Simultaneous degradation of nitroaromatic compounds TNT, RDX, atrazine, and simazine by Pseudomonas putida HK‐6 in bench‐scale bioreactors

Abstract

BACKGROUND: Environmental contamination by nitroaromatic compounds such as 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX), atrazine, and/or simazine (TRAS) generated as waste from military and agricultural activities is a serious worldwide problem. Microbiological treatment of these compounds is an attractive method because many explosives and herbicides are biodegradable and the process can be made cost-effective. We explored the feasibility of using cultures of Pseudomonas putida HK-6 for simultaneous degradation of TRAS with the aim of microbial application in wastewater treatment in bench-scale bioreactors.

Aerobic degradation 2,4-dinitrotoluene: effect of raw organic wastes and nitrogen amendment

“…It is noteworthy that fortification of the growth medium with yeast extract and KNO 3 awesomely supported proliferation of cells which, unfortunately, was not translated to 2,4-DNT consumption. Similar trend was previously documented by Cho et al[20] and Shen et al[21] while investigating conditions necessary for optimization of TNT degradation but not 2,4-DNT. By implication, amendment by exogenous nitrogen sources in systems inoculated with OSES2 may not be necessary since the organism could also utilize the substrate as a nitrogen source.Under this condition, the presence of additional nitrogen sources may present some metabolic bottlenecks to the organism thus impairing DNT degradation.Considering the hydrophobic nature of 2,4-DNT, the addition of Tween 80 in combination with KNO 3 increased the rate of 2,4-DNT degradation, biomass production and decreased the degradation time by 12 h in comparison with when the surfactant was used alone.…”

“…In another report, the degradation capability of Pseudomonas sp. strain HK-6 on some NACs (TNT, royal demolition explosive [RDX], atrazine and simazine) showed significant improvement when amended with different carbon sources [20] while fortification with nitrogen sources revealed no enhancement. Amendment with peptone and yeast also significantly improved the biodegradation of 2,4,6-trinitrophenol (TNP) and biomass formation using Rhodococcus pyridinivorans strain NT2 as a source of inoculum compared with non-fortification of the culture fluid [21].…”

Improved TNT detoxification by starch addition in a nitrogen-fixing Methylophilus-dominant aerobic microbial consortium

“…The (specific) rate of aerobic TNT degradation by the MIK consortium grown on starch (2.5 g/L) was greater (P < 0.05) than the rate for most of the previously known aerobic TNTdegrading bacterial isolates belonging to a variety of genus groups (Pseudomonas, Methylobacterium, and Rhizobium) [12,51,52] and was comparable to the rate for the strongest aerobic TNT degraders (Stenotrophomonas sp. OK-5 [33,53] and Pseudomonas putida HK-6 [31]) ( Table 2).…”

“…Approximately six major TNT degradation intermediates, including nitrite, nitrate, and DNT (probably produced via denitration pathway [6,25,54]), DANT, 2-ADNT and 4-ADNT (produced via nitro group reduction pathways [15,31]), were detected in all the TNT-degrading microcosms (Fig. 3).…”

“…To maintain the diversity and activity of microbial degradation in consortia or mixed cultures, it is practical and cost-effective to use slow-releasing complex carbon sources, such as molasses and starch [17,22,29,30]. In previous TNT degradation studies, the addition of molasses improved the rate of aerobic TNT degradation but not TNT detoxification, exhibiting the accumulation of potentially toxic TNT degradation intermediates [3,23,[31][32][33]. Starch, a plant-produced carbohydrate polymer, is another alternative slow-releasing complex carbon source for stimulating aerobic biodegrading bacteria, particularly for rhizospheric bacteria [34].…”