טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentAharonovich Dikla
SubjectMarine Picoplankton Molecular Ecology: Genes versus
Transcripts
DepartmentDepartment of Biology
Supervisor Professor Oded Beja
Full Thesis textFull thesis text - English Version


Abstract

Molecular techniques as microbial ecology tools have brought new insights into the community structure and dynamics of marine bacteria. Most of the molecular studies on marine picoplankton are based on the analysis of DNA or RNA. However, comprehensive results of the simultaneous analysis of marine bacterioplankton on their DNA and RNA levels using the same experimental approach are still missing. The aim of this study was to compare the genetic potential (DNA) versus actively expressed genes (RNA) of picoplankton assemblage derived from the same marine environment. We focused on two marine significant processes, nitrogen fixation and oxygenic photosynthesis, by studying their key genes, nifH and psbA.

In this study, we examined the spatial and seasonal distribution of nifH and psbA genes and transcripts in the eastern Mediterranean Sea. Clone libraries constructed from both DNA and reverse-transcribed PCR-amplified mRNA were examined and compared. We observed different nifH genes from diverse microbial groups, such as Cyanobacteria, Proteobacteria and methanogenic Archaea. Interestingly, numerous nifH phylotypes were observed in coastal stations at the DNA level but none were active. However, in far offshore stations, the phylotypes observed at the DNA level were the ones that were actually active. Our results demonstrate the spatial distribution of Synechococcus and Prochlorococcus psbA genes and transcripts according to water column mixing and light intensity. In addition, marine photosynthetic picoeukaryotes psbA sequences represented about 50% of total RNA-derived clones and were retrieved from RNA only.

We present here the effective use of RT-PCR versus PCR to detect and differentiate between organisms that possess and express genes in the marine environment.