, methanogenesis until >600 days of SO42--influenced bioreactor operation. Temporal microbial community development was monitored by denaturation gradient gel electrophoresis (DGGE) of 16S rRNA genes. Fluorescence in situ hybridizations (FISH), qPCR and microsensor analysis were combined to investigate the distribution of microbial groups, and particularly SRB and methanogens, along the structure of granular biofilms. qPCR data indicated that sulfidogenic genes were present in methanogenic and sulfidogenic biofilms, indicating the potential for sulfate reduction even in bioreactors not exposed to SO42-. Although the architecture of methanogenic and sulfidogenic granules was similar, indicating the presence of SRB even in methanogenic systems, FISH with rRNA targets found that the SRB were more abundant in the sulfidogenic biofilms. Methanosaeta species were the predominant, keystone members of the archaeal community, with the complete absence of the Methanosarcina species in the experimental bioreactor by trial conclusion. Microsensor data suggested the ordered distribution of sulfate reduction and sulfide accumulation, even in methanogenic granules.Pádhraig Madden was supported by a scholarship from the Irish Research Council. Gavin Collins is supported by a European Research Council (ERC) Starting Grant (‘3C-BIOTECH’; project no. 261330). Profs. Michael Böttcher and Tim Ferdelman, and Dr. Raeid Abed, are thanked for their insightful conversations

Vertical distribution of activity (i.e., photosynthesis and SR) and incident irradiance inside the studies mat.

<p>The upper panel shows steady state O₂ profiles inside the mat (A) in dark (filled circles), and at incident irradiances of 130 and 510 μmol photon m⁻² s⁻¹ (empty squares and triangles, respectively), while (B) represents vertical distribution of rates of gross photosynthesis (in mmol O₂ m⁻³ s⁻¹) measured in light/dark shift method. Vertical profiles of scalar irradiance integrated over PAR and were normalized to the value measured at the mat surface, and are plotted in linear scale (C). Sulfate reduction rates (in nmol cm⁻³ d⁻¹) and the vertical distribution of sulfate and sulfide in the mat (D), note that depth is in cm in (D).</p

Comparison between ion and nutrients contents of the seawater overlaying Um Alhool mat and seawater of the open ocean and the one covering the mat of Cheprana in Spain.

a<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0092405#pone.0092405-Earle1" target="_blank">[32]</a>.</p>b<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0092405#pone.0092405-Hansell1" target="_blank">[49]</a>,</p>c<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0092405#pone.0092405-Jonkers1" target="_blank">[34]</a>, ^d<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0092405#pone.0092405-Ludwig2" target="_blank">[50]</a>.</p

Graphical representation of the sequence frequency in the studied mat, showing major detected classes within the Archaeal and Eukaryotic domains.

<p>The symbols and sample naming are explained in detail in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0092405#pone-0092405-g006" target="_blank">Fig. 6</a>. Note different legends for OTU/path for each panel, and scale-bars for relative sequence frequency for several combined panels.</p

Vertical distribution of photopigments in a representative piece of the Um Alhool mat shown in true color image (A), using hyperspectral imaging and HPLC.

<p>Panel (B) represents the false color image of Chl <i>a</i> distribution calculated using MPBI. The color code ranges from blue (less Chl <i>a</i>) to red (high Chl <i>a</i>). Composite RGB image (C) shows distributions of Chl <i>a</i> (green channel), phycocyanin (PC; red channel) and bacteriochlorophyll <i>a</i> (BChl <i>a</i>; blue channel), as derived from hyperspectral imaging based on their characteristic spectral signatures (D). Scale bar is 1 cm. The lower panel shows the vertical distribution and the concentration (in μg m⁻³) of photopigments (Scytonemin, fucoxanthin, zeaxanthin, chl, and β-carotene) measured using HPLC (E), and the distribution of Bacteriochlorophyll (F) calculated as arbitrary units.</p

Total number of aligned sequences of bacteria, archaea, and eukaryotes in each layer of the studied mats.

<p>The number between the parentheses represent the percentage of potential new lineages (to the total number of sequences) on the phylum level (<80% identity to the best hit in NCBI).</p