Microbial diversity in hypersaline wastewater: the example of tanneries

Growth-dependent cr(VI) reduction by Alteromonas sp. ORB2 under haloalkaline conditions: toxicity, removal mechanism and effect of heavy metals

Bacterial reduction of hexavalent chromium (VI) to chromium (III) is a sustainable bioremediation approach. However, the Cr(VI) containing wastewaters are often characterized with complex conditions such as high salt, alkaline pH and heavy metals which severely impact the growth and Cr(VI) reduction potential of microorganisms. This study investigated Cr(VI) reduction under complex haloalkaline conditions by an Alteromonas sp. ORB2 isolated from aerobic granular sludge cultivated from the seawater-microbiome. Optimum growth of Alteromonas sp. ORB2 was observed under haloalkaline conditions at 3.5-9.5% NaCl and pH 7-11. The bacterial growth in normal culture conditions (3.5% NaCl; pH 7.6) was not inhibited by 100 mg/l Cr(VI)/ As(V)/ Pb(II), 50 mg/l Cu(II) or 5 mg/l Cd(II). Near complete reduction of 100 mg/l Cr(VI) was achieved within 24 h at 3.5-7.5% NaCl and pH 8-11. Cr(VI) reduction by Alteromonas sp. ORB2 was not inhibited by 100 mg/L As(V), 100 mg/L Pb(II), 50 mg/L Cu(II) or 5 mg/L Cd(II). The bacterial cells grew in the medium with 100 mg/l Cr(VI) contained lower esterase activity and higher reactive oxygen species levels indicating toxicity and oxidative stress. In-spite of toxicity, the cells grew and reduced 100 mg/l Cr(VI) completely within 24 h. Cr(VI) removal from the medium was driven by bacterial reduction to Cr(III) which remained in the complex medium. Cr(VI) reduction was strongly linked to aerobic growth of Alteromonas sp. The Cr(VI) reductase activity of cytosolic protein fraction was pronounced by supplementing with NADPH in vitro assays. This study demonstrated a growth-dependent aerobic Cr(VI) reduction by Alteromonas sp. ORB2 under complex haloalkaline conditions akin to wastewaters.

Adaptation and evolution of freshwater Anammox communities treating saline/brackish wastewater

The most common way to apply Anammox for saline wastewater treatment is via salt adaptation of freshwater Anammox bacteria (FAB). To better apply this process in practice, it's essential to understand the salt adaptation process of FBA, as well as the underlying mechanisms. This study investigated the long-term salt adaptation process of a fixed-film FAB culture in three reactors (namely R1-R3), under salinities of 2, 8, and 12 NaCl g/L, correspondingly. All three reactors were under stable operation and achieved 80-90% total inorganic nitrogen removal efficiency throughout the 425-day operation period. R1 servers as a blank control, based on the clear microbial community shifts in R2 and R3, the operation period was divided into 2 phases. During Phase 1, all FAB in the three reactors belonged to Ca. Brocadia sp.. The Anammox activity (AA) and the ratio of nitrite/ammonium (NO₂^--N/NH₄⁺-N) consumption in R2 and R3 decreased with the increase of salinity and did not recover to the initial levels. During Phase 2, the relative abundance of Ca. Kuenenia sp. in R2 and R3 increased from nearly 0 to about 60 and 77%, respectively. With the growth of Ca. Kuenenia sp., the AA and stoichiometry of R2 and R3 gradually recovered. AA of R2 and R3 both reached 1.0 g NH₄⁺-N/L/day at the end of this phase, which was about 80% of that in R1. These results indicated that the salt adaptation of FAB culture was achieved by species shift from a low salt-tolerance one to a high salt-tolerance one.

Bioremediation: an alternative approach for detoxification of polymers from the contaminated environment

The industries and metropolitan wastes produced by anthropogenic activities are of great concern for nature as it causes soil contamination and deteriorate the environment. Plastic utilization is rapidly enhancing globally with passing days that last for a more extended period in the environment due to slow decomposition and natural degradation. Excessive use of polymer has risked the life of both marine, freshwater and terrestrial organisms. Lack of proper waste management and inappropriate disposal leads to environmental threats. Bioremediation processes involve microbes such as fungi, bacteria, etc. which contribute a crucial role in the breakdown of plastics. Extremophiles secrete extremozymes that are functionally active in extreme conditions and are highly crucial for polymer disaggregation in those conditions.

