Study on aerobic degradation of 2,4,6-trinitrotoluene (TNT) using Pseudarthrobacter chlorophenolicus collected from the contaminated site.

2,4,6-trinitrotoluene or TNT, a commonly used explosive, can pollute soil and groundwater. Conventional remediation practices for the TNT-contaminated sites are neither eco-friendly nor cost-effective. However, exploring bacteria to biodegrade TNT into environment-friendly compound(s) is an interesting area to explore. In this study, an indigenous bacterium, Pseudarthrobacter chlorophenolicus, strain S5-TSA-26, isolated from explosive contaminated soil, was investigated for potential aerobic degradation of TNT for the first time. The isolated strain of P. chlorophenolicus was incubated in a minimal salt medium (MSM) containing 120 mg/L TNT for 25 days at specified conditions. TNT degradation pattern by the bacterium was monitored at regular interval using UV-Vis spectrophotometry, high-performance liquid chromatography, and liquid chromatography mass spectrophotometric, by estimating nitrate, nitrite, and ammonium ion concentration and other metabolites such as 2,4-dinitrotoluene (DNT), 2-amino-4,6-dinitrotoluene (2-ADNT), and 2,4-diamino-6-nitrotoluene (2-DANT). It was observed that, in the presence of TNT, there was no reduction in growth of the bacterium although it multiplied well in the presence of TNT along with no considerable morphological changes. Furthermore, it was found that TNT degraded completely within 15 days of incubation. Thus, from this study, it may be concluded that the bacterium has the potential for degrading TNT completely with the production of non-toxic by-products and might be an important bacterium for treating TNT (i.e., a nitro-aromatic compound)-contaminated sites.

Aerobic biodegradation of high explosive hexahydro-1,3,5- trinitro-1,3,5-triazine by Janibacter cremeus isolated from contaminated soil.

OBJECTIVE: To evaluate the ability of Janibacter cremeus a soil bacterium isolated from explosive contaminated site in degradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and to study enzyme responsible for degradation. RESULTS: The isolate exhibited 88% degradation of RDX in 30 days of incubation. The biodegradation process followed the first order kinetics. The half- life of RDX was calculated to be 11.088 days. The RDX degradation process was complemented by concomitant release of nitrite ions with 0.78 mol of nitrite released per mole of RDX. The metabolites; Trinitroso- RDX, diamino-RDX, trimino-RDX, bis- (hydroxymethyl) nitramine and methylenedintramine derivative, viz, methylene- N- (hydroxy- methyl)- hydroxylamine- N-(hydroxymethyl) nitroamine corresponding to the molecular weights 174, 162, 132, 122 and 167 Da respectively were also detected. Nitroreductase enzyme was found to be responsible for RDX degradation. CONCLUSION: J. cremeus could degrade RDX as sole source of nitrogen, via three different pathways wherein, Nitroreductase enzyme was found to play a major role. The efficient degradation of RDX makes J. cremeus suitable in treatment of contaminated water and soil at field scale levels.

Biodegradation of octogen and hexogen by Pelomonas aquatica strain WS2-R2A-65 under aerobic condition.

Biodegradation ability of a native bacterial species Pelomonas aquatica strain WS2-R2A-65, isolated from nitramine explosive-contaminated effluent, for octogen (HMX) and hexogen (RDX) under aerobic condition has been explored in this study. Scanning electron microscopy indicated that the isolate WS2-R2A-65 retained its morphology both in the presence and absence of HMX or RDX. During an incubation period of 20 days, the isolate cometabolically degraded 78 and 86% of HMX and RDX with initial concentrations 6 and 60 mg L-1, respectively. The degradation mechanism followed the first-order kinetics for both the nitramines with a 50% degradation time of 9.9 and 7.7 days for HMX and RDX, respectively. Positive electrospray ionisation mass spectroscopy indicates that biodegradation of nitamines follows multiple degradation pathways with one involving ring cleavage via single-electron transfer to nitramines leading to the elimination of single nitrite ion as evident from the formation of methylenedinitramine (MEDINA) and its methyl derivatives. The other pathways involve the reduction of both the nitramines to their nitroso, hydroxylamino and amino derivatives. These metabolites get further ring cleaved to give secondary metabolites viz. N-hydroxymethylmethylenedintramine, N-nitrosoamino and hydrazinyl derivatives leading to simpler less hazardous end products. Thus, the isolate WS2-R2A-65 proves to be an efficient microbial species for bioremediation of nitramines-contaminated effluent.

A sketch of microbiological remediation of explosives-contaminated soil focused on state of art and the impact of technological advancement on hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) degradation.

