Analysis of Carotenoid Production by Halorubrum sp. TBZ126; an Extremely Halophilic Archeon from Urmia Lake

Characterization of carotenoids extracted from Haloferax larsenii NCIM 5678 isolated from Pachpadra salt lake, Rajasthan

Carotenoids are a diverse group of pigments known for their broad range of biological functions and applications. This study delves into multifaceted potential of carotenoids extracted from Haloferax larsenii NCIM 5678 previously isolated from Pachpadra Salt Lake in Rajasthan, India. H. larsenii NCIM 5678 was able to grow up to OD600 1.77 ± 0.03 with carotenoid concentration, 3.3 ± 0.03 µg/ml. The spectrophotometric analysis of carotenoid extract indicated the presence of three-fingered peak (460, 490 and 520 nm) which is a characteristic feature of bacterioruberin and its derivatives. The bacterioruberin was purified using silica gel column chromatography and thin layer chromatography. The carotenoid extract showed 12.3 ± 0.09 mm zone of growth inhibition with a minimum inhibitory concentration 546 ng/ml against indicator strain, H. larsenii HA4. The percentage antioxidant activity of carotenoid was found to be 84% which was higher as compared to commercially available ascorbic acid (56.74%). Thus, carotenoid extract from H. larsenii NCIM 5678 possesses unique attributes with compelling evidence of antimicrobial and antioxidant potential for the development of novel pharmaceuticals and nutraceuticals.

Microbial diversity in polyextreme salt flats and their potential applications

Recent geological, hydrochemical, and mineralogical studies performed on hypersaline salt flats have given insights into similar geo-morphologic features on Mars. These salt-encrusted depressions are widely spread across the Earth, where they are characterized by high salt concentrations, intense UV radiation, high evaporation, and low precipitation. Their surfaces are completely dry in summer; intermittent flooding occurs in winter turning them into transitory hypersaline lakes. Thanks to new approaches such as culture-dependent, culture-independent, and metagenomic-based methods, it is important to study microbial life under polyextreme conditions and understand what lives in these dynamic ecosystems and how they function. Regarding these particular features, new halophilic microorganisms have been isolated from some salt flats and identified as excellent producers of primary and secondary metabolites and granules such as halocins, enzymes, carotenoids, polyhydroxyalkanoates, and exopolysaccharides. Additionally, halophilic microorganisms are implemented in heavy metal bioremediation and hypersaline wastewater treatment. As a result, there is a growing interest in the distribution of halophilic microorganisms around the world that can be looked upon as good models to develop sustainable biotechnological processes for all fields. This review provides insights into diversity, ecology, metabolism, and genomics of halophiles in hypersaline salt flats worldwide as well as their potential uses in biotechnology.

Optimization of bacterioruberin production from Halorubrum ruber and assessment of its antioxidant potential

Haloarchaea produce bacterioruberin, a major C50 carotenoid with antioxidant properties that allow for its potential application in the food, cosmetic, and pharmaceutical industries. This study aimed to optimize culture conditions for total carotenoid, predominantly comprising bacterioruberin, production using Halorubrum ruber MBLA0099. A one-factor-at-a-time and statistically-based experimental design were applied to optimize the culture conditions. Culture in the optimized medium caused an increase in total carotenoid production from 0.496 to 1.966 mg L- 1 Maximal carotenoid productivity was achieved in a 7-L laboratory-scale fermentation and represented a 6.05-fold increase (0.492 mg L-1 d-1). The carotenoid extracts from strain MBLA0099 exhibited a 1.8-10.3-fold higher antioxidant activity in vitro, and allowed for a higher survival rate of Caenorhabditis elegans under oxidative stress conditions. These results demonstrated that Hrr. ruber MBLA0099 has significant potential as a haloarchaon for the commercial production of bacterioruberin.

