Exopolymeric Substances Research Articles

Characterization of Novel Species of Potassium-Dissolving Purple Nonsulfur Bacteria Isolated from In-Dyked Alluvial Upland Soil for Maize Cultivation

Potassium (K) is immobilized within the clay minerals, making it unavailable for plant use. Therefore, the current study aimed to (i) select isolates of purple nonsulfur bacteria that can dissolve K (K-PNSB) and (ii) evaluate the production of plant-growth-promoting substances by the K-PNSB isolates. The results revealed that from in-dyked alluvial soils in hybrid maize fields, 61 K-PNSB isolates were obtained under the pH 5.50 conditions. The total dissolved K content (Kdis) by the 61 K-PNSB isolates fluctuated from 56.2 to 98.6 mg L−1. Therein, three isolates, including M-Sl-09, M-So-11, and M-So-14 had Kdis of 48.1–48.8 mg L−1 under aerobic dark condition (ADC) and 47.6–49.7 mg L−1 under microaerobic light condition (MLC). Moreover, these three isolates can also fix nitrogen (19.1–21.5 mg L−1 and 2.64–7.24 mg L−1), solubilize Ca-P (44.3–46.8 mg L−1 and 0.737–6.965 mg L−1), produce indole-3-acetic acid (5.34–7.13 and 2.40–3.23 mg L−1), 5-aminolevulinic acid (1.85–2.39 and 1.53–2.47 mg L−1), siderophores (1.06–1.52 and 0.92–1.26 mg L−1), and exopolymeric substances (18.1–18.8 and 52.0–56.0%), respectively, under ADC and MLC. The bacteria were identified according to their 16S rDNA as Cereibacter sphaeroides M-Sl-09, Rhodopseudomonas thermotolerans M-So-11, and Rhodospeudomonas palustris M-So-14. These potential bacteria should be further investigated as a plant-growth-promoting biofertilizer.

Towards the mechanical stability of biocrusts in drylands: Insights from inorganic ions and organic compounds and their interactions

Biocrusts are an important component of dryland ecosystems as they perform crucial ecological functions like stabilizing soils, mediating the hydrological cycle, and improving nutrient availability. The high mechanical stability of biocrusts is understood to be linked to exopolymeric substances (EPS), which in turn, are responsible for the adsorption of various ions and chemical compounds. This study aimed to investigate the chemical composition of biocrusts and assess potential correlations between their chemical composition and mechanical stability. Samples of three types of biocrusts (cyanobacteria, cyanobacteria and moss mixed, and moss crusts) and bare soil (as control) were collected from the northern Loess Plateau of China. The inorganic ions and organic compounds present in biocrusts were quantified using inductively coupled plasma-optic emission spectrometry, ion chromatography, and gas chromatography-mass spectrometry. Biocrust mechanical stability was assessed by penetration resistance (PR) and the mean weight diameter (MWD) of aggregates. Finally, the contribution of inorganic ions and organic compounds to the stability of the biocrusts was elucidated. The results indicated that all three types of biocrusts were more stable than bare soil, with moss crusts being the most stable. Chemical analyses revealed an enrichment of inorganic ions such as K+, Ca2+, Na+, Mg2+, SO42–, and halogen ions within the biocrusts, while they showed a depletion of Fe2+, Al3+, and NO3–. Ten types of organic compounds were identified in biocrusts and bare soil, with medium-chain alkanes and long-chain acids being the dominant compounds. In some cases, acids accounted for more than 40 % of the total organic compound content of the biocrusts. Redundancy analysis showed that the content of inorganic ions, such as Ca2+ and Mg2+, and organic compounds such as acids, amides, and alkenes, exhibited the closest association with the biocrust stability. Partial least squares path modeling indicated that both inorganic ions and organic compounds indirectly affected biocrust stability by influencing electric conductivity, bulk density, EPS, and fine particle (clay and silt) content. A strong association was found between the inorganic ions and PR or MWD (0.658 and 0.744, respectively), whilst the total effect of organic compounds on PR and MWD was 0.814 and 0.801, respectively. It is suggested that both the magnitude and types of chemicals associated with EPS indicate their capability to grant mechanical stability of the biocrusts, which in turn is conducive to maintaining the critical functions of biocrusts in global drylands.

