Influence of chlorobenzoates on the utilisation of chlorobiphenyls and chlorobenzoate mixtures by chlorobiphenyl/chlorobenzoate-mineralising hybrid bacterial strains

Abstract

Chlorobenzoates (CBA) arise as intermediates during the degradation of polychlorinated biphenyls (PCBs) and some chlorinated herbicides. Since PCBs were produced as complex mixtures, a range of mono-, di-, and possibly trichloro-substituted benzoates would be formed. Chlorobenzoate degradation has been proposed to be one of the rate-limiting steps in the overall PCB-degradation process. Three hybrid bacteria constructed to have the ability to completely mineralise 2-, 3-, or 4-monochlorobiphenyl respectively, have been studied to establish the range of mono- and diCBAs that can be utilised. The three strains were able to mineralise one or more of the following CBAs: 2-, 3-, and 4-monochlorobenzoate and 3,5-dichlorobenzoate. No utilisation of 2,3-, 2,5-, 2,6-, or 3,4-diCBA was observed, and only a low concentration (0.11 mM) of 2,4-diCBA was mineralised. When the strain with the widest substrate range (Burkholderia cepacia JHR22) was simultaneously supplied with two CBAs, one that it could utilise plus one that it was unable to utilise, inhibitory effects were observed. The utilisation of 2-CBA (2.5 mM) by this strain was inhibited by 2,3-CBA (200 microM) and 3,4-CBA (50 microM). Although 2,5-cba and 2,6-cba were not utilised as carbon sources by strain jhr22, they did not inhibit 2-cba utilisation at the concentrations studied, whereas 2,4-cba was co-metabolised with 2-cba. The utilisation of 2-, 3-, and 4-chlorobiphenyl by strain JHR22 was also inhibited by the presence of 2,3- or 3,4-diCBA. We conclude that the effect of the formation of toxic intermediates is an important consideration when designing remediation strategies.

3-Chloro-, 2,3- and 3,5-dichlorobenzoate co-metabolism in a 2-chlorobenzoate-degrading consortium: role of 3,5-dichlorobenzoate as antagonist of 2-chlorobenzoate degradation

“…Effect of 3,5-diCB on 2-CB degradation by the mixed culture Several Authors have shown 3,5-diCB to have a strong inhibitory effect on the growth of different microorganisms in pure culture when the dichloroaromatic was supplied in combination with another CB as growth substrate (Baggi & Zangrossi 1995;Hernandez et al 1991;Miguez et al 1990;Stratford et al 1996). In a previous work we observed a similar effect on the growth of 2m.c.…”

“…In fact we and other Authors have reported the occurrence of antagonistic effects on microbial growth when CB mixtures were supplied to CBdegrading microorganisms (Baggi & Zangrossi 1995Miguez et al 1990;Stratford et al 1996). In all cases 3,5-diCB was shown to be an inhibitory compound when present in combination with another CB as growth substrate.…”

“…In all cases 3,5-diCB was shown to be an inhibitory compound when present in combination with another CB as growth substrate. The causes for this were not always elucidated, or were tentatively attributed to the toxicity of some metabolites like 3-chlorocatechol(s) and its meta-fission product(s), as suggested by Stratford et al (1996), who, however, did not detect such intermediates in the cultures. In another case, interference in degradative enzyme induction has been postulated as being involved in the failure of Alcaligenes denitrificans CB strain to grow on 4-CB in the copresence of 3,5-, 3,4-and 2,3-diCB.…”

“…(Alvarez & Vogel 1991;Baggi 2000;Baggi & Zangrossi 1999). In the particular case of CBs, the formation of 3-chlorocatechol(s) and the correlated meta-fission product(s), well known to be toxic to microorganisms (Bartels et al 1984), has been proposed as a potential cause of inhibitory phenomena (Stratford et al 1996). In earlier work we selected a versatile mixed culture (2m.c.)…”

Inhibitory mechanisms by chlorobenzoate mixtures in chlorobenzoate-degrading microorganisms

“…To date, the causes for growth interaction in the presence of mixed CBs have not yet been sufficiently elucidated. The formation of toxic metabolic intermediates such as chlorocatechol(s) and/or their meta-fission product(s) was hypothesized, but this has not always been demonstrated experimentally (Stratford et al, 1996). In other cases, interactions at the level of enzyme induction (Weissenfels et al, 1990, Baggi andZangrossi, 1999), the type of the carbon source utilised for growth (Hernandez et al, 1991) or competitive interferences with uptake systems or key enzymes involved in the first steps of the CB degradative process (Stringfellow and Aitken, 1985;Adriaens and Focht, 1991;Miguez et al, 1995;Corbella et al, 2001;Baggi et al, 2005), were postulated as the most important causes of the inhibitory phenomena.…”