Microbial Diversity in Engineered Haloalkaline Environments Shaped by Shared Geochemical Drivers Observed in Natural Analogues

Amelioration of the physicochemical properties enhanced the resilience of bacteria in bauxite residues

Bacteria-driven strategies have gained attention because of their effectiveness, viability, and cost-efficiency in the soil formation process of bauxite residues. However, further investigation is needed to enhance the extreme environment of bauxite residues and facilitate long-term sustainable development of bacteria. Here, soil, phosphogypsum, and leaf litter were selected as amendments, and soil and leaf litter were also used as bacterial inoculants in a 12-month microcosm experiment with bauxite residues. The results showed significant improvements in physicochemical properties, including alkalinity, organic carbon content, nutrient availability, and physical structure, when bauxite residue was mixed with amendments, particularly when different amendments were combined. The diversity, structure, and function of the bacterial community were significantly enhanced with the amelioration of the physicochemical properties. In the treated samples, especially those treated with a combination of different amendments, the relative abundance (RA) of alkali-resistant bacterial taxa decreased, whereas the RA of some common taxa found in normal soil increased, and the structure of the bacterial community gradually changed towards that of normal soil. A strong correlation between physicochemical and biological properties was found. These findings suggest that rational application of soil, phosphogypsum, and leaf litter effectively improves the environmental conditions of bauxite residues and facilitate long-term sustainable bacterial communities.

The potential of Hungarian bauxite residue isolates for biotechnological applications

Bauxite residue (red mud) is considered an extremely alkaline and salty environment for the biota. We present the first attempt to isolate, identify and characterise microbes from Hungarian bauxite residues. Four identified bacterial strains belonged to the Bacilli class, one each to the Actinomycetia, Gammaproteobacteria, and Betaproteobacteria classes, and two to the Alphaproteobacteria class. All three identified fungi strains belonged to the Ascomycota division. Most strains tolerated pH 8-10 and salt content at 5-7% NaCl concentration. Alkalihalobacillus pseudofirmus BRHUB7 and Robertmurraya beringensis BRHUB9 can be considered halophilic and alkalitolerant. Priestia aryabhattai BRHUB2, Penicillium chrysogenum BRHUF1 and Aspergillus sp. BRHUF2 are halo- and alkalitolerant strains. Most strains produced siderophores and extracellular polymeric substances, could mobilise phosphorous, and were cellulose degraders. These strains and their enzymes are possible candidates for biotechnological applications in processes requiring extreme conditions, e.g. bioleaching of critical raw materials and rehabilitation of alkaline waste deposits.

Coupling microbial and abiotic amendments accelerates in situ remediation of bauxite residue at field scale

Bauxite residue is a highly saline-sodic tailings material formed as a by-product of the Bayer process for alumina production. In situ remediation of bauxite residue has the potential to provide an effective means for accelerated rehabilitation of residue storage areas. However, previous work has predominantly only used chemical and physical amendments to date, limiting rates of pH neutralisation and extent of remediation. Combining these abiotic amendments with recently developed microbial biotechnology for pH neutralisation may transform bauxite residue into a productive soil material in a shorter timeframe. Here we investigated the effects of microbial and abiotic amendments (compost plus tillage), both in isolation and combined, on remediation of key bauxite residue properties in field scale trials (10 × 15 m × 2 m deep field plots). Triplicate residue samples were collected to 30 cm depth from each plot in quarterly field sampling campaigns. Changes in chemical and physical properties were monitored to assess remediation performance under different amendments. After one year, field plots amended with a microbial treatment had significantly (p < 0.05) lower average pH (8.99-9.46) in the upper 20 cm than the control (10.3). The combined microbial-abiotic treatment also had improved physical structure, higher organic C and lower electrical conductivity than the microbial treatment alone. The strong performance of the microbial-abiotic treatment is attributed to the combined benefits of bioneutralisation from microbial fermentation products, enhanced leaching of alkaline pore water and salts due to tillage and compost, and addition of highly stable C and N in compost. Combining novel microbial biotechnology with common abiotic amendments is therefore suggested for accelerating in situ remediation progress towards a material amenable for plant growth.