Carbonate mud production in lakes is driven by degradation of microbial substances

Carbonate mud is crucial in the global carbon cycle and serves as a key sedimentary archive for paleoclimate reconstruction. Understanding the mechanisms behind its formation is crucial for explaining long-term carbon storage, including atmospheric carbon dioxide transfer to the hydrosphere and variations in mud production over geological timescales. Various mechanisms explain carbonate mud formation in both lake and marine sediments. Using bio-physicochemical methods on deep sediments of Lake Ilay, Jura, France, we propose a model of micrite formation. Our study shows that micrite mineralization occurs in sediments due to the degradation of ooze rich in exopolymeric substances throughout the sediment core’s depth. This mineralization continues as long as exopolymeric substances are present, persisting for at least 2000 years. Cryo-Scanning electron microscope imaging reveals calcite nucleation at degraded exopolymeric substance nodes, advancing with substance degradation and calcium release. These findings provide insights into fossil carbonate mud origins and formation processes.

The potential of phosphorus-solubilizing purple nonsulfur bacteria in agriculture: Present and future perspectives

Abstract Phosphorus (P) is one of the essential macronutrients for crops. It is present in soil in two forms: soluble and insoluble. However, plants cannot absorb the insoluble forms, including Al-P, Fe-P, and Ca-P; thus, the phosphorus use efficiency is reduced. Therefore, the biological approaches should focus more on sustainable agriculture to overcome this constraint. This article cites publications relating to the biological P solubilizer group of bacteria, which have a highly potential adaptation to many conditions in soils. Among the biological approaches, purple nonsulfur bacteria (PNSB) are a potent group of bacteria according to their adaptability in acidic, saline, and toxic conditions based on their mechanisms in producing exopolymeric substances and siderophores under such adverse environments like acid-sulfate and saline soils. PNSB can solubilize P in soil to have more P availability for soil microbes and plants. This particular group of bacteria has been widely applied in liquid and solid forms from agricultural waste to promote plant growth under submerged conditions. Moreover, this article summarized the P-solubilizing mechanisms of P-solubilizing bacteria and introduced future research perspectives on patterns of PNSB in aspects of nutrient-providing potency, plant growth-promoting capability, and biological control capacity. However, the specific mechanisms of P solubilization by PNSB have not been well documented since the P-solubilizing mechanisms have been investigated on general P-solubilizing bacteria. Thus, specific pathways and metabolites relating to the P-solubilizing PNSB should be investigated, and attention should be addressed to them soon.

Micro- and Nano-Plastics Induced Release of Protein-Enriched Microbial Exopolymeric Substances (EPSs) in Marine Environments

Plastics are produced, consumed, and disposed of worldwide, with more than eight million tons of plastic litter entering the ocean each year. Plastic litter accumulates in marine and terrestrial environments through a variety of pathways. Large plastic debris can be broken down into micro- and nano-plastic particles through physical/mechanical mechanisms and biologically or chemically mediated degradation. Their toxicity to aquatic organisms includes the scavenging of pollutant compounds and the production of reactive oxygen species (ROS). Higher levels of ROS cause oxidative damages to microalgae and bacteria; this triggers the release of large amounts of exopolymeric substances (EPSs) with distinct molecular characteristics. This review will address what is known about the molecular mechanisms phytoplankton and bacteria use to regulate the fate and transport of plastic particles and identify the knowledge gaps, which should be considered in future research. In particular, the microbial communities react to plastic pollution through the production of EPSs that can reduce the plastic impacts via marine plastic snow (MPS) formation, allowing plastics to settle into sediments and facilitating their removal from the water column to lessen the plastic burden to ecosystems.