Some novel bioactivities of Virgibacillus halodenitrificans carotenoids, isolated from Wadi El-Natrun lakes

Carotenoids come in second among the most frequent natural pigments and are utilized in medications, nutraceuticals, cosmetics, food pigments, and feed supplements. Based on recent complementary work, Virgibacillus was announced for the first time as a member of Wadi El-Natrun salt and soda lakes microbiota, identified as Virgibacillus halodenitrificans, and named V. halodenitrificans DASH; hence, this work aimed to investigate several in vitro medicinal bioactivities of V. halodenitrificans DASH carotenoids. The carotenoid methanolic extract showed antioxidant activity based on diphenylpicrylhydrazyl (DPPH) scavenging capacity with a half-maximal concentration (IC50) of 1.6 mg/mL as well as nitric oxide (NO) scavenging action expressed by an IC50 of 46.4 µg/mL. The extract showed considerable inhibitory activity for alpha-amylase (α-amylase) and alpha-glucosidase (α-glucosidase) enzymes (IC50 of 100 and 173.4 μg/mL, respectively). Moreover, the extract displayed selective anticancer activity against Caco-2 (IC50 = 138.96 µg/mL) and HepG-2 cell lines (IC50 = 31.25 µg/mL), representing colorectal adenocarcinoma and hepatoblastoma. Likewise, the extract showed 98.9 % clearance for human hepatitis C virus (HCV) using reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR), HCV-NS5B polymerase activity inhibition (IC50 = 27.4 µg/mL), and selective inhibitory activity against human coronavirus (HCoV 229E) using the plaque reduction assay (IC50 = 53.5 µg/mL). As far as we can tell, the anticancer, antiviral, and antidiabetic attributes of Virgibacillus carotenoids are, de novo, reported in this work which accordingly invokes further exploration of the other medicinal, biotechnological, and industrial applications of Virgibacillus and haloalkaliphilic bacteria carotenoids.

Biocolorants in food: Sources, extraction, applications and future prospects

Color of a food is one of the major factors influencing its acceptance by consumers. At presently synthetic dyes are the most commonly used food colorant in food industry by providing more esthetically appearance and as a means to quality control. However, the growing concern about health and environmental due to associated toxicity with synthetic food colorants has accelerated the global efforts to replace them with safer and healthy food colorants obtained from natural resources (plants, microorganisms, and animals). Further, many of these biocolorants not only provide myriad of colors to the food but also exert biological properties, thus they can be used as nutraceuticals in foods and beverages. In order to understand the importance of nature-derived pigments as food colorants, this review provides a thorough discussion on the natural origin of food colorants. Following this, different extraction methods for isolating biocolorants from plants and microbes were also discussed. Many of these biocolorants not only provide color, but also have many health promoting properties, for this reason their physicochemical and biological properties were also reviewed. Finally, current trends on the use of biocolorants in foods, and the challenges faced by the biocolorants in their effective utilization by food industry and possible solutions to these challenges were discussed.

Carbon Source Influences Antioxidant, Antiglycemic, and Antilipidemic Activities of Haloferax mediterranei Carotenoid Extracts

Haloarchaeal carotenoids have attracted attention lately due to their potential antioxidant activity. This work studies the effect of different concentrations of carbon sources on cell growth and carotenoid production. Carotenoid extract composition was characterized by HPLC-MS. Antioxidant activity of carotenoid extracts obtained from cell cultures grown under different nutritional conditions was determined by 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH), Ferric Reducing Ability Power (FRAP) and β-carotene bleaching assays. The ability of these carotenoid extracts to inhibit α-glucosidase, α-amylase, and lipase enzymes was also assessed to determine if they could be used to reduce blood glucose and lipid absorption. The maximum production of carotenoids (92.2 µg/mL) was observed combining 12.5% inorganic salts and 2.5% of glucose/starch. Antioxidant, hypoglycemic, and antilipidemic studies showed that higher carbon availability in the culture media leads to changes in the extract composition, resulting in more active haloarchaeal carotenoid extracts. Carotenoid extracts obtained from high-carbon-availability cell cultures presented higher proportions of all-trans-bacterioruberin, 5-cis-bacterioruberin, and a double isomeric bacterioruberin, whereas the presence 9-cis-bacterioruberin and 13-cis-bacterioruberin decreased. The production of haloarchaeal carotenoids can be successfully optimized by changing nutritional conditions. Furthermore, carotenoid composition can be altered by modifying carbon source concentration. These natural compounds are very promising in food and nutraceutical industries.

