The Combined Effects of Additives on the Conventional and High-Temperature Performance Properties of Warm Mix Asphalt Binders

The present study investigates the effects of the simultaneous use of two additives, an organosilane warm mix asphalt (WMA) agent and a grade-bumping polyolefin compound, on the conventional and high-temperature performance properties of a paving grade 50/70 bitumen and a polymer-modified 45/80-55 bitumen. The WMA agent and polyolefin additive were introduced to the binders at rates of up to 0.3% and 2%, respectively. The base asphalt binders and their blends with the additives were tested before and after aging in a rolling thin film oven test at a temperature of 143 °C. The effects of the investigated additives were found to be dependent on the type of base binder and its aging state. It was generally observed that the WMA additive decreased the performance of the asphalt binders and limited the effects of the other additive, which increased the high-temperature stiffness and non-recoverable compliance of the blends. This interaction amounted to as much as an approx. 20% decrease in high-temperature stiffness and non-recoverable compliance of the binders. The additives caused a small increase in the elasticity of the binders and improved their creep performance when measured in multiple stress creep recovery tests.

Simulation of the Time Needed for Long-Term Asphalt Ageing in the Rolling Thin Film Oven Relative to That of the Pressure Ageing Vessel

Rheological test standards require asphalt samples, both original and under ageing conditions. The most common laboratory equipment in specifications for short-term and long-term ageing simulation tests are the rolling thin film oven (RTFO) and the pressure ageing vessel (PAV). However, the cost of acquiring PAV and the duration of long-term ageing tests can be a limiting factor. This work aimed to establish the equivalent time of the long-term ageing test in the RTFO that corresponds to the PAV. For this, the Brazilian asphalt PEN 50/70, specified by penetration, was aged at different times (85, 170, 255, and 340 min) in the RTFO at the standard temperature (163 °C). For each time, using a dynamic shear rheometer (DSR), tests such as Multiple Stress Creep Recovery (MSCR) and Linear Amplitude Sweep (LAS) were performed, and the rheological properties (complex modulus (G*) and phase angle (δ)) were measured. The same tests were conducted on the samples aged in the long term and in the PAV. The test parameters obtained from applying different times while using the RTFO were compared with the PAV results, and the equivalent time was settled through linear regression, resulting in 300 min. In order to confirm the equivalent time, samples aged in the RTFO for 300 min were assessed using the same rheological tests, and the parameters were compared to those obtained after PAV ageing. At the equivalent time, the difference between RTFO and the PAV for the rutting parameter (G*/sinδ, 58 °C) was 6%, while for the fatigue parameter (G*.sinδ, 19 °C), the difference was 1.0%. The MSCR non-recoverable creep compliance parameter differences, considering stress levels of 0.1 kPa and 3.2 kPa, were 9.7% and 11.7%, respectively. For the fatigue life obtained in the LAS test at strain levels of 1.25% and 2.5%, the difference between RTFO and PAV, at the equivalent time, was 7.6% and 7.8%, respectively. For the Brazilian unmodified asphalt PEN 50/70 and parameters evaluated in this work, 300 min is the equivalent time that simulates long-term ageing in the RTFO.

Ageing Evaluation of Foamed Polymer Modified Bitumen with Bio-Flux Additive

This paper presents the results of an analysis of the changes in the stiffness of asphalt binders modified with a bio-flux additive and subjected to the processes of foaming and short-term ageing. The purpose of the analyses was to determine changes in the rheological properties of asphalt binder as a result of technological processes characteristic of hot and warm mix asphalt technology. Three asphalt binders with similar penetration but varying degrees of polymer modification were tested: 50/70, 45/80-55 polymer-modified bitumen, and 45/80-80 highly modified bitumen. Tests were carried out on four groups of binders: original binders, foamed binders after 14 days of storage, non-foamed binders after Rolling Thin Film Oven Test (RTFOT) ageing, and foamed binders after 14 days of storage subjected to RTFOT ageing. The master curves of the complex shear modulus G* were analysed, and three indexes of binder stiffening were determined, characterising the investigated effects. The tests showed that some of the stiffening indices significantly depended on the degree of polymer modification and the content of the bio-flux additive. Moreover, it was found that the foaming process in the case of paving-grade bitumen and polymer-modified bitumen did not contribute to the additional stiffening of the binders.