Alkaliphiles for comprehensive utilization of red mud (bauxite residue)-an alkaline waste from the alumina refinery

The mining industry has powered the human endeavor to make life more innovative, flexible, and comfortable. However, it has also led to concerns due to the increasing amount of mining and associated industrial waste. Special attention is highly desired for its proper management and safe disposal in the environment. The problem has only augmented with the increase in the mining costs because of the investments needed for ecological remediation after the mining operation. It is pertinent that the targeted technologies need to be developed to utilize mining and associated industrial waste as a secondary resource to ensure sustainable mining operations. Every perceived waste is a valuable resource that is needed to be utilized to create additional value. In this review, the case of alkaline bauxite residue (red mud)-alumina refinery waste has been discussed at length. The highlight of the proposed work is to understand the importance of alkaliphile-assisted biomining-a sustainable alternative to conventional metal recovery processes. Along with the recovery of metals, pH reduction of red mud is possible through biomining, which ultimately paves the way for its complete utilization. The unique adaptation strategies of alkaliphiles make them more suitable for biomining of red mud through bioleaching, biosorption, and bioaccumulation, which have been discussed here. Furthermore, we have focused on the potential of the indigenous microflora of red mud for metal recovery in addition to its neutralization. The study of indigenous alkaliphiles from red mud, including its isolation and propagation, is crucial for the industrial-scale application of alkaliphile-based technology and has been emphasized.

Recovery of microbial community in strongly alkaline bauxite residues after amending biomass residue

The aim of this study was to characterize the effects of cornstalk biomass amendments on microbial communities in bauxite residues (BRs) by phylogenetic analysis. Improvements in soil geochemical, physical, and biological properties were assessed to identify the major factors controlling microbial community development in BRs. After one year of incubation, the salinity and structure of the amended BRs had gradually improved, with pH dropping from 11.39 to 9.89, the exchangeable sodium percentage (ESP) dropping from 86.3% to 35.2%, and the mean weight diameter (MWD) rising from 0.12 mm to 0.38 mm. Further analysis of community level physiological profiles (CLPP) showed that the microbial utilization of different carbohydrates had shifted significantly, in addition to increases in the diversity index H' (0.7-7.34), U (2.16-3.14), and the average well color development (0.059-1.08). Over the one-year outside incubation, the dominant fungal phyla in the BRs had shifted gradually from Ascomycota (85.64%) to Ascomycota (52.07%) and Basidiomycota (35.53%), while the dominant bacterial phyla had shifted from Actinobacteria (38.47%), Proteobacteria (21.39%), and Gemmatimonadetes (12.72%) to Actinobacteria (14.87%), Proteobacteria (23.53%), and Acidobacteria (14.37%). Despite these shifts, microbial diversity remained lower in the amended BRs than in the natural soil. Further redundancy analysis indicated that pH was the major factor driving shifts in the bacterial community, while aggregates were the major factor driving shifts in the fungal community. This study demonstrated that amendment with cornstalk biomass shifted the microbial community in the BRs from halophilic groups to acidogenic groups by improving the soil environmental conditions.

Contrasted microbial community colonization of a bauxite residue deposit marked by a complex geochemical context

Bauxite residue is the alkaline byproduct generated during alumina extraction and is commonly landfilled in open-air deposits. The growth in global alumina production have raised environmental concerns about these deposits since no large-scale reuses exist to date. Microbial-driven techniques including bioremediation and critical metal bio-recovery are now considered sustainable and cost-effective methods to revalorize bauxite residues. However, the establishment of microbial communities and their active role in these strategies are still poorly understood. We thus determined the geochemical composition of different bauxite residues produced in southern France and explored the development of bacterial and fungal communities using Illumina high-throughput sequencing. Physicochemical parameters were influenced differently by the deposit age and the bauxite origin. Taxonomical analysis revealed an early-stage microbial community dominated by haloalkaliphilic microorganisms and strongly influenced by chemical gradients. Microbial richness, diversity and network complexity increased significantly with the deposit age, reaching an equilibrium community composition similar to typical soils after decades of natural weathering. Our results suggested that salinity, pH, and toxic metals affected the bacterial community structure, while fungal community composition showed no clear correlations with chemical variations.