Archaea Carotenoids: Natural Pigments with Unexplored Innovative Potential

For more than 40 years, marine microorganisms have raised great interest because of their major ecological function and their numerous applications for biotechnology and pharmacology. Particularly, Archaea represent a resource of great potential for the identification of new metabolites because of their adaptation to extreme environmental conditions and their original metabolic pathways, allowing the synthesis of unique biomolecules. Studies on archaeal carotenoids are still relatively scarce and only a few works have focused on their industrial scale production and their biotechnological and pharmacological properties, while the societal demand for these bioactive pigments is growing. This article aims to provide a comprehensive review of the current knowledge on carotenoid metabolism in Archaea and the potential applications of these pigments in biotechnology and medicine. After reviewing the ecology and classification of these microorganisms, as well as their unique cellular and biochemical characteristics, this paper highlights the most recent data concerning carotenoid metabolism in Archaea, the biological properties of these pigments, and biotechnological considerations for their production at industrial scale.

Carotenoids from Haloarchaea: Extraction, Fractionation, and Characterization

Carotenoids are bioactive molecules known to promote human health. Many extreme halophilic archaea synthesize carotenoids, mainly represented by C₅₀ bacterioruberin (BR) and its derivatives. BR has a potent antioxidant capacity, even higher than that of β-carotene, thus, there is an increasing interest to advance the study of its biological properties as well as to extend its current applications. Here, we describe a procedure to extract and characterize carotenoids (enriched in BR) from haloarchaea using a "hyperpigmented" genetically modified strain of Haloferax volcanii.

Characterization and biological activities of carotenoids produced by three haloarchaeal strains isolated from Algerian salt lakes

Halophilic archaea represent a promising natural source of carotenoids. However, little information is available about these archaeal metabolites and their biological effects. In the present work, carotenoids of strains Haloferax sp. ME16, Halogeometricum sp. ME3 and Haloarcula sp. BT9, isolated from Algerian salt lakes, were produced, extracted and identified by high-performance liquid chromatography-diode array detector and liquid chromatography-mass spectrometry. Analytical results revealed a variation in the composition depending on the strain with a predominance of bacterioruberin. The evaluation of antioxidant capacity using ABTS [(2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)] and DPPH (2,2-diphenyl-1-picrylhydrazyl) assays showed that these extracts have a strong antioxidant potential, in particular those of Haloferax sp. ME16 which displayed antioxidant power significantly higher than that of ascorbic acid used as standard. Antibacterial activity of carotenoid extracts against four human-pathogenic strains and four fish-pathogenic strains was evaluated by agar disk diffusion method. The results showed a good antibacterial activity. These findings suggest that the C₅₀ carotenoids from the studied strains offer promising prospects for biotechnological applications.

Microalgae Xanthophylls: From Biosynthesis Pathway and Production Techniques to Encapsulation Development

In the last 20 years, xanthophylls from microalgae have gained increased scientific and industrial interests. This review highlights the essential issues that concern this class of high value compounds. Firstly, their chemical diversity as the producer microorganisms was detailed. Then, the use of conventional and innovative extraction techniques was discussed. Upgraded knowledge on the biosynthetic pathway of the main xanthophylls produced by photosynthetic microorganisms was reviewed in depth, providing new insightful ideas, clarifying the function of these active biomolecules. In addition, the recent advances in encapsulation techniques of astaxanthin and fucoxanthin, such as spray and freeze drying, gelation, emulsification and coacervation were updated. Providing information about these topics and their applications and advances could be a help to students and young researchers who are interested in chemical and metabolic engineering, chemistry and natural products communities to approach the complex thematic of xanthophylls.

