Large-scale bioreactor production of the herbicide-degrading Aminobacter sp. strain MSH1

Abstract

The Aminobacter sp. strain MSH1 has potential for pesticide bioremediation because it degrades the herbicide metabolite 2,6-dichlorobenzamide (BAM). Production of the BAM-degrading bacterium using aerobic bioreactor fermentation was investigated. A mineral salt medium limited for carbon and with an element composition similar to the strain was generated. The optimal pH and temperature for strain growth were determined using shaker flasks and verified in bioreactors. Glucose, fructose, and glycerol were suitable carbon sources for MSH1 (μ = 0.1 h(-1)); slower growth was observed on succinate and acetic acid (μ = 0.01 h(-1)). Standard conditions for growth of the MSH1 strain were defined at pH 7 and 25 °C, with glucose as the carbon source. In bioreactors (1 and 5 L), the specific growth rate of MSH1 increased from μ = 0.1 h(-1) on traditional mineral salt medium to μ = 0.18 h(-1) on the optimized mineral salt medium. The biomass yield under standard conditions was 0.47 g dry weight biomass/g glucose consumed. An investigation of the catabolic capacity of MSH1 cells harvested in exponential and stationary growth phases showed a degradation activity per cell of about 3 × 10(-9) μg BAM h(-1). Thus, fast, efficient, large-scale production of herbicide-degrading Aminobacter was possible, bringing the use of this bacterium in bioaugmentation field remediation closer to reality.

Degradation of trace concentrations of the persistent groundwater pollutant 2,6-dichlorobenzamide (BAM) in bioaugmented rapid sand filters

“…A specific BAM degradation rate of 4 Â 10 À13 mg BAM/cell/minute can then be calculated assuming 50% degradation of the inlet 0.2 mg/L BAM in the upper 20 cm with 10 8 /cm 3 MSH1-bacteria and a water residence time of 4 min. This specific rate is close to the 10 À12 mg BAM/ cell/minute previously reported for the degradation of 3 mg/L BAM in laboratory columns (Albers et al, 2014) but lower than 1% of the 10 À10 mg BAM/cell/minute reported for batch experiments (Simonsen et al, 2012;Schultz-Jensen et al, 2014). If similar BAM degradation rates were obtained for the inoculated bacteria as reported for batch experiments, the apparently stable population of 10 7 MSH1-bacteria/cm 3 would be enough to degrade the BAM.…”

Genetic (In)stability of 2,6-Dichlorobenzamide Catabolism in Aminobacter sp. Strain MSH1 Biofilms under Carbon Starvation Conditions

“…This relates first of all to its cultivation under high-nutrient conditions to produce sufficient biomass for bioaugmentation. Recently, Schultz-Jensen et al (25) presented optimal conditions for culturing MSH1 at high densities. Those authors cultured the strain using glucose as the nonselective C source, and according to our calculations, the Dcba ϩ phenotype might have dropped to 5% of the total MSH1 population.…”

“…Those authors cultured the strain using glucose as the nonselective C source, and according to our calculations, the Dcba ϩ phenotype might have dropped to 5% of the total MSH1 population. The propagated final MSH1 suspension in its entirety tested positive for BAM mineralization, but the BAM-catabolic capacity at the single-cell level was not tested (25). During cultivation prior to bioaugmentation, MSH1 cultures need to be monitored for the occurrence of the Dcba ϩ phenotype and preferably precultured under selective conditions prior to mass cultivation in reactors.…”

Degradation of three benzonitrile herbicides by AminobacterMSH1 versus soil microbial communities: pathways and kinetics

“…MSH1, isolated from a former plant nursery, was used in this study. Cells were precultured in glucose‐amended minimal medium MSNC at pH 7, because this has previously been reported to give a high yield of degradation‐active biomass . Cells were harvested in the late exponential phase, washed twice and resuspended in glucose‐free MSN (pH 7).…”

“…We investigated the mineralization potential of benzonitrile herbicides at two pH values appropriate for the Aminobacter MSH1. At pH 7, MSH1 was isolated, and grows fastest; at pH 6, MSH1 behaved most steadily (was not acidifying the medium while growing) . Samples were assayed in three replicates.…”