Microbial response during treatment of different types of landfill leachate in a semi-aerobic aged refuse biofilter

In this research, for the first time, three kinds of landfill leachate (young (YL), mature (ML) and mixed (MYL) leachate) were treated in a semi-aerobic aged refuse biofilter (SAARB) to compare the effectiveness of, and microbial changes in, this biofilter when treating leachates that have significantly different characteristics. The SAARB achieved stable removal of organic matter from all three leachates and reduced the concentrations of aromatic substances. The best treatment was achieved with YL, followed in order by MYL and ML. The removal of nitrogen from all three leachates by the SAARB was particularly significant. The microbial abundance and diversity in the media of the SAARB changed after treatment of the three leachates, and the order of change from small to large was ML# < MYL# < YL#. The microbial communities were mainly affected by (and negatively correlated to) the relative content of refractory organics in leachate. Proteobacteria was the dominant microorganism. Deinococcus-thermus responded most to the quality of leachate being treated, increasing in relative abundance as the content of refractory organics increased. This was opposite to the response of Chloroflexi. In YL# the dominant species at the genus level was Thauera, and in ML# the dominant species were Truepera and Iodidimonas. The microbial activity and metabolic intensity were enhanced after treatment of the different leachates. The expression of nitrification-related genes was the strongest and the total abundance was the highest when YL was treated. This study promotes the optimization and application of SAARB.

How the bacterial community of a tannery effluent responds to bioaugmentation with the consortium SFC 500-1. Impact of environmental variables

Bioaugmentation with the consortium SFC 500-1 is a promising alternative to remediate wastewaters, such as tannery effluents. With the aim of assessing the changes produced in response to bioaugmentation, bacterial 16S rDNA genes were sequenced with Illumina MiSeq Platform. Additionally, bacterial and fungal groups were analyzed through standard culture dependent methods. The impact of diverse physico-chemical and microbiological parameters on the prokaryotic diversity was also evaluated throughout. Bacteroidetes, Firmicutes and Proteobacteria, represented together up to 91% of the total number of sequences obtained from the tannery effluent. Diversity decreased immediately after inoculation, due to an increase in the representation of the taxa to which the added consortium belongs. However, bioaugmentation produced no greater variations since only a 10% of unique operational taxonomic units were found in the inoculated treatment. An increase in the abundance of Myroides and a reduction in the representation of Proteiniclasticum and Halomonas were major observed variations. On the other hand, pH and dissolved oxygen constituted main environmental factors affecting the structure of the prokaryotic communities. In all treatments yeasts increased over time, to the detriment of filamentous fungi. Together, data from this report may contribute to the development of improved bioremediation strategies of industrial wastewaters.

Performance evaluation of a hybrid sequencing batch reactor under saline and hyper saline conditions

Significant rise in concentration of saline wastewater entering the treatment plants has been resulting in many problems in the biological treatment processes. On the other hand, the specific conditions of physicochemical treatment methods for saline and hyper saline wastewater have limited their application on a large-scale. Over the past few decades, Sequencing Batch Reactor (SBR) process has been widely used as an efficient, well-designed and practical approach for treatment of domestic and industrial wastewater due to its cost-effectiveness and simplicity. SBR Performance can enhance by providing simultaneous suspended and attached growth of microorganisms which act as a hybrid growth. In this study, a lab-scale Hybrid Sequencing Batch Reactor (HSBR) with 6.4 l working volume was used to examine the effect of salinity (NaCl), increased from 0 to 6.7% (g NaCl/ L wastewater), on the biological treatment. Therefore, COD, MLSS, MLVSS and SVI parameters have been measured over a period of 7 months of operation. The operational parameters namely pH, dissolved oxygen (DO) and temperature were 7.5–8.5, 1.5–6.8 mg /L and 20–25 °C respectively during whole experiment. Influent COD of synthetic wastewater was maintained at 650 ± 25 mg/L. The HSBR Cycle time including, influent feeding, React, Settling and effluent discharge were 1/20/1/1 h respectively. Results indicated that by increasing salt concentration from 0 to 67.7 g NaCl/L, the COD removal efficiency reduced from 94.22 to 53.69%. Moreover, as the NaCl concentration increased, MLSS rose up to 69%, while MLVSS almost stayed constant and SVI dropped by 83%. The results indicated that the simultaneous use of suspended and attached growth of microorganisms and gradual increasing of salt content of wastewater could lead to greater biomass concentration and ultimately improvement in the degradation of organic matter. Besides, settling performance and its velocity were noticeably improved by increasing salinity.

Desiccation- and Saline-Tolerant Bacteria and Archaea in Kalahari Pan Sediments

More than 41% of the Earth's land area is covered by permanent or seasonally arid dryland ecosystems. Global development and human activity have led to an increase in aridity, resulting in ecosystem degradation and desertification around the world. The objective of the present work was to investigate and compare the microbial community structure and geochemical characteristics of two geographically distinct saline pan sediments in the Kalahari Desert of southern Africa. Our data suggest that these microbial communities have been shaped by geochemical drivers, including water content, salinity, and the supply of organic matter. Using Illumina 16S rRNA gene sequencing, this study provides new insights into the diversity of bacteria and archaea in semi-arid, saline, and low-carbon environments. Many of the observed taxa are halophilic and adapted to water-limiting conditions. The analysis reveals a high relative abundance of halophilic archaea (primarily Halobacteria), and the bacterial diversity is marked by an abundance of Gemmatimonadetes and spore-forming Firmicutes. In the deeper, anoxic layers, candidate division MSBL1, and acetogenic bacteria (Acetothermia) are abundant. Together, the taxonomic information and geochemical data suggest that acetogenesis could be a prevalent form of metabolism in the deep layers of a saline pan.

