Working Report 2005-65 Microbial Community Analysis of Shallow Subsurface Samples with PCR

This work is part of the site investigations for the disposal of spent nuclear fuel in Olkiluoto bedrock. The purpose of the research was to study the suitability of PCR-DGGE (polymerase chain reaction denaturing gradient gel electrophoresis) method for monitoring of hydrogeomicrobiology of Olkiluoto repository site. PCR-DGGE method has been applied for monitoring microbial processes in several applications. The benefit of the method is that microorganisms are not cultivated but the presence of microbial communities can be monitored by direct DNA extractions from the environmental samples. Partial 16SrDNA gene sequence is specifically amplified by PCR (polymerase chain reaction) which detect bacteria as a group. The gene sequences are separated in DGGE, and the nucleotide bands are then cut out, extracted, sequenced and identified by the genelibraries by e.g. Blast program. PCR-DGGE method can be used to detect microorganisms which are present abundantly in the microbial communities because small quantities of genes cannot be separated reliably. However, generally the microorganisms involved in several environmental processes are naturally enriched and present as major population. This makes it possible to utilize PCRDGGE as a monitoring method. In this study, we studied the structure of microbial communities in ten ground water samples originating from Olkiluoto. Two universal bacterial primer sets were compared which amplified two different regions of the 16S rDNA gene. The longer sequence amplified resulted in fewer bands in DGGE, in addition there were problems with purification of the sequences after DGGE. The shorter sequence gave more bands in DGGE and more clear results without any amplification problems. Comparison of the sequences from the gene-libraries resulted in the detection of the same species by both primer sets, in addition some different species were detected. Several species were anaerobic bacteria, such as acetogenic and sulphate reducing bacteria (SRB) indicating low redox potential of the samples. In addition phylogenetic trees were constructed for the sequences identified with both long and short primer sets. Phylogenetic trees were in good agreement with each other and indicated similar communties with both methods. In addition we also evaluated the suitability of primers amplifying SRB from the water samples. However, even though the microbial community analysis with the 16S rDNA gene indicated that SRB were present in the microbial community their amplification with the primers used was not successful. MIKROBIEN ANAL YSOINTI POHJAVEDESTA PCR-DGGE -MENETELMALLA TIIVISTELMA Olkiluodon kaytetyn polttoaineen loppusijoitustutkimuksiin liittyen selvitettiin PCR-DGGE menetelman soveltuvuutta geomikrobiologisten ilmioiden monitorointimenetelmana. PCR-DGGE menetelmaa on hyodynnetty aiemmin erilaisten mikrobiprosessien seurannassa. Menetelman etuna on, ettei mikrobeja tarvitse viljella, vaan mikrobilajiston esiintymista voidaan tutkia uuttamalla mikrobien DNA suoraan ymparistOnaytteesta. DNAsta monistetaan PCR:lla (polymeraasiketjureaktio) spesifisesti 16S rDNA-geenialueita, jotka tunnistavat bakteerit ryhmana. Geenisekvenssit erotellaan denaturoivassa gradientti geelielektroforeesissa (DGGE), josta nukleotidijuovat sitten leikataan, uutetaan ja niiden geenirakenne tunnistetaan geenikirjastosta ns. Blast ohjelmalla. PCR-DGGE-menetelmalla voidaan havaita mikrobit, jotka esiintyvat riittavan runsaasti populaatiossa. Menetelmalla voidaan saada selville vain paalajisto, koska pienet maarat DNAta eivat erotu DGGE:ssa riittavan voimakkaasti. Ympariston erilaisissa prosesseissa kuitenkin ne mikrobilajitja ryhmat joiden toimintaa olosuhteet suosivat rikastuvat ja esiintyvat paalajistona. Tama mahdollistaa menetelman hyodyntamisen monitorointimenetelmana. Tassa tutkimuksessa selvitettiin kymmenen Olkiluodon kallioperan pintosasta ja pohjavesiputkesta otetun vesinaytteen mikrobiyhteison paalajistoa. Tutkimuksessa verrattiin kahdenlaisia yleisalukkeita, jotka monistavat bakteereista eri alueita ja myos eri pituisia alueita. Yleisalukkeet, jotka monistavat pitempaa geenialuetta olivat ongelmallisia ja DGGE juovien puhdistaminen onnistui huonosti. Niilla saatiin myos vahemman selvia sekvensseja kuin alukkeilla, jotka monistivat lyhyempaa 16S rDNA-geenin aluetta. Sekvenssien vertailu geenikirjastoista osoitti, etta alukkeilla saatiin osa samoja lajeja ja lyhyilla alukkeilla useampia alukkeita. Tunnistetut mikrobilajit kuuluivat mm. Asetogeenisiin ja sulfaatin pelkistajaryhmiin (SRB). Tama kertoo, etta olosuhteet olivat redox olosuhteiltaan matalat, koska hapettomissa olosuhteissa toimivat mikrobiryhmat olivat valtalajistona. Lisaksi rakennettiin sukulaisuuspuut seka pitkilla etta lyhyilla alukkeilla monistetuille sekvensseille. Sukulaisuuspuut olivat keskenaan hyvin yhtenevat ja osoittivat lajiston olevan saman tyyppiset molemmilla alukkeilla. Lisaksi tavoitteena oli selvittaa sulfaatin pelkistajille spesifisten alukkeiden kayttoa. Tama osio vaatii lisatutkimuksia ja alukkeiden optimointia, eika PCR onnistunut taman tutkimuksen puitteissa. Tama voi johtua myos siita, etta kyseiset alukkeet oli kehitetty muissa ymparistoissa esiintyvien sulfaatinpelkistajien tunnistamiseen.