Synergistic Degradation of Linuron by a Bacterial Consortium and Isolation of a Single Linuron-Degrading Variovorax Strain

Abstract

The bacterial community composition of a linuron-degrading enrichment culture and the role of the individual strains in linuron degradation have been determined by a combination of methods, such as denaturing gradient gel electrophoresis of the total 16S rRNA gene pool, isolation and identification of strains, and biodegradation assays. Three strains, Variovorax sp. strain WDL1, Delftia acidovorans WDL34, and Pseudomonas sp. strain WDL5, were isolated directly from the linuron-degrading culture. In addition, subculture of this enrichment culture on potential intermediates in the degradation pathway of linuron (i.e., N,O-dimethylhydroxylamine and 3-chloroaniline) resulted in the isolation of, respectively, Hyphomicrobium sulfonivorans WDL6 and Comamonas testosteroni WDL7. Of these five strains, only Variovorax sp. strain WDL1 was able to use linuron as the sole source of C, N, and energy. WDL1 first converted linuron to 3,4-dichloroaniline (3,4-DCA), which transiently accumulated in the medium but was subsequently degraded. To the best of our knowledge, this is the first report of a strain that degrades linuron further than the aromatic intermediates. Interestingly, the rate of linuron degradation by strain WDL1 was lower than that for the consortium, but was clearly increased when WDL1 was coinoculated with each of the other four strains. D. acidovorans WDL34 and C. testosteroni WDL7 were found to be responsible for degradation of the intermediate 3,4-DCA, and H. sulfonivorans WDL6 was the only strain able to degrade N,O-dimethylhydroxylamine. The role of Pseudomonas sp. strain WDL5 needs to be further elucidated. The degradation of linuron can thus be performed by a single isolate, Variovorax sp. strain WDL1, but is stimulated by a synergistic interaction with the other strains isolated from the same linuron-degrading culture.

Aerobic Mineralization of Nitroguanidine by Variovorax Strain VC1 Isolated from Soil

“…The strain was named Variovorax strain VC1. Variovorax species display multiple metabolic features including the biotransformation of the herbicides linuron 13 and diuron 14 and of synthetic (2,4-dinitrotoluene) and naturally occurring (3-nitrotyrosine) nitroaromatic compounds. 15,16 Growth of VC1 with NQ as the sole nitrogen source in the presence of 10 mM glucose is presented in Figure 2a.…”

New insights into a bacterial metabolic and detoxifying association responsible for the mineralization of the thiocarbamate herbicide molinate

“…The literature available shows that the distribution of metabolic steps among consortium members may rely upon different forms of association, namely crossfeeding (e.g. De Souza et al, 1998;Dejonghe et al, 2003), detoxification (e.g. Feigel & Knackmuss, 1993;Pelz et al, 1999) or supply of nutritional requirements (e.g.…”

“…The stability of consortia for long periods may be based upon a complex set of microbial interrelationships, which may include synergistic interactions involving carbon sharing, consumption of toxic metabolites, commensalism and/or competition (e.g. Pelz et al, 1999;Christensen et al, 2002;Dejonghe et al, 2003;Kato et al, 2005).…”

Herbicides: the Face and the Reverse of the Coin. An in Vitro Approach to the Toxicity of Herbicides in Non-Target Organisms

“…In the literature, we can find a significant amount of studies showing herbicide-sensitive bacteria (Cserháti et al, 1992;Hernando et al, 2003) and micro-algae (Nystrom et al, 1999;Li et al, 2008), as well as microorganisms that not only tolerate the presence of high concentrations of herbicides but also are able to degrade them (Dejonghe et al, 2003;Sorensen et al, 2003;Neumann et al, 2004). If, on the one hand, the biodegradation constitutes an important factor favoring the removal of herbicides from the environment, on the other hand, the elimination of sensitive microorganisms and the proliferation of the most tolerant ones, due to the selection pressure exerted by those compounds, may cause changes to the existing microbiological balances with potential adverse consequences for the ecosystem.…”

“…Thus, toxicological data concerning soil bacteria may be used to define upper limits for concentration of pollutants and to predict environmental toxicity risks; secondly, several of those microorganisms have shown to be able to thrive in high concentrations of organic pollutants converting them into non-toxic metabolites (Dejonghe et al, 2003;Sorensen et al, 2003;Neumann et al, 2004). The interest here is to use these microorganisms for the removal of pollutants from the environment (bioremediation).…”