Warm Mix Asphalt Binder Utilizing Water Foaming and Fluxing Using Bio-Derived Agent

The present paper investigates the effects of simultaneous mechanical foaming using water and fluxing with a bio-derived agent on the properties of three distinct asphalt binders: 50/70 paving-grade bitumen, 45/80-55 polymer-modified bitumen, and 45/80-80 highly modified asphalt binder. The testing involved classical tests for assessing binder consistency (penetration at 25 °C, ring and ball softening point, Fraass breaking point, and dynamic viscosity) as well as performance tests (high and low Superpave critical temperatures and multiple stress creep recovery). The tests included assessment directly after asphalt binder foaming and were repeated after a 14-day period. It was shown that bitumen foaming had only short-term effects on the asphalt binders, which did not persist in the repeated tests after 14 days. The fluxing agent that was utilized caused significant changes in the consistency of all asphalt binders. The changes in the performance characteristics of the 50/70 and 45/80-55 binders were severe and amounted to a significant decrease in high-temperature performance of these binders. On the other hand, an improvement in all performance characteristics in the case of the 45/80-80 asphalt binder was observed as a result of the applied processes, particularly when measured 14 days after foaming. This study shows that the simultaneous use of foaming and the fluxing additive decreased the dynamic viscosity of the 45/80-80 binder, while improving its properties relating the pavement performance.

Upcycling Discarded Shoe Polish into High Value-Added Asphalt Fluxing Agent for Use in Hot Mix Paving Applications

This research effort is geared towards revealing the latent potential of discarded shoe polish that might be repurposed as an asphalt fluxing agent for the construction of durable and sustainable road surfaces. To drive this creative invention, the effect of various proportions of waste shoe polish (e.g., 5, 10 and 15 wt. % WSP) on the performance of base AP-5 bitumen was inspected in great detail. A meticulous investigation of the chemical, physical, and rheological properties of the resultant combinations was carried out using a variety of state-of-the-art laboratory techniques, specifically: thin-layer chromatography-flame ionization detection (TLC-FID), Fourier transform-infrared spectroscopy (FT-IR), needle penetration, ring-and-ball softening point, Brookfield viscometer, ductility, flash/fire points, dynamic shear rheometer (DSR), multiple stress-creep recovery (MSCR), and bending beam rheometer (BBR) tests. The Iatroscan data disclosed that the continuous feeding of binder with WSP had a minor impact on SARA fractional distribution, regardless of aging. According to the FT-IR scan, the stepwise addition of WSP to the binder did not result in any significant chemical alterations in the blends. The combined outcomes of the DSR/BBR/empirical test methods forecasted that the partly bio-sourced additive would greatly improve the mixing-compaction temperatures, workability, and coating-adhesion properties of bituminous mixtures while imparting them with outstanding anti-aging/cracking attributes. In short, the utilization of waste shoe polish as a fluxing agent for hot asphalt mix production and application is not only safe, feasible, and affordable, but it has the potential to abate the pollution caused by the shoe-care market while simultaneously enhancing the overall performance of the pavement and extending its service lifespan.

Rheological, Aging, and Microstructural Properties of Polycarbonate and Polytetrafluoroethylene Modified Bitumen

Deterioration of asphalt pavements due to massive load of vehicles and climatic variation has demanded the use of pavements construction material with an excellent resilience characteristic, resistance to permanent deformation, and most importantly, a much longer service lifespan. The main structural distresses in pavement construction are permanent deformation at high temperatures and fatigue cracking under repetitive traffic loadings. To comprehensively investigate the performance of bitumen penetration grade (PG) 70 against rutting, fatigue, and high temperature cracking in hot mix asphalt (HMA) pavements, polycarbonate (PC) and polytetrafluoroethylene (PTFE) were used. The investigation of the internal structure, rheological, and physical properties of base and modified bitumen (MB) mixes with different percentages of modifiers (0%, 2.5%, and 5%) by weight were performed via scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) analysis, X-ray diffraction (XRD) pattern analysis, rolling thin-film oven test (RTFOT), pressurized aging vessel (PAV), dynamic shear rheometer (DSR), rotational viscosity (RV), and bending beam rheometer (BBR). The results of the RV test indicate that modification of neat bitumen with polycarbonate and polytetrafluoroethylene increased the viscosity for polycarbonate-modified bitumen (PCMB), polytetrafluoroethylene-modified bitumen (PTFEMB), and for a blend of PCMB-PTFEMB by 44%, 50%, and 55.75% at 135 °C and 111.10%, 127.80%, and 138.88% at 165 °C, accordingly. BBR test results revealed that modifiers increased the rigidity of neat bitumen by 74.8%, 75.8%, and 74.5% at −16 °C, −22 °C, and −28 °C, respectively.

