Five bacterial strains (Acidovorax facilis B517, Cellulomonas turbata B529, Pseudomonas veronii B547, Pseudomonas veronii B549, and Paenibacillus polymyxa B550) isolated on chlorobenzene as the sole source of carbon and energy were screened for the accumulation of the putative metabolic intermediate 3-chlorocatechol during growth on chlorobenzene under oxygen-limited conditions in the presence and absence of nitrate (1 mM). 3-Chlorocatechol accumulated in the growth media of all five strains, but accumulation was significantly less in cultures of A. facilis B517 compared to the other four strains. The presence of nitrate did not influence the biological conversion pattern. However, biologically produced nitrite reacted with 3-chlorocatechol chemically, a reaction that masked the accumulation of 3-chlorocatechol. For P. veronii B549, a clear relationship between the presence of 3-chlorocatechol in the medium and low oxygen concentrations was demonstrated. The assumption is made that accumulation of 3-chlorocatechol is due to the low enzymatic turnover of the 3-chlorocatechol cleaving enzyme, catechol-1,2-dioxygenase, at low oxygen concentrations.

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Ralstonia eutropha JMP 134 was continuously grown on phenol and 2,4-dichlorophenoxyacetate under nutristatic conditions at elevated stationary concentrations of 90±650 mg phenol/l and 25±100 mg 2,4-D/l, respectively, in order to study the response of the bacterial population to long-term exposure to these potentially toxic substrates. The course of the cells' response over time was observed by determining distinctive growth parameters and by the on-line measurement of¯uorescence spectra of intracellular and extracellular¯uorophores. The latter were monitored using a modi®ed¯uorescence spectrophotometer. The results of the nutristat experiments indicate that the adaptation of the culture to long-term exposure to phenol and 2,4-D exhibited dynamic characteristics of the growth pattern determined by the individual substrates and their concentration, including enforced and reduced levels of substrate conversion. This growth pattern is interpreted as an expression of superimposing cellular events in order to withstand unfavorable environmental conditions. Finally, the growth rate attained retarded levels under stationary conditions, slowing down to almost zero for example in the case of about 100 mg 2,4-D/l.The growth rate pro®le within the various phases of adaptation was well re¯ected by the¯uorescence signals. The NAD(P)H¯uorescence was almost exclusively emitted by the cellular pool of NADPH and behaved inversely to the growth rate. A similar relationship was obtained for the cellular¯uorescence of a¯avin-containing compound. Sharply reduced growth was additionally accompanied by a rapid rise of the background¯uorescence. These data indicate that¯uorescence-derived signals provide a useful re¯ection of cellular events in inhibited growth situations.

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