Degradation of BTEX by anaerobic bacteria: physiology and application

Pollution of the environment with aromatic hydrocarbons, such as benzene, toluene, ethylbenzene and xylene (so-called BTEX) is often observed. The cleanup of these toxic compounds has gained much attention in the last decades. In situ bioremediation of aromatic hydrocarbons contaminated soils and groundwater by naturally occurring microorganisms or microorganisms that are introduced is possible. Anaerobic bioremediation is an attractive technology as these compounds are often present in the anoxic zones of the environment. The bottleneck in the application of anaerobic techniques is the lack of knowledge about the anaerobic biodegradation of benzene and the bacteria involved in anaerobic benzene degradation. Here, we review the existing knowledge on the degradation of benzene and other aromatic hydrocarbons by anaerobic bacteria, in particular the physiology and application, including results on the (per)chlorate stimulated degradation of these compounds, which is an interesting new alternative option for bioremediatio

Evidence for perchlorates and the origin of chlorinated hydrocarbons detected by SAM at the Rocknest aeolian deposit in Gale Crater

A single scoop of the Rocknest aeolian deposit was sieved (< 150 µm), and four separate sample portions, each with a mass of ~50 mg, were delivered to individual cups inside the Sample Analysis at Mars (SAM) instrument by the Mars Science Laboratory rover's sample acquisition system. The samples were analyzed separately by the SAM pyrolysis evolved gas and gas chromatograph mass spectrometer analysis modes. Several chlorinated hydrocarbons including chloromethane, dichloromethane, trichloromethane, a chloromethylpropene, and chlorobenzene were identified by SAM above background levels with abundances of ~0.01 to 2.3 nmol. The evolution of the chloromethanes observed during pyrolysis is coincident with the increase in O_2 released from the Rocknest sample and the decomposition of a product of N‐methyl‐N‐(tert‐butyldimethylsilyl)‐trifluoroacetamide (MTBSTFA), a chemical whose vapors were released from a derivatization cup inside SAM. The best candidate for the oxychlorine compounds in Rocknest is a hydrated calcium perchlorate (Ca(ClO_4)_2·nH_2O), based on the temperature release of O_2 that correlates with the release of the chlorinated hydrocarbons measured by SAM, although other chlorine‐bearing phases are being considered. Laboratory analog experiments suggest that the reaction of Martian chlorine from perchlorate decomposition with terrestrial organic carbon from MTBSTFA during pyrolysis can explain the presence of three chloromethanes and a chloromethylpropene detected by SAM. Chlorobenzene may be attributed to reactions of Martian chlorine released during pyrolysis with terrestrial benzene or toluene derived from 2,6‐diphenylphenylene oxide (Tenax) on the SAM hydrocarbon trap. At this time we do not have definitive evidence to support a nonterrestrial carbon source for these chlorinated hydrocarbons, nor do we exclude the possibility that future SAM analyses will reveal the presence of organic compounds native to the Martian regolith

Large sulfur isotope fractionations in Martian sediments at Gale crater

Variability in the sulfur isotopic composition in sediments can reflect atmospheric, geologic and biological processes. Evidence for ancient fluvio-lacustrine environments at Gale crater on Mars and a lack of efficient crustal recycling mechanisms on the planet suggests a surface environment that was once warm enough to allow the presence of liquid water, at least for discrete periods of time, and implies a greenhouse effect that may have been influenced by sulfur-bearing volcanic gases. Here we report in situ analyses of the sulfur isotopic compositions of SO_2 volatilized from ten sediment samples acquired by NASA’s Curiosity rover along a 13 km traverse of Gale crater. We find large variations in sulfur isotopic composition that exceed those measured for Martian meteorites and show both depletion and enrichment in ^(34)S. Measured values of δ^(34)S range from −47 ± 14‰ to 28 ± 7‰, similar to the range typical of terrestrial environments. Although limited geochronological constraints on the stratigraphy traversed by Curiosity are available, we propose that the observed sulfur isotopic signatures at Gale crater can be explained by equilibrium fractionation between sulfate and sulfide in an impact-driven hydrothermal system and atmospheric processing of sulfur-bearing gases during transient warm periods

Deposition, Accumulation, and Alteration of Cl(-), NO3(-), ClO4(-) and ClO3(-) Salts in a Hyper-Arid Polar Environment: Mass Balance and Isotopic Constraints

The salt fraction in permafrost soils/sediments of the McMurdo Dry Valleys (MDV) of Antarctica can be used as a proxy for cold desert geochemical processes and paleoclimate reconstruction. Previous analyses of the salt fraction in MDV permafrost soils have largely been conducted in coastal regions where permafrost soils are variably affected by aqueous processes and mixed inputs from marine and stratospheric sources. We expand upon this work by evaluating permafrost soil/sediments in University Valley, located in the ultraxerous zone where both liquid water transport and marine influences are minimal. We determined the abundances of Cl(-), NO3(-, ClO4(-)and ClO3(-)in dry and ice-cemented soil/sediments, snow and glacier ice, and also characterized Cl(-) and NO3(-) isotopically. The data are not consistent with salt deposition in a sublimation till, nor with nuclear weapon testing fall-out, and instead point to a dominantly stratospheric source and to varying degrees of post depositional transformation depending on the substrate, from minimal alteration in bare soils to significant alteration (photodegradation and/or volatilization) in snow and glacier ice. Ionic abundances in the dry permafrost layer indicate limited vertical transport under the current climate conditions, likely due to percolation of snowmelt. Subtle changes in ClO4(-)/NO3(-) ratios and NO3(-) isotopic composition with depth and location may reflect both transport related fractionation and depositional history. Low molar ratios of ClO3(-)/ClO4(-) in surface soils compared to deposition and other arid systems suggest significant post depositional loss of ClO3(-), possibly due to reduction by iron minerals, which may have important implications for oxy-chlorine species on Mars. Salt accumulation varies with distance along the valley and apparent accumulation times based on multiple methods range from approximately 10 to 30 kyr near the glacier to 70-200 kyr near the valley mouth. The relatively young age of the salts and relatively low and homogeneous anion concentrations in the ice-cemented sediments point to either a mechanism of recent salt removal, or to relatively modern permafrost soils (less than 1 million years). Together, our results show that near surface salts in University Valley serve as an end-member of stratospheric sources not subject to biological processes or extensive remobilization