Spent Graphite from End-of-Life Lithium-Ion Batteries (LIBs) as a Promising Nanoadditive to Boost Road Pavement Performance

To take swift action towards tackling the global pollution crisis of discarded lithium-ion batteries (LIBs) while reinforcing road structures, this investigation was undertaken. The influence of various proportions of spent graphite (e.g., 5, 10, and 15 wt.% SG), harvested from end-of-life LIBs, on the performance of base AP-5 asphalt cement was studied. Multiple laboratory techniques have been employed to characterize the internal physiochemical interaction between the additive and the binder. These techniques include: elemental analysis (EA), thin-layer chromatography-flame ionization detection (TLC-FID), Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), empirical test methods (e.g., penetration, softening point, viscosity, and ductility), dynamic shear rheometer (DSR), and multiple stress-creep recovery (MSCR). Prior to aging, SARA analysis demonstrated that the incremental SG addition into the AP-5 bitumen reduced the contents of saturates, aromatics, and resins, and increased the proportion of asphaltenes. After aging, the saturated and aromatic hydrocarbons kept decreasing; however, the resins increased and the asphaltenes declined. Accordingly, this has brought a progressive shift tendency in the stable–colloidal system for all binders from sol-state towards sol-gel-state. FT-IR scan revealed that the SG has no apparent chemical interaction with the binder, and is endowed solely with filling effects. XRD diagnosis highlighted that the steady SG incorporation into the binder amplified its crystallinity; thereby boosting the thermomechanical properties of mastics. SEM imaging unveiled that the lower-dose of SG exhibited higher compatibility within the bitumen matrix; nevertheless, the intermediate/higher-doses made the binder body relatively rougher. DSR/MSCR/conventional tests indicated that when the asphalt is blended with the graphitic powder under unaged/aged conditions, it becomes stiffer, more viscous, and less cohesive; thereby rendering it more resistant to deformation but not to cracking. In summary, it is promisingly proven that the SG could be successfully used as an asphalt additive and could be beneficial for improving paving performance and mitigating the pollution caused by dead LIBs as well.

Energy Efficient Routing Protocol in Sensor Networks Using Genetic Algorithm

In this paper, we examine routing protocols with the shortest path in sensor networks. In doing this, we propose a genetic algorithm (GA)-based Ad Hoc On-Demand Multipath Distance Vector routing protocol (GA-AOMDV). We utilize a fitness function that optimizes routes based on the energy consumption in their nodes. We compare this algorithm with other existing ad hoc routing protocols including LEACH-GA, GA-AODV, AODV, DSR, EPAR, EBAR_BFS. Results prove that our protocol enhances the network performance in terms of packet delivery ratio, throughput, round trip time and energy consumption. GA-AOMDV protocol achieves average gain that is 7 to 22% over other protocols. Therefore, our protocol extends the network lifetime for data communications.

Exploring the technological acceptance of a mobile learning tool used in the teaching of an indigenous language

Language is the primordial element for cultural transfer in indigenous communities; if it is not practiced, there is a risk of losing it and with it, a large part of the history of a community. Ecuador is a multicultural and multiethnic country with 18 indigenous peoples. Currently, in this country, some native languages are at risk of disappearing due to factors such as racial discrimination, underestimation of the language, and, above all, the lack of interest and motivation of the new generations to learn this language. Information technologies have made it possible to create mobile applications such as games, dictionaries, and translators that promote the learning of the Kichwa language. However, the acceptance of technology has not been evaluated, nor the intention to involve mobile devices in the process of teaching this language. Subsequently the objective of this work is to explore the acceptance of technology and the use of mobile devices to motivate the learning of the Kichwa language. For this purpose, the mobile application "Otavalo Rimay" was used with several students of a Kichwa language learning center. The methodology used to verify the hypothesis of this work was Design Sciences Research (DSR) together with the theory of acceptance and use of technology (UTAUT). The instrument used for this evaluation was a survey carried out after the use of the mobile application. The statistical analysis of the results obtained indicates characteristics such as the utility and perceived ease of use, positively influence students to motivate the use of mobile devices in learning a language. The results also show the great technological acceptance by students for learning and confirm that currently, mobile learning is accepted for use in education.