Resilience of fungal flora in bauxite residues amended with organic matter and vermiculite/fly ash

The fungal community and soil geochemical, physical and biological parameters were analyzed, respectively, in bauxite residues (BRs) treated with organic matter and vermiculite/fly ash by phylogenetic analysis of ITS-18 S rRNA, community level physiological profiles (CLPP) and so on. The results indicated that after amendment of the BR, microbial utilization of carbohydrates and their enzyme activities were significantly increased, but fungal compositions at the phylum level were similar and dominated by the phylum of Ascomycota (82.05-98.96%, RA: relative abundance) after one year of incubation. The fungal taxa in the amended BR treatments, however, show significantly less alpha and beta diversity compared with the reference soils, although they still harbor a substantial novel taxon. The combined amendment of organic matter (OM) and vermiculite/fly ash significantly increases the fungal taxa at the genus and species level compared with solely OM amendment. The results of the following canonical correspondence analysis found that, over 90% variation of the fungal community could be explained by pH, OM and mean weight diameter (MWD) of aggregates; but the biological indicators, including urease (UR), dehydrogenase (DHA) and the value of average well color development (AWCD) could explain only 50% variation of the fungal flora in BRs. This paper indicated that resilience of fungal community in BRs was positively correlated with the BRs' improvement in fertility as well as biogeochemical properties, but alkalinity must be firstly decreased to the target level of BRs' rehabilitation.

The dynamic development of bacterial community following long-term weathering of bauxite residue

Bauxite residue is the industrial waste generated from alumina production and commonly deposited in impoundments. These sites are bare of vegetation due to the extreme high salinity and alkalinity, as well as lack of nutrients. However, long term weathering processes could improve residue properties to support the plant establishment. Here we investigate the development of bacterial communities and the geochemical drivers in bauxite residue, using Illumina high-throughput sequencing technology. Long term weathering reduced the pH in bauxite residue and increased its nutrients content. The bacterial community also significantly developed during long term weathering processes. Taxonomic analysis revealed that natural weathering processes encouraged the populations of Proteobacteria, Chloroflexi, Acidobacteria and Planctomycetes, whereas reducing the populations of Firmicutes and Actinobacteria. Redundancy analysis (RDA) indicated that total organic carbon (TOC) was the dominant factors affecting microbial structure. The results have demonstrated that natural weathering processes improved the soil development on the abandoned bauxite residue disposal areas, which also increased our understanding of the correlation between microbial variation and residue properties during natural weathering processes in Bauxite residue disposal areas.

Isolation of haloalkaliphilic fungi from Lake Magadi in Kenya

In this study we explored the cultivable fungal diversity in Lake Magadi and their secondary metabolite production. Isolation was done on alkaline media (Potato dextrose agar, Malt extract agar, Oatmeal agar and Sabouraud dextrose agar). A total of 52 unique isolates were recovered from the lake and were characterized using different techniques. Growth was observed at pH, temperature and salinity ranges of between 6 - 10, 25 °C - 40 °C and 0%–20% respectively. Phylogenetically, the isolates were affiliated to 18 different genera with Aspergillus, Penicillium, Cladosporium, Phoma and Acremonium being dominant. A screen for the ability to produce extracellular enzymes showed that different isolates could produce proteases, chitinases, cellulases, amylases, pectinases and lipases. Production of antimicrobial metabolites was noted for isolate 11M affiliated to Penicillium chrysogenum (99%). Cell free extracts and crude extracts from this isolate had inhibitory effects on Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Salmonella spp., Shigella spp., Candida albicans and fungal plant pathogens Schizophyllum commune, Epicoccum sorghinum strain JME-11, Aspergillus fumigatus strain EG11-4, Cladosporium halotolerans CBS 119416, Phoma destructive and Didymella glomerata). In this study we showed that different cultivation strategies can lead to recovery of more phylotypes from the extreme environments. Growth under different physiological characteristics typical of the soda lake environment (elevated temperature, pH and salts) confirmed the haloalkaliphilic nature of the fungal isolates. The use of suitable antimicrobial production media can also lead to discovery of more phylotypes producing diverse biocatalysts and bioactive metabolites.

Bacterial and archaeal spatial distribution and its environmental drivers in an extremely haloalkaline soil at the landscape scale

Background

A great number of studies have shown that the distribution of microorganisms in the soil is not random, but that their abundance changes along environmental gradients (spatial patterns). The present study examined the spatial variability of the physicochemical characteristics of an extreme alkaline saline soil and how they controlled the archaeal and bacterial communities so as to determine the main spatial community drivers.

Methods

The archaeal and bacterial community structure, and soil characteristics were determined at 13 points along a 211 m transect in the former lake Texcoco. Geostatistical techniques were used to describe spatial patterns of the microbial community and soil characteristics and determine soil properties that defined the prokaryotic community structure.