Latitudinal variations of iron chemical speciation in the euphotic zone of the central Pacific Ocean

The concentrations of dissolved iron (DFe), iron-binding ligands (LFe), and electroactive humic-like substances (eHS) were revealed in the upper 200 m along the 170°W latitudinal transect of the central Pacific Ocean in summer, which was weakly influenced by terrestrial input. DFe was largely depleted throughout the transect, except in the Bering Sea, and below 100 m in the North Pacific Subarctic Gyre. The concentration of LFe was lowest within the subtropical gyres and was lower in the Southern Hemisphere, which is consistent with the results from the Atlantic Ocean. The vertical distribution of LFe was relatively constant in the subtropical regions, whereas in the subarctic regions the subsurface maximum appeared around or over the subsurface chlorophyll maximum at some stations. The higher concentration of LFe in the subarctic regions coincides with a lower stability constant, which suggests a higher contribution of weaker ligands, including humic and exopolymeric substances. The horizontal and vertical distribution patterns of eHS were largely similar to those of LFe, supporting their significant contribution to iron-binding capacity in the upper 200 m, particularly in the subarctic regions. However, the eHS concentration was only weakly correlated with that of the fluorescently determined humic-like substances, demonstrating the substantially different chemical properties of the two humic-like substances. The strong positive correlation between the concentrations of eHS and chlorophyll a and Synechococcus strongly suggests their biological origins. However, further research is required to examine whether eHS are directly produced by phytoplankton or released via relevant biological processes, such as grazing, bacterial composition, and viral lysis.

Genomic insight of phosphate solubilization and plant growth promotion of two taxonomically distinct winter crops by Enterobacter sp. DRP3.

Study of rhizospheric microbiome-mediated plant growth promotional attributes currently highlighted as a key tool for the development of suitable bio-inoculants for sustainable agriculture purposes. In this context, we have conducted a detailed study regarding the characterization of phosphate solubilizing potential by plant growth-promoting bacteria that have been isolated from the rhizosphere of a pteridophyte Dicranopteris sp., growing on the lateritic belt of West Bengal. We have isolated three potent bacterial strains, namely DRP1, DRP2, and DRP3 from the rhizoids-region of Dicranopteris sp. Among the isolated strains, DRP3 is found to have the highest phosphate solubilizing potentiality and is able to produce 655.89 and 627.58µg ml-1 soluble phosphate by solubilizing tricalcium phosphate (TCP) and Jordan rock phosphate, respectively. This strain is also able to solubilize Purulia rock phosphate moderately (133.51µg ml-1). Whole-genome sequencing and further analysis of the studied strain revealed the presence of pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase gdh gene along with several others that were well known for their role in phosphate solubilization. Further downstream, quantitative reverse transcriptase PCR-based expression study revealed 1.59-fold upregulation of PQQ-dependent gdh gene during the solubilization of TCP. Root colonization potential of the studied strain on two taxonomically distinct winter crops viz. Cicer arietinum and Triticum aestivum has been checked by using scanning electron microscopy. Other biochemical analyses for plant growth promotion traits including indole acetic acid production (132.02µg ml-1), potassium solubilization (3mg l-1), biofilm formation, and exopolymeric substances productions (1.88-2.03µg ml-1) also has been performed. This study highlighted the active involvement of PQQ-dependent gdh gene during phosphate solubilization from any Enterobacter group. Moreover, our study explored different roadmaps for sustainable farming methods and the preservation of food security without endangering soil health in the future.

Isolation and characterization of hexavalent chromium-tolerant endophytic bacteria inhabiting Solanum virginicum L. roots: A study on potential for chromium bioremediation and plant growth promotion

Present study was performed with the aim to isolate Heavy metal Tolerant- PGPB (HMT-PGPB) from metal-contaminated site and use them for Cr bioremediation. Six different bacterial strains were obtained from the endosphere of Solanum virginicum L. roots and cultured using nutrient agar media amended with 20 mg/L of Cr(VI). The ability of these Cr(VI) tolerant bacterial isolates were assessed for PGP traits like producing siderophores, indole-3-acetic acid (IAA), and phosphate solubilization. The findings indicated that all of the isolates could produce exopolymeric substances and IAA, five of them could produce siderophores, and three could solubilize phosphate. Furthermore, the minimum inhibitory concentrations of these strains werealso determined. These strains were identified as Bacillus licheniformis SxR1, B. tequilensis SxR2, B. subtilis SxR3, B. velezensis SxR4, B. amyloliquefaciens SxR6, and B. stercoris SxR8. To validate the findings, it is crucial to comprehend how Cr(VI) affects Bacillus sp. SxR1 cells to determine the course of uptake and bacterial cell alteration, which was assessed via Fourier Transform-Infrared Spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM).

