Extracellular polymer substance synthesized by a halophilic bacterium Chromohalobacter canadensis 28

Exopolysaccharide production by salt-tolerant bacteria: Recent advances, current challenges, and future prospects

Natural biopolymers derived from exopolysaccharides (EPSs) are considered eco-friendly and sustainable alternatives to available traditional synthetic counterparts. Salt-tolerant bacteria inhabiting harsh ecological niches have evolved a number of unique adaptation strategies allowing them to maintain cellular integrity and assuring their long-term survival; among these, producing EPSs can be adopted as an effective strategy to thrive under high-salt conditions. A great diversity of EPSs from salt-tolerant bacteria have attracted widespread attention recently. Because of factors such as their unique structural, physicochemical, and functional characteristics, EPSs are commercially valuable for the global market and their application potential in various sectors is promising. However, large-scale production and industrial development of these biopolymers are hindered by their low yields and high costs. Consequently, the research progress and future prospects of salt-tolerant bacterial EPSs must be systematically reviewed to further promote their application and commercialization. In this review, the structure and properties of EPSs produced by a variety of salt-tolerant bacterial strains isolated from different sources are summarized. Further, feasible strategies for solving production bottlenecks are discussed, which provides a scientific basis and direct reference for more scientific and rational EPS development.

Exploring Extremophiles from Bulgaria: Biodiversity, Biopolymer Synthesis, Functional Properties, Applications

Bulgaria stands out as a country rich in diverse extreme environments, boasting a remarkable abundance of mineral hot waters, which positions it as the second-largest source of such natural resources in Europe. Notably, several thermal and coastal solar salterns within its territory serve as thriving habitats for thermophilic and halophilic microorganisms, which offer promising bioactive compounds, including exopolysaccharides (EPSs). Multiple thermophilic EPS producers were isolated, along with a selection from several saltern environments, revealing an impressive taxonomic and bacterial diversity. Four isolates from three different thermophilic species, Geobacillus tepidamans V264, Aeribacillus pallidus 418, Brevibacillus thermoruber 423, and Brevibacillus thermoruber 438, along with the halophilic strain Chromohalobacter canadensis 28, emerged as promising candidates for further exploration. Optimization of cultivation media and conditions was conducted for each EPS producer. Additionally, investigations into the influence of aeration and stirring in laboratory bioreactors provided valuable insights into growth dynamics and polymer synthesis. The synthesized biopolymers showed excellent emulsifying properties, emulsion stability, and synergistic interaction with other hydrocolloids. Demonstrated biological activities and functional properties pave the way for potential future applications in diverse fields, with particular emphasis on cosmetics and medicine. The remarkable versatility and efficacy of biopolymers offer opportunities for innovation and development in different industrial sectors.

Exploring the potential of Halomonas levan and its derivatives as active ingredients in cosmeceutical and skin regenerating formulations

Demand on natural products that contain biological ingredients mimicking growth factors and cytokines made natural polysaccharides popular in pharmaceutical and cosmetic industries. Levan is the β-(2-6) linked, nontoxic, biocompatible, water-soluble, film former fructan polymer that has diverse applications in pharmacy and cosmeceutical industries with its moisturizing, whitening, anti-irritant, anti-aging and slimming activities. Driven by the limited reports on few structurally similar levan polymers, this study presents the first systematic investigation on the effects of structurally different extremophilic Halomonas levan polysaccharides on human skin epidermis cells. In-vitro experiments with microbially produced linear Halomonas levan (HL), its hydrolyzed, (hHL) and sulfonated (ShHL) derivatives as well as enzymatically produced branched levan (EL) revealed increased keratinocyte and fibroblast proliferation (113-118 %), improved skin barrier function through induced expressions of involucrin (2.0 and 6.43 fold changes for HL and EL) and filaggrin (1.74 and 3.89 fold changes for hHL and ShHL) genes and increased type I collagen (2.63 for ShHL) and hyaluronan synthase 3 (1.41 for HL) gene expressions together with fast wound healing ability within 24 h (100 %, HL) on 2D wound models clearly showed that HL and its derivatives have high potential to be used as natural active ingredients in cosmeceutical and skin regenerating formulations.