Results

A high variability in electrolytic conductivity (EC) and water content (WC) was found. Euryarchaeota dominated Archaea, except when the EC was low. Proteobacteria, Bacteroidetes and Actinobacteria were the dominant bacterial phyla independent of large variations in certain soil characteristics. Multivariate analysis showed that soil WC affected the archaeal community structure and a geostatistical analysis found that variation in the relative abundance of Euryarchaeota was controlled by EC. The bacterial alpha diversity was less controlled by soil characteristics at the scale of this study than the archaeal alpha diversity.

Discussion

Results indicated that WC and EC played a major role in driving the microbial communities distribution and scale and sampling strategies were important to define spatial patterns.

Microbial decomposition of biomass residues mitigated hydrogeochemical dynamics in strongly alkaline bauxite residues

Effective neutralization of strongly alkaline conditions in bauxite residues (BR) is the fundamental step to initiate the process of eco-engineering BR into growth substrate (or soil-like medium) for direct phytostabilization with pioneer plant species. The present study aimed to evaluate the effectiveness of microbial decomposition of organic matter (OM) (i.e., biomass residues) in neutralizing the strong alkalinity of residues under saturated conditions, together with the regulatory role of calcium sulfate (CaSO₄) addition. Admixing OM (i.e., sugarcane mulch, Lucerne hay) alone in the BR significantly lowered the porewater pH from 11.4 to around 9.0 by Day 7, which persisted until the end of incubation (Day 28). The pH reduction in the porewater of OM-amended BR coincided with the production of acidic organic compounds (mainly acetic acid). Diverse species of organotrophic bacteria (e.g., Enterobacteriales, Pasteurellales, Lactobacillales, and Streptophyta) were found to have colonized in the OM-amended BR, but which were dominated by haloalkaliphilic bacteria (e.g., Halomonas and Bacillaceae). The CaSO₄ addition in the OM-amended BR further lowered pH to 8.3 in the porewater. Besides, the bioneutralization effects resulted in dramatic reduction (>90%) of soluble Al in the porewater, which is a prerequisite to lowering Al toxicity in plants. At the same time, the levels of major cations (i.e., K, Ca, Mg) in the porewater were elevated by the OM + CaSO₄ amendment, which would facilitate subsequent leaching of these soluble salts to lower the salinity in the BR, and improve the diversity of organotrophic bacterial communities in the amended BR.

Salino-alkaline lime of anthropogenic origin a reservoir of diverse microbial communities

This paper presents study on the microbiome of a unique extreme environment - saline and alkaline lime, a by-product of soda ash and table salt production in Janikowo, central Poland. High-throughput 16S rDNA amplicon sequencing was used to reveal the structure of bacterial and archaeal communities in the lime samples, taken from repository ponds differing in salinity (2.3-25.5% NaCl). Surprisingly abundant and diverse bacterial communities were discovered in this extreme environment. The most important geochemical drivers of the observed microbial diversity were salinity, calcium ions, nutrients, and water content. The bacterial and archaeal communities in saline, alkaline lime were similar to those found in natural haloalkaline environments. Although the archaeal contribution to the whole microbial community was lower than 4%, the four archaeal genera Natronomonas, Halorubrum, Halobellus, and Halapricum constituted the core microbiome of saline, alkaline lime - a set of OTUs (> 0.1% of total archaeal relative abundance) present in all samples under study. The high proportion of novel, unclassified archaeal and bacterial sequences (not identified at 97% similarity level) in the 16S rRNA gene libraries indicated that potentially new genera, especially within the class of Thermoplasmata inhabit this unique environment.

