Comparing Metabolic Functionalities, Community Structures, and Dynamics of Herbicide-Degrading Communities Cultivated with Different Substrate Concentrations

Abstract

Two 4-chloro-2-methylphenoxyacetic acid (MCPA)-degrading enrichment cultures selected from an aquifer on low (0.1 mg liter ؊1 ) or high (25 mg liter ؊1 ) MCPA concentrations were compared in terms of metabolic activity, community composition, population growth, and single cell physiology. Different community compositions and major shifts in community structure following exposure to different MCPA concentrations were observed using both 16S rRNA gene denaturing gradient gel electrophoresis fingerprinting and pyrosequencing. The communities also differed in their MCPA-mineralizing activities. The enrichments selected on low concentrations mineralized MCPA with shorter lag phases than those selected on high concentrations. Flow cytometry measurements revealed that mineralization led to cell growth. The presence of low-nucleic acid-content bacteria (LNA bacteria) was correlated with mineralization activity in cultures selected on low herbicide concentrations. This suggests that LNA bacteria may play a role in degradation of low herbicide concentrations in aquifers impacted by agriculture. This study shows that subpopulations of herbicide-degrading bacteria that are adapted to different pesticide concentrations can coexist in the same environment and that using a low herbicide concentration enables enrichment of apparently oligotrophic subpopulations.

Geographic distribution pattern of low and high nucleic acid content bacteria on a river-catchment scale

“…When first observed in FCM, LNA bacteria were considered to be inactivated or dead cells and HNA bacteria were proposed to be an indicator of active bacteria (Lebaron et al 2001). However, further studies have shown that LNA bacteria not only possess activities similar to HNA bacteria (Wang et al 2009), but also play an important role in various ecosystems (Gozdereliler et al 2013). Multiple novel physiological strategies, for example, simplified metabolism, high affinity and binding protein-dependent uptake system and special cellular membrane constitution, enable LNA bacteria to respond quickly to various stresses, such as low substrate concentrations (Salcher et al 2011), oxidising agents (Ramseier et al 2011) and viral infection (Bouvier and Maurice 2011).…”

Novel Insight into the Genetic Context of the cadAB Genes from a 4-chloro-2-methylphenoxyacetic Acid-Degrading Sphingomonas

“…recently isolated from MCPA-degrading bacterial communities that originated from a herbicide-impacted groundwater aquifer [14]. This transposable element, which contains the catabolic genes cadAB in a novel genetic context, was situated on a conjugative plasmid.…”

The potential for bioaugmentation of sand filter materials from waterworks using bacterial cultures degrading 4-chloro-2-methylphenoxyacetic acid

“…ERG4a and Sphingomonas sp. ERG5 have been isolated in the authors' lab from the MCPA‐degrading bacterial communities described in Gözdereliler et al …”

“…11,15,16 This problem could be enhanced by the bias toward selection of strains adapted to degradation at high concentrations in classical isolation attempts. 17 Thus, the initial step for evaluation of the applicability of strains for bioremediation purposes is to determine whether the bacteria can degrade realistic concentrations in the μg L −1 range.…”