Whole-genome sequencing and genome-scale metabolic modeling of Chromohalobacter canadensis 85B to explore its salt tolerance and biotechnological use

Salt tolerant organisms are increasingly being used for the industrial production of high-value biomolecules due to their better adaptability compared to mesophiles. Chromohalobacter canadensis is one of the early halophiles to show promising biotechnology potential, which has not been explored to date. Advanced high throughput technologies such as whole-genome sequencing allow in-depth insight into the potential of organisms while at the frontiers of systems biology. At the same time, genome-scale metabolic models (GEMs) enable phenotype predictions through a mechanistic representation of metabolism. Here, we sequence and analyze the genome of C. canadensis 85B, and we use it to reconstruct a GEM. We then analyze the GEM using flux balance analysis and validate it against literature data on C. canadensis. We show that C. canadensis 85B is a metabolically versatile organism with many features for stress and osmotic adaptation. Pathways to produce ectoine and polyhydroxybutyrates were also predicted. The GEM reveals the ability to grow on several carbon sources in a minimal medium and reproduce osmoadaptation phenotypes. Overall, this study reveals insights from the genome of C. canadensis 85B, providing genomic data and a draft GEM that will serve as the first steps towards a better understanding of its metabolism, for novel applications in industrial biotechnology.

Production and Characterization of a Bioemulsifier Derived from Microorganisms with Potential Application in the Food Industry

There is a growing interest in the development and use of natural emulsifiers, which provide biodegradability as well as non-toxicity along with giving better performance compared to existing emulsifying agents used in the food industry. A large variety of sources of starting material, i.e., the microorganisms, are available to be used, hence giving a diverse range of applications. The focus of this review paper is on the production of bioemulsifiers, which are said to be "green surfactants", from fungi, bacteria and yeasts; furthermore, an overview pertaining to the knowledge gained over the years in terms of characterization techniques is reported. The methods used for the characterization and isolation such as TLC, GC-MS, HPLC, NMR have also been studied. The end-application products such as cookies, muffins, and doughs along with the methods used for the incorporation of bioemulsifiers, microorganisms from which they are derived, properties imparted to the product with the use of a particular bioemulsifier and comparison with the existing food grade emulsifiers has been discussed in detail. The future prospects indicate that newer bioemulsifiers with anti-microbial, anti-oxidant and stabilization properties will prove to have a larger impact, and emphasis will be on improving the performance at an economically viable methodology.

Microbiota dynamics and volatile compounds in lupine based Moromi fermented at different salt concentrations

Fermented soy sauces are used as food seasonings in Eastern countries and all over the world. Depending on their cultural origins, their production differs in parameters such as wheat addition, temperature, and salt concentration. The fermentation of lupine seeds presents an alternative to the use of soybeans; however, the microbiota and influencing factors are currently unknown. In this study, we analyse the microbiota of lupine Moromi (mash) fermentations for a period of six months and determine the influence of different salt concentrations on the microbiota dynamics and the volatile compound composition. Cultured microorganisms were identified by protein profiling using matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS), and 16S rRNA gene amplicon sequencing provided an overview of the microbiota including non-cultured bacteria. The volatile compounds were determined by gas chromatography-mass spectrometry (GC-MS). At all salt concentrations, we found that Tetragenococcus halophilus (up to 1.4 × 10⁹ colony forming units (CFU)/mL on day 21) and Chromohalobacter japonicus (1.9 × 10⁹ CFU/mL, day 28) were the dominating bacteria during Moromi fermentation. Debaryomyces hansenii (3.6 × 10⁸ CFU/mL, day 42) and Candida guilliermondii (2.2 × 10⁸ CFU/mL, day 2) were found to be the most prevalent yeast species. Interestingly, Zygosaccharomyces rouxii and other yeasts described as typical for soy Moromi were not found. With increasing salinity, we found lower diversity in the microbiota, the prevalence-gain of typical species was delayed, and ratios differed depending on their halo- or acid tolerance. GC-MS analysis revealed aroma-active compounds, such as pyrazines, acids, and some furanones, which were mostly different from the aroma compounds found in soy sauce. The absence of wheat may have caused a change in yeast microbiota, and the use of lupine seeds may have led to the differing aromatic composition. Salt reduction resulted in a more complex microbiome, higher cell counts, and did not show any spoiling organisms. With these findings, we show that seasoning sauce that uses lupine seeds as the sole substrate is a suitable gluten-free, soy-free and salt reduced alternative to common soy sauces with a unique flavour.

