Integration of Physiological, Transcriptomic, and Metabolomic Analyses Reveal Molecular Mechanisms of Salt Stress in Maclura tricuspidata.

Salt stress is a universal abiotic stress that severely affects plant growth and development. Understanding the mechanisms of Maclura tricuspidate's adaptation to salt stress is crucial for developing salt-tolerant plant varieties. This article discusses the integration of physiology, transcriptome, and metabolome to investigate the mechanism of salt adaptation in M. tricuspidata under salt stress conditions. Overall, the antioxidant enzyme system (SOD and POD) of M. tricuspidata exhibited higher activities compared with the control, while the content of soluble sugar and concentrations of chlorophyll a and b were maintained during salt stress. KEGG analysis revealed that deferentially expressed genes were primarily involved in plant hormone signal transduction, phenylpropanoid and flavonoid biosynthesis, alkaloids, and MAPK signaling pathways. Differential metabolites were enriched in amino acid metabolism, the biosynthesis of plant hormones, butanoate, and 2-oxocarboxylic acid metabolism. Interestingly, glycine, serine, and threonine metabolism were found to be important both in the metabolome and transcriptome-metabolome correlation analyses, suggesting their essential role in enhancing the salt tolerance of M. tricuspidata. Collectively, our study not only revealed the molecular mechanism of salt tolerance in M. tricuspidata, but also provided a new perspective for future salt-tolerant breeding and improvement in salt land for this species.

Halophilic filamentous fungi and their enzymes: Potential biotechnological applications.

Recently, interest in the study of microorganisms growing under extreme conditions, particularly halophiles, has increased due to their potential use in industrial processes. Halophiles are the class of microorganisms that grow optimally at high NaCl concentrations and are capable of producing halophilic enzymes capable of catalyzing reactions under harsh conditions. So far, fungi are the least studied halophilic microorganisms, even though they have been shown to counteract these extreme conditions by producing secondary metabolites with very interesting properties. This review highlights mechanisms that allow halophilic fungi to adapt high salinity and the specificity of their enzymes to a spectrum of action in industrial and environmental applications. The peculiarities of these enzymes justify the urgent need to apply green alternative compounds in industries.

Long-term adaptation of two anammox granules with different ratios of Candidatus Brocadia and Candidatus Jettenia under increasing salinity and their application to treat saline wastewater.

Nitrogen removal in saline wastewater is a challenge of the anaerobic ammonium oxidation (anammox) process, which is dominated by freshwater anammox bacteria (FAB). Candidatus Brocadia and Candidatus Jettenia, the most widely used FABs, have been separately applied and evaluated for their ability to treat saline wastewater. To understand the effect of salinity on nitrogen removal capability when they present together in an anammox granule, we compared two anammox granules: GRN1 was evenly dominated by Ca. Brocadia (42 %) and Ca. Jettenia (43 %), while GRN2 was dominated with mostly Ca. Brocadia (90 %) and a small amount of Ca. Jettenia (1 %). Each granule was inoculated into a continuous column reactor to treat artificial wastewater containing 150 mg NH4+-N/L and 150 mg NO2--N/L under increasing saline conditions for 250 days. GRN1 showed superior and more stable nitrogen removal than GRN2 under saline conditions of up to 15 g NaCl/L. Under high-saline conditions, both the granules' sizes decreased (larger GRN1 than GRN2 in initial). The mass percent of Na salt increased (more in GRN2) and mineral contents decreased more in GRN1. High-throughput sequencing for microbial community analysis showed that Planctomycetes in GRN1 (85 %) and GRN2 (92 %) decreased to 14 % and 12 %, respectively. The ratio of Ca. Brocadia and Ca. Jettenia in GRN1 changed to 37 % and 63 %, respectively, whereas the ratio in GRN2 (99 % and 1 %, respectively) did not change. Both salt-adapted granules were applied to the two-stage partial nitritation and anammox (PN/A) process to treat high strength ammonium (400 mg/L) wastewater under high saline condition (15 g NaCl/L). The PN/A process containing GRN1 showed more stable nitrogen removal performance during approximately 100 days of operation. These results suggest that the anammox granules evenly dominated by two FABs, Ca. Brocadia and Ca. Jettenia, would be advantageous to treat high-strength NH4+ wastewater under high-saline conditions.

