EFFECTS OF TRIBUTYLTIN, LINEAR ALKYLBENZENESULFONATES, AND NUTRIENTS (NITROGEN AND PHOSPHORUS) ON NUCLEOID-CONTAINING BACTERIA

Effects of tributyltin (TBT) and linear alkylbenzenesulfonate (LAS) on the number of nucleoid-containing bacteria (NCB) were examined in 15 marine enclosures situated in Knebel Vig, Denmark. Nucleoid-containing bacteria were enumerated using a newly revised methodological approac h including glutaraldehyde fixed 4',6'-diamidino-2-phenylindole (DAPI) preparations rinsed with 2-propanol. Additions of TBT (0.0025-9.7 nM) reduced the number of NCB up to 62%, whereas additions of LAS (15 mu M) increased the numbers. Total counts were not affected by the two to xicants. Values of no-observed-effect concentration, lowest-observed-e ffect concentration, and concentration at 30% effectiveness for TBT on NCB were 0.020, 0.16, and 0.0036 nM, respectively. These values are m uch lower than those previously reported by other techniques and are s imilar to or lower than TBT concentrations measured in harbors and coa stal sea regions, suggesting that natural bacterial assemblages in man y marine environments are toxified by TBT. Additions of nutrients stim ulated both total counts (twofold) and NCB (fourfold), whereas additio n of LAS + nutrients stimulated only NCB. Results from two diel studie s demonstrated that NCB varied more on a diel scale than did total cou nts. Nevertheless, the effects of the two toxicants on NCB were signif icantly higher than the measured diel changes, suggesting that NCB can be used as a sensitive parameter to test effects of toxicants on pela gic ecosystems.