Formation and ripening of alginate-like exopolymer gel layers during and after membrane filtration

The properties of biofilm EPS are determined by the multiple interactions between its constituents and the surrounding environment. Because of the high complexity of biofilm EPS, its constituents' characterisation is still far from thorough, and identification of these interactions cannot be done yet. Therefore, we use gels of bacterial alginate-like exopolysaccharides (ALEs) as a model component for biofilm EPS in this work. These gels have been examined for their cohesive properties as a function of CaCl₂ and KCl concentration. Hereto, ALE gel layers were formed on membranes by dead-end filtration of ALE solutions. Accumulation of the cations Ca²⁺ and K⁺ in the gels could be well predicted from a Donnan equilibrium model based on the fixed negative charges in the ALE. This suggests that there is no specific binding of Ca²⁺ to the ALE and that on the time scale of the experiments, the Ca²⁺ ions can distribute freely over the gel and the surrounding solution. The concentration of fixed negative charges in the ALE was estimated around 1 mmol/g VSS (volatile suspended solids, organic mass) from the Donnan equilibrium. Moreover, an accumulation of H⁺ was predicted. Gels with more CaCl₂ in the supernatant were more compact and bore a higher osmotic pressure than those with less CaCl₂, revealing the role of Ca²⁺ ions in the network crosslinking. It is hypothesised that this mechanism later transitions into a rearrangement of the ALE molecules, which eventually leads to a fibrous network structure with large voids.

Molecular determinants of surface colonisation in diarrhoeagenic Escherichia coli (DEC): from bacterial adhesion to biofilm formation

Escherichia coli is primarily known as a commensal colonising the gastrointestinal tract of infants very early in life but some strains being responsible for diarrhoea, which can be especially severe in young children. Intestinal pathogenic E. coli include six pathotypes of diarrhoeagenic E. coli (DEC), namely, the (i) enterotoxigenic E. coli, (ii) enteroaggregative E. coli, (iii) enteropathogenic E. coli, (iv) enterohemorragic E. coli, (v) enteroinvasive E. coli and (vi) diffusely adherent E. coli. Prior to human infection, DEC can be found in natural environments, animal reservoirs, food processing environments and contaminated food matrices. From an ecophysiological point of view, DEC thus deal with very different biotopes and biocoenoses all along the food chain. In this context, this review focuses on the wide range of surface molecular determinants acting as surface colonisation factors (SCFs) in DEC. In the first instance, SCFs can be broadly discriminated into (i) extracellular polysaccharides, (ii) extracellular DNA and (iii) surface proteins. Surface proteins constitute the most diverse group of SCFs broadly discriminated into (i) monomeric SCFs, such as autotransporter (AT) adhesins, inverted ATs, heat-resistant agglutinins or some moonlighting proteins, (ii) oligomeric SCFs, namely, the trimeric ATs and (iii) supramolecular SCFs, including flagella and numerous pili, e.g. the injectisome, type 4 pili, curli chaperone-usher pili or conjugative pili. This review also details the gene regulatory network of these numerous SCFs at the various stages as it occurs from pre-transcriptional to post-translocational levels, which remains to be fully elucidated in many cases.