Comparative genomics reveals the molecular mechanism of salt adaptation for zoysiagrasses.

BACKGROUND: Zoysiagrass (Zoysia spp.) is a warm-season turfgrass. It is widely used as turfgrasses throughout the world, offers good turf qualities, including salt tolerance, resistance to drought and heat. However, the underlying genetic mechanism of zoysiagrass responsive to salt stress remains largely unexplored. RESULTS: In present study, we performed a whole-genome comparative analysis for ten plant genomes. Evolutionary analysis revealed that Chloridoideae diverged from Panicoideae approximately 33.7 million years ago (Mya), and the phylogenetic relationship among three zoysiagrasses species suggested that Zoysia matrella may represent an interspecific hybrid between Zoysia japonica and Zoysia pacifica. Genomic synteny indicated that Zoysia underwent a genus-specific whole-genome duplication (WGD) event approximately 20.8 Mya. The expression bais of homologous genes between the two subgenomes suggested that the B subgenome of Z. japonica contributes to salt tolerance. In additon, comparative genomic analyses revealed that the salt adaptation of Zoysia is likely attributable to the expanded cytochrome P450 and ABA biosynthetic gene families. Furthermore, we further found that many duplicated genes from the extra WGD event exhibited distinct functional divergence in response to salt stress using transcriptomic analysis, suggesting that this WGD event contributed to strong resistance to salt stress. CONCLUSIONS: Here, our results revealed that expanded cytochrome P450 and ABA biosynthetic gene families, and many of those duplicated genes from recent zoysia-specific WGD event contributed to salt adaptation of zoysiagrass, which provided insight into the genetic underpinning of salt adaptation and valuable information for further studies on salt stress-related traits in Zoysia.

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.

Screening New Xylanase Biocatalysts from the Mangrove Soil Diversity.

Mangrove sediments from New Caledonia were screened for xylanase sequences. One enzyme was selected and characterized both biochemically and for its industrial potential. Using a specific cDNA amplification method coupled with a MiSeq sequencing approach, the diversity of expressed genes encoding GH11 xylanases was investigated beneath Avicenia marina and Rhizophora stylosa trees during the wet and dry seasons and at two different sediment depths. GH11 xylanase diversity varied more according to tree species and season, than with respect to depth. One complete cDNA was selected (OFU29) and expressed in Pichia pastoris. The corresponding enzyme (called Xyn11-29) was biochemically characterized, revealing an optimal activity at 40-50 °C and at a pH of 5.5. Xyn11-29 was stable for 48 h at 35 °C, with a half-life of 1 h at 40 °C and in the pH range of 5.5-6. Xyn11-29 exhibited a high hydrolysis capacity on destarched wheat bran, with 40% and 16% of xylose and arabinose released after 24 h hydrolysis. Its activity on wheat straw was lower, with a release of 2.8% and 6.9% of xylose and arabinose, respectively. As the protein was isolated from mangrove sediments, the effect of sea salt on its activity was studied and discussed.

Microtubule Dynamics Plays a Vital Role in Plant Adaptation and Tolerance to Salt Stress.