Statistical Evaluation of the Material-Source Effects on the DSR Rheological Properties of Plant-Mix Extracted Asphalt-Binders

The work presented in this paper was carried out to statistically evaluate and quantify the material-source effect on the asphalt-binder's rheological properties using Analysis of Variance (ANOVA) and Tukey's Honestly Significant Difference (Tukey´s HSD) test. The study focused on the Asphalt-Binders' high-temperature rheological properties, namely, the G*, δ, G*/Sin(δ) and G*/(1 - (1/Tan(δ)Sin(δ))) parameters, measured using the Dynamic Shear Rheometer (DSR) device. The DSR data analyzed in the study were extracted from the Texas flexible pavements and overlays database, namely, the Texas Data Storage System (DSS), covering two Asphalt-Binders (ABs), performance grade (PG) 64-22 and PG 76-22 plant-mix extracted ABs that were treated as rolling thin film oven (RTFO) residue, and sourced from 14 different suppliers. The study findings substantiate that material-source has an effect on the high-temperature rheological properties of ABs. Additionally, it was also concluded that in as much as performance superiority and costs are crucial issues in deciding the AB source/provider, consistency and quality aspects cannot be disregarded. Therefore, material-source effects should be inclusively evaluated from both performance (rheological properties) and quality (consistence) standpoints as well as cost considerations when choosing a supplier. In general, the study contributes to the state-of-the-art enrichment on aspects of material-source effects on RTFO residue ABs' high-temperature rheological properties, consistency, variability, and data quality.

Optimal design and experiment study of the double spherical rotor of the MSCSG

The magnetically suspended control and sense gyroscope (MSCSG) integrates spacecraft attitude measurement and control function; this paper proposes a double spherical rotor (DSR) for MSCSG. The DSR realizes the five degrees of freedom (DOFs) full active control and full channel magnetic path decoupling by the following design: the spherical axial/radial reluctance magnetic bearings are adopted to control the 3DOFs translation of rotor in the range of double spherical envelope, Lorentz force magnetic bearing (LFMB) is used to precisely drive the 2DOFs universal deflection of rotor. The optimization model is established based on the structural mechanical analysis, taking the deviation between rotor centroid and shape center as the optimization objective, choosing the first order resonance frequency, maximum equivalent stress, rigid body displacement, polar moment of inertia and inertia ratio as constraints. Then the DSR is optimized and simulated by the finite element, the MSCSG principle prototype based on DSR is successfully developed, the online dynamic balance experiment and modal test of the DSR are conducted, where the vibration amount of the DSR decreases from 20 μm before the experiment to 0.14 μm after the experiment, which decreases by 99.3%, the first test modal is 2881 Hz which is 5% different from the finite element simulation value of 3034 Hz. The results show that the DSR has the good mechanical properties and magnetic circuit decoupling characteristics.

Marker Assisted Development and Characterization of Herbicide Tolerant Near Isogenic Lines of a Mega Basmati Rice Variety, "Pusa Basmati 1121"

BACKGROUND

Direct-seeded rice (DSR) is a potential technology for sustainable rice farming as it saves water and labor. However, higher incidence of weed under DSR limits productivity. Therefore, there is a need to develop herbicide tolerant (HT) rice varieties.

RESULTS

We used marker assisted backcross breeding (MABB) to transfer a mutant allele of Acetohydroxy acid synthase (AHAS) gene, which confers tolerance to imidazolinone group of herbicides from the donor parent (DP) "Robin" into the genetic background of an elite popular Basmati rice variety, Pusa Basmati 1121 (PB 1121). Foreground selection was done using the AHAS gene linked Simple Sequence Repeat (SSR) marker RM6844 and background selection was performed using 112 genome-wide SSR markers polymorphic between PB 1121 and Robin. Phenotypic selection for agronomic, Basmati grain and cooking quality traits in each generation was carried out to improve the recovery of recurrent parent phenome (RPP). Finally, a set of 12 BC₄F₄ near isogenic lines (NILs), with recurrent parent genome (RPG) recovery ranging from 98.66 to 99.55% were developed and evaluated. PB 1121-HT NILs namely 1979-14-7-33-99-10, 1979-14-7-33-99-15 and 1979-14-7-33-99-66 were found superior to PB 1121 in yield with comparable grain and cooking quality traits and herbicide tolerance similar to Robin.