Biopolymer production by halotolerant bacteria isolated from Caatinga biome

Saline environments are extreme habitats with a high diversity of microorganisms source of a myriad of biomolecules. These microorganisms are assigned as extremophiles recognized to be producers of new natural compounds, which can be synthesized by helping to survive under harshness and extreme conditions. In Brazil, in the saline and semi-arid region of Areia Branca (Caatinga biome), halotolerant bacteria (able to growth at high NaCl concentrations) were isolated from rhizosphere of native plants Blutaparon portulacoides and Spergularia sp. and their biopolymer production was studied. A total of 25 bacterial isolates were identified at genus level based on 16S rRNA gene sequence analysis. Isolates were mainly Gram-positive bacteria from Bacillaceae, Staphylococcaceae, Microbacteriaceae, and Bacillales XII incertae sedis families, affiliates to Bacillus, Staphylococcus, Curtobacterium, and Exiguobacterium genera, respectively. One of the Gram-negative isolates was identified as member of the Pseudomonadaceae family, genus Pseudomonas. All the identified strains were halotolerant bacteria with optimum growth at 0.6-2.0 M salt concentrations. Assays for biopolymer production showed that the halotolerant strains are a rich source of compounds as polyhydroxyalkanoates (PHA), biodegradable biopolymer, such as poly(3-hydroxybutyrate) (PHB) produced from low-cost substrates, and exopolysaccharides (EPS), such as hyaluronic acid (HA), metabolite of great interest to the cosmetic and pharmaceutical industry. Also, eight bacterial EPS extracts showed immunostimulatory activity, promising results that can be used in biomedical applications. Overall, our findings demonstrate that these biomolecules can be produced in culture medium with 0.6-2.0 M NaCl concentrations, relevant feature to avoid costly production processes. This is the first report of biopolymer-producing bacteria from a saline region of Caatinga biome that showed important biological activities.

Improved Exopolymer Production by Chromohalobacter canadensis Cultures for Its Potential Cosmeceutical Applications

Several exopolymers with different chemical composition and correspondingly variety in their physico-chemical properties from halophilic microorganisms have still been described, however, with a low production yield. Chromohalobacter canadensis 28 isolated from Pomorie saltern synthesized an unusual exopolymer (EP) containing 72% γ-polyglutamic acid (PGA), an essential cosmeceutical additive. Current work suggests a novel approach for effective EP synthesis by C. canadensis 28 using continuous cultures. Highest production was observed at low dilution rates reaching a level of 2.1 mg/mL at D = 0.035, similar to those in batch cultures (2.34 mg/mL), however avoiding all disadvantages of discontinuous fermentation processes. At steady state, the total quantities of the synthesized EP after 48 h cultivation for the given equipment volume in D = 0.035 h⁻¹ and D = 0.075 h⁻¹ were 8.67 and 12 g, correspondingly, while it was 2.9 g for batch culture. Process parameters did not change after a ten-day run at D = 0.35 h⁻¹. A degree of purity of EP fraction received from continuous cultures was significantly increased up to 93–96%. A lack of cytotoxicity and high cell viability were observed for human dermal fibroblast cells after 24 h incubation with crude EP from C. canadensis 28 and purified PGA fraction that could suggest its high potential for cosmetic applications.