C50 carotenoids extracted from Haloterrigena thermotolerans strain K15: antioxidant potential and identification

Halophilic archaea are one of the microorganism groups that have adapted to living in high saline environments and are important in terms of their potential use in biotechnology industry. One of the most important compounds they have, carotenoid, is used in food, cosmetics, and medical industries. The selected strain was identified as an extremely halophilic and thermophilic archaeon, Haloterrigena thermotolerans K15, based on morphological, biochemical, and physiological evidence as well as 16S rRNA analysis and screened by a scanning electron microscope and an atomic force microscope for the first time. The carotenoid contents of H. thermotolerans K15 isolated from Salt Lake (Tuz Gölü, Turkey) were determined by RP-HPLC-DAD and their isomers were characterized according to UV-Vis spectra by cis peak intensity and spectral fine structure. In addition to all-trans bacterioruberin as a major carotenoid, many isomers of the bacterioruberin such as monoanhydrobacterioruberin and bisanhydrobacterioruberin were also found. The antioxidant activity of carotenoid extract from H. thermotolerans was analyzed by the 2,2-diphenyl-1-picrylhydrazyl radical scavenging method. The carotenoid extract showed antioxidant activity statistically significantly higher than ascorbic acid and butylated hydroxytoluene as reference compounds (p < 0.05). This is the first study about carotenoid characterization and antioxidant activity of H. thermotolerans K15. The obtained results suggest the potential use of H. thermotolerans K15 products as a substitute for synthesized chemical carotenoids and antioxidants.

Ubiquitousness of Haloferax and Carotenoid Producing Genes in Arabian Sea Coastal Biosystems of India

This study presents a comparative analysis of halophiles from the global open sea and coastal biosystems through shotgun metagenomes (n = 209) retrieved from public repositories. The open sea was significantly enriched with Prochlorococcus and Candidatus pelagibacter. Meanwhile, coastal biosystems were dominated by Marinobacter and Alcanivorax. Halophilic archaea Haloarcula and Haloquandratum, predominant in the coastal biosystem, were significantly (p < 0.05) enriched in coastal biosystems compared to the open sea. Analysis of whole genomes (n = 23,540), retrieved from EzBioCloud, detected crtI in 64.66% of genomes, while cruF was observed in 1.69% Bacteria and 40.75% Archaea. We further confirmed the viability and carotenoid pigment production by pure culture isolation (n = 1351) of extreme halophiles from sediments (n = 410 × 3) sampling at the Arabian coastline of India. All red-pigmented isolates were represented exclusively by Haloferax, resistant to saturated NaCl (6 M), and had >60% G + C content. Multidrug resistance to tetracycline, gentamicin, ampicillin, and chloramphenicol were also observed. Our study showed that coastal biosystems could be more suited for bioprospection of halophiles rather than the open sea.

Analysis of Carotenoids in Haloarchaea Species from Atacama Saline Lakes by High Resolution UHPLC-Q-Orbitrap-Mass Spectrometry: Antioxidant Potential and Biological Effect on Cell Viability

Haloarchaea are extreme halophilic microorganisms belonging to the domain Archaea, phylum Euryarchaeota, and are producers of interesting antioxidant carotenoid compounds. In this study, four new strains of Haloarcula sp., isolated from saline lakes of the Atacama Desert, are reported and studied by high-resolution mass spectrometry (UHPLC-Q-Orbitrap-MS/MS) for the first time. In addition, determination of the carotenoid pigment profile from the new strains of Haloarcula sp., plus two strains of Halorubrum tebenquichense, and their antioxidant activity by means of several methods is reported. The effect of biomass on cellular viability in skin cell lines was also evaluated by MTT assay. The cholinesterase inhibition capacity of six haloarchaea (Haloarcula sp. ALT-23; Haloarcula sp. TeSe-41; Haloarcula sp. TeSe-51; Haloarcula sp. Te Se-89 and Halorubrum tebenquichense strains TeSe-85 and Te Se-86) is also reported for the first time. AChE inhibition IC₅₀ was 2.96 ± 0.08 μg/mL and BuChE inhibition IC₅₀ was 2.39 ± 0.09 μg/mL for the most active strain, Halorubrum tebenquichense Te Se-85, respectively, which is more active in BuCHe than that of the standard galantamine. Docking calculation showed that carotenoids can exert their inhibitory activity fitting into the enzyme pocket by their halves, in the presence of cholinesterase dimers.

