Biodegradation of RDX nitroso products MNX and TNX by cytochrome P450 XplA

Anaerobic transformation of the explosive RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) by microorganisms involves sequential reduction of N-NO(2) to the corresponding N-NO groups resulting in the initial formation of MNX (hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine). MNX is further reduced to the dinitroso (DNX) and trinitroso (TNX) derivatives. In this paper, we describe the degradation of MNX and TNX by the unusual cytochrome P450 XplA that mediates metabolism of RDX in Rhodococcus rhodochrous strain 11Y. XplA is known to degrade RDX under aerobic and anaerobic conditions, and, in the present study, was found able to degrade MNX to give similar products distribution including NO(2)(-), NO(3)(-), N(2)O, and HCHO but with varying stoichiometric ratio, that is, 2.06, 0.33, 0.33, 1.18, and 1.52, 0.15, 1.04, 2.06, respectively. In addition, the ring cleavage product 4-nitro-2,4,-diazabutanal (NDAB) and a trace amount of another intermediate with a [M-H](-) at 102 Da, identified as ONNHCH(2)NHCHO (NO-NDAB), were detected mostly under aerobic conditions. Interestingly, degradation of TNX was observed only under anaerobic conditions in the presence of RDX and/or MNX. When we incubated RDX and its nitroso derivatives with XplA, we found that successive replacement of N-NO(2) by N-NO slowed the removal rate of the chemicals with degradation rates in the order RDX > MNX > DNX, suggesting that denitration was mainly responsible for initiating cyclic nitroamines degradation by XplA. This study revealed that XplA preferentially cleaved the N-NO(2) over the N-NO linkages, but could nevertheless degrade all three nitroso derivatives, demonstrating the potential for complete RDX removal in explosives-contaminated sites.     

Shrinkage of Mirabelle Plum during Hot Air Drying as Influenced by Ultrasound-Assisted Osmotic Dehydration

Convective drying in hot air is still the most popular method applied to reduce the moisture content of fruits and vegetables. Conventional hot-air drying of Mirabelle plum is considered to be a slow and energy intensive process. This is due to the fact that the waxy skin of Mirabelle plum has low permeability to moisture, a fact which results in high shrinkage. The aim of this study was to investigate the effect of ultrasound-assisted osmotic dehydration pretreatment on shrinkage of Mirabelle plum as a function of moisture content with the end goal of optimizing operating conditions that minimize shrinkage of the produce during drying. Results showed that application of ultrasound-assisted osmotic dehydration led to a significant (p < 0.05) decrease in shrinkage (from 76.41 to 64.05%). A linear relation between moisture loss and shrinkage was observed. Results indicated that shrinkage may be easily estimated from changes in moisture content, and independent of the drying rate. Inversely, determination of shrinkage would provide an indirect indication of moisture content.     

Insights into the formation and degradation mechanisms of methylenedinitramine during the incubation of RDX with anaerobic sludge

In an earlier study, we reported that hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) biodegraded with domestic anaerobic sludge to produce a key RDX ring cleavage intermediate that was tentatively identified as methylenedinitramine (O2NNHCH2NHNO2) using LC/MS with negative electrospray ionization (ES-). Recently, we obtained a standard material of methylenedinitramine and thus were able to confirm its formation as the key initial RDX intermediate. In water alone or in the presence of sludge, methylenedinitramine decomposed to N20 and HCHO. Only in the presence of sludge HCHO converted further to carbon dioxide. To test our hypothesis that water was involved in the formation of methylenedinitramine during incubation of RDX with sludge, we allowed the energetic compound to biodegrade in several D2O/H2O solutions (90, 50, and 0% v/v). We observed three distinctive deprotonated or dedeuterated mass ions at 135, 136, and 137 Da that were attributed to the formation of nondeuterated (H-methylenedinitramine), monodeuterated (D1-methylenedinitramine), and dideuterated methylenedinitramine (D2-methylenedinitramine), respectively. Two controls were prepared in D2O both in the absence of sludge; the first contained methylenedinitramine, and the second contained RDX. Neither control produced any deuterated methylenedinitramine, thus excluding the occurrence of any abiotic D/H exchange between D2O and either methylenedinitramine or RDX. The results supported the occurrence of an initial enzymatic reaction on RDX, yet they did not provide compelling evidence on whether methylenedinitramine was an initial RDX enzymatic hydrolysis product or simply formed via the spontaneous hydrolysis of an anonymous initial RDX enzymatic product.     

Combined effect of bacteriophage and antibiotic on the inhibition of the development of antibiotic resistance in Salmonella typhimurium

Food Science and Biotechnology - This study was designed to evaluate the combined effects of bacteriophage and antibiotic on the reduction of the development of antibiotic-resistance in Salmonella...     

Online sequential extreme learning machine in river water quality (turbidity) prediction: a comparative study on different data mining approaches

As a measure of water quality, water turbidity might be a source of water pollution in drinking water resources. Henceforth, having a reliable tool for predicting turbidity values based on common water quantity/quality measured parameters is of great importance. In the present paper, the performance of the online sequential extreme learning machine (OS‐ELM) in predicting daily values of turbidity in Brandywine Creek, Pennsylvania, is evaluated. For this purpose, in addition to the developed OS‐ELM, several data‐driven models, that is, multilayer perceptron neural network (MLPANN), the classification and regression tree (CART), the group method of data handling (GMDH) and the response surface method (RSM) have been applied. The general findings of the study confirm the superiority of the OS‐ELM model over the other applied models so that the OS‐ELM improved the averaged RMSE of the predicted values 9.1, 11.7, 20.5 and 29.3% over the MLPANN, GMDH, RSM and CART models, respectively.     

Variations in isotopic composition of desalinated water

Variations in isotopic ratios of water samples collected from three plants functioning on two different desalination processes were evaluated by comparing their measured δ¹⁸O, δ¹⁷O and the δ²H isotopic ratios before and after desalination using a system based on tunable off‐axis integrated‐cavity‐output diode laser spectroscopy (OA‐ICOS). The δ¹⁸O, δ¹⁷O and the δ²H isotopic ratio measurements for water samples collected before desalination are compared against their peers of desalinated water from two desalination plants on the Arabian Gulf that are operating under the Multistage Flash (MSF) process. Also, variations in the δ¹⁸O, δ¹⁷O and the δ²H isotopic ratio measurements due to desalination from a Reversal Osmosis (RO) facility in Dhahran, Saudi Arabia were also reported and compared against variations in isotopic composition of water desalinated in two MSF plants.