Change in Emiliania huxleyi Virus Assemblage Diversity but Not in Host Genetic Composition during an Ocean Acidification Mesocosm Experiment.

Effects of elevated pCO2 on Emiliania huxleyi genetic diversity and the viruses that infect E. huxleyi (EhVs) have been investigated in large volume enclosures in a Norwegian fjord. Triplicate enclosures were bubbled with air enriched with CO2 to 760 ppmv whilst the other three enclosures were bubbled with air at ambient pCO2; phytoplankton growth was initiated by the addition of nitrate and phosphate. E. huxleyi was the dominant coccolithophore in all enclosures, but no difference in genetic diversity, based on DGGE analysis using primers specific to the calcium binding protein gene (gpa) were detected in any of the treatments. Chlorophyll concentrations and primary production were lower in the three elevated pCO2 treatments than in the ambient treatments. However, although coccolithophores numbers were reduced in two of the high-pCO2 treatments; in the third, there was no suppression of coccolithophores numbers, which were very similar to the three ambient treatments. In contrast, there was considerable variation in genetic diversity in the EhVs, as determined by analysis of the major capsid protein (mcp) gene. EhV diversity was much lower in the high-pCO2 treatment enclosure that did not show inhibition of E. huxleyi growth. Since virus infection is generally implicated as a major factor in terminating phytoplankton blooms, it is suggested that no study of the effect of ocean acidification in phytoplankton can be complete if it does not include an assessment of viruses.

Genome comparison of two Coccolithoviruses.

BACKGROUND: The Coccolithoviridae is a recently discovered family of viruses that infect the marine coccolithophorid Emiliania huxleyi. Following on from the sequencing of the type strain EhV-86, we have sequenced a second strain, EhV-163. RESULTS: We have sequenced approximately 80% of the EhV-163 genome, equating to more than 200 full length CDSs. Conserved and variable CDSs and a gene replacement have been identified in the EhV-86 and EhV-163 genomes. CONCLUSION: The sequencing of EhV-163 has provided a wealth of information which will aid the re-annotating of the EhV-86 genome and identified a gene insertion in EhV-163.

The response of Thalassiosira pseudonana to long-term exposure to increased CO2 and decreased pH.

The effect of ocean acidification conditions has been investigated in cultures of the diatom Thalassiosira pseudonana CCMP1335. Expected end-of-the-century pCO(2) (aq) concentrations of 760 µatm (equivalent to pH 7.8) were compared with present-day condition (380 µatm CO(2), pH 8.1). Batch culture pH changed rapidly because of CO(2) (aq) assimilation and pH targets of 7.8 and 8.1 could not be sustained. Long-term (∼100 generation) pH-auxostat, continuous cultures could be maintained at target pH when cell density was kept low (<2×10(5) cells mL(-1)). After 3 months continuous culture, the C:N ratio was slightly decreased under high CO(2) conditions and red fluorescence per cell was slightly increased. However, no change was detected in photosynthetic efficiency (F(v)/F(m)) or functional cross section of PS II (σ(PSII)). Elevated pCO(2) has been predicted to be beneficial to diatoms due to reduced cost of carbon concentration mechanisms. There was reduced transcription of one putative δ-carbonic anhydrase (CA-4) after 3 months growth at increased CO(2) but 3 other δ-CAs and the small subunit of RUBISCO showed no change. There was no evidence of adaptation or clade selection of T. pseudonana after ∼100 generations at elevated CO(2). On the basis of this long-term culture, pH change of this magnitude in the future ocean may have little effect on T. pseudonana in the absence of genetic adaption.