COMPARATIVE PHYSIOLOGY OF SYNECHOCOCCUS AND PROCHLOROCOCCUS - INFLUENCE OF LIGHT AND TEMPERATURE ON GROWTH, PIGMENTS, FLUORESCENCE AND ABSORPTIVE PROPERTIES
Lr. Moore et al., COMPARATIVE PHYSIOLOGY OF SYNECHOCOCCUS AND PROCHLOROCOCCUS - INFLUENCE OF LIGHT AND TEMPERATURE ON GROWTH, PIGMENTS, FLUORESCENCE AND ABSORPTIVE PROPERTIES, Marine ecology. Progress series, 116(1-3), 1995, pp. 259-275
Prochlorococcus marinus is abundant and widespread throughout the worl
d's oceans and always co-occurs geographically with the marine cyanoba
cterium Synechococcus. In the Atlantic Ocean, these 2 picoplankters ex
hibit different spatial and seasonal distributions. In order to better
understand the ecology of these species, we measured growth and photo
acclimation responses including fluorescence excitation [F(ph)(lambda
)] and in vivo absorption [a(ph)(lambda)] spectra over a range of gro
wth irradiances for P. marinus (clone SS120) and Synechococcus WH8103,
both isolated from the Sargasso Sea. To explore the physiological div
ersity of P. marinus, we measured the physiological responses of anoth
er P. marinus clone, MED4, isolated from the Mediterranean Sea. Growth
rate as a function of temperature was also examined for all 3 clones.
P. marinus SS120 and Synechococcus WH8103 have different temperature
optima for growth, but these do not explain the different latitudinal
distributions in the North Atlantic. P. marinus SS120 is adapted for g
rowth at low light intensities relative to Synechococcus WH8103, which
is consistent with the relative depth distribution of P. marinus and
Synechococcus in the field. The light-dependent growth response of P.
marinus MED4 is more similar to Synechococcus WH8103 than to P. marinu
s SS120. The unique pigment content of P. marinus (which contain divin
yl chlorophylls a and b) results in maximal absorbance in the blue wav
elengths. The high total chl b/chl a ratio of P. marinus SS120 enables
it to absorb more light, grow faster than Synechococcus WH8103 (and P
. marinus MED4) at low light intensities, and presumably to outcompete
Synechococcus in the deep euphotic zone. At high growth irradiances,
P. marinus SS120 contains measureable amounts of normal (monovinyl) ch
l b, whereas this pigment was not found in P. marinus MED4 at any grow
th irradiance. Photoacclimative changes in pigment ratios, and not pac
kage effect, account for most of the changes in a(ph)(lambda) and F*(
ph)(lambda) With Light intensity for all 3 picoplankters. At high ligh
t intensities, zeaxanthin contributes substantially to a(ph)(lambda)
in the blue, but appears to transfer little or no excitation energy to
the reaction centers, based on F(ph)(lambda) measurements. For P. ma
rinus, high absorption in the blue due to divinyl chl a and b relative
to normal chi a and b, absorption due to zeaxanthin, and small cell s
ize result in unusually high a(ph) (blue) relative to a*(ph) (red).