Bj. Binder et Yc. Liu, GROWTH-RATE REGULATION OF RIBOSOMAL-RNA CONTENT OF A MARINE SYNECHOCOCCUS (CYANOBACTERIUM) STRAIN, Applied and environmental microbiology, 64(9), 1998, pp. 3346-3351
The relationship between growth rate and rRNA content in a marine Syne
chococcus strain was examined. A combination of flow cytometry and who
le-cell hybridization with fluorescently labeled 16S rRNA-targeted oli
gonucleotide probes was used to measure the rRNA content of Synechococ
cus strain WH8101 cells grown at a range of light-limited growth rates
. The sensitivity of this approach was sufficient for the analysis of
rRNA even in very slowly growing Synechococcus cells (mu = 0.15 day(-1
)). The relationship between growth rate and cellular rRNA content com
prised three phases: (i) at low grow-th rates (<similar to 0.7 day(-1)
), rRNA cell(-1) remained approximately constant; (ii) at intermediate
rates (similar to 0.7 - 1.6 day(-1)), rRNA cell(-1) increased proport
ionally with growth rate; and (iii) at the highest, light-saturated ra
tes (> similar to 1.6 day(-1)), rRNA cell(-1) dropped abruptly, Total
cellular RNA (as measured with the nucleic acid stain SYBR Green II) w
as well correlated with the probe-based measure of rRNA and varied in
a similar manner with growth rate. Mean cell volume and rRNA concentra
tion (amount of rRNA per cubic micrometer) were related to growth rate
in a manner similar to rRNA cell(-1), although the overall magnitude
of change in both cases was reduced, These patterns are hypothesized t
o reflect an approximately linear increase in ribosome efficiency with
increasing growth rate, which is consistent with the prevailing proka
ryotic model at low growth rates. Taken together, these results suppor
t the notion that measurements of cellular rRNA content might be usefu
l for estimating in situ growth rates in natural Synechococcus populat
ions.