Although recent studies suggest that the plant cytoskeleton is associated with plant stress responses, such as salt, cold, and drought, the molecular mechanism underlying microtubule function in plant salt stress response remains unclear. We performed a comparative proteomic analysis between control suspension-cultured cells (A0) and salt-adapted cells (A120) established from Arabidopsis root callus to investigate plant adaptation mechanisms to long-term salt stress. We identified 50 differentially expressed proteins (45 up- and 5 down-regulated proteins) in A120 cells compared with A0 cells. Gene ontology enrichment and protein network analyses indicated that differentially expressed proteins in A120 cells were strongly associated with cell structure-associated clusters, including cytoskeleton and cell wall biogenesis. Gene expression analysis revealed that expressions of cytoskeleton-related genes, such as FBA8, TUB3, TUB4, TUB7, TUB9, and ACT7, and a cell wall biogenesis-related gene, CCoAOMT1, were induced in salt-adapted A120 cells. Moreover, the loss-of-function mutant of Arabidopsis TUB9 gene, tub9, showed a hypersensitive phenotype to salt stress. Consistent overexpression of Arabidopsis TUB9 gene in rice transgenic plants enhanced tolerance to salt stress. Our results suggest that microtubules play crucial roles in plant adaptation and tolerance to salt stress. The modulation of microtubule-related gene expression can be an effective strategy for developing salt-tolerant crops.

Exploring the Diversity of Fungal DyPs in Mangrove Soils to Produce and Characterize Novel Biocatalysts.

The functional diversity of the New Caledonian mangrove sediments was examined, observing the distribution of fungal dye-decolorizing peroxidases (DyPs), together with the complete biochemical characterization of the main DyP. Using a functional metabarcoding approach, the diversity of expressed genes encoding fungal DyPs was investigated in surface and deeper sediments, collected beneath either Avicennia marina or Rhizophora stylosa trees, during either the wet or the dry seasons. The highest DyP diversity was observed in surface sediments beneath the R. stylosa area during the wet season, and one particular operational functional unit (OFU1) was detected as the most abundant DyP isoform. This OFU was found in all sediment samples, representing 51-100% of the total DyP-encoding sequences in 70% of the samples. The complete cDNA sequence corresponding to this abundant DyP (OFU 1) was retrieved by gene capture, cloned, and heterologously expressed in Pichia pastoris. The recombinant enzyme, called DyP1, was purified and characterized, leading to the description of its physical-chemical properties, its ability to oxidize diverse phenolic substrates, and its potential to decolorize textile dyes; DyP1 was more active at low pH, though moderately stable over a wide pH range. The enzyme was very stable at temperatures up to 50 °C, retaining 60% activity after 180 min incubation. Its ability to decolorize industrial dyes was also tested on Reactive Blue 19, Acid Black, Disperse Blue 79, and Reactive Black 5. The effect of hydrogen peroxide and sea salt on DyP1 activity was studied and compared to what is reported for previously characterized enzymes from terrestrial and marine-derived fungi.

Nanoparticles potentially mediate salt stress tolerance in plants.

In the era of climate change, salt stress is a promising threat to agriculture, limiting crop production via imposing primary effects such as osmotic and ionic, as well as secondary effects such as oxidative stress, perturbance in hormonal homeostasis, and nutrient imbalance. On the other hand, production areas are expanding into the salt affected regions due to excessive pressure for fulfilling food security targets to meet the needs of continuously increasing human population. Accumulating evidences demonstrate that supplementation of nanoparticles to plants can significantly alleviate the injurious effects caused by various harsh conditions including salt stress, and hence, regulate adaptive mechanisms in plants. Various types of NPs and nanofertilizers have shown a promising evidence so far regarding salt stress management. In this review, we recapitulate recent pioneering progress made towards acquiring salt stress tolerance in crop plants utilizing NPs. Finally, future research directions in this domain to explicate the comprehensive roles of nanoparticles in improving salt tolerance in plants are underscored. To ensure social acceptance and safe use of NPs, some conclusive directions have been elaborated in order to achieve sustainable progress in crop production under saline environments.

How Plant Hormones Mediate Salt Stress Responses.