Cyclic di-peptide Cyclo (L-Phe-L-Pro) mitigates the quorum-sensing mediated virulence in Salmonella typhi and biofilm formation in poultry and plastic system

Salmonella typhi is a predominant foodborne pathogen, posing a significant threat to food quality and safety through typhoid outbreaks. Quorum sensing (QS) and its pathways are crucial for typhoid antigen regulation and S. typhi-mediated spoilage and pathogenesis. Therefore, this study intends to identify secondary metabolites from extracts of 15 bacterial isolates sourced from wild Mangifera indica (mango) brine pickles as novel anti-QS agents against S. typhi. Cell-free supernatants (CFS) of 15 bacterial isolates from fermented mango brine pickles were assessed and identified for anti-QS positive metabolites using GC-MS. Anti-QS metabolite was tested on early and mature biofilms, as well as violacein inhibition, EPS, cellular adherence, motility, antibiotics, and immune resistance of S. typhi. Gene expression and in-silico studies were also conducted to validate the compound's efficacy. The results depicted that among the 15 isolates, Bacillus subtilis P89 exhibited potent anti-QS properties. Gas chromatography-mass spectrometry (GC-MS) analysis identified twelve potential quorum-sensing inhibiting compounds, with Cyclo (L-Phenylalanine-L-Proline) (CPP) demonstrating the maximum anti-QS activity against S. typhi. CPP disrupted the pathogen's early and mature biofilms, reducing exo-polymeric substance production, cell hydrophobicity, and motility at sub-lethal concentrations. It also enhanced the immune response against S. typhi and improved traditional efficacy. Real-time qPCR analyses revealed CPP's modulation of essential quorum-sensing regulatory genes. Molecular docking studies indicated competitive binding of CPP with the SdiA receptor. CPP inhibited S. typhi biofilm formation on chicken skin, plastics, and eggshells. To our knowledge, this study is the first to highlight CPP's potential in food and clinical environments to combat S. typhi via quorum sensing-based mechanisms.

Modifying luteolin’s algicidal effect on Microcystis by virgin and diversely-aged polystyrene microplastics: Unveiling novel mechanisms through microalgal adaptive strategies

Luteolin has shown great potential in inhibiting Microcystis-dominated cyanobacterial blooms. However, widespread microplastics (MPs) in natural aquatic systems often serve as substrates for cyanobacterial growth, which could impact cyanobacterial resistance to external stresses and interfere with luteolin’s algicidal effect. This study explored the influence of virgin and diversely-aged polystyrene microplastics (PS-MPs) on inhibitory effect of luteolin on Microcystis growth and its microcystins (MCs) production/release. Moreover, the underlying mechanisms were also revealed by jointly analyzing SEM image, antioxidant response, exopolymeric substances (EPSs) production, and functional gene expression. Results suggested that 0.5, 5, and 50 mg/L virgin and diversely-aged PS-MPs almost weakened growth inhibition and oxidative damage of two doses of luteolin against Microcystisby stimulating its EPSs production and inducing self-aggregation of Microcystis cells and/or hetero-aggregation between Microcystis cells and PS-MPs. Compared to virgin PS-MPs, photo-aged PS-MPs possessed rougher flaky surfaces, and hydrothermal-aged PS-MPs showed internal cracking. These characteristics led to greater stimulation of EPS production and exhibited more significant protective effects on Microcystis. Notably, PS-MPs also decreased MCs content in aqueous phase, likely because they adsorbed some MCs. Such toxigenic hetero-aggregates formed by MCs, MPs, and Microcystis cells would directly poison grazing organisms that consume them and create more pathways for MCs into food web, posing greater eco-risks. This is the first study to clarify the influence and mechanisms of virgin and diversely-aged MPs on allelopathic algicidal effects from the perspective of microalgal inherent adaptive strategies.

