hybridize well with our A. nidulans probe. We are examining production of probes from oceanic 

 picocyanobacteria we have in culture to mitigate this potential limitation, as well as using our 

 diatom probe to get the "golden" clade of phytoplankton. 



A second concern is how to do diel studies. Current studies with deck top incubators 

 suggest that conditions in these deteriorated in as few as 12 hr, which make studies of any 

 duration difficult. The alternative, tracking a water mass by a drogued buoy, does not enable 

 manipulation of light regimes and does not preclude vertical migration of the phytoplankton 

 population out of the zone of sampling. 



STATUS OF RESEARCH 



As mentioned above, we are making good progress in lab studies with phytoplankton 

 isolates and in field studies of natural populations in terms of the regulation of RubisCO. In 

 October, we participated in laboratory studies on the regulation of rbcL using Pacific 

 Prochlorococcus cultures in the lab of Dr. Lisa Campbell, University of Hawaii. The regulation 

 of rbcL was studied through light and dark cycles of a 52 hr diel study. The results of these 

 experiments are forthcoming as the data is being processed. We participated in a cruise in 

 September to study regulation of RubisCO in vertical profiles and during a diel experiment. We 

 have planned a cruise for August, funded by a NSF project. This cruise will examine regulation 

 of RubisCO in the field, as well as look for transcriptional regulation throughout the water 

 column. A third cruise is scheduled off the Hatteras area in summer of 1995, again funded by 

 NSF. 



A major publication based on this work will be submitted to a leading journal by the time 

 this report is received. Most important, however, is the fact that our experience with Anabaena 

 has provided us with the necessary expertise to tackle aspects of regulation in open oceanic 

 strains, organisms which are much more difficult to cultivate. To assist in these efforts, we have 

 isolated an oceanic unicellular strain from the Gulf of Mexico, obtained on a cruise in September 

 of 1993. This strain grows fairly rapidly (unusual for such organisms) both on liquid and solid 

 marine growth media. The latter point is particularly important for any future studies on the 

 genetic regulation of C0 2 fixation in marine cyanobacteria. Most interesting is the fact that this 

 new isolate may be capable of fixing nitrogen. If confirmed, this will be an exciting observation, 

 for it may mean that such organisms contribute to the nitrogen budget of the oceanic environment 

 as well. 



Keywords: photosynthesis, ribulose bisphosphate carboxylase, nutrient limitation 



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