Enhancement of biomass and total carotenoid content of a UV-resistant strain of Dietzia maris in response to different carbon and nitrogen sources

In the present study, the effect of various fermentation media on the production of carotenoid pigment in a radiation-resistant strain of Dietzia maris was reported. The biomass and pigment production of this strain was evaluated using various sources of carbon and nitrogen as well as different concentrations of whey medium. The antioxidant and cytotoxic activities of the extracted pigment were also determined using ferric reducing antioxidant power (FRAP), 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH), and MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assays. The antibacterial activity of the carotenoid pigment was also evaluated. All carbon sources increased the pigment production of D. maris in the following order: glucose > raffinose = starch = xylose > sorbitol > sucrose. However, only glucose, xylose, and sorbitol significantly increased the microbial biomass as compared to the control. Moreover, all organic nitrogen sources and ammonium sulfate enhanced the pigment production of the studied strain by approximately 6-9 folds. The free radical scavenging capacity and FRAP of the D. maris carotenoid extract were reported as half-maximal effective concentration or EC50 = 3.30 mg/ml and EC50 =28.46 μg/ml, respectively. The maximum amount of biomass and carotenoid pigment produced by D. maris was obtained in the fermentation medium containing 1 g/l glucose and 1 g/l yeast extract (18 mg/l). This strain can be considered as a promising biocatalyst for the commercial production of natural carotenoids due to its antioxidant capacity and noncytotoxic activity.

Nano-metals forming bacteria in Egypt. I. Synthesis, characterization and effect on some phytopathogenic bacteria in vitro

Bacterial metal reducers were isolated from water samples collected from harsh condition locations in Egypt. Four selected isolates were identified as Enterococcus thailandicus, Pseudomonas putida, Marinobacter hydrocarbonoclasticus, and P. geniculata for Copper (Cu), Iron (Fe), Cobalt (Co) and Zinc (Zn) Nanoparticles (NPs) production sequentially. Nitrate reductase enzyme was assayed for bacterial isolates which demonstrated that P. putida, and M. hydrocarbonoclasticus have the maximum enzyme production. The produced NPs were characterized by using XRD, TEM, UV-VIS spectroscopy. Magnetic properties for all selected metals NPs were measured using Vibrating Sample Magnetometer (VSM) and demonstrated that FeNPs recorded the highest magnetization value. The antibacterial activity of selected metals NPs was tested against some phytopathogenic bacteria causing the following diseases: soft rot (Pectobacterium carotovorum, Enterobacter cloacae), blackleg (Pectobacterium atrosepticum and Dickeya solani), brown rot (Ralstonia solanacearum), fire blight (Erwinia amylovora) and crown gall (Agrobacterium tumefaciens). All metals NPs showed an antagonistic effect against the tested isolates, particularly, FeNPs showed the highest antibacterial activity followed by CuNPs, and ZnNPs. Due to the small size, high reactivity, and large surface area of biologically synthesized NPs, they are used as a good disinfector, and can be considered as a new and alternative approach to traditional disease management methods.

Effect of Carbon Sources in Carotenoid Production from Haloarcula sp. M1, Halolamina sp. M3 and Halorubrum sp. M5, Halophilic Archaea Isolated from Sonora Saltern, Mexico

The isolation and molecular and chemo-taxonomic identification of seventeen halophilic archaea from the Santa Bárbara saltern, Sonora, México, were performed. Eight strains were selected based on pigmentation. Molecular identification revealed that the strains belonged to the Haloarcula, Halolamina and Halorubrum genera. Neutral lipids (quinones) were identified in all strains. Glycolipid S-DGD was found only in Halolamina sp. strain M3; polar phospholipids 2,3-O-phytanyl-sn-glycerol-1-phosphoryl-3-sn-glycerol (PG), 2,3-di-O-phytanyl-sn-glycero-1-phospho-3′-sn-glycerol-1′-methyl phosphate (PGP-Me) and sodium salt 1-(3-sn-phosphatidyl)-rac-glycerol were found in all the strains; and one unidentified glyco-phospholipid in strains M1, M3 and M4. Strains M1, M3 and M5 were selected for further studies based on carotenoid production. The effect of glucose and succinic and glutamic acid on carotenoid production was assessed. In particular, carotenoid production and growth significantly improved in the presence of glucose in strains Haloarcula sp. M1 and Halorubrum sp. M5 but not in Halolamina sp. M3. Glutamic and succinic acid had no effect on carotenoid production, and even was negative for Halorubrum sp. M5. Growth was increased by glutamic and succinic acid on Haloarcula sp. M1 but not in the other strains. This work describes for first time the presence of halophilic archaea in the Santa Bárbara saltern and highlights the differences in the effect of carbon sources on the growth and carotenoid production of haloarchaea.

