Cm. Turley, THE EFFECT OF PRESSURE ON LEUCINE AND THYMIDINE INCORPORATION BY FREE-LIVING BACTERIA AND BY BACTERIA ATTACHED TO SINKING OCEANIC PARTICLES, Deep-sea research. Part 1. Oceanographic research papers, 40(11-12), 1993, pp. 2193-2206
The effect of pressure on upper ocean free-living bacteria and bacteri
a attached to rapidly sinking particles was investigated through study
ing their ability to synthesize DNA and protein by measuring their rat
e of H-3-thymidine and H-3-leucine incorporation. Studies were carried
out on samples from the NE Atlantic under the range of pressures (1-4
30 atm) encountered by sinking aggregates during their journey to the
deep-sea bed. Thymidine and leucine incorporation rates per bacterium
attached to sinking particles from 200 m were about six and ten times
higher, respectively, than the free-living bacterial assemblage. The r
atio of leucine incorporation rate per cell to thymidine incorporation
rate per cell was significantly different between the larger attached
(18.9:1) and smaller free-living (10.4:1) assemblages. The rates of l
eucine and thymidine incorporation decreased exponentially with increa
sing pressure for the free-living and linearly for attached bacteria,
while there was no significant influence of pressure on cell numbers.
At 100 atm leucine and thymidine incorporation rate per free-living ba
cterium was reduced to 73 and 20%, respectively, relative to that meas
ured at I atm. Pressure of 100 atm reduced leucine and thymidine incor
poration per attached bacterium to 94 and 70%, and at 200 atm these ra
tes were reduced to 34 and 51%, respectively, relative to those measur
ed at 1 atm. There was no significant uncoupling of thymidine and leuc
ine incorporation for either the free-living or attached bacterial ass
emblages with increasing pressure. indicating that the processes of DN
A and protein synthesis may be equally affected by increasing pressure
. It is therefore unlikely that bacteria, originating from surface wat
ers, attached to rapidly sinking particles play a role in particle rem
ineralization below approximately 1000-2000 m. These results may help
to explain the occurrence of relatively fresh aggregates on the deep-s
ea bed that still contain sufficient organic carbon to fuel the rapid
growth of benthic micro-organisms; they also indicate that the effect
of pressure on microbial processes may be important in oceanic biogeoc
hemical cycles.