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Diversity of nifH-containing and nitrogen fixing microorganisms in the microbial mat of "Greenbeach"

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Diversity of nifH-containing and nitrogen fixing microorganisms in the microbial mat of "Greenbeach"

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This research aims at investigating the diversity of nifH-containing and nitrogen fixing microorganisms in the microbial mat of Greenbeach. A microbial mat is a vertically stratified ecosystem. The microbial mat on Greenbeach is located at the beach of Schiermonnikoog and covers an area of more than 4 km2. Although microorganisms containing the nifH gene can potentially fix nitrogen, it does not mean they perform this process. By extracting DNA from soil samples, amplifying the nifH gene, making a clone library and sequencing microorganisms containing the nifH can be identified. This identification is done by submitting the obtained sequences into BLAST and performing a phylogenetic analysis. The same procedure was applied to cDNA transcribed from mRNA isolated from duplicates used to extract DNA from. In this way, it is examined which microorganisms where actively fixing nitrogen at the time of sampling. While the clone libraries produced with undiluted DNA did not give the expected results, clone libraries were made with 150 times diluted DNA.
Diluting the DNA improved the recovery of sequenes related to cyanobacteria. This was more consistent with the expectancy, because it was expected to find many cyanobacterial the nifH genes.
Two different sample sites were studied. In site 1 approximately 80% of the nifH-containing microorganisms were cyanobacteria and 20% proteobacteria. Almost all nitrogen fixing microorganisms (98%) were cyanobacteria. Dominant species for nitrogen fixation were Nodularia, Oscillatoria and an unknown cyanobacterium closely related to Leptolyngbia.
The composition of site 2 was more difficult to determine. The two duplicates showed a big difference in composition of the microbial mat. Duplicate 1 (3GB227*) showed the mat contained only nifH-containing proteobacteria while duplicate 2 (3GB228*) showed it contained 70% cyanobacteria and 30% proteobacteria containing the nifH gene. Nitrogen fixation was performed by cyanobacteria (49%), mainly Nodularia and an unknown cyanobacterium closely related to Leptolyngbia, and gamma- & delta-proteobacteria (51%).
Diluting the DNA provided more expected results, however, the question is; are these results correct? Because the results are influenceable by diluting the DNA, the results could be incorrect. Further research has to proof if this is the case.
The results for sample site 2 also raise questions, because there is such a big difference in duplicates. A cause could be the sample site is located near the waterline, having therefore much interaction with the sea and is thereby influenced by a constant supply and removal of microorganisms.

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OrganisatieHZ University of Applied Sciences
OpleidingChemie
AfdelingAcademie voor Technologie & Innovatie
PartnersNIOO-KNAW, Yerseke
Datum2006-06-29
TypeBachelor
TaalEngels

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