oil indicators in Mangrove sediment is revealed by 18s rDNA sequencing.

A review of: Santos, H. Cury, J. Carmo, F. Rosado, S. Peixoto, R. 2010. 18s rDNA sequences from microeukaryotes reveal oil indicators in Mangrove sediment. Plos one 5 (8): e12437

The microeukaryotes are of vital importance to marine ecosystems, as they represent the base of the pelagic food web in the ocean, and changes in the composition and structure of this web can lead to profound changes at all trophic levels. Mangrove sediment is a well known habitat that provides a unique ecological niche to a number of endemic organisms- which includes many microeukaryotic species.

microeukayotes are used as an effective measure of a contaminant, as they demonstate the key features of a bioindicator, including their abundance, genetuc diversity and reduced generation time. This allows for rapid responces to environmental changes to occur.

in the past decade, 18s rDNA clone libraries have been crucial in the development of molecular surveys for the studying marine microbial diversity. recent studies have focused on the small subunits 18s ribosomal RNA gene fragments have revealed a great diversity of microeukaryotes. Mangroves are usually exposed to pollutants such as those released by oil spills.

This study, aimed to evaluate the impacts of oil on major microeukaryotes groups in mangrove sediment by PCR/DGGE and using clone libraries to search for potential candidates for use as bioindicators of oil, or in further studies of mangroves bioremediation and biomonitoring using microeukaryotes.

Methods:This study was conducted using opaque tube microcosms. Each microcosm then recieved 350g/L dry weight of sediment from the Restingua da inarambaia, rio de janerio, Brazil. after a setting period of 3 hours, oil contamination of the microcosm then occured. (2% v/w contamination)

T0 = Before oil contamination.

T23= 0% 23 days without oil.

T23= 2% 23 days with oil.

T66= 0% 66 days without oil

T66= 2% 66 days with oil.

to replace evaporated water 100ml of distilled water was added every 2 days. For each microcosm a 200g sediment a liquot was extracted so a total petroleum hydrocarbon analysis could be conducted. 0.5g from each microcosm sample was then used to extract the DNA and the clone library complete.

Results:

Library NS9 OTUs OUTs, Richness Shannons ESCd

0 125 46 97 69 319 080

23 91 20 47 37 205 087

66 87 32 51 42 289 083

The study found that the clone library analysis revealed a decrease in both diversity and species richness after contamination. The phylogenetic group that showed the greatest sensitivity to oil was the nematode. After contamination a large increase in the abundance of the groups Bacillariophyta and Biosoecida was detected. The oil contaminated samples were almost entirly dominated by organisms related to Bacillariophyta sp and cafetenia minima, which indicates that these groups are possible targets for biomonitoring oil in Mangroves. The DGGE fingerprints also indicated shifts in Microeukaryote profiles, specific band sequencing indicated the apperance of Bacillariophyta sp only in contaminated samples and nematoda only in non contaminated sediment. The richness estimators and the Shannon diversity index showed a decrease in microeukaryotic diversity and species richness after oil contamination occured.

The study was able to consider the application of molecular tools to evaluate the effects of oil on microeukaryotes in mangrove sediments.The clone library indicated a predominance of the fungi/ metazoa (70%), stramenoplies (25%), and alveolata (9%). The specifity of the groups suggests this diversity pattern is directly related to mangrove sediment. A number of Trichosporon sp, which was found in high numbers of the samples are extremely common in marine sediments and polluted waters. They are also able to assimilate phenolic compounds. The species that showed the greatest sensitivity to the oil contamination was nematodes. This species have been used in biomonitoring surveys as they are excellent indicators of pollution in marine ecosystem. in contaminated samples a large abundance of Bacillariophyta was detected. In conclusion the use of molecular techniques for the monitoring of oil contaminated mangroves is a quick and effective tool to indicate anthropogenic effects. With the presence of Bacillaiophyta sp and Cafeteria minima as targets for the presence of petroleum hydrocarbon in Mangrove sediments.