Salt-tolerance aerobic granular sludge: Formation and microbial community characteristics

The salt-tolerance aerobic granular sludge (SAGS) dominated by moderately halophilic bacteria was successfully cultured in a 9% (w/v) salty, lab-scale sequence batch reactor (SBR) system. Influence of high salinity (0-9% w/v NaCl) on the formation, performance and microbial succession of the SAGS were explored. Crystal nucleus hypothesis, selection pressure hypothesis and compressed double electric layers hypothesis were used to discuss the formation mechanism of SAGS. Notably, salinity could be seen as a kind of selection pressure contributed to the formation of SAGS, while salinity also declined the performance of SAGS system. High throughput 16S rRNA gene analysis showed that the salinity had great influence on the species succession and community structure of SAGS. Moreover, Salinicola and Halomonas were dominant at 9% salt concentration, therefore moderate halophiles were identified as functional groups for the tolerance of hypersaline stress.

Dynamics of a microbial community during an effective boost MEOR trial using high-throughput sequencing

Using 454 pyrosequencing of 16S rRNA gene amplicons, microbial communities in samples of injection water and production water during a serial microbial enhanced oil recovery (MEOR) field trial in a water flooded high pour point oil reservoir were determined. There was a close microbial community compositional relationship between the injection water and the successful first round MEOR processed oil reservoir which was indicated by the result of 43 shared dominant operational taxonomic units detected in both the injection water and the production water. Alterations of microbial community after the injection of boost nutrients showed that microbes giving positive responses were mainly those belonging to the genera of Comamonas, Brevundimonas, Azospirillum, Achromobacter, Pseudomonas, and Hyphomonas, which were detected both in the injection water and in the production water and usually detected in oil reservoir environments or associated with hydrocarbon degradation. Additionally, microbes only dominant in the production waters were significantly inhibited with a sharp decline in their relative abundance. Based on these findings, a suggestion of re-optimization of the boost nutrients, targetting the microbes co-existing in the injection water and the oil reservoir and having survival ability in both surface and subsurface environments, rather than simple repeats for the subsequent in situ MEOR applications was proposed.

Bacterial community structure in simultaneous nitrification, denitrification and organic matter removal process treating saline mustard tuber wastewater as revealed by 16S rRNA sequencing

A simultaneous nitrification, denitrification and organic matter removal (SNDOR) process in sequencing batch biofilm reactor (SBBR) was established to treat saline mustard tuber wastewater (MTWW) in this study. An average COD removal efficiency of 86.48% and total nitrogen removal efficiency of 86.48% were achieved at 30gNaClL^-1 during 100days' operation. The underlying mechanisms were investigated by PacBio SMRT DNA sequencing (V1-V9) to analyze the microbial community structures and its variation from low salinity at 10gNaClL^-1 to high salinity at 30gNaClL^-1. Results showed elevated salinity did not affect biological performance but reduced microbial diversity in SBBR, and halophilic bacteria gradually predominated by succession. Despite of high C/N, autotrophic ammonia-oxidizing bacteria (AOB) Nitrosomonas and ammonia-oxidizing archaea (AOA) Candidatus Nitrososphaera both contributed to ammonium oxidation. As salinity increasing, nitrite-oxidizing bacteria (NOB) were significantly inhibited, partial nitrification and denitrification (PND) process gradually contributed to nitrogen removal.

Evolution of bacterial consortia in an integrated tannery wastewater treatment process

PCR-DGGE and Illumina HiSeq revealed the composition of bacterial communities in tannery sewage treatment and their linkages with the physicochemical characteristics of wastewater.

Long-term impact of salinity on the performance and microbial population of an aerobic granular reactor treating a high-strength aromatic wastewater

The effect of salinity over granular biomass treating a mixture of aromatic compounds (phenol, o-cresol and p-nitrophenol) was evaluated in a continuous airlift reactor. To mimic an industrial wastewater, increasing concentrations (from 2.0 to 29.0 g salts L(-1)) of a mixture of salts (MgSO4, NaCl, KCl, CaCl2 and NaHCO3) were introduced in the influent. The gradual salinity increase led to a good acclimation of the biomass obtaining complete biodegradation of the aromatic compounds and no accumulation of metabolic intermediates. However, a deterioration of the morphology of aerobic granules with a complete loss of granulation after 125 days was produced at 29.0 g salts L(-1). At that moment, anaerobic granules were added to promote granulation and after 50 days new aerobic granules were formed. These new aerobic granules remained stable for more than 100 days at the highest salinity condition with 100% removal of the mixture of aromatic compounds.