CONCLUSION

Overall, the present study reports successful development of HT NILs in the genetic background of popular Basmati rice variety, PB 1121 by introgression of mutated AHAS allele. This is the first report on the development of HT Basmati rice. Superior NILs are being evaluated in the national Basmati trials, the release of which is likely to provide a viable option for the adoption of DSR technology in Basmati rice cultivation.

The characterization of a short chain dehydrogenase/reductase (SDRx) in Comamonas testosteroni

C. testosteroni is a research topic that can degrade steroid hormones into water and carbon dioxide through a series of enzymes in the body. Short-chain dehydrogenase (SDR) are a class of NAD (P) H-dependent oxidoreductases in C. testosteroni. Its main function is catalyzing the redox of the hydroxyl/ketone group of the hormone. In this paper, a SDR gene(SDRx) is cloned from C. testosteroni ATCC11996 and expressed. The polyclonal antibody was prepared and the SDRx gene knocked out by homologous recombination. Wild type and mutant C. testosteroni induced by testosterone, estradiol, estrone and estriol. The growth curves of the bacteria were measured by spectrophotometer. ELISA established the expression of SDRx protein, and high-performance liquid chromatography(HPLC) detected the contents of various hormones. The results show that the growth of wild type was faster than mutant type induced by testosterone. The concentration of SDRx is 0.318 mg/ml under testosterone induction. It has a great change in steroid hormones residue in culture medium measured by HPLC: Testosterone residue in the mutant type group was 42.4 % more than the wild type in culture medium. The same thing happens with induced by estrone. In summary, this SDRx gene involved in the degradation of testosterone and estradiol, and effects the growth of C. testosteroni.

Trait-based mapping to identify the genetic factors underlying anaerobic germination of rice: Phenotyping, GXE, and QTL mapping

BACKGROUND

Anaerobic germination is one of the most important traits for rice under direct-seeded conditions. The trait reduces risk of crop failure due to waterlogged conditions after seeding and allows water to be used as a means of weed control. The identification of QTLs and causal genes for anaerobic germination will facilitate breeding for improved direct-seeded rice varieties. In this study, we explored a BC₁F_2:3 population developed from a cross between BJ1, an indica landrace, and NSIC Rc222, a high-yielding recurrent parent. The population was phenotyped under different screening methods (anaerobic screenhouse, anaerobic tray, and aerobic screenhouse) to establish the relationship among the methods and to identify the most suitable screening method, followed by bulk segregant analysis (BSA) to identify large-effect QTLs.

RESULTS

The study showed high heritability for survival (SUR) under all three phenotyping conditions. Although high correlation was observed within screening environments between survival at 14 and 21 days after seeding, the correlation across environments was low. Germination under aerobic and anaerobic conditions showed very low correlation, indicating the independence of their genetic control. The results were further confirmed through AMMI analysis. Four significant markers with an effect on anaerobic germination were identified through BSA. CIM analysis revealed qAG1-2, qAG6-2, qAG7-4, and qAG10-1 having significant effects on the trait. qAG6-2 and qAG10-1 were consistent across screening conditions and seedling age while qAG1-2 and qAG7-4 were specific to screening methods. All QTLs showed an effect when survival across all screening methods was analyzed. Together, the QTLs explained 39 to 55% of the phenotypic variation for survival under anaerobic conditions. No QTL effects were observed under aerobic conditions.

CONCLUSIONS

The study helped us understand the effect of phenotyping method on anaerobic germination, which will lead to better phenotyping for this trait in future studies. The QTLs identified through this study will allow the improvement of breeding lines for the trait through marker-assisted selection or through forward breeding approaches such as genomic selection. The high frequency of the BJ1 allele of these QTLs will enhance the robustness of germination under anaerobic conditions in inbred and hybrid rice varieties.