Salt stress is one of the major environmental stresses limiting plant growth and productivity. To adapt to salt stress, plants have developed various strategies to integrate exogenous salinity stress signals with endogenous developmental cues to optimize the balance of growth and stress responses. Accumulating evidence indicates that phytohormones, besides controlling plant growth and development under normal conditions, also mediate various environmental stresses, including salt stress, and thus regulate plant growth adaptation. In this review, we mainly discuss and summarize how plant hormones mediate salinity signals to regulate plant growth adaptation. We also highlight how, in response to salt stress, plants build a defense system by orchestrating the synthesis, signaling, and metabolism of various hormones via multiple crosstalks.

Crystal Structure and Active Site Engineering of a Halophilic γ-Carbonic Anhydrase.

Environments previously thought to be uninhabitable offer a tremendous wealth of unexplored microorganisms and enzymes. In this paper, we present the discovery and characterization of a novel γ-carbonic anhydrase (γ-CA) from the polyextreme Red Sea brine pool Discovery Deep (2141 m depth, 44.8°C, 26.2% salt) by single-cell genome sequencing. The extensive analysis of the selected gene helps demonstrate the potential of this culture-independent method. The enzyme was expressed in the bioengineered haloarchaeon Halobacterium sp. NRC-1 and characterized by X-ray crystallography and mutagenesis. The 2.6 Å crystal structure of the protein shows a trimeric arrangement. Within the γ-CA, several possible structural determinants responsible for the enzyme's salt stability could be highlighted. Moreover, the amino acid composition on the protein surface and the intra- and intermolecular interactions within the protein differ significantly from those of its close homologs. To gain further insights into the catalytic residues of the γ-CA enzyme, we created a library of variants around the active site residues and successfully improved the enzyme activity by 17-fold. As several γ-CAs have been reported without measurable activity, this provides further clues as to critical residues. Our study reveals insights into the halophilic γ-CA activity and its unique adaptations. The study of the polyextremophilic carbonic anhydrase provides a basis for outlining insights into strategies for salt adaptation, yielding enzymes with industrially valuable properties, and the underlying mechanisms of protein evolution.

Stability of microbial functionality in anammox sludge adaptation to various salt concentrations and different salt-adding steps.

The stability of community functioning in anaerobic ammonia oxidation (anammox) sludge adaptation to various salinity changes are concerned but not fully explored. In this study, two anammox reactors were designed in response to different salt levels and salt-adding methods. The reactor PI, run with small stepwise salt increments (0.5%-1.0%), removed >90% of nitrite and ammonium in the influent over the range of 0%-4% salt. By contrast, the reactor SI, run with a sharp salt increment (>2.5%), exhibited a reduced performance (by up to 44%) over the same salt range with a new steady state. The observed resilience times after salt perturbations indicated that the PI reactor recovered substantially and rapidly at all imposed salt levels. Principal coordinates analysis of 16S rRNA gene amplicon sequences revealed that bacterial community structures of the anammox sludge altered conspicuously in response to the salinity changes. However, quantitative PCR analysis showed that the shift in copy number of studied nitrogen-converting genes encoding hydrazine synthase (hzsA), bacterial and archaeal ammonia monooxygenases (amoA), nitrite oxidoreductase (nxrB), nitrite reductase (nirK), and nitrous oxide reductase (nosZ) was not significant (p > 0.05) in anammox sludge across the salt levels of 0.5%-4%, which suggests the stability of microbial community functioning in the osmoadaptation processes. The freshwater anammox Ca. Kuenenia showed high osmoadaptation by potentially adopting both high-salt-in and low-salt-in strategies to dominate in both reactors. The quantitative transcript analysis showed that the active anammox bacteria represented by hzsA transcripts in the SI reactor were approximately two orders of magnitude lower than those in the PI reactor during the long-term exposure to 4% salinity, manifesting the influence by the salt-increasing methods. These results provided new insight into osmo-adaptation of the anammox microbiome and will be useful for managing salinity effects on nitrogen removal processes.

Molecular adaptation to salinity fluctuation in tropical intertidal environments of a mangrove tree Sonneratia alba.