Electrical stimulation improves microbial salinity resistance and organofluorine removal in bioelectrochemical systems

Fed batch bioelectrochemical systems (BESs) based on electrical stimulation were used to treat p-fluoronitrobenzene (p-FNB) wastewater at high salinities. At a NaCl concentration of 40 g/liter, p-FNB was removed 100% in 96 h in the BES, whereas in the biotic control (BC) (absence of current), p-FNB removal was only 10%. By increasing NaCl concentrations from 0 g/liter to 40 g/liter, defluorination efficiency decreased around 40% in the BES, and in the BC it was completely ceased. p-FNB was mineralized by 30% in the BES and hardly in the BC. Microorganisms were able to store 3.8 and 0.7 times more K(+) and Na(+) intracellularly in the BES than in the BC. Following the same trend, the ratio of protein to soluble polysaccharide increased from 3.1 to 7.8 as the NaCl increased from 0 to 40 g/liter. Both trends raise speculation that an electrical stimulation drives microbial preference toward K(+) and protein accumulation to tolerate salinity. These findings are in accordance with an enrichment of halophilic organisms in the BES. Halobacterium dominated in the BES by 56.8% at a NaCl concentration of 40 g/liter, while its abundance was found as low as 17.5% in the BC. These findings propose a new method of electrical stimulation to improve microbial salinity resistance.

Investigation of intertidal wetland sediment as a novel inoculation source for anaerobic saline wastewater treatment

Biological treatment of saline wastewater is considered unfavorable due to salinity inhibition on microbial activity. In this study, intertidal wetland sediment (IWS) collected from a high saline environment was investigated as a novel inoculation source for anaerobic treatment of saline pharmaceutical wastewater. Two parallel lab-scale anaerobic sequencing batch reactors (AnSBR) were set up to compare the organic removal potential of IWS with conventional anaerobic digested sludge (ADS). Under steady-state condition, IWS reactor (R(i)) showed organic reduction performance significantly superior to that of ADS reactor (R(a)), achieving COD removal efficiency of 71.4 ± 3.7 and 32.3 ± 6.1%, respectively. In addition, as revealed by fluorescent in situ hybridization (FISH) analysis, a higher relative abundance of methanogenic populations was detected in R(i). A further 16S rRNA gene pyrosequencing test was conducted to understand both the bacterial and archaeal community populations in the two AnSBRs. A predominance of halophilic/tolerant microorganisms (class Clostridia of bacteria, genera Methanosarcina, and Methanohalophilus of archaea) in R(i) enhanced its organic removal efficiency. Moreover, several microbial groups related with degradation of hardly biodegradable compounds (PAHs, n-alkenes, aliphatic hydrocarbons, and alkanes, etc.) were detected in the IWS. All these findings indicated that IWS is a promising inoculation source for anaerobic treatment of saline wastewater.

Changing bacterial profile of Sundarbans, the world heritage mangrove: impact of anthropogenic interventions

Mangrove microbial communities and their associated activities have profound impact on biogeochemical cycles. Although microbial composition and structure are known to be influenced by biotic and abiotic factors in the mangrove sediments, finding direct correlations between them remains a challenge. In this study we have explored sediment bacterial diversity of the Sundarbans, a world heritage site using a culture-independent molecular approach. Bacterial diversity was analyzed from three different locations with a history of exposure to differential anthropogenic activities. 16S rRNA gene libraries were constructed and partial sequencing of the clones was performed to identify the microbial strains. We identified bacterial strains known to be involved in a variety of biodegradation/biotransformation processes including hydrocarbon degradation, and heavy metal resistance. Canonical Correspondence Analysis of the environmental and exploratory datasets revealed correlations between the ecological indices associated with pollutant levels and bacterial diversity across the sites. Our results indicate that sites with similar exposure of anthropogenic intervention reflect similar patterns of microbial diversity besides spatial commonalities.

Microbial community structure and diversity in an integrated system of anaerobic-aerobic reactors and a constructed wetland for the treatment of tannery wastewater in Modjo, Ethiopia

A culture-independent approach was used to elucidate the microbial diversity and structure in the anaerobic-aerobic reactors integrated with a constructed wetland for the treatment of tannery wastewater in Modjo town, Ethiopia. The system has been running with removal efficiencies ranging from 94%-96% for COD, 91%-100% for SO4(2-) and S(2-), 92%-94% for BOD, 56%-82% for total Nitrogen and 2%-90% for NH3-N. 16S rRNA gene clone libraries were constructed and microbial community assemblies were determined by analysis of a total of 801 unique clone sequences from all the sites. Operational Taxonomic Unit (OTU)--based analysis of the sequences revealed highly diverse communities in each of the reactors and the constructed wetland. A total of 32 phylotypes were identified with the dominant members affiliated to Clostridia (33%), Betaproteobacteria (10%), Bacteroidia (10%), Deltaproteobacteria (9%) and Gammaproteobacteria (6%). Sequences affiliated to the class Clostridia were the most abundant across all sites. The 801 sequences were assigned to 255 OTUs, of which 3 OTUs were shared among the clone libraries from all sites. The shared OTUs comprised 80 sequences belonging to Clostridiales Family XIII Incertae Sedis, Bacteroidetes and unclassified bacterial group. Significantly different communities were harbored by the anaerobic, aerobic and rhizosphere sites of the constructed wetland. Numerous representative genera of the dominant bacterial classes obtained from the different sample sites of the integrated system have been implicated in the removal of various carbon- containing pollutants of natural and synthetic origins. To our knowledge, this is the first report of microbial community structure in tannery wastewater treatment plant from Ethiopia.