Assessment of 16S rRNA Gene-Based Phylogenetic Diversity of Archaeal Communities in Halite-Crystal Salts Processed from Natural Saharan Saline Systems of Southern Tunisia

A thorough assessment of the phylogenetic diversity and community structure of halophilic archaea from three halite-crystal salts, processed from two separated saline systems of Southern Tunisia has been performed using culture dependent and independent methods targeting different regions of 16S rRNA gene sequences including DGGE, 16S rRNA clone libraries and Illumina Miseq sequencing. Two samples, CDR (red halite-crystal salts) and CDW (white halite-crystal salts), were collected from Chott-Eljerid and one sample CDZ (white halite-crystal salts) from Chott Douz. Fourteen isolates were identified as Halorubrum, Haloferax, Haloarcula, and Halogeometricum genera members. Culture-independent approach revealed a high diversity of archaeal members present in all samples, represented by the Euryarchaeal phylum and the dominance of the Halobacteria class. Nanohaloarchaea were also identified only in white halite samples based on metagenomic analysis. In fact, a total of 61 genera were identified with members of the Halorhabdus, Halonotius, Halorubrum, Haloarcula, and unclassified. Halobacteriaceae were shared among all samples. Unexpected diversity profiles between samples was observed where the red halite crust sample was considered as the most diverse one. The highest diversity was observed with Miseq approach, nevertheless, some genera were detected only with 16S rRNA clone libraries and cultured approaches.

Haloferax mediterranei Cells as C50 Carotenoid Factories

Haloarchaea produce C50 carotenoids such as bacterioruberin, which are of biotechnological in-terest. This study aimed to analyze the effect of different environmental and nutritional conditions on the cellular growth and dynamics of carotenoids accumulation in Haloferax mediterranei. The maximum production of carotenoids (40 µg·mL⁻¹) was obtained during the stationary phase of growth, probably due to nutrient-limiting conditions (one-step culture). By seven days of culture, 1 mL culture produced 22.4 mg of dry weight biomass containing 0.18 % (w/w) of carotenoids. On the other hand, carbon-deficient cultures (low C/N ratio) were observed to be optimum for C50 bacterioruberin production by Hfx. mediterranei, but negatively affected the growth of cells. Thus, a two-steps process was evaluated for optimum carotenoids yield. In the first step, a nutri-ent-repleted culture medium enabled the haloarchaea to produce biomass, while in the second step, the biomass was incubated under osmotic stress and in a carbon-deficient medium. Under the conditions used, the obtained biomass contained 0.27% (w/w) of carotenoids after seven days, which accounts for 58.49 µg·mL⁻¹ of carotenoids for a culture with turbidity 14.0.

Biochemical and Taxonomic Characterization of Novel Haloarchaeal Strains and Purification of the Recombinant Halotolerant α-Amylase Discovered in the Isolate

Haloarchaea are salt-loving archaea and potential source of industrially relevant halotolerant enzymes. In the present study, three reddish-pink, extremely halophilic archaeal strains, namely wsp1 (wsp-water sample Pondicherry), wsp3, and wsp4, were isolated from the Indian Solar saltern. The phylogenetic analysis based on 16S rRNA gene sequences suggests that both wsp3 and wsp4 strains belong to Halogeometricum borinquense while wsp1 is closely related to Haloferax volcanii species. The comparative genomics revealed an open pangenome for both genera investigated here. Whole-genome sequence analysis revealed that these isolates have multiple copies of industrially/biotechnologically important unique genes and enzymes. Among these unique enzymes, for recombinant expression and purification, we selected four putative α-amylases identified in these three isolates. We successfully purified functional halotolerant recombinant Amy2, from wsp1 using pelB signal sequence-based secretion strategy using Escherichia coli as an expression host. This method may prove useful to produce functional haloarchaeal secretory recombinant proteins suitable for commercial or research applications. Biochemical analysis of Amy2 suggests the halotolerant nature of the enzyme having maximum enzymatic activity observed at 1 M NaCl. We also report the isolation and characterization of carotenoids purified from these isolates. This study highlights the presence of several industrially important enzymes in the haloarchaeal strains which may potentially have improved features like stability and salt tolerance suitable for industrial applications.

