picocyanobacteria). Our preliminary studies on the Pacific Prochlorococcus by sequence 

 analysis suggests that it would 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 



112 



