The production of hydrocarbons from photoautotrophic growth ofDunaliella salina 1650

Expressed sequence tag (EST) profiling in hyper saline shocked Dunaliella salina reveals high expression of protein synthetic apparatus components

The unicellular, halotolerant, green alga, Dunaliella salina (Chlorophyceae) has the unique ability to adapt and grow in a wide range of salt conditions from about 0.05 to 5.5M. To better understand the molecular basis of its salinity tolerance, a complementary DNA (cDNA) library was constructed from D. salina cells adapted to 2.5M NaCl, salt-shocked at 3.4M NaCl for 5h, and used to generate an expressed sequence tag (EST) database. ESTs were obtained for 2831 clones representing 1401 unique transcripts. Putative functions were assigned to 1901 (67.2%) ESTs after comparison with protein databases. An additional 154 (5.4%) ESTs had significant similarity to known sequences whose functions are unclear and 776 (27.4%) had no similarity to known sequences. For those D. salina ESTs for which functional assignments could be made, the largest functional categories included protein synthesis (35.7%), energy (photosynthesis) (21.4%), primary metabolism (13.8%) and protein fate (6.8%). Within the protein synthesis category, the vast majority of ESTs (80.3%) encoded ribosomal proteins representing about 95% of the approximately 82 subunits of the cytosolic ribosome indicating that D. salina invests substantial resources in the production and maintenance of protein synthesis. The increased mRNA expression upon salinity shock was verified for a small set of selected genes by real-time, quantitative reverse-transcription-polymerase chain reaction (qRT-PCR). This EST collection also provided important new insights into the genetic underpinnings for the biosynthesis and utilization of glycerol and other osmoprotectants, the carotenoid biosynthetic pathway, reactive oxygen-scavenging enzymes, and molecular chaperones (heat shock proteins) not described previously for D. salina. EST discovery also revealed the existence of RNA interference and signaling pathways associated with osmotic stress adaptation. The unknown ESTs described here provide a rich resource for the identification of novel genes associated with the mechanistic basis of salinity stress tolerance and other stress-adaptive traits.

Marine biotechnology in education: a competitive approach

This paper describes the development of a practical, which is taught to third year biotechnology students. We wanted to motivate the students by making them responsible for a research project. Competition was added as a stimulus for interaction between the students. A virtual company called CaroTech employed the students for 2 weeks. They worked in groups of two persons and each group was responsible for a 0.8 l flat panel photobioreactor. They had to produce as much beta-carotene as possible using the marine alga strain Dunaliella salina in this photobioreactor. On the first day, students developed a strategy to obtain optimal algal growth rate. They putted this plan into practice the second day and while cultivating the organism, they developed a second strategy how and when to stress the alga to initiate beta-carotene production. At the end of the ninth day, the total amount of beta-carotene was measured. To stimulate competition, the group that produced the most beta-carotene obtained half a point bonus on the final practical mark. On the tenth day, each group presented their results and an evaluation of their chosen strategies to the CaroTech board. Most groups were successful in growing algae. In the second phase some groups failed to stress the alga. The best group produced more than two times beta-carotene than the runner-up. The students were motivated by being responsible for their own results and the competitive approach. All students liked the practical and indicated that they learned a lot by following this practical.