BACKGROUND: Mangroves have adapted to intertidal zones - the interface between terrestrial and marine ecosystems. Various studies have shown adaptive evolution in mangroves at physiological, ecological, and genomic levels. However, these studies paid little attention to gene regulation of salt adaptation by transcriptome profiles. RESULTS: We sequenced the transcriptomes of Sonneratia alba under low (fresh water), medium (half the seawater salinity), and high salt (seawater salinity) conditions and investigated the underlying transcriptional regulation of salt adaptation. In leaf tissue, 64% potential salinity-related genes were not differentially expressed when salinity increased from freshwater to medium levels, but became up- or down-regulated when salt concentrations further increased to levels found in sea water, indicating that these genes are well adapted to the medium saline condition. We inferred that both maintenance and regulation of cellular environmental homeostasis are important adaptive processes in S. alba. i) The sulfur metabolism as well as flavone and flavonol biosynthesis KEGG pathways were significantly enriched among up-regulated genes in leaves. They are both involved in scavenging ROS or synthesis and accumulation of osmosis-related metabolites in plants. ii) There was a significantly increased percentage of transcription factor-encoding genes among up-regulated transcripts. High expressions of salt tolerance-related TF families were found under high salt conditions. iii) Some genes up-regulated in response to salt treatment showed signs of adaptive evolution at the amino acid level and might contribute to adaptation to fluctuating intertidal environments. CONCLUSIONS: This study first elucidates the mechanism of high-salt adaptation in mangroves at the whole-transcriptome level by salt gradient experimental treatments. It reveals that several candidate genes (including salt-related genes, TF-encoding genes, and PSGs) and major pathways are involved in adaptation to high-salt environments. Our study also provides a valuable resource for future investigation of adaptive evolution in extreme environments.

Lignin biosynthesis genes play critical roles in the adaptation of Arabidopsis plants to high-salt stress.

Salinity is a major abiotic stressor that limits the growth, development, and reproduction of plants. Our previous metabolic analysis of high salt-adapted callus suspension cell cultures from Arabidopsis roots indicated that physical reinforcement of the cell wall is an important step in adaptation to saline conditions. Compared to normal cells, salt-adapted cells exhibit an increased lignin content and thickened cell wall. In this study, we investigated not only the lignin biosynthesis gene expression patterns in salt-adapted cells, but also the effects of a loss-of-function of CCoAOMT1, which plays a critical role in the lignin biosynthesis pathway, on plant responses to high-salt stress. Quantitative real-time PCR analysis revealed higher mRNA levels of genes involved in lignin biosynthesis, including CCoAOMT1, 4CL1, 4CL2, COMT, PAL1, PAL2, and AtPrx52, in salt-adapted cells relative to normal cells, which suggests activation of the lignin biosynthesis pathway in salt-adapted cells. Moreover, plants harboring the CCoAOMT1 mutants, ccoaomt1-1 and ccoaomt1-2, were phenotypically hypersensitive to salt stress. Our study has provided molecular and genetic evidence indicating the importance of enhanced lignin accumulation in the plant cell wall during the responses to salt stress.

Metabolic Adjustment of Arabidopsis Root Suspension Cells During Adaptation to Salt Stress and Mitotic Stress Memory.