Abundance and diversity of bacterial nitrifiers and denitrifiers and their functional genes in tannery wastewater treatment plants revealed by high-throughput sequencing

Biological nitrification/denitrification is frequently used to remove nitrogen from tannery wastewater containing high concentrations of ammonia. However, information is limited about the bacterial nitrifiers and denitrifiers and their functional genes in tannery wastewater treatment plants (WWTPs) due to the low-throughput of the previously used methods. In this study, 454 pyrosequencing and Illumina high-throughput sequencing, combined with molecular methods, were used to comprehensively characterize structures and functions of nitrification and denitrification bacterial communities in aerobic and anaerobic sludge of two full-scale tannery WWTPs. Pyrosequencing of 16S rRNA genes showed that Proteobacteria and Synergistetes dominated in the aerobic and anaerobic sludge, respectively. Ammonia-oxidizing bacteria (AOB) amoA gene cloning revealed that Nitrosomonas europaea dominated the ammonia-oxidizing community in the WWTPs. Metagenomic analysis showed that the denitrifiers mainly included the genera of Thauera, Paracoccus, Hyphomicrobium, Comamonas and Azoarcus, which may greatly contribute to the nitrogen removal in the two WWTPs. It is interesting that AOB and ammonia-oxidizing archaea had low abundance although both WWTPs demonstrated high ammonium removal efficiency. Good correlation between the qPCR and metagenomic analysis is observed for the quantification of functional genes amoA, nirK, nirS and nosZ, indicating that the metagenomic approach may be a promising method used to comprehensively investigate the abundance of functional genes of nitrifiers and denitrifiers in the environment.

Time course transcriptome changes in Shewanella algae in response to salt stress

Shewanella algae, which produces tetrodotoxin and exists in various seafoods, can cause human diseases, such as spondylodiscitis and bloody diarrhea. In the present study, we focused on the temporal, dynamic process in salt-stressed S. algae by monitoring the gene transcript levels at different time points after high salt exposure. Transcript changes in amino acid metabolism, carbohydrate metabolism, energy metabolism, membrane transport, regulatory functions, and cellular signaling were found to be important for the high salt response in S. algae. The most common strategies used by bacteria to survive and grow in high salt environments, such as Na+ efflux, K+ uptake, glutamate transport and biosynthesis, and the accumulation of compatible solutes, were also observed in S. algae. In particular, genes involved in peptidoglycan biosynthesis and DNA repair were highly and steadily up-regulated, accompanied by rapid and instantaneous enhancement of the transcription of large- and small-ribosome subunits, which suggested that the structural changes in the cell wall and some stressful responses occurred in S. algae. Furthermore, the transcription of genes involved in the tricarboxylic acid (TCA) cycle and the glycolytic pathway was decreased, whereas the transcription of genes involved in anaerobic respiration was increased. These results, demonstrating the multi-pathway reactions of S. algae in response to salt stress, increase our understanding of the microbial stress response mechanisms.

Metagenomic profiling of antibiotic resistance genes and mobile genetic elements in a tannery wastewater treatment plant

Antibiotics are often used to prevent sickness and improve production in animal agriculture, and the residues in animal bodies may enter tannery wastewater during leather production. This study aimed to use Illumina high-throughput sequencing to investigate the occurrence, diversity and abundance of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in aerobic and anaerobic sludge of a full-scale tannery wastewater treatment plant (WWTP). Metagenomic analysis showed that Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria dominated in the WWTP, but the relative abundance of archaea in anaerobic sludge was higher than in aerobic sludge. Sequencing reads from aerobic and anaerobic sludge revealed differences in the abundance of functional genes between both microbial communities. Genes coding for antibiotic resistance were identified in both communities. BLAST analysis against Antibiotic Resistance Genes Database (ARDB) further revealed that aerobic and anaerobic sludge contained various ARGs with high abundance, among which sulfonamide resistance gene sul1 had the highest abundance, occupying over 20% of the total ARGs reads. Tetracycline resistance genes (tet) were highly rich in the anaerobic sludge, among which tet33 had the highest abundance, but was absent in aerobic sludge. Over 70 types of insertion sequences were detected in each sludge sample, and class 1 integrase genes were prevalent in the WWTP. The results highlighted prevalence of ARGs and MGEs in tannery WWTPs, which may deserve more public health concerns.

