Desert stream phototrophic mats: a promising source for biofuel production

<p>Desert streams occur in abundance in the mountain regions of the Arabian Peninsula, where massive areas are covered by phototrophic microbial mats. In this study, 11 different phototrophic microbial mats were screened for their carbohydrate and lipid contents and their ability to produce methane, and mats with potential were further used for biofuel production. A maximum bioethanol yield of 0.76 ± 0.1 g/L was obtained by enzymatic saccharification of one mat, which was dominated by the alga <i>Spirogyra</i>, followed by fermentation of the produced sugars using the native <i>Clostridium</i> strain AK-1. A lipid content of 9–18 wt% was measured from the microbial mats. An increase of 4% and 9% was observed, when the mat with the highest lipid content was incubated under 3% salinity and nitrogen deprivation conditions, respectively. Anaerobic digestion of one selected cyanobacterial mat for biomethane production yielded a maximum of 95 mL CH₄/g VS (volatile solids) after 49 days. MiSeq analysis revealed that the microbial community of this mat was 99.5% dominated by archaea, mainly belonging to the genera <i>Methanoculleus</i> (56.7%), <i>Methanobacterium</i> (27%) and <i>Methanosarcina</i> (7.6%). Our results demonstrate the potential of using microbial mats from desert streams to produce bioethanol, biodiesel and biomethane.</p

Diversity, Distribution and Hydrocarbon Biodegradation Capabilities of Microbial Communities in Oil-Contaminated Cyanobacterial Mats from a Constructed Wetland - Figure 4

<p>(A) Sequence frequency in the investigated wetland mat samples (B1 is missing) showing the major encountered bacterial classes. The shape of the symbol represents the number of sequences in each taxonomic bath, the size of the symbol represents the number of OTUs_0.03 at deeper taxonomic levels with that taxonomic path and the color of the symbol indicates the relative frequency of the taxonomic path within the sample. (B) a heatmap representing a comparison of the relative abundance (% of total sequences) of the major bacterial genera and families in each bacterial class between the different samples. Only the distribution of sulfate reducing bacteria was indicated at the family level either due to the very low abundance of single genera or because of their unresolved taxonomy.</p

Diversity, Distribution and Hydrocarbon Biodegradation Capabilities of Microbial Communities in Oil-Contaminated Cyanobacterial Mats from a Constructed Wetland

<div><p>Various types of cyanobacterial mats were predominant in a wetland, constructed for the remediation of oil-polluted residual waters from an oil field in the desert of the south-eastern Arabian Peninsula, although such mats were rarely found in other wetland systems. There is scarce information on the bacterial diversity, spatial distribution and oil-biodegradation capabilities of freshwater wetland oil-polluted mats. Microbial community analysis by Automated Ribosomal Spacer Analysis (ARISA) showed that the different mats hosted distinct microbial communities. Average numbers of operational taxonomic units (OTUs_ARISA) were relatively lower in the mats with higher oil levels and the number of shared OTUs_ARISA between the mats was <60% in most cases. Multivariate analyses of fingerprinting profiles indicated that the bacterial communities in the wetland mats were influenced by oil and ammonia levels, but to a lesser extent by plant density. In addition to oil and ammonia, redundancy analysis (RDA) showed also a significant contribution of temperature, dissolved oxygen and sulfate concentration to the variations of the mats’ microbial communities. Pyrosequencing yielded 282,706 reads with >90% of the sequences affiliated to <i>Proteobacteria</i> (41% of total sequences), C<i>yanobacteria</i> (31%<i>)</i>, <i>Bacteriodetes</i> (11.5%), <i>Planctomycetes</i> (7%) and <i>Chloroflexi</i> (3%). Known autotrophic (e.g. <i>Rivularia</i>) and heterotrophic (e.g. <i>Azospira</i>) nitrogen-fixing bacteria as well as purple sulfur and non-sulfur bacteria were frequently encountered in all mats. On the other hand, sequences of known sulfate-reducing bacteria (SRBs) were rarely found, indicating that SRBs in the wetland mats probably belong to yet-undescribed novel species. The wetland mats were able to degrade 53–100% of C₁₂–C₃₀ alkanes after 6 weeks of incubation under aerobic conditions. We conclude that oil and ammonia concentrations are the major key players in determining the spatial distribution of the wetland mats’ microbial communities and that these mats contribute directly to the removal of hydrocarbons from oil field wastewaters.</p></div

Effects of contextual parameters on variation in the wetland mat bacterial community structure.