Sessile plants reprogram their metabolic and developmental processes during adaptation to prolonged environmental stresses. To understand the molecular mechanisms underlying adaptation of plant cells to saline stress, we established callus suspension cell cultures from Arabidopsis roots adapted to high salt for an extended period of time. Adapted cells exhibit enhanced salt tolerance compared with control cells. Moreover, acquired salt tolerance is maintained even after the stress is relieved, indicating the existence of a memory of acquired salt tolerance during mitotic cell divisions, known as mitotic stress memory. Metabolite profiling using 1H-nuclear magnetic resonance (NMR) spectroscopy revealed metabolic discrimination between control, salt-adapted and stress-memory cells. Compared with control cells, salt-adapted cells accumulated higher levels of sugars, amino acids and intermediary metabolites in the shikimate pathway, such as coniferin. Moreover, adapted cells acquired thicker cell walls with higher lignin contents, suggesting the importance of adjustments of physical properties during adaptation to elevated saline conditions. When stress-memory cells were reverted to normal growth conditions, the levels of metabolites again readjusted. Whereas most of the metabolic changes reverted to levels intermediate between salt-adapted and control cells, the amounts of sugars, alanine, γ-aminobutyric acid and acetate further increased in stress-memory cells, supporting a view of their roles in mitotic stress memory. Our results provide insights into the metabolic adjustment of plant root cells during adaptation to saline conditions as well as pointing to the function of mitotic memory in acquired salt tolerance.

Characterization and mutation analysis of a halotolerant serine protease from a new isolate of Bacillus subtilis.

OBJECTIVES: A bacterial halotolerant enzyme was characterized to understand the molecular mechanism of salt adaptation and to explore its protein engineering potential. RESULTS: Halotolerant serine protease (Apr_No16) from a newly isolated Bacillus subtilis strain no. 16 was characterized. Multiple alignments with previously reported non-halotolerant proteases, including subtilisin Carlsberg, indicated that Apr_No16 has eight acidic or polar amino acid residues that are replaced by nonpolar amino acids in non-halotolerant proteases. Those residues were hypothesized to be one of the primary contributors to salt adaptation. An eightfold mutant substituted with Ala residues exhibited 1.2- and 1.8-fold greater halotolerance at 12.5% (w/v) NaCl than Apr_No16 and Carlsberg, respectively. Amino acid substitution notably shifted the theoretical pI of the eightfold mutant, from 6.33 to 9.23, compared with Apr_No16. The resulting protein better tolerated high salt conditions. CONCLUSIONS: Changing the pI of a bacterial serine protease may be an effective strategy to improve the enzyme's halotolerance.

Salt management strategy defines the stem and leaf hydraulic characteristics of six mangrove tree species.

Mangroves in hypersaline coastal habitats are under constant high xylem tension and face great risk of hydraulic dysfunction. To investigate the relationships between functional traits and salt management, we measured 20 hydraulic and photosynthetic traits in four salt-adapted (SA) and two non-SA (NSA) mangrove tree species in south China. The SA species included two salt secretors (SSs), Avicennia marina (Forsskål) Vierhapper and Aegiceras corniculatum (L.) Blanco and two salt excluders (SEs), Bruguiera gymnorrhiza (L.) Savigny and Kandelia obovata (L.) Sheue et al. The two NSA species were Hibiscus tiliaceus (L.) and Pongamia pinnata (L.) Merr. Extremely high xylem cavitation resistance, indicated by water potential at 50% loss of xylem conductivity (Ψ50; -7.85 MPa), was found in SEs. Lower cavitation resistance was observed in SSs, and may result from incomplete salt removal that reduces the magnitude of xylem tension required to maintain water uptake from the soil. Surprisingly, the NSA species, P. pinnata, had very low Ψ50 (-5.44 MPa). Compared with NSAs, SAs had lower photosynthesis, vessel density, hydraulic conductivity and vessel diameter, but higher sapwood density. Eight traits were strongly associated with species' salt management strategies, with predawn water potential (ΨPD) and mean vessel diameter accounting for 95% flow (D95) having the most significant association; D95 separated SAs from NSAs and SEs had the lowest ΨPD. There was significant coupling between hydraulic traits and carbon assimilation traits. Instead of hydraulic safety being compromised by xylem efficiency, mangrove species with higher safety had higher efficiency and greater sapwood density (ρSapwood), but there was no relationship between ρSapwood and efficiency. Principal component analysis differentiated the species of the three salt management strategies by loading D, D95 and vessel density on the first axis and loading ΨPD, Ψ50 and water potential at 12% loss of xylem conductivity (Ψ12), ρSapwood and quantum yield on the second axis. Our results provide the first comparative characterization of hydraulic and photosynthetic traits among mangroves with different salt management strategies.

