Pollution effects most but not all microbial communities

Coastal pollution is a major problem creating worldwide negative impacts on ecosystems from the deep ocean, water columns, sediment communities and holobiont species. As well as ocean acidification, pollutants change eukaryote, archaea, bacteria and fungi microbial communities allowing opportunistic pathogenic bacteria to dominate, increasing disease. The resulting nutrient type and pH increase or decrease, with environmental fluctuations, influences microbes persisting however, few microbial communities are not affected. The Mediterranean sponge (Crambe crambe) exhibits stable communities, with Proteobacteria dominating, across habitats from a polluted harbour in Blanes, Spain, up to a distance of <1km (Gantt et al., 2017). However, most microbial communities studied are affected by pollution. The Boulder star coral (Montastraea annularis), depth distribution of 0-25m, is environmentally sensitive with high disease susceptibility in polluted shallow coastal habitats. Its microbial community was studied with proximity to the urban centre and seaport of Willemstad, Netherlands Antilles (Klaus et al., 2007).

Klaus et al., 2007 sampled tissue, coral mucus and small colony fragments from 36 colonies, at depths 5, 10 and 20m (control). Bacteria and zooxanthellae were collected from the top 2cm of the highest branch. The 16SrRNA was analysed in PCR and sequences classified using clone libraries and GenBank primers, with monosaccharide and amino-acid composition of healthy mucus determined, visualising the microbial community’s potential role. The authors recorded data on light availability, temperature, seawater pollution, symbiotic algae’s community structure and photosynthetic activity levels, by measuring 𝛿¹³C and 𝛿 ¹⁵N of the upper growing 25cm² branch, for reef classification. Nitrogen levels also determined the amount of sewage-derived compounds absorbed, via mass spectrometry and microbial communities were compared using similarity matrix. They studied only one species, therefore, including multiple corals could have enhanced understanding of the microbial pool and pathogenic microbe distribution. Looking into behaviour of dominant bacteria, rather than stating other studies findings, to see possible causes for disease at 5m, could have also enhanced documented studies.

Results showed light intensity varied with depth: 5m (33-36%), 10m (18-22%) and 20m (9-11%) with temperatures consistently 27.5±0.5°C. Coral tissue 𝛿 ¹⁵N was 1.75‰ heavier at 5-10m, showing greater sewage uptake and 𝛿 ¹³C was 1.0‰ lighter at 5m than 20m due to increased light. No significant difference between amino acid or monosaccharide composition was found with location. However, variation of the symbiotic algae genus Symbiodinium and enzymes associated with each of its clades was seen, clade B at 5m, C at 10 and 20m. Bacterial communities also showed patterns within polluted and controlled localities; CAB-1 decreased abundance whereas clones of plastids, Cyanobacteria and Firicutes showed increasing abundance with depth. Terminal restriction fragments showed a difference between 5-20m but not between 5-10m or 10-20m suggesting importance in polluted areas, when the disease cyanobacterium clone CD1C11 and CAB-1 had greater abundance on healthy corals <10m.

This was the first study to identify the importance of each bacterial abundance on this species providing comprehensive analysis of potential issues but, further work is required for CAB-1. It interested me as it demonstrated the effect of pollutants spreading and acted on the understanding of how host and mucus microbiota are important in pathogen inhibition and coral health. This study enhances knowledge of the susceptibility of microbes to pollution, tolerance and environmental change, allowing us to predict future microbial fluctuation and disease incidences potentially occurring in areas not yet affected by pollution for similar genus. Finding ways to inhibit the disease would be a main focus for future research investment. Another future focus is to decrease pollution, sewage discharge and underwater seepage, into our waters and find solutions to stop it spreading to extensive coral reefs.

Reviewed Article

Klaus, J. S., Janse, I., Helkoop, J. M., Sanford, R. A & Fouke, B. W. (2007). Coral microbial communities, zooxanthellae and mucus along gradients of seawater depth and coastal pollution. Environmental Microbiology, 9(5), 1291-1305

https://pdfs.semanticscholar.org/a940/c971466dd703b6e80e05864c8fe5349b5804.pdf

Extra Reading

Gantt, S. E., López-Legentil, S & Erwin, P. M. (2017). Stable microbial communities in the sponge Crambe crambe from inside and outside a polluted Mediterranean harbour. FEMS Microbiology Letters, 364 http://www.imesalab.com/iMESA/Erwin_files/Gantt_etal_2017.pdf