A comparative study on routing protocols for VANETs

Vehicular Ad Hoc Networks (VANETs) is an emerging area of research and have been gaining significant attention over recent years due to its role in designing intelligent transportation system. It includes vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) message flows, supported by wireless access technology such as, IEEE 1609 WAVE and IEEE 802.11p. One of the major scientific challenge in VANET implementation, is the design of routing protocol that could provide efficient and reliable node-to-node packet transmission. Routing in VANETs is a complex task in urban environment. This paper reports the overall performance evaluation of two existing routing protocols namely, Ad hoc On-Demand Distance Vector (AODV) and Dynamic Source Routing (DSR) for VANETs. This study aims at optimizing the selection of best possible routing protocol for providing reliability to data packet dissemination in an efficient way. The impact and effectiveness of existing topology based routing protocol for VANETs application has been evaluated through the use of NetSim software tool. The simulated results shows that a combination of proper channel model together with an efficient routing protocol enhance the link throughput of the VANET for a fixed network size. Further, performance evaluation also demonstrate the impact of network sizes and routing protocols on packet loss, packet delivery ratio, average end-to-end delay and overhead transmission.

A comparative study on routing protocols for VANETs

Vehicular Ad Hoc Networks (VANETs) is an emerging area of research and have been gaining significant attention over recent years due to its role in designing intelligent transportation system. It includes vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) message flows, supported by wireless access technology such as, IEEE 1609 WAVE and IEEE 802.11p. One of the major scientific challenge in VANET implementation, is the design of routing protocol that could provide efficient and reliable node-to-node packet transmission. Routing in VANETs is a complex task in urban environment. This paper reports the overall performance evaluation of two existing routing protocols namely, Ad hoc On-Demand Distance Vector (AODV) and Dynamic Source Routing (DSR) for VANETs. This study aims at optimizing the selection of best possible routing protocol for providing reliability to data packet dissemination in an efficient way. The impact and effectiveness of existing topology based routing protocol for VANETs application has been evaluated through the use of NetSim software tool. The simulated results shows that a combination of proper channel model together with an efficient routing protocol enhance the link throughput of the VANET for a fixed network size. Further, performance evaluation also demonstrate the impact of network sizes and routing protocols on packet loss, packet delivery ratio, average end-to-end delay and overhead transmission.

Investigation of the Effect of Induction Heating on Asphalt Binder Aging in Steel Fibers Modified Asphalt Concrete

Induction heating is a valuable technology to repair asphalt concrete damage inside. However, in the process of induction heating, induced particles will release a large amount of heat to act on asphalt binder in a short time. The purpose of this paper was to study the effect of induction heating on asphalt binder aging in steel fibers modified asphalt concrete. The experiments were divided into two parts: induction heating of Dramix steel fibers coated with asphalt binder (DA) and steel wool fibers modified asphalt concrete. After induction heating, the asphalt binders in the samples were extracted for testing aging indices with Fourier Transform Infrared (FTIR), Dynamic Shear Rheometer (DSR), and Four-Components Analysis (FCA) tests. The aging of asphalt binder was analyzed identifying the change of chemical structure, the diversification of rheological properties, and the difference of component. The experiments showed that the binder inside asphalt concrete began aging during induction heating due to thermal oxygen reaction and volatilization of light components. However, there was no peak value of the carbonyl index after induction heating of ten cycles, and the carbonyl index of DA was equivalent to that of binder in asphalt concrete after three induction heating cycles, which indicated the relatively closed environment inside asphalt concrete can inhibit the occurrence of the aging reaction.

Disguised as a Sulfate Reducer: Growth of the Deltaproteobacterium Desulfurivibrio alkaliphilus by Sulfide Oxidation with Nitrate

This study demonstrates that the deltaproteobacterium Desulfurivibrio alkaliphilus can grow chemolithotrophically by coupling sulfide oxidation to the dissimilatory reduction of nitrate and nitrite to ammonium. Key genes of known sulfide oxidation pathways are absent from the genome of D. alkaliphilus. Instead, the genome contains all of the genes necessary for sulfate reduction, including a gene for a reductive-type dissimilatory bisulfite reductase (DSR). Despite this, growth by sulfate reduction was not observed. Transcriptomic analysis revealed a very high expression level of sulfate-reduction genes during growth by sulfide oxidation, while inhibition experiments with molybdate pointed to elemental sulfur/polysulfides as intermediates. Consequently, we propose that D. alkaliphilus initially oxidizes sulfide to elemental sulfur, which is then either disproportionated, or oxidized by a reversal of the sulfate reduction pathway. This is the first study providing evidence that a reductive-type DSR is involved in a sulfide oxidation pathway. Transcriptome sequencing further suggests that nitrate reduction to ammonium is performed by a novel type of periplasmic nitrate reductase and an unusual membrane-anchored nitrite reductase.

