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Applied and Environmental Microbiology, September 1998, p. 3352-3358, Vol. 64, No. 9
Ocean Research Institute, University of
Tokyo, Nakano, Tokyo 164-8639, Japan
Received 30 January 1998/Accepted 17 June 1998
In order to better estimate bacterial biomass in marine
environments, we developed a novel technique for direct measurement of
carbon and nitrogen contents of natural bacterial assemblages. Bacterial cells were separated from phytoplankton and detritus with
glass fiber and membrane filters (pore size, 0.8 µm) and then
concentrated by tangential flow filtration. The concentrate was used
for the determination of amounts of organic carbon and nitrogen by a
high-temperature catalytic oxidation method, and after it was stained
with 4',6-diamidino-2-phenylindole, cell abundance was determined by
epifluorescence microscopy. We found that the average contents of
carbon and nitrogen for oceanic bacterial assemblages were 12.4 ± 6.3 and 2.1 ± 1.1 fg cell
0099-2240/98/$04.00+0
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Direct Determination of Carbon and Nitrogen
Contents of Natural Bacterial Assemblages in Marine
Environments
1 (mean ± standard
deviation; n = 6), respectively. Corresponding values
for coastal bacterial assemblages were 30.2 ± 12.3 fg of C
cell
1 and 5.8 ± 1.5 fg of N cell
1
(n = 5), significantly higher than those for oceanic
bacteria (two-tailed Student's t test; P < 0.03). There was no significant difference (P > 0.2) in the bacterial C:N ratio (atom atom
1) between
oceanic (6.8 ± 1.2) and coastal (5.9 ± 1.1) assemblages. Our estimates support the previous proposition that bacteria contribute substantially to total biomass in marine environments, but they also
suggest that the use of a single conversion factor for diverse marine
environments can lead to large errors in assessing the role of bacteria
in food webs and biogeochemical cycles. The use of a factor, 20 fg of C
cell
1, which has been widely adopted in recent studies
may result in the overestimation (by as much as 330%) of bacterial
biomass in open oceans and in the underestimation (by as much as 40%)
of bacterial biomass in coastal environments.
*
Corresponding author. Mailing address: Ocean Research
Institute, University of Tokyo, 1-15-1 Minami-dai, Nakano, Tokyo
164-8639, Japan. Phone: 81-3-5351-6457. Fax: 81-3-5351-6461. E-mail:
rfukuda{at}ori.u-tokyo.ac.jp.
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