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

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

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