Draft Genome of Scalindua rubra, Obtained from the Interface Above the Discovery Deep Brine in the Red Sea, Sheds Light on Potential Salt Adaptation Strategies in Anammox Bacteria.

Several recent studies have indicated that members of the phylum Planctomycetes are abundantly present at the brine-seawater interface (BSI) above multiple brine pools in the Red Sea. Planctomycetes include bacteria capable of anaerobic ammonium oxidation (anammox). Here, we investigated the possibility of anammox at BSI sites using metagenomic shotgun sequencing of DNA obtained from the BSI above the Discovery Deep brine pool. Analysis of sequencing reads matching the 16S rRNA and hzsA genes confirmed presence of anammox bacteria of the genus Scalindua. Phylogenetic analysis of the 16S rRNA gene indicated that this Scalindua sp. belongs to a distinct group, separate from the anammox bacteria in the seawater column, that contains mostly sequences retrieved from high-salt environments. Using coverage- and composition-based binning, we extracted and assembled the draft genome of the dominant anammox bacterium. Comparative genomic analysis indicated that this Scalindua species uses compatible solutes for osmoadaptation, in contrast to other marine anammox bacteria that likely use a salt-in strategy. We propose the name Candidatus Scalindua rubra for this novel species, alluding to its discovery in the Red Sea.

Comparative proteome analysis reveals proteins involved in salt adaptation in Photobacterium damselae subsp. piscicida.

Proteomic approaches were applied to investigate whether Photobacterium damselae subsp. piscicida (Phdp) can directly sense and respond to growth conditions under different salinities, 0.85% and 3.5% NaCl concentrations, mimicking the osmotic conditions in host and marine water bodies, respectively. Proteins significantly altered were analyzed by two-dimensional gel electrophoresis (2-DE), liquid chromatography-electrospray ionization-quadrupole-time-of-flight tandem mass spectrometry (LC-ESI-Q-TOF MS/MS) and bioinformatics analysis, thus resulting in 16 outer membrane proteins (OMPs), 12 inner membrane proteins (IMPs), and 20 cytoplasmic proteins (CPs). Quantitative real-time PCR was also applied to monitor the mRNA expression level of these target proteins. Cluster of orthologous groups of protein (COG) analysis revealed that when shifting from 3.5% to 0.85% salinity, the majority of the up-regulated proteins were involved in posttranslational modification, protein turnover, and chaperones, while the down-regulated proteins were mainly related to energy production and conversion, compatible solutes (carbohydrates, amino acids and their derivatives) biogenesis and transport. Differentially expressed proteins identified in the current study could be used to elucidate the salt adaptation mechanisms of Phdp during their transition between host cells and the marine habitats.

Nitrification and microalgae cultivation for two-stage biological nutrient valorization from source separated urine.

Urine contains the majority of nutrients in urban wastewaters and is an ideal nutrient recovery target. In this study, stabilization of real undiluted urine through nitrification and subsequent microalgae cultivation were explored as strategy for biological nutrient recovery. A nitrifying inoculum screening revealed a commercial aquaculture inoculum to have the highest halotolerance. This inoculum was compared with municipal activated sludge for the start-up of two nitrification membrane bioreactors. Complete nitrification of undiluted urine was achieved in both systems at a conductivity of 75mScm(-1) and loading rate above 450mgNL(-1)d(-1). The halotolerant inoculum shortened the start-up time with 54%. Nitrite oxidizers showed faster salt adaptation and Nitrobacter spp. became the dominant nitrite oxidizers. Nitrified urine as growth medium for Arthrospira platensis demonstrated superior growth compared to untreated urine and resulted in a high protein content of 62%. This two-stage strategy is therefore a promising approach for biological nutrient recovery.