Extreme Geochemical Conditions and Dispersal Limitation Retard Primary Succession of Microbial Communities in Gold Tailings

Microbial community succession in tailings materials is poorly understood at present, and likely to be substantially different from similar processes in natural primary successional environments due to the unusual geochemical properties of tailings and the isolated design of tailings storage facilities. This is the first study to evaluate processes of primary succession in microbial communities colonizing unamended tailings, and compare the relative importance of stochastic (predominantly dust-borne dispersal) and deterministic (strong selection pressures from extreme geochemical properties) processes in governing community assembly rates and trajectories to those observed in natural environments. Dispersal-based recruitment required > 6 months to shift microbial community composition in unamended, field-weathered gold tailings; and in the absence of targeted inoculants, recruitment was dominated by salt- and alkali-tolerant species. In addition, cell numbers were less than 10⁶ cells/g tailings until > 6 months after deposition. Laboratory experiments simulating microbial cell addition via dust revealed that high (>6 months' equivalent) dust addition rates were required to effect stabilization of microbial cell counts in tailings. In field-weathered tailings, topsoil addition during rehabilitation works exerted a double effect, acting as a microbial inoculant and correcting geochemical properties of tailings. However, microbial communities in rehabilitated tailings remained compositionally distinct from those of reference soils in surrounding environments. pH, water extractable Mg, and water extractable Fe emerged as major controls on microbial community composition in the field-weathered gold tailings. Overall, this study highlights the need for application of targeted microbial inoculants to accelerate rates of microbial community succession in tailings, which are limited primarily by slow dispersal due to physical and spatial isolation of tailings facilities from inoculant sources; and for geochemical properties of tailings to be amended to moderate values to encourage microbial community diversification and succession.

Analysis of the bacterial community from high alkaline (pH > 13) drainage water at a brown mud disposal site near Žiar nad Hronom (Banská Bystrica region, Slovakia) using 454 pyrosequencing

Brown mud, as a waste product of the industrial process of aluminum production, represents a great environmental burden due to its toxicity to living organisms. However, some microorganisms are able to survive in this habitat, and they can be used in bioremediation processes. Traditional cultivation methods have a limited capacity to characterize bacterial composition in environmental samples. Recently, next-generation sequencing methods have provided new perspectives on microbial community studies. The aim of this study was to analyze the bacterial community in the drainage water of brown mud disposal site near Žiar nad Hronom (Banská Bystrica region, Slovakia) using 454 pyrosequencing. We obtained 9964 sequences assigned to 163 operational taxonomic units belonging to 10 bacterial phyla. The phylum Proteobacteria showed the highest abundance (80.39%) within the bacterial community, followed by Firmicutes (13.05%) and Bacteroidetes (5.64%). Other bacterial phyla showed an abundance lower than 1%. The classification yielded 85 genera. Sulfurospirillum spp. (45.19%) dominated the bacterial population, followed by Pseudomonas spp. (13.76%) and Exiguobacterium spp. (13.02%). These results indicate that high heavy metals content, high pH, and lack of essential nutrients are the drivers of a dramatic reduction of diversity in the bacterial population in this environment.

The geomicrobiology of mining environments

As the global population increases, so does the demand for minerals and energy resources. Demand for some of the major global commodities is currently growing at rates of: copper – 1.6% p.a.1; iron ore: 1.4% p.a.2; aluminium – 5% p.a.3; rare earth elements – 7% p.a.4, driven not only by population growth in China, India, and Africa, but also by increasing urbanisation and industrialisation globally. Technological advances in renewable energy production and storage, construction materials, transport, and computing could see demand for some of these resources spike by 2600% over the next 25 years under the most extreme demand scenarios5. Coupled with declining ore grades, this demand means that the global extent of mining environments is set to increase dramatically. Land disturbance attributed to mining was estimated to be 400 000 km2 in 20076, with projected rates of increase of 10 000 km2 per year7. This will increase the worldwide extent of mining environments from around 500 000 km2 at present to 1 330 000 km2 by 2100, larger than the combined land area of New South Wales and Victoria (1 050 000 km2), making them a globally important habitat for the hardiest of microbial life. The extreme geochemical and physical conditions prevalent in mining environments present great opportunities for discovery of novel microbial species and functions, as well as exciting challenges for microbiologists to apply their understanding to solve complex remediation problems.

Simultaneous treatment of dimethyl disulfide and hydrogen sulfide in an alkaline biotrickling filter