Microbial interactions with microplastics: Insights into the plastic carbon cycle in the ocean

The fate of microplastics (MPs) in the ocean is mostly driven by (i) photo-oxidation to smaller particles and dissolved constituents, which fuel the dissolved organic carbon pool (plastic-derived DOC, pDOC), and (ii) interactions with organic matter forming sinking aggregates (marine plastic snow). Two separate laboratory experiments were conducted to investigate the two pathways of MPs. In the first experiment, we measured potential rates of microbial pDOC utilization in bottle incubations over 15 days with microbial assemblages from coastal and offshore waters. Microbial utilization of pDOC was more efficient in the coastal (72% bioreactive pDOC) compared with the offshore experiment (32% bioreactive pDOC) 15 days. Changes in bacterial cell abundance and extracellular enzyme activities (glucosidase, peptidase, esterases) indicated that a fraction of pDOC was repackaged into microbial exopolymeric substances (EPS), stimulating growth of known EPS degrading bacteria within the phyla Verrucomicrobiota and Planctomycetota. Microbial EPS likely also played a key role in our second experiment that showed the formation of marine plastic snow in roller tanks with cultured cells of Emiliana huxleyi but not with cells of an Isocrysis sp. culture. Average sinking velocities of marine plastic snow were a factor of 1.2 lower compared with marine snow without MPs. Both aggregate types showed reduced sinking velocities in a density stratified sinking column. Our results from the two experiments on (i) microbial utilization of pDOC and (ii) the formation and sinking of marine plastic snow indicate potential effects of plastic-derived compounds on microbial elemental cycles (i.e., pDOC repackaged into EPS) with consequences for the efficiency of the biological carbon pump (i.e., marine plastic snow reduces carbon export) and the fate of plastic-derived compounds in the ocean.

Cell density and extracellular matrix composition mitigate bacterial biofilm sensitivity to UV-C LED irradiation

Ultraviolet-C light-emitting diodes (UV-C LEDs) are an emerging technology for decontamination applications in different sectors. In this study, the inactivation of bacterial biofilms was investigated by applying an UV-C LED emitting at 280 nm and by measuring both the influence of the initial cell density (load) and presence of an extracellular matrix (biofilm). Two bacterial strains exposing diverging matrix structures and biochemical compositions were used: Pseudomonas aeruginosa and Leuconostoc citreum. UV-C LED irradiation was applied at three UV doses (171 to 684 mJ/cm2) on both surface-spread cells and on 24-h biofilms and under controlled cell loads, and bacterial survival was determined. All surface-spread bacteria, between 105 and 109 CFU/cm2, and biofilms at 108 CFU/cm2 showed that bacterial response to irradiation was dose-dependent. The treatment efficacy decreased significantly for L. citreum surface-spread cells when the initial cell load was high, while no load effect was observed for P. aeruginosa. Inactivation was also reduced when bacteria were grown under a biofilm form, especially for P. aeruginosa: a protective effect could be attributed to abundant extracellular DNA and proteins in the matrix of P. aeruginosa biofilms, as revealed by Confocal Laser Scanning Microscopy observations. This study showed that initial cell load and exopolymeric substances are major factors influencing UV-C LED antibiofilm treatment efficacy.Key points• Bacterial cell load (CFU/cm2) could impact UV-C LED irradiation efficiency• Characteristics of the biofilm matrix have a paramount importance on inactivation• The dose to be applied can be predicted based on biofilm propertiesGraphical

Unveiling the functional significance of the 14.3.3 protein: A key player in Paracoccidioides brasiliensis biofilm formation

Paracoccidioidomycosis (PCM) is a systemic mycosis caused by Paracoccidioides spp. The interaction mediated by the presence of adhesins on the fungal surface and receptors in the extracellular matrix of the host, as well as the biofilm formation, is essential in its pathogenesis. Adhesins such as gp43, enolase, GAPDH (glyceraldehyde-3-phosphate dehydrogenase), and 14-3-3 have been demonstrated in the Paracoccidioides brasiliensis (Pb18) strain and recognized as necessary in the fungus-host interaction. The Pb 18 strain silenced to 14-3-3 showed changes in morphology, virulence, and adhesion capacity. The study aimed to evaluate the role of adhesin 14-3-3 in P. brasiliensis biofilm formation and the differential expression of genes related to adhesins, comparing planktonic and biofilm forms. The presence of biofilm was also verified in sutures in vitro and in vivo. The silenced strain (Pb14-3-3 aRNA) was compared with the wild type Pb18, determining the differential metabolic activity between the strains by the XTT reduction assay; the biomass by violet crystal and the polysaccharides by safranin, even as morphological differences by microscopic techniques. Differential gene expression for adhesins was also analyzed, comparing the relative expression of these in planktonic and biofilm forms at different times. The results suggested that the silencing of 14-3-3 protein altered the ability to form biofilm and its metabolism. The quantity of biomass was similar in both strains; however, the formation of exopolymeric substances and polysaccharide material was lower in the silenced strain. Our results showed increased expression of enolase, GAPDH, and 14-3-3 genes in the first periods of biofilm formation in the Pb18 strain. In contrast, the silenced strain showed a lower expression of these genes, indicating that gene silencing can influence the expression of other genes and be involved in the biofilm formation of P. brasiliensis. In vitro and in vivo assays using sutures confirmed this yeast's ability to form biofilm and may be implicated in the pathogenesis of paracoccidioidomycosis.

