Adenosine content and growth in the diatom Phaeodactylum tricornutum (Bacillariophyceae): effect of salinity, light, temperature and nitrate

Abstract

There are many known functions and regulatory mechanisms of the key metabolite adenosine in animal and plant cells, but little is known about its metabolism and how growth conditions affect the adenosine content in microalgae. In this study, we examined the influence of salinity, light intensity, temperature and nitrate concentration on growth rates and adenosine content in batch cultures of the diatom Phaeodactylum tricornutum Bohlin. A strong negative correlation was found between growth rate, as a function of both salinity and light, and adenosine content. Growth rate as a function of temperature and nitrate did not correlate with adenosine content. In silico and empirical tests revealed an apparent lack of adenosine degradation in P. tricornutum and from these analyses, we suggest that adenosine content reflects the balance between its formation from S-adenosyl-_L-homocysteine (SAH) hydrolysis and AMP dephosphorylation, and its consumption by phosphorylation to AMP. The high and varying adenosine levels in the growth and stationary phases could be an important physiological adaptation to support the cellular energy charge for the cells to survive in highly fluctuating environments. Adenosine content in microalgae could also be an important parameter to describe physiological responses to different growth conditions when optimizing growth conditions to increase valuable microalgal products, such as lipids for feed in aquaculture or as biofuels.

Keywords:

• adenosine
• AMP
• diatoms
• Phaeodactylum tricornutum
• S-adenosyl-_L-homocysteine (SAH)
• S-adenosyl-l-methionine (SAM)

Acknowledgements

This research was supported by the Norwegian Research Council (Grant no. 139710/140) and the Western Norway Regional Health Authority. We thank Dr Svein Rune Erga for comments to the manuscript and Rosie Theresa Coyne for initial work on HPLC-detection of adenosine. Finally we thank Dr Knut Helge Jensen for valuable advice and help with statistical analyses.