Diversity of Bacteria and Archaea in hypersaline sediment from Death Valley National Park, California

The objective of this study was to phylogenetically analyze microorganisms from the domains Bacteria and Archaea in hypersaline sediment from Death Valley National Park. Using domain-specific primers, a region of the 16S rRNA gene was amplified using polymerase chain reaction (PCR), and the product was subsequently used to create a clone library. A total of 243 bacterial clones, 99 archaeal clones, and 209 bacterial isolates were examined. The 243 clones from Bacteria were affiliated with the following groups: the Bacilli (59 clones) and Clostridia (1) of the Firmicutes, Bacteroidetes (90), Proteobacteria (27), Cyanobacteria (18), Gemmatimonadetes (41), candidate division OP1 (5), Actinobacteria (1), and the Deinococcus-Thermus division (1). Within the class Bacilli, 46 of 59 clones were tentatively identified as 10 unclassified species. The majority of bacterial isolates (130 of 209) were more closely related to the Bacillus subtilis–B. licheniformis clade than to any other recognized taxon, and an Ecotype Simulation analysis of B. subtilis relatives identified four previously unknown ecotypes. Several new genera were discovered within the Bacteroidetes (4) and the Gemmatimonadetes (2). Of the 99 archaeal clones, 94 were tentatively identified as belonging to 3 new genera within the Halobacteriaceae; other clones represented novel species within each of 4 established genera.

Effect of increasing anodic NaCl concentration on microbial fuel cell performance

High salinity effluents represent an estimated 5% of the wastewater generated worldwide. In microbial fuel cells, high salinity is usually considered beneficial to power production because increased conductivity facilitates proton transfer and therefore decreases the internal resistance of the system. However, high salt concentrations are known to adversely affect the physiology of anaerobic microbial consortia. In this study, the effect of increasing NaCl concentration in the anode chamber of a microbial fuel cell fed with sodium acetate was tested. Adding up to 20 g L(-1) of NaCl enhanced the overall performance of the system, reducing the internal resistance by 33% and increasing the maximum power production by 30%. Higher NaCl concentration proved detrimental to the system. However, the Coulombic efficiency started to be affected at a much lower NaCl concentration of 10 g L(-1), showing that the anodophilic bacteria are sensitive to NaCl at relatively low concentrations.

Do patterns of bacterial diversity along salinity gradients differ from those observed for macroorganisms?

It is widely accepted that biodiversity is lower in more extreme environments. In this study, we sought to determine whether this trend, well documented for macroorganisms, also holds at the microbial level for bacteria. We used denaturing gradient gel electrophoresis (DGGE) with phylum-specific primers to quantify the taxon richness (i.e., the DGGE band numbers) of the bacterioplankton communities of 32 pristine Tibetan lakes that represent a broad salinity range (freshwater to hypersaline). For the lakes investigated, salinity was found to be the environmental variable with the strongest influence on the bacterial community composition. We found that the bacterial taxon richness in freshwater habitats increased with increasing salinity up to a value of 1‰. In saline systems (systems with >1‰ salinity), the expected decrease of taxon richness along a gradient of further increasing salinity was not observed. These patterns were consistently observed for two sets of samples taken in two different years. A comparison of 16S rRNA gene clone libraries revealed that the bacterial community of the lake with the highest salinity was characterized by a higher recent accelerated diversification than the community of a freshwater lake, whereas the phylogenetic diversity in the hypersaline lake was lower than that in the freshwater lake. These results suggest that different evolutionary forces may act on bacterial populations in freshwater and hypersaline lakes on the Tibetan Plateau, potentially resulting in different community structures and diversity patterns.

Time-course analysis of the Shewanella amazonensis SB2B proteome in response to sodium chloride shock

Shewanellae are microbial models for environmental stress response; however, the sequential expression of mechanisms in response to stress is poorly understood. Here we experimentally determine the response mechanisms of Shewanella amazonensis SB2B during sodium chloride stress using a novel liquid chromatography and accurate mass-time tag mass spectrometry time-course proteomics approach. The response of SB2B involves an orchestrated sequence of events comprising increased signal transduction associated with motility and restricted growth. Following a metabolic shift to branched chain amino acid degradation, motility and cellular replication proteins return to pre-perturbed levels. Although sodium chloride stress is associated with a change in the membrane fatty acid composition in other organisms, this is not the case for SB2B as fatty acid degradation pathways are not expressed and no change in the fatty acid profile is observed. These findings suggest that shifts in membrane composition may be an indirect physiological response to high NaCl stress.

Are compatible solutes compatible with biological treatment of saline wastewater? Batch and continuous studies using submerged anaerobic membrane bioreactors (SAMBRs)

This study investigated fundamental mechanisms that anaerobic biomass employ to cope with salinity, and applied these findings to a continuous SAMBR. When anaerobic biomass was exposed to 20 and 40 g NaCl/L for 96 h, the main solute generated de novo by biomass was trehalose. When we separately introduced trehalose, N-acetyl-β-lysine and potassium into a batch culture a slight decrease in sodium inhibition was observed. In contrast, the addition of 0.1 mM and 1 mM of glycine betaine dramatically improved the adaptation of anaerobic biomass to 35 g NaCl/L, and it continued to enhance the adaptation of biomass to the salt for the next three batch feedings without further addition. No shift in archaeal microbial diversity was found when anaerobic biomass was exposed in batch mode to 35 g NaCl/L for 360 h, and no changes were found when glycine betaine was added. The dominant species identified under these conditions were Methanosarcina mazeii and Methanosaeta sp. The addition of 5 mM glycine betaine to a continuous SAMBR at 12 h hydraulic retention time (HRT), and operation in batch mode for 2 days can significantly enhance saline (35 g NaCl/L) synthetic sewage degradation. In addition, the injection of 1 mM of glycine betaine into a SAMBR for five subsequent days also significantly enhanced dissolved organic carbon (DOC) removal from sewage under these conditions. The main compatible solutes generated by anaerobic biomass after 44 days exposure to 35 g NaCl/L in a SAMBR were N-acetyl-β-lysine and glycine betaine. Finally, the addition of 1 mM glycine betaine to the medium was beneficial for anaerobic biomass in batch mode at 20 °C under saline and non saline conditions.

