S
0..
U
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AA
AM Q9
p~-----\
A
Determination of Microbial Production
201
S 0...
Z
o
S 0..
(j)
Fig. 4.12. Scheme of pathways of thymidine nucleoside incorpora tion into the bacterial cell involving its exogenous and eudogenous pools. CM Cellular metabolism; CPW,
DNPW, SPW respectively, catabolism, de novo and salvation pathways of TDR incorporation into DNA; TM thymidine; TMP, TDP , TDP thymidine mono-, di- and triphosphate ; UDP, CTP deoxyuridine and deoxycytidine monophosphates; symbols in circles
e nzymes: pm permeases; tk thymidine kinases; dp DNA-polymerase; ces catabolic
enzyme system; cw cell wall
5. CH)-TDR is incorporated by bacterial cells only or at least majorely into
the cellular DNA.
6. The specific radioactivity of the CH)-TDR written in the label attached to
its batch by the supplying company is the Gospel Truth, and remains constant for a couple of months during its preservation in the refrigerator.
7. It is possible to calculate realistic absolute rates ofTDR incorporation by
bacterioplankton having radioassayed the insoluble in cold TeA (trichloracetic acid) fraction of bacterial cell material.
8. Finally, a universal conversion factor may be derived for the translation of
the TDR incorporation rates thus measured to the numbers of divided bacterial cells or to the production of bacterial biomass.
The thymidine method was adapted also for measuring bacterial production in bottom sediments (Moriarty and Pollard 1981, 1982) and, soon became
extremely popular. Dozens of scores of papers were published during the fol-