Two new exopolysaccharides from a thermophilic bacterium Geobacillus sp. WSUCF1: Characterization and bioactivities

The production, characterization and bioactivities of exopolysaccharides (EPSs) from a thermophilic bacterium Geobacillus sp. strain WSUCF1 were investigated. Using glucose as a carbon source 525.7 mg/L of exoproduct were produced in a 40-L bioreactor at 60 °C. Two purified EPSs were obtained: EPS-1 was a glucomannan containing mannose and glucose in a molar ratio of 1:0.21, while EPS-2 was composed of mannan only. The molecular weights of both EPSs were estimated to be approximately 1000 kDa, their FTIR and NMR spectra indicated the presence of α-type glycosidic bonds in a linear structure, and XRD analysis indicated a low degree of crystallinity of 0.11 (EPS-1) and 0.27 (EPS-2). EPS-1 and EPS-2 demonstrated high degradation temperatures of 319 °C and 314 °C, respectively, and non-cytotoxicity to HEK-293 cells at 2 and 3 mg/mL, respectively. In addition, both showed antioxidant activities. EPSs from strain WSUCF1 may expand the applications of microorganisms isolated from extreme environments and provide a valuable resource for exploitation in biomedical fields such as drug delivery carriers.

Hetero-exopolysaccharide from the extremely halophilic Halomonas smyrnensis K2: production, characterization and functional properties in vitro

In this study, we firstly reported the production and the structural characterization of a novel hetero-exopolysaccharide namely EPS-K2 from the extremely halophilc Halomonas smyrnensis K2. Results revealed that EPS-K2 was mainly composed of three monosaccharides including mannose (66.69%), glucose (19.54%) and galactose (13.77%). EPS-K2 showed high thermostability with a degradation temperature around 260 °C, which could make it a suitable candidate for application in thermal processes. Moreover, EPS-K2 showed attractive functional properties. In fact, it exhibited potent antioxidant activity in a dose-dependent manner as assessed in analyses of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, iron chelating and DNA protection ability. Furthermore, EPS-K2 showed strong adhesion inhibition activity against Enterococcus faecalis (75.52 ± 3.35%) and Escherichia coli (61.95 ± 2.48%) at 1 g/l concentration, as well as a high biofilm disruption activity especially against E. coli (70.73 ± 2.78%), at 2 g/l concentration. According to its biotechnological properties, EPS-K2 could be exploited as functional ingredient in food, biomedicine, and pharmaceutical industries.

High bioreactor production and emulsifying activity of an unusual exopolymer by Chromohalobacter canadensis 28

Unusual composition of an exopolymer (EP) from an obligate halophilic bacterium Chromohalobacter canadensis 28 has triggered an interest in development of an effective bioreactor process for its production. Its synthesis was investigated in 2-L bioreactor at agitation speeds at interval 600-1000 rpm, at a constant air flow rate of 0.5 vvm; aeration rates of 0.5, 1.0, and 1.5 vvm were tested at constant agitation rate of 900 rpm. EP production was affected by both, agitation and aeration. As a result twofold increase of EP yield was observed and additionally increased up to 3.08 mg/mL in a presence of surfactants. For effective scale-up of bioreactors mass transfer parameters were estimated and lowest values of KLa obtained for the highest productivity fermentation was established. Emulsification activity of EP exceeded that of trade hydrocolloids xanthan, guar gum, and cellulose. A good synergism between EP and commercial cellulose proved its potential exploration as an enhancer of emulsifying properties of trade emulsions. A pronounced lipophilic effect of EP was established toward olive oil and liquid paraffin. Cultivation of human keratinocyte cells (HaCaT) with crude EP and purified γ-polyglutamic acid (PGA) showed higher viability than control group.

Structural characterization and functional properties of novel exopolysaccharide from the extremely halotolerant Halomonas elongata S6

Production of extracellular polysaccharides by halophilic Archaea and Bacteria has been widely reported and the members of the genus Halomonas have been identified as the most potential producers. In the present work, a novel exopolysaccharide (EPS-S6) produced by the extremely halotolerant newly isolated Halomonas elongata strain S6, was characterized. According to the HPAE-PAD results, EPS-S6 was mainly composed of glucosamine, mannose, rhamnose and glucose (1:0.9:0.7:0.3). EPS-S6 was highly negatively charged and its molecular weight was about 270 kDa. Studies on its functional properties showed that EPS-S6 had several potential features. It has noticeable antioxidant activities on 2,2-diphenyl-1-picrylhydrazyl (DPPH^•) inhibition and DNA protection, good ability to inhibit and to disrupt pathogenic biofilms, excellent flocculation of kaolin suspension and interesting emulsifying properties at acidic, neutral and basic pH. Therefore, EPS-S6 could have potential biotechnological concern in several fields such as in food, cosmetic and environmental industries.