Bacterial community dynamics in horizontal flow constructed wetlands with different plants for high salinity industrial wastewater polishing

This study is focused on the diversity of bacterial communities from two series of horizontal subsurface flow constructed wetlands (CW) polishing high salinity tannery wastewater. Each series was planted with Arundo donax or Sarcocornia sp. in a substrate composed by expanded clay and sand. Chemical and biochemical oxygen demand removal efficiencies were similar in each series, varying between 58 and 67% (inlet COD 218 ± 28 mg L(-1)) and 60 and 77% (inlet BOD(5) 37 ± 6 mg L(-1)), respectively. High numbers of culturable bacteria were obtained from substrate and root samples - 5.75 × 10(6)-3.95 × 10(8) CFU g(-1) recovered on marine agar and 1.72 × 10(7)-8.46 × 10(8) CFU g(-1) on nutrient agar. Fifty bacterial isolates were retrieved from the CW, related phylogenetically to Firmicutes, Actinobacteria, Bacteroidetes, α-, β-, and γ-Proteobacteria. Changes in the bacterial communities, from roots and substrate of each series, related to the plant species, hydraulic loading rates and along CW operation were examined using denaturating gradient gel electrophoresis (DGGE). The clustering analysis suggested that a diverse and distinct bacterial community inhabits each series, which was related to the type of plant present in each CW.

The effect of the application of halotolerant microorganisms on the efficiency of a pilot-scale constructed wetland for saline wastewater treatment

In order to find the optimal design characteristics of constructed wetlands for saline wastewater treatment, halotolerant microorganisms, isolated from the water of the Secovlje salterns, were inoculated into the media of a pilot-scale constructed wetland (CW). The purpose of this study was to examine the influence of different salinities on the efficiency of halotolerant microorganisms for the removal of pollutants in order to evaluate the possibility of their employment for saline wastewater treatment. The efficiency of ammonium removal (34.1 %) was the highest with 0 % NaCl in wastewater and slightly lower (31.8 %) when 2 g/dm3 saccharose was added to aerated 1.5 % NaCl wastewater. The highest removal efficiency of chemical oxygen demand (COD) in the pilot-scale subsurface flow (SSF) CW was 83.6 % when saccharose (2 g/dm3) was added to aerated 1.5 % NaCl wastewater. It was found that removal efficiency of the pilot-scale constructed wetland with inoculated halotolerant microorganisms showed a higher sensitivity to aeration and the presence of saccharose than to variation of the salinity of the wastewater. It can be concluded that halotolerant microorganisms, isolated from the Secovlje salterns, are not sensitive to the changes in salinity and are, therefore, an alternative in the treatment of saline wastewater with a constructed wetland. However, with aeration their efficiency could be further improved.

Changes in the bacterial community structure in two-stage constructed wetlands with different plants for industrial wastewater treatment

This study focused on the diversity of bacterial communities from two series of two-stage constructed wetlands (CWs) treating tannery wastewater, under different hydraulic conditions. Series were separately planted with Typha latifolia and Phragmites australis in expanded clay aggregates and operated for 31 months. The effect of plant species, hydraulic loading and unit stage on bacterial communities was addressed through bacterial enumeration and denaturating gradient gel electrophoresis (DGGE). Diverse and distinct bacterial communities were found in each system unit, which was related in part to the type of plant and stage position (first or second unit in the series). Numerical analysis of DGGE profiles showed high diversity in each unit with an even distribution of species. No clear relation was established between the sample collection time, hydraulic loading applied and the bacterial diversity. Isolates retrieved from plant roots and substrates of CWs were affiliated with gamma-Proteobacteria, Firmicutes, alpha-Proteobacteria, Sphingobacteria, Actinobacteria and Bacteroidetes. Both series were effective in removing organic matter from the inlet wastewater, however, based on batch degradation experiments it seems that biodegradation was limited by the recalcitrant properties of the wastewater.

