labeling DNA w/ 14C

[Mark]

What is the best way to get 13C into the DNA of non-enteric organisms
(pseudomonads and others)?

I have already used general substrates (acetate), but I was wondering if
there is something I could use to target the label into the DNA. 
Apparently (as per Stanier et al.), pseudomonads lack the ability to
take up exogenous thymine.  What about cytosine?

Any help would be much appreciated.

Thanks,

Mark Fuller
fuller at envirogen.com