<p>Total and pure effects (i.e. when controlling for all other factors of the analysis) of explanatory factors were calculated by using canonical redundancy analysis (RDA) models. The proportion of explained community variation is expressed as <i>R²</i> values. Significances of the respective <i>F</i>-ratios were tested by performing 1000 Monte Carlo permutation tests and are indicated by • marginally significant (<i>P</i>≤0.1), * significant (<i>P</i>≤0.05), ** very significant (<i>P</i>≤0.01), *** highly significant (<i>P</i>≤0.001), and <i>ns</i> when not significant (<i>P</i>>0.05).</p><p>Effects of contextual parameters on variation in the wetland mat bacterial community structure.</p

Physical-chemical water quality characteristics of the different wetland sample locations, where the cyanobacterial mats were collected.

<p>++ highly vegetated (75–100%); +moderately vegetated (25–75%); − sparsely vegetated (0–25%). ORP: Oxidation reduction potential.</p><p>Physical-chemical water quality characteristics of the different wetland sample locations, where the cyanobacterial mats were collected.</p

The layout of the produced water treatment plant and wetland sampling locations (left) and a photograph depicting the wetland and the cyanobacterial mats covering the sediments (right).

<p>The layout of the produced water treatment plant and wetland sampling locations (left) and a photograph depicting the wetland and the cyanobacterial mats covering the sediments (right).</p

Pyrosequencing and bacterial diversity estimators for the constructed wetland mat samples.

<p>The diversity indices marked with an asterisk represent the average values calculated after performing three randomized sampling of the sequences to enable comparison among different samples.</p>†<p>Operational taxonomic unit at 3% sequence dissimilarity; $ Singletons are sequences that were observed once.</p><p>Pyrosequencing and bacterial diversity estimators for the constructed wetland mat samples.</p

Long-term microfouling on commercial biocidal fouling control coatings

<div><p>The current study investigated the microbial community composition of the biofilms that developed on 11 commercial biocidal coatings, including examples of the three main historic types, namely self-polishing copolymer (SPC), self-polishing hybrid (SPH) and controlled depletion polymer (CDP), after immersion in the sea for one year. The total wet weight of the biofilm and the total bacterial density were significantly influenced by all coatings. Pyrosequencing of 16S rRNA genes revealed distinct bacterial community structures on the different types of coatings. Flavobacteria accounted for the dissimilarity between communities developed on the control and SPC (16%) and the control and SPH coatings (17%), while Alphaproteobacteria contributed to 14% of the dissimilarity between the control and CDP coatings. The lowest number of operational taxonomic units was found on Intersmooth 100, while the lowest biomass and density of bacteria was detected on other SPC coatings. The experiments demonstrated that the nature and quantity of biofilm present differed from coating to coating with clear differences between copper-free and copper-based biocidal coatings.</p></div

Photographs showing the soil surface colour in crust pieces before (A) and 20 minutes after addition of water (B).

<p>Photographs showing the soil surface colour in crust pieces before (A) and 20 minutes after addition of water (B).</p

Net oxygen production and recovery of respiration and photosynthesis was monitored in the wet crust piece using oxygen microsensor measurements.

<p>The time after wetting is indicated at the bottom of each profile. Note that respiration started within 4 minutes and increased up to 13 minutes, after which oxygen was produced via photosynthesis and net oxygen production reached a maximum after 118 minutes. The oxygen profiles did not shift upward and oxygen maxima stayed at the same depth, indicating the absence of upward migration of cyanobacteria.</p