Monitoring the cellular phosphate status in bloom-forming cyanobacteria of the Baltic Sea

Sammanfattning: In the Baltic Sea dense cyanobacterial blooms occur regularly during late summer. Since the dominant bloom-forming cyanobacteria, Nodularia spp. and Apanizomenon spp. are capable of fixing atmospheric dinitrogen, the macronutrient predominantly limiting their growth is phosphorus. The main aim of this thesis was to develop molecular tools for monitoring the cellular P status in bloom-forming cyanobacteria in Baltic Sea. In this thesis I describe the development and the use of competitive RT-PCR, Pyrosequencing and Real-time PCR technology for determination of mRNA levels of two cyanobacterial pstS gene copies, encoding proteins involved in phosphate uptake. I have also studied the expression of three other typical P-stress induced genes involved in assimilation (phoA) and storage (ppk and ppx) of phosphate, using Real-time PCR. The model system used was laboratory cultures of Anabaena 7120 and Nodularia spumigena. The method was then implemented on field samples collected from the Baltic Sea during the summer of 2005.The gene expressions of the two pstS genes showed satisfied response to varied Pi levels and were induced simultaneously while the three other genes investigated did not solely respond to depleting Pi concentration. The two pstS genes are therefore more suitable for indicators of Pi stress. The phoA gene was continuously expressed while the ppk gene and the ppx gene responded to varied Pi levels, but their expressions are dependent on the cell capacity for phosphate storage, which may differ from one cell to another.This thesis also includes method development and analysis of the expression of the nda gene cluster, encoding the toxic compound nodularin, which is produced by Nodularia spumigena. During Pi depletion the gene expression increased while gene expression decreased during N supplementation. The results also suggests that cells keep a certain amount of nodularin inside the cell, and concentrations above this threshold level will either be degraded intracellulary or transported out of the cell.