Foul odors comprise generally a complex mixture of molecules, where reduced sulfur compounds play a key role due to their toxicity and low odor threshold. Previous reports on treating mixtures of sulfur compounds in single biofilters showed that hydrogen sulfide (H₂S) interferes with the removal and degradation of other sulfur compounds. In this study, hydrogen sulfide (H₂S) and dimethyl disulfide (DMDS) were fed to an alkaline biotrickling filter (ABTF) at pH 10, to evaluate the simultaneous removal of inorganic and organic sulfur compounds in a single, basic-pH system. The H₂S-DMDS mixture was treated for more than 200 days, with a gas residence time of 40 s, attaining elimination capacities of 86 g_DMDS m^-3 h^-1 and 17 g_H2S m^-3 h^-1 and removal efficiencies close to 100%. Conversion of H₂S and DMDS to sulfate was generally above 70%. Consumption of sulfide and formaldehyde was verified by respirometry, suggesting the coexistence of both methylotrophic and chemoautotrophic breakdown pathways by the immobilized alkaliphilic biomass. The molecular biology analysis showed that the long-term acclimation of the ABTF led to a great variety of bacteria, predominated by Thioalkalivibrio species, while fungal community was notoriously less diverse and dominated by Fusarium species.

Microbial Fermentation of Organic Carbon Substrates Drives Rapid pH Neutralization and Element Removal in Bauxite Residue Leachate

Globally, mineral processing activities produce an estimated 680 GL/yr of alkaline wastewater. Neutralizing pH and removing dissolved elements are the main goals of wastewater treatment prior to discharge. Here, we present the first study to explicitly evaluate the role of microbial communities in driving pH neutralization and element removal in alkaline wastewaters by fermentation of organic carbon, using bauxite residue leachate as a model system, and evaluate the effects of organic carbon complexity and microbial inoculum addition rates on the performance of these treatment systems at laboratory scale. Rates and extents of pH neutralization were higher in bioreactors fed with simpler organic carbon substrates (glucose and banana: 6 days to reach pH ≤ 8) than those fed with more complex organic carbon substrates (eucalyptus mulch: 15 days to reach pH ≤ 8; woodchips: equilibrium pH around 9). Concentrations of dissolved Al, As, B, Mo, Na, S, and V all significantly decreased after bioremediation. Increasing soil inoculant addition rate accelerated rates and extent of pH neutralization and element removal up to 0.1 wt %; further increases had little effect. Overall, glucose added at 1.8 wt % and soil inoculum added at 0.1 wt % provided the most effective minimal combination of carbon substrate and inoculum to drive pH neutralization and element removal.

pH and Organic Carbon Dose Rates Control Microbially Driven Bioremediation Efficacy in Alkaline Bauxite Residue

Bioremediation of alkaline tailings, based on fermentative microbial metabolisms, is a novel strategy for achieving rapid pH neutralization and thus improving environmental outcomes associated with mining and refining activities. Laboratory-scale bioreactors containing bauxite residue (an alkaline, saline tailings material generated as a byproduct of alumina refining), to which a diverse microbial inoculum was added, were used in this study to identify key factors (pH, salinity, organic carbon supply) controlling the rates and extent of microbially driven pH neutralization (bioremediation) in alkaline tailings. Initial tailings pH and organic carbon dose rates both significantly affected bioremediation extent and efficiency with lower minimum pHs and higher extents of pH neutralization occurring under low initial pH or high organic carbon conditions. Rates of pH neutralization (up to 0.13 mM H⁺ produced per day with pH decreasing from 9.5 to ≤6.5 in three days) were significantly higher in low initial pH treatments. Representatives of the Bacillaceae and Enterobacteriaceae, which contain many known facultative anaerobes and fermenters, were identified as key contributors to 2,3-butanediol and/or mixed acid fermentation as the major mechanism(s) of pH neutralization. Initial pH and salinity significantly influenced microbial community successional trajectories, and microbial community structure was significantly related to markers of fermentation activity. This study provides the first experimental demonstration of bioremediation in bauxite residue, identifying pH and organic carbon dose rates as key controls on bioremediation efficacy, and will enable future development of bioreactor technologies at full field scale.

Ecology and application of haloalkaliphilic anaerobic microbial communities

Haloalkaliphilic microorganisms that grow optimally at high-pH and high-salinity conditions can be found in natural environments such as soda lakes. These globally spread lakes harbour interesting anaerobic microorganisms that have the potential of being applied in existing technologies or create new opportunities. In this review, we discuss the potential application of haloalkaliphilic anaerobic microbial communities in the fermentation of lignocellulosic feedstocks material subjected to an alkaline pre-treatment, methane production and sulfur removal technology. Also, the general advantages of operation at haloalkaline conditions, such as low volatile fatty acid and sulfide toxicity, are addressed. Finally, an outlook into the main challenges like ammonia toxicity and lack of aggregation is provided.