April, 2012 THE PHOTOPHYSIOLOGY OF BOLIDOMONAS PACIFICA
Thomas, Sara, Dr. Douglas Campbell1, Dr. David Kristie2
Department of Biochemistry, Mount Allison University, Sackville, NB1
Department of Biology, Acadia University, Wolfville, NS2
Bolidomonas pacifica is a cholorophyll
a/c marine phytoplankter in a sister
lineage to the more widely distributed
diatoms. In contrast to the diatoms, B.
pacifica lacks siliceous frustules but has
cell motility driven by two flagella. Marine
diatoms thrive under conditions of
fluctuating light, so we sought to
characterize the photophysiology of B.
pacifica, and its responses to upward
fluctuations in light. We grew B. pacifica
under six light levels between 30 to 450
µmol photons·m-2·s-1, a range spanning
the bottom 10% of the photic zone up to
the near-surface top 30% of the photic zone. The cells achieved maximum growth at
250 umol photons·m-2·s-1, equivalent to the middle of the photic zone. Light capture
measures showed the effective absorbance cross sections for PSII photochemistry
were much larger than comparable measures from marine diatoms, and B. pacifica did
not show acclimatory changes in these light capture measures across cells grown from
low to high light. When analyzing B. pacifica responses to mixing through the water
column, we found that within 15 minutes of being shifted to a higher light, B. pacifica
cultures with active PSII repair cycles induced PSII repair, thus stabilizing PSII function
in the face of accelerated photoinactivation. When we used a chloroplast protein
synthesis inhibitor (lincomycin) to block PSII repair, the cells suffered progressive loss
of PSII function, with a susceptibility to photoinactivation about double that of marine
diatoms under comparable conditions. Thus a rapid induction of metabolically expensive
PSII repair would be necessary for B. pacifica during upward mixing through the water
column. In comparison to the marine diatoms, B. pacifica shows higher light capture per
PSII, but also suffered more rapid photoinactivation of PSII which it must counter with
rapid induction of metabolically expensive PSII repair during upward mixing through the
water column. We hypothesize these differences result from the lack of the siliceous
frustule that modifies the optics of their diatom cousins.
Sara Thomas graduated from Tantramar
Regional High School in Sackville, NB in 2008.
Sara is currently completing her Honours thesis in
fourth year Biology at Acadia. She has been a
member of the Acadia Cross Country and Track
and Field Teams for the past four years and also
takes dance classes with the Acadia Dance
Collective. Sara has also worked as a New Student
Orientation Leader and a Resident Assistant during
her time at Acadia. During her time at Acadia, Sara
received a number of Academic awards including the Clarke K. McLeod Pre-Medical
Scholarship. Next year she plans on taking some time off from school to do some
travelling!