Evaluation of microbial transport during aerobic bioaugmentation of an RDX-contaminated aquifer

Abstract

In situ bioaugmentation with aerobic hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)-degrading bacteria is being considered for treatment of explosives-contaminated groundwater at Umatilla Chemical Depot, Oregon (UMCD). Two forced-gradient bacterial transport tests of site groundwater containing chloride or bromide tracer and either a mixed culture of Gordonia sp. KTR9 (xplA (+)Km(R)), Rhodococcus jostii RHA1 (pGKT2 transconjugant; xplA (+)Km(R)) and Pseudomonas fluorescens I-C (xenB (+)), or a single culture of Gordonia sp. KTR9 (xplA (+); i.e. wild-type) were conducted at UMCD. Groundwater monitoring evaluated cell viability and migration in the injection well and downgradient monitoring wells. Enhanced degradation of RDX was not evaluated in these demonstrations. Quantitative PCR analysis of xplA, the kanamycin resistance gene (aph), and xenB indicated that the mixed culture was transported at least 3 m within 2 h of injection. During a subsequent field injection of bioaugmented groundwater, strain KTR9 (wild-type) migrated up to 23-m downgradient of the injection well within 3 days. Thus, the three RDX-degrading strains were effectively introduced and transported within the UMCD aquifer. This demonstration represents an innovative application of bioaugmentation to potentially enhance RDX biodegradation in aerobic aquifers.

Enhanced bioremediation of RDX and Co-Contaminants perchlorate and nitrate using an anaerobic dehalogenating consortium in a fractured rock aquifer

“…Although many RDX bioremediation studies have focused on biostimulation with an organic donor, recent studies have turned to bioaugmentation as an alternative bioremediation method to address the wide variety of site characteristics and the low cleanup goals for RDX. Initial bioaugmentation studies involved addition of aerobic RDXdegrading microbes (Crocker et al, 2015;Fuller et al, 2015Fuller et al, , 2017Michalsen et al, 2016). Achieving and maintaining aerobic conditions may be difficult in many contaminant plumes, however, especially when an organic donor source also needs to be added to support aerobic degradation.…”

Impact of glycerin and lignosulfonate on biodegradation of high explosives in soil

“…However, RDX can be utilized as a source of nitrogen under aerobic conditions when other nitrogen sources are limited (Binks et al 1995;Fuller et al 2010a). 4-nitro-2,4-diazabutanal (4-NDAB) and methylenedinitramine (MEDINA) are typically produced in aerobic biodegradation of RDX associated with the XplA⁄XplB enzymes (Fournier et al 2004;Fuller et al 2010a;Crocker et al 2015). Despite the potential for RDX biodegradation under aerobic conditions, several studies have reported that aerobic RDX degraders may not be widespread in soil and groundwater, resulting in little or no RDX degradation under aerobic conditions (Fuller et al 2010b;Crocker et al 2015;Fuller et al 2015).…”

Right on target: using plants and microbes to remediate explosives

“…Despite encouraging initial results, both bacterial numbers of Gordonia sp. KTR9 and xplA levels declined over time (Crocker et al 2015;Michalsen et al 2016;Fuller et al 2017). Factors preventing the accumulation of sufficient numbers of xplAB-containing soil bacteria to remove RDX-contamination, preventing downstream contamination are unknown, but xplAB-engineered plant endophytic, and associated rhizospheric bacterial communities indigenous to a contaminated site would be predicted to successfully reestablish in that environment.…”