A review of sample analysis at mars-evolved gas analysis laboratory analog work supporting the presence of perchlorates and chlorates in gale crater, mars

Funding Information: The research reviewed in this paper was funded by the Mars Science Laboratory (MSL) project office. M.-P.Z. acknowledges funding from the Ministerio de Ciencia e Innovacion (ref. PID2019-104205GB-C21). The authors are grateful to the engineers and scientists of the MSL Curiosity team, who have made the mission possible and the reported data available. The authors would also like to thank the two anonymous reviewers who provided careful reviews that increased the quality of this manuscript. The authors would like to remember and recognize the contributions of Rafael Navarro-Gonzalez, a dedicated SAM and HABIT team member who passed away on 28 January 2021. Navarro-Gonzalez, who was a distinguished researcher, conducted laboratory experiments that demonstrated that chloromethanes could form through a reaction between perchlorates and organics during sample heating, which greatly advanced our understanding of perchlorates and organic detection on Mars. Data Availability Statement: SAM data are publicly available through the NASA Planetary Data System at: http://pds-geosciences.wustl.edu/missions/msl/sam.htm, which was updated in March 2021. See references for the original research articles that contain the data reviewed in this paper.Peer reviewedPublisher PD

Organic molecules in the Sheepbed Mudstone, Gale Crater, Mars

The Sample Analysis at Mars (SAM) instrument on board the Mars Science Laboratory Curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of Mars at Gale Crater. Central to this task is the development of an inventory of any organic molecules present to elucidate processes associated with their origin, diagenesis, concentration, and long-term preservation. This will guide the future search for biosignatures. Here we report the definitive identification of chlorobenzene (150–300 parts per billion by weight (ppbw)) and C_2 to C_4 dichloroalkanes (up to 70 ppbw) with the SAM gas chromatograph mass spectrometer (GCMS) and detection of chlorobenzene in the direct evolved gas analysis (EGA) mode, in multiple portions of the fines from the Cumberland drill hole in the Sheepbed mudstone at Yellowknife Bay. When combined with GCMS and EGA data from multiple scooped and drilled samples, blank runs, and supporting laboratory analog studies, the elevated levels of chlorobenzene and the dichloroalkanes cannot be solely explained by instrument background sources known to be present in SAM. We conclude that these chlorinated hydrocarbons are the reaction products of Martian chlorine and organic carbon derived from Martian sources (e.g., igneous, hydrothermal, atmospheric, or biological) or exogenous sources such as meteorites, comets, or interplanetary dust particles

Isolation and Identification of Chlorate-Reducing Hafnia sp. From Milk

Chlorate has become a concern in the food and beverage sector, related to chlorine sanitizers in industrial food production and water treatment. It is of particular concern to regulatory bodies due to the negative health effects of chlorate exposure. This study investigated the fate of chlorate in raw milk and isolated bacterial strains of interest responsible for chlorate breakdown. Unpasteurized milk was demonstrated to have a chlorate-reducing capacity, breaking down enriched chlorate to undetectable levels in 11 days. Further enrichment and isolation using conditions specific to chlorate-reducing bacteria successfully isolated three distinct strains of Hafnia paralvei . Chlorate-reducing bacteria were observed to grow in a chlorate-enriched medium with lactate as an electron donor. All isolated strains were demonstrated to reduce chlorate in liquid medium; however, the exact mechanism of chlorate degradation was not definitively identified in this study

On Chlorine Salts: Their Detection, Stability and Implications for Water on Mars and Europa

Chlorine salts (e.g. chlorides, chlorates and perchlorates) are an important factor in the stability of water on the surfaces of planetary bodies. Here we have shown that perchlorate and chlorate salts will lower the freezing point of water, allowing it to be liquid down to ~204 K. These salts will also slow down the evaporation rate, extending the lifetime of the liquid water solution. Chlorine salts have been detected on Mars, which has significant implications for the stability of water and hence its habitability. To study their effects on the stability of water on planetary surfaces, we need to first locate where these chlorine salts exist; this is typically done by remote sensing. To date, only anhydrous chlorides have been remotely detected, mostly due to the lack of hydrated chlorine salts in the spectral libraries used to identify features. To address this deficit, we measured reflectance spectra for numerous chlorine salts. Hydration bands were most common in near-infrared spectra, with band depth and width increasing with increasing hydration state. In the mid-infrared, oxychlorine salts exhibit spectral features due to Cl-O vibrations. We also investigated the spectral features of these salts at low temperature (80 K) to compare with remote sensing data of the outer satellites, specifically Europa. At low temperature, water bands become narrower and shallower than their room temperature counterparts. We show that chlorine salts do possess distinct spectral features that should allow for their detection by remote sensing, though care must be taken to acquire laboratory spectra of all hydrated phases at the relevant conditions (e.g. temperature, pressure) for the planetary body being studied