Antimony precipitation and removal by antimony hyper resistant strain Achromobacter sp. 25-M

Microbes have been confirmed to play key role in biogeochemistry of antimony. However, the impact of indigenous bacteria (from active mines) on the behavior of dissolved antimony remained poorly understood. In current study, the hyper antimony-resistant strain, Achromobacter sp. 25-M, isolated from the world largest antimony deposit, Xikuangshan antimony deposit, was evaluated for its role in dissolved Sb(V) and Sb(III) precipitation and removal. Despite of the high resistance to Sb(III) (up to 50 mM), the facultative alkaliphile, 25-M was not capable of Sb(III) oxidation. Meanwhile 25-M can produce high amount of exopolymeric substance (EPS) with the presence of Sb, which prompted us to investigate the potential role of EPS in the precipitation and removal of Sb. To this end, 2 mM of Sb(III) and Sb(V) were added into the experimental systems with and without 25-M to discern the interaction mechanism between microbe and antimony. After 96 hrs’ incubation, 88% [1.73 mM (210 mg/L)] of dissolved Sb(V) and 80% [1.57 mM (190 mg/L)] of dissolved Sb(III) were removed. X-ray diffraction and energy dispersive spectroscopy analysis confirmed the formation of valentinite (Sb2O3) in Sb(III) amended system and a solitary Sb(V) mineral mopungite [NaSb(OH)6] in Sb(V) amended group with microbes. Conversely, no precipitate was detected in abiotic systems. Morphologically valentinite was bowtie and mopungite was pseudo-cubic as indicated by scanning electronic microscopy. EPS was subjected to fourier transform infrared (FT-IR) analysis. FT-IR analysis suggested that –OH and –COO groups were responsible for the complexation and ligand exchange with Sb(III) and Sb(V), respectively. Additionally, the C–H group and N–H group could be involved in π-π interaction and chelation with Sb species. All these interactions between Sb and functional groups in EPS may subsequently favore the formation of valentinite and mopungite. Collectively, current results suggested that EPS play fundamental role in bioprecipitation of Sb, which offered a new strategy in Sb bioremediation.

Insights into the interaction between mineral formation and heavy metals immobilization, mediated by Virgibacillus exopolymeric substances

Heavy metal pollution poses significant risks to both the environment and human health due to their toxicity, long residence times, and their ability to bioaccumulate and bio magnify across the food chain. To address this issue, microbial biomineralization has emerged as a promising approach to the bio-removal of heavy metals through immobilization. This process is facilitated by extracellular polymeric substances (EPS), which also play a crucial role in mediating mineral formation. In this study, the interactions between several selected heavy metals (Cd2+, Cu2+, Ni2+, Zn2+), EPS, and mineral formation were investigated using two mineral-forming Virgibacillus strains isolated from the Qatari sabkhas, which are known to be suitable sites for the formation of biominerals. An additional non-mineral-forming Virgibacillus strain isolated from the Dukhan oil waste dumpsite was also investigated. Cd2+ and Zn2+ were to inhibit mineral formation, likely due to competition with Ca2+ and Mg2+ ions during biomineralization. However, exposure to Ni2+ or Cu2+ resulted in changes in the FTIR spectra of the EPS, suggesting the presence of specific functional group bindings within the EPS matrix. The EPS produced by each strain was also directly associated with their efficiency (%) at removing heavy metals. Notably, the EPS from Virgibacillus halodenitrificans Z4D1, the non-mineral-forming strain, exhibited the highest heavy metal removal efficiency of 31.7 % for Zn2+. These findings reveal that EPS do not only affect the biomineralization process but also that the functional groups in EPS have a direct effect on the immobilization of several heavy metals. Conditions that are not suitable for mineral formation may instead be appropriate for the removal of specific heavy metals.