Marine-Derived Surface Active Agents: Health-Promoting Properties and Blue Biotechnology-Based Applications

Surface active agents are characterized for their capacity to adsorb to fluid and solid-water interfaces. They can be classified as surfactants and emulsifiers based on their molecular weight (MW) and properties. Over the years, the chemical surfactant industry has been rapidly increasing to meet consumer demands. Consequently, such a boost has led to the search for more sustainable and biodegradable alternatives, as chemical surfactants are non-biodegradable, thus causing an adverse effect on the environment. To these ends, many microbial and/or marine-derived molecules have been shown to possess various biological properties that could allow manufacturers to make additional health-promoting claims for their products. Our aim, in this review article, is to provide up to date information of critical health-promoting properties of these molecules and their use in blue-based biotechnology (i.e., biotechnology using aquatic organisms) with a focus on food, cosmetic and pharmaceutical/biomedical applications.

Whole Genome Sequencing and Comparative Genomic Analyses of Lysinibacillus pakistanensis LZH-9, a Halotolerant Strain with Excellent COD Removal Capability

Halotolerant microorganisms are promising in bio-treatment of hypersaline industrial wastewater. Four halotolerant bacteria strains were isolated from wastewater treatment plant, of which a strain LZH-9 could grow in the presence of up to 14% (w/v) NaCl, and it removed 81.9% chemical oxygen demand (COD) at 96 h after optimization. Whole genome sequencing of Lysinibacillus pakistanensis LZH-9 and comparative genomic analysis revealed metabolic versatility of different species of Lysinibacillus, and abundant genes involved in xenobiotics biodegradation, resistance to toxic compound, and salinity were found in all tested species of Lysinibacillus, in which Horizontal Gene Transfer (HGT) contributed to the acquisition of many important properties of Lysinibacillus spp. such as toxic compound resistance and osmotic stress resistance as revealed by phylogenetic analyses. Besides, genome wide positive selection analyses revealed seven genes that contained adaptive mutations in Lysinibacillus spp., most of which were multifunctional. Further expression assessment with Codon Adaption Index (CAI) also reflected the high metabolic rate of L. pakistanensis to digest potential carbon or nitrogen sources in organic contaminants, which was closely linked with efficient COD removal ability of strain LZH-9. The high COD removal efficiency and halotolerance as well as genomic evidences suggested that L. pakistanensis LZH-9 was promising in treating hypersaline industrial wastewater.

Saline Environments as a Source of Potential Quorum Sensing Disruptors to Control Bacterial Infections: A Review

Saline environments, such as marine and hypersaline habitats, are widely distributed around the world. They include sea waters, saline lakes, solar salterns, or hypersaline soils. The bacteria that live in these habitats produce and develop unique bioactive molecules and physiological pathways to cope with the stress conditions generated by these environments. They have been described to produce compounds with properties that differ from those found in non-saline habitats. In the last decades, the ability to disrupt quorum-sensing (QS) intercellular communication systems has been identified in many marine organisms, including bacteria. The two main mechanisms of QS interference, i.e., quorum sensing inhibition (QSI) and quorum quenching (QQ), appear to be a more frequent phenomenon in marine aquatic environments than in soils. However, data concerning bacteria from hypersaline habitats is scarce. Salt-tolerant QSI compounds and QQ enzymes may be of interest to interfere with QS-regulated bacterial functions, including virulence, in sectors such as aquaculture or agriculture where salinity is a serious environmental issue. This review provides a global overview of the main works related to QS interruption in saline environments as well as the derived biotechnological applications.