Sulfide oxidation and sulfate reduction, the two major branches of the sulfur cycle, are usually ascribed to distinct sets of microbes with distinct diagnostic genes. Here we show a more complex picture, as D. alkaliphilus, with the genomic setup of a sulfate reducer, grows by sulfide oxidation. The high expression of genes typically involved in the sulfate reduction pathway suggests that these genes, including the reductive-type dissimilatory bisulfite reductases, are also involved in as-yet-unresolved sulfide oxidation pathways. Finally, D. alkaliphilus is closely related to cable bacteria, which grow by electrogenic sulfide oxidation. Since there are no pure cultures of cable bacteria, D. alkaliphilus may represent an exciting model organism in which to study the physiology of this process.

Carbon and Sulfur Cycling below the Chemocline in a Meromictic Lake and the Identification of a Novel Taxonomic Lineage in the FCB Superphylum, Candidatus Aegiribacteria

Mahoney Lake in British Columbia is an extreme meromictic system with unusually high levels of sulfate and sulfide present in the water column. As is common in strongly stratified lakes, Mahoney Lake hosts a dense, sulfide-oxidizing phototrophic microbial community where light reaches the chemocline. Below this "plate," the euxinic hypolimnion is anoxic, eutrophic, saline, and rich in sulfide, polysulfides, elemental sulfur, and other sulfur intermediates. While much is known regarding microbial communities in sunlit portions of euxinic systems, the composition and genetic potential of organisms living at aphotic depths have rarely been studied. Metagenomic sequencing of samples from the hypolimnion and the underlying sediments of Mahoney Lake indicate that multiple taxa contribute to sulfate reduction below the chemocline and that the hypolimnion and sediments each support distinct populations of sulfate reducing bacteria (SRB) that differ from the SRB populations observed in the chemocline. After assembling and binning the metagenomic datasets, we recovered near-complete genomes of dominant populations including two Deltaproteobacteria. One of the deltaproteobacterial genomes encoded a 16S rRNA sequence that was most closely related to the sulfur-disproportionating genus Dissulfuribacter and the other encoded a 16S rRNA sequence that was most closely related to the fatty acid- and aromatic acid-degrading genus Syntrophus. We also recovered two near-complete genomes of Firmicutes species. Analysis of concatenated ribosomal protein trees suggests these genomes are most closely related to extremely alkaliphilic genera Alkaliphilus and Dethiobacter. Our metagenomic data indicate that these Firmicutes contribute to carbon cycling below the chemocline. Lastly, we recovered a nearly complete genome from the sediment metagenome which represents a new genus within the FCB (Fibrobacteres, Chlorobi, Bacteroidetes) superphylum. Consistent with the geochemical data, we found little or no evidence for organisms capable of sulfide oxidation in the aphotic zone below the chemocline. Instead, comparison of functional genes below the chemocline are consistent with recovery of multiple populations capable of reducing oxidized sulfur. Our data support previous observations that at least some of the sulfide necessary to support the dense population of phototrophs in the chemocline is supplied from sulfate reduction in the hypolimnion and sediments. These studies provide key insights regarding the taxonomic and functional diversity within a euxinic environment and highlight the complexity of biogeochemical carbon and sulfur cycling necessary to maintain euxinia.

Denitrifying sulfide removal by Pseudomonas sp. C27 at excess carbon supply: mechanisms

Pseudomonas sp. C27 can effectively conduct mixotrophic denitrifying sulfide removal (DSR) reactions using both organic matters and sulfide as electron donors. This study conducted DSR tests using C27 and quantitatively analyzed the protein abundances at C/N=1.26, 1.63 and 3.0. At C/N=1.26, C27 principally adopted autotrophic denitrification pathway in DSR reaction. As C/N ratio was increased to 1.63, C27 enhanced heterotrophic denitrification pathway for removing nitrous compounds. As the C/N ratio was further increased to 3.0, C27 accelerated metabolism via coupled-cycles pathway. The C/N ratio for coupled-cycles pathway was estimated ranging 2.0-2.3 in the studied medium. Optimal C/N ratio of traditional DSR processes ranged 1.05-1.26. With the coupled-cycles pathway, the accessible C/N/S regime for C27 on DSR reactions is enlarged. Minor revision of the coupled-cycles pathway considering production of ammonium step was made.