Competition for oxygen and 3-chlorobenzoate between two aerobic bacteria using different degradation pathways

Abstract

In nature a significant part of the microbial activity is concentrated at or near oxic/anoxic interfaces, where oxygen concentrations are often low. Bacteria possessing different kinetic characteristics for oxygen and employing distinct metabolic pathways for the degradation of (halo)aromatic substrates for which oxygen is needed as co-substrate may have to compete with each other in such environments. In this study the competitiveness of Pseudomonas sp. strain A3 relative to Alcaligenes sp. strain L6 was tested in batch and in continuous cultures. While both of these strains are able to metabolise 3-chlorobenzoate (3CBA), the former was isolated under air saturating conditions and employs the catechol pathway, whereas the latter was isolated under reduced partial pressures of oxygen and was capable of metabolising 3CBA via the gentisate pathway. Competition experiments in batch culture resulted in pure cultures of Pseudomonas sp. strain A3 under air saturating conditions. However, if reduced partial pressures of oxygen (2%) were used, Alcaligenes sp. strain L6 remained present in substantial numbers after three transfers. Continuous culture experiments demonstrated that Alcaligenes sp. strain L6 was able to outcompete Pseudomonas sp. strain A3 under oxygen-as well as under carbon-limiting conditions as long as the dilution rate remained below 0.136 h 3I (low oxygen) and below 0.178 h 3I (high oxygen). These results support the hypothesis that organisms metabolising chlorobenzoate via the gentisate pathway may play a significant role in natural ecosystems where xenobiotic compounds and naturally produced aromatics occur at very low concentrations and in combination with limiting oxygen tensions. z

Biodegradation of chlorobenzene under hypoxic and mixed hypoxic-denitrifying conditions

“…Different levels as observed during CB conversion are assumed to be stabilized by different CC12Os activities specific to each investigated culture and were shown to correspond to the oxygen affinity of the respective CC12O (Balcke GU et al 2007 (submitted)). This is of major importance because the accumulation of catechols is critical due to inhibitory effects on the degradation of aromatic compounds (Fritz et al 1991;Pé rez-Pantoja et al 2003;Schweigert et al 2001), and only few bacterial strains were reported to achieve productive turnover of catechols at severe oxygen limitation (Krooneman et al 1998;Kukor and Olsen 1996). Extremely low steady state dissolved oxygen concentrations as measured for the consortium (Fig.…”

“…Typically, microorganisms compensate for low oxygen availability by the expression of oxygenrequiring enzymes adapted to function in hypoxic environments as found for terminal oxidases (Otten et al 2001;Rice and Hempfling 1978;Tseng et al 1996) and for dioxygenases of different organisms (Balcke GU et al 2007 (submitted); Krooneman et al 1998;Kukor and Olsen 1996), or they compensate by elevating the synthesis of such enzymes in response to oxygen limitation (Dikshit et al 1990). …”

“…The following enzymes are involved: A, chlorobenzene 1,2-dioxygenase; B, chlorobenzene-cis-1,2-dihydrodiol dehydrogenase; C, chlorocatechol 1,2-dioxygenase; D, chloromuconate cycloisomerase; E, dienelactone hydrolase; F, maleylacetate reductase; G, terminal oxidoreductase, TCC = tricarboxylic acid cycle. Transfer of reducing equivalents [H] generated in the TCC to oxygen or nitrate takes place via the respiratory chain et al 1998;Vogt et al 2004b) reflects insufficient activity of chlorocatechol 1,2-dioxygenase (CC12O). Also the excretion of CM has been observed under hypoxic conditions (Balcke et al 2004 and2007 (submitted)), but a simple biochemical explanation for its accumulation is elusive.…”

Microbial transformation of chlorinated benzoates

“…CPE2 25-DCBc Fava et al (1993Fava et al ( , 1996 3-CBc (Johnston et al 1972;Hartmann et al 1979;Focht and Shelton 1987;Sahasrabudhe et al 1988;Hernandez et al 1991), 4-CBc (Hartmann et al 1979;Reineke and Knackmuss 1980;Karasevich and Zaitsev 1984;Shimao et al 1989;Hernandez et al 1991;Chae and Kim 1997;Kim and Picardal 2000), 2,5-DCBc (Miguez et al 1990) and 3,5-DCBc (Hartmann et al 1979;Reineke and Knackmuss 1980). Direct measurement of bacterial growth linked to the utilization of the chlorobenzoate provides additional evidence which has been observed in the case of 2-CBc (Sylvestre et al 1989), 3-CBc (Hartmann et al 1979;Focht and Shelton 1987;Hernandez et al 1991;Muller et al 1996;Krooneman et al 1998), 4-CBc (Shimao et al 1989;Muller et al 1996;Kim and Picardal 2000;Yi et al 2000;Rodrigues et al 2001), 2,5-DCBc (Miguez et al 1990) and 3,5-DCBc (Hartmann et al 1979). Lastly, evidence of biodegradation is also based on the conversion of carbon in chlorobenzoates to CO 2 .…”

Characterization of 3-chlorobenzoate degrading aerobic bacteria isolated under various environmental conditions

“…Under both oxygen and 3CBA limiting conditions it was competitively superior to a Pseudomonas sp. which degraded 3‐chlorobenzoate via chlorocatechol [13]. Based on these observations we speculated that enrichment cultures with either a reduced partial pressure of oxygen or under 3CBA limiting conditions will be dominated by bacteria using the gentisate or protocatechuate pathway (gp‐type of bacteria) and not by bacteria using the catechol pathway (cat‐type bacteria).…”