Thermodynamic and Kinetic Studies of Dolomite Formation: A Review

The “dolomite problem”, which has confused scientists for nearly two centuries, is an important fundamental geological problem. The mineralogical characteristics of carbonate minerals show that the dolomite structure consists of an ordered arrangement of alternating layers of Ca2+ and Mg2+ cations interspersed with CO32− anion layers normal to the c-axis. The dolomite structure violates the c glide plane in the calcite structure, which means that dolomite has R3¯ space group symmetry. The ordered dolomite has superlattice XRD reflections [e.g., (101), (015) and (021)], which distinguish it from calcite and high-Mg calcite. The calculation of thermodynamic parameters shows that modern seawater has a thermodynamic tendency of dolomite precipitation and the dolomitization reaction can be carried out in standard state. However, the latest thermodynamic study shows that modern seawater is not conducive to dolomitization, and that seawater is favorable for dolomitization in only a few regions, such as Abu Dhabi, the Mediterranean and the hypersaline lagoons in Brazil. The kinetic factors of dolomite formation mainly consist of the hydration of Mg2+, the presence of sulfate and the activity of carbonate. Current studies have shown that the presence of microorganisms, exopolymeric substances (EPS), organic molecules, carboxyl and hydroxyl functional groups associated with microorganisms and organic molecules, clay minerals with negative charges and dissolved silica facilitate magnesium ions to overcome hydration and thus promote Mg2+ incorporation into growing Ca-Mg carbonates. Similarly, the metabolic activity of microorganisms is conducive to the increase in alkalinity. However, the inhibitory effect of sulfate on dolomite formation seems to be overestimated, and sulfate may even be a catalyst for dolomite formation. Combining the carbonate crystallization mechanism with thermodynamic and kinetic factors suggests that the early stage of dolomite precipitation or the dolomitization reaction may be controlled by kinetics and dominated by unstable intermediate phases, while metastable intermediate phases later transform to ordered dolomite via an Ostwald’s step rule.

Antibiotic-Induced Biofilm Formations in Pseudomonas aeruginosa Strains KPW.1-S1 and HRW.1-S3 are Associated with Increased Production of eDNA and Exoproteins, Increased ROS Generation, and Increased Cell Surface Hydrophobicity.

Pseudomonas aeruginosais a medically important opportunistic pathogen due to its intrinsic ability to form biofilmson different surfaces as one of the defense mechanisms for survival. The fact that it can formbiofilms on various medical implants makes it more harmful clinically. Although variousantibiotics are used to treatPseudomonas aeruginosainfections, studies have shown thatsub-MIClevels of antibiotics could inducePseudomonasbiofilm formation. Thepresent study thus explored the effect of the aminoglycoside antibiotic gentamicin on the biofilm dynamics of two Pseudomonas aeruginosa strains KPW.1-S1 and HRW.1-S3.Biofilm formation was found to be increased in the presence of increased concentrations of gentamicin. Confocal,scanning electronmicroscopy,and other biochemical tests deduced that biofilm-forming components exoproteins, eDNA, and exolipids as exopolymeric substances inPseudomonas aeruginosabiofilms were increased in the presence of gentamicin. An increase in reactive oxygen species generation along with increased cell surface hydrophobicity was also seen for both strains when treated with gentamicin. The observed increase in the adherence of the cells accompanied by the increase in the components of exopolymeric substances may have largely contributed to the increased biofilm production by the Pseudomonas aeruginosa strains under the stress of the antibiotic treatment.