When high-energy explosives such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), 2,4,6-trinitrotoluene (TNT) are discharged into the surrounding soil and water during production, testing, open dumping, military, or civil activities, they leave a toxic footprint. The US Environmental Protection Agency has labeled RDX as a potential human carcinogen that must be degraded from contaminated sites quickly. Bioremediation of RDX is an exciting prospect that has received much attention in recent years. However, a lack of understanding of RDX biodegradation and the limitations of current approaches have hampered the widespread use of biodegradation-based strategies for RDX remediation at contamination sites. Consequently, new bioremediation technologies are required to enhance performance. In this review, we explore the requirements for in-silico analysis for producing biological models of microbial remediation of RDX in soil. On the other hand, potential gene editing methods for getting the host with target gene sequences responsible for the breakdown of RDX are also reported. Microbial formulations and biosensors for detection and bioremediation are also briefly described. The biodegradation of RDX offers an alternative remediation method that is both cost-effective and ecologically acceptable. It has the potential to be used in conjunction with other cutting-edge technologies to further increase the efficiency of RDX degradation.

Bioaugmentation for remediation of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) contaminated soil using a clay based bioformulation.

Bioaugmentation is an important remediation strategy for hazardous organic compounds. A microcosm study was conducted to evaluate the remediation of soils contaminated with hazardous high explosive, Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) using an eco-friendly bioformulation. Janibacter cremeus, an enriched indigenous soil bacterium isolated from the explosive contaminated site was immobilized in a mixture of calcite and cocopeat for bioaugmentation. The developed bioformulation showed a consistent viability for 150 days, at 4 °C storage conditions. HMX at field concentrations was degraded in microcosms for 35 days under unsaturated (aerobic) and saturated (anoxic) moisture conditions. Negligible degradation was observed under unsaturated moisture conditions, whereas, saturated conditions led to substantial decrease in HMX. Mass spectrometric (MS) analysis revealed the formation of nitroso derivatives of HMX during the anoxic degradation. Also, observed was the presence of 5-hydroxy-4-nitro-2,4-diazapentanal, a precursor of 4- nitro-2,4-diazabutanal, which eventually could be mineralized. An inexpensive and natural carrier when chosen for immobilization of explosive degrading microbes was found to be effective in the in situ remediation of explosive.

A novel egg shell-based bio formulation for remediation of RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) contaminated soil.

Environmental contamination by secondary explosive has been posing threat to human health and the ecosystem. We investigated the potential of a novel bioformulation developed from poultry waste for the bioremediation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) contaminated soils. Eggshells and additives immobilized with an indigenous explosive degrading microbe Janibacter cremeus were utilized for the development of the wettable powder bioformulation. Treatments carried out under unsaturated and saturated soil conditions resulted in 62 and 73 % removal of RDX respectively in 35 days meeting the soil clean up goals. The saturated treatment sets exhibited better microbial growth during the study in terms of live cell count and total enzyme activity. The bacteria, J. cremeus was observed to exhibit significant release of nitrite under both unsaturated as well as saturated conditions. Mass spectrometric studies showed that, both the conditions lead to the formation of nitroso-derivatives of RDX. But under saturated condition, an intermediate, 5-hydroxy-4-nitro-2,4-diazapentanal was observed which is a precursor to 4-nitro-2,4-diazabuatnal ultimately leading to mineralization. An accessible bio resource from poultry waste when used as a carrier for explosive degrading microbe has proven effective for in situ remediation of explosive contaminated soils.

Aerobic biodegradation of HMX by Planomicrobium flavidum.

In this report, aerobic biodegradation of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine or high melting explosive (HMX), a highly explosive chemical by Planomicrobium flavidum strain S5-TSA-19, an isolate from an explosive-contaminated soil, was investigated. The isolate S5-TSA-19 degraded 70% of HMX in 20 days during which time nitrite ion was produced with the subsequent formation of metabolites, viz. methylenedintramine and N-methyl-N,N'-dinitromethanediamine with molecular weights 136 Da and 149 Da, respectively. The degradation mechanism was found to follow first-order kinetics with a half-life of 11.55 days and formation of above intermediates indicate single nitrite elimination pathway. The proliferation of isolate S5-TSA-19 in the absence of nitramines indicates the cometabolic degradation of HMX. Isolate S5-TSA-19 can thus be used as futuristic microbe for degradation of HMX at explosive-contaminated site.

Studies on photo-degradation of 2,4-dinitro toluene in aqueous phase.

The efficiency of different photo-degradation processes was evaluated for degrading 2,4-dinitro toluene (DNT) in aqueous phase. The rate and extent of DNT degradation and removal of total organic carbon (TOC) and total nitrogen (TN) contents were compared for direct photolytic and photo-oxidative reactions using various concentrations of H2O2 and Fenton's reagent with a 125 W medium pressure UV lamp. DNT was degraded rapidly under photo-oxidative conditions. Complete destruction was obtained using Fenton's reagent, wherein 100 ppm of DNT was degraded within 60 min of irradiation time. Removal of TOC and TN contents in the photo-Fenton system was 96% and 57%, respectively, after 2 h of UV irradiation. Degradation of DNT followed first order reaction kinetics. Photo-Fenton oxidation is found to be the most suitable technique to degrade DNT in aqueous phase.