Prokaryotic community profiles at different operational stages of a Greek solar saltern

A combination of culture-dependent and independent approaches was employed to identify the microbial community structure in a Greek solar saltern. A total of 219 and 132 isolates belonging, respectively, to Bacteria and Archaea, were recovered. All bacterial isolates were phylogenetically related to 43 members of Actinobacteria, Firmicutes and gamma-Proteobacteria. The archaeal isolates were placed within the Halobacteriaceae. At least four groups of isolates represented novel species among the Bacteria. High bacterial diversity, consisting of 417 subfamilies, was revealed using a high-density oligonucleotide microarray (PhyloChip). At the four stages of saltern operation analyzed, the archaeal community consisted of both Crenarchaeota and Euryarchaeota, except for the sediment where Crenarchaeota were not detected. The bacterial community in sediment consisted mainly of gamma-Proteobacteria and Actinobacteria, while, in hypersaline water, it was restricted to a few representatives of Bacteria. Members of alpha-Proteobacteria were the main constituents in saturated brine and crude salt, followed by gamma-Proteobacteria, Actinobacteria and Firmicutes. A large Bacteroidetes and Verrucomicrobia diversity was identified in saturated brine, while delta-Proteobacteria and Cloroflexi were abundant in crude salt. Significant changes in the microbial community structure were detected during a short time period, denoting a rapidly adaptive dynamic ecosystem and viable diversity. Prokaryotic members reported for the first time in solar salterns were identified.

Biological treatment of tannery wastewater by using salt-tolerant bacterial strains

BACKGROUND

High salinity (1-10% w/v) of tannery wastewater makes it difficult to be treated by conventional biological treatment. Salt tolerant microbes can adapt to these saline conditions and degrade the organics in saline wastewater.

RESULTS

Four salt tolerant bacterial strains isolated from marine and tannery saline wastewater samples were identified as Pseudomonas aeruginosa, Bacillus flexus, Exiguobacterium homiense and Staphylococcus aureus. Growth factors of the identified strains were optimized. Tannery saline wastewater obtained from a Common Effluent Treatment Plant (CETP) near Chennai (southern India) was treated with pure and mixed consortia of four salt tolerant bacterial strains. Experiments with optimized conditions and varying salt content (between 2 and 10% (w/v) were conducted. Salt inhibition effects on COD removal rate were noted. Comparative analysis was made by treating the tannery saline wastewater with activated sludge obtained from CETP and with natural habitat microbes present in raw tannery saline wastewater.

CONCLUSION

Salt tolerant bacterial mixed consortia showed appreciable biodegradation at all saline concentrations (2%, 4%, 6%, 8% and 10% w/v) with 80% COD reduction in particular at 8% salinity level the consortia could be used as suitable working cultures for tannery saline wastewater treatment.

The division "Synergistes"

The "Synergistes" group of organisms are a phylogenetic cluster of Gram-negative anaerobes related to Synergistes jonesii, sufficiently distinct from all other phyla to be considered a distinct phylum or Division. They are widely distributed in nature although normally only a minor constituent of the bacterial community in each habitat. They have evolved to adapt to each habitat, and therefore exhibit a wide range of physiological and biochemical characteristics, although all cultivable taxa so far studied have the ability to degrade amino acids. They are found in the human mouth where they appear to be more numerous in tooth and gum disease than health. They have also been found in the human gut and soft tissue infections. Their role in human disease has yet to be established but improved knowledge of the characteristics that enable their identification should increase the likelihood of their recognition when present at diseased sites.

Impact of increasing NaCl concentrations on the performance and community composition of two anaerobic reactors

The anaerobic treatment of saline effluents using halophilic and halotolerant microbial consortia is of major interest. Inhibition of anaerobic digestion is known to occur at high salt content. However, it seems that the suitable adaptation of an anaerobic sludge makes possible the treatment of saline wastewater. In this study, a non-saline anaerobic sludge was inoculated in two anaerobic batch reactors operating with a different substrate (distillery vinasse and ethanol) and subjected to increasing NaCl concentrations. The performance of the digesters appeared to be highly dependent on the nature of the substrate, and a similar level of inhibition (i.e. around 90% of the specific loading rate and specific methanogenic activity) was stated at 10 g l(-1) of NaCl with distillery vinasse and 60 g l(-1) of NaCl with ethanol. The characterization of the microflora and its adaptation to increasing NaCl conditions were also investigated using molecular tools based on the analysis of genomic 16S rDNA. The microbial communities revealed a high diversity that could be maintained in both reactors despite the increase in NaCl concentrations.

Treatment of organic pollution in industrial saline wastewater: a literature review

Many industrial sectors are likely to generate highly saline wastewater: these include the agro-food, petroleum and leather industries. The discharge of such wastewater containing at the same time high salinity and high organic content without prior treatment is known to adversely affect the aquatic life, water potability and agriculture. Thus, legislation is becoming more stringent and the treatment of saline wastewater, both for organic matter and salt removal, is nowadays compulsory in many countries. Saline effluents are conventionally treated through physico-chemical means, as biological treatment is strongly inhibited by salts (mainly NaCl). However, the costs of physico-chemical treatments being particularly high, alternative systems for the treatment of organic matter are nowadays increasingly the focus of research. Most of such systems involve anaerobic or aerobic biological treatment. Even though biological treatment of carbonaceous, nitrogenous and phosphorous pollution has proved to be feasible at high salt concentrations, the performance obtained depends on a proper adaptation of the biomass or the use of halophilic organisms. Another major limit is related to the turbidity problems inherent in saline effluents. For this reason, the major need for research in the future will be the combination of physico-chemical/biological treatment of saline industrial effluents, with regard to the global treatment chain, in order to meet the regulations.