Simultaneous production of polyhydroxybutyrate and biogas from paper mill sludge through sodium citrate-mediated disperser-induced phase separated pretreatment

Paper mill waste activated sludge is an excess sludge produced from the paper industry wastewater treatment plant. Because of the bulk nature, its disposal concerns both economic and environmental perspectives. However, it widely consists of organic components and is considered a major attraction for its valorization to produce bioenergy and valued products. During the bioenergy and valued product retrieval, the enzymatic hydrolysis got hampered due to the presence of exopolymeric substances and thus require proper pretreatment prior to the product recovery. The application of two different phases of pretreatment by removing the flocs in the first step and then followed by the cell disintegration by mechanical means helps in enhancing the organics efficiently in soluble phase. In this study, the upshot of sodium citrate mediated disperser disintegration on sludge from a paper mill was explored enhance enzymatic hydrolysis. Firstly, the floc deaggregation results at 0.05 g sodium citrate per g suspended solid with the maximum floc deaggregation degree of 89 %. Further, the consequence of disperser disintegration on the floc deaggregated sludge sample shows solid reduction and solubilization of 12.5 % and 17.5 %, respectively, higher than the disperser alone disintegration (9.57 % and 13.4 %). The anaerobic biodegradability assay shows the maximum biogas production of 174.3 mL/g of chemical oxygen demand while utilizing pretreated settled sludge as substrate. There was no accumulation of polyhydroxybutyrate using pretreated sludge supernatant. Thus, the phase-separated pretreatment by sodium citrate-induced disperser pretreatment is a suitable approach for enhancing hydrolysis during bioenergy recovery.

Emerging Technologies for the Discovery of Novel Diversity in Cyanobacteria and Algae and the Elucidation of Their Valuable Metabolites

Until recently, the study of cyanobacteria and microalgae has been hampered by the need to cultivate these organisms to gain insight into their cytomorphology, life cycle and molecular biology. However, various microbial species characterized by thick sheaths of exopolymeric substances were difficult to isolate in culture due to their associated symbiotic bacteria. Other microbes evaded culture. Such challenges have now been overcome by the development of metagenomic techniques that allow direct DNA sequencing from environmental samples, as well as high resolution microscopy techniques that permit direct imaging of environmental samples. The sampling of understudied taxa from extreme environments and of toxic species has been facilitated by specialized robotic equipment. Single-cell sequencing has allowed for the proper characterization of microalgal species and their response to environmental changes. Various strains of cyanobacteria, microalgae and macroalgae have gained renewed interest for their high-value metabolites. This paper provides an overview of the emerging technologies and explains how they are being used to identify such strains and their products for industrial application. Advances in genetic engineering and CRISPR technology have facilitated the production of strains that are more amenable to culture, metabolite extraction, scale-up and application in biorefinery approaches. Emerging analytical techniques are discussed, with the advent of multiomics and its application in this field.

Novel ecological implications of non-toxic Microcystis towards toxic ecotype in population-promoting toxic ecotype dominance at various N levels and cooperative defense against luteolin-stress.

Microcystin (MC)-producing (MC+) and MC-free (MC-) Microcystis always co-exist and interact during Microcystis-dominated cyanobacterial blooms (MCBs), where MC+Microcystis abundance and extracellular MC-content (EMC) determine the hazard extent of MCBs. The current study elucidated intraspecific interaction between MC+ and MC-Microcystis at various nitrogen (N) levels (0.5-50mg/L) and how such N-mediated interaction impacted algicidal and EMC-inhibiting effect of luteolin, a natural bioalgicide. Conclusively, MC+ and MC-Microcystis were inhibited mutually at N-limitation (0.5mg/L), which enhanced the algicidal and EMC-inhibiting effects of luteolin. However, at N-sufficiency (5-50mg/L), MC-Microcystis promoted MC+ ecotype growth and dominance, and such intraspecific interaction induced the cooperative defense of two ecotypes, weakening luteolin's algicidal and EMC-inhibiting effects. Mechanism analyses further revealed that MC+Microcystis in luteolin-stress co-culture secreted exopolymeric substances (EPSs) for self-protection against luteolin-stress and also released more EMC to induce EPS-production by MC-Microcystis as protectants, thus enhancing their luteolin-resistance and promoting their growth. This study provided novel ecological implications of MC-Microcystis toward MC+ ecotype in terms of assisting the dominant establishment of MC+Microcystis and cooperative defense with MC+ ecotype against luteolin, which guided the application of bioalgicide (i.e. luteolin) for MCBs and MCs pollution mitigation in different eutrophication-degree waters.