Deciphering Pathways for Carotenogenesis in Haloarchaea

Bacterioruberin and its derivatives have been described as the major carotenoids produced by haloarchaea (halophilic microbes belonging to the Archaea domain). Recently, different works have revealed that some haloarchaea synthetize other carotenoids at very low concentrations, like lycopene, lycopersene, cis- and trans-phytoene, cis- and trans-phytofluene, neo-β-carotene, and neo-α-carotene. However, there is still controversy about the nature of the pathways for carotenogenesis in haloarchaea. During the last decade, the number of haloarchaeal genomes fully sequenced and assembled has increased significantly. Although some of these genomes are not fully annotated, and many others are drafts, this information provides a new approach to exploring the capability of haloarchaea to produce carotenoids. This work conducts a deeply bioinformatic analysis to establish a hypothetical metabolic map connecting all the potential pathways involved in carotenogenesis in haloarchaea. Special interest has been focused on the synthesis of bacterioruberin in members of the Haloferax genus. The main finding is that in almost all the genus analyzed, a functioning alternative mevalonic acid (MVA) pathway provides isopentenyl pyrophosphate (IPP) in haloarchaea. Then, the main branch to synthesized carotenoids proceeds up to lycopene from which β-carotene or bacterioruberin (and its precursors: monoanhydrobacterioriberin, bisanhydrobacterioruberin, dihydrobisanhydrobacteriuberin, isopentenyldehydrorhodopsin, and dihydroisopenthenyldehydrorhodopsin) can be made.

Marine Bacteria versus Microalgae: Who Is the Best for Biotechnological Production of Bioactive Compounds with Antioxidant Properties and Other Biological Applications?

Natural bioactive compounds with antioxidant activity play remarkable roles in the prevention of reactive oxygen species (ROS) formation. ROS, which are formed by different pathways, have various pathological influences such as DNA damage, carcinogenesis, and cellular degeneration. Incremental demands have prompted the search for newer and alternative resources of natural bioactive compounds with antioxidant properties. The marine environment encompasses almost three-quarters of our planet and is home to many eukaryotic and prokaryotic microorganisms. Because of extreme physical and chemical conditions, the marine environment is a rich source of chemical and biological diversity, and marine microorganisms have high potential as a source of commercially interesting compounds with various pharmaceutical, nutraceutical, and cosmeceutical applications. Bacteria and microalgae are the most important producers of valuable molecules including antioxidant enzymes (such as superoxide dismutase and catalase) and antioxidant substances (such as carotenoids, exopolysaccharides, and bioactive peptides) with various valuable biological properties and applications. Here, we review the current knowledge of these bioactive compounds while highlighting their antioxidant properties, production yield, health-related benefits, and potential applications in various biological and industrial fields.

Haloarchaeal Carotenoids: Healthy Novel Compounds from Extreme Environments

Haloarchaea are halophilic microorganisms belonging to the archaea domain that inhabit salty environments (mainly soils and water) all over the world. Most of the genera included in this group can produce carotenoids at significant concentrations (even wild-type strains). The major carotenoid produced by the cells is bacterioruberin (and its derivatives), which is only produced by this kind of microbes and few bacteria, like Micrococcus roseus. Nevertheless, the understanding of carotenoid metabolism in haloarchaea, its regulation, and the roles of carotenoid derivatives in this group of extreme microorganisms remains mostly unrevealed. Besides, potential biotechnological uses of haloarchaeal pigments are poorly explored. This work summarises what it has been described so far about carotenoids from haloarchaea and their production at mid- and large-scale, paying special attention to the most recent findings on the potential uses of haloarchaeal pigments in biomedicine.

Differential Production of Pigments by Halophilic Bacteria Under the Effect of Salt and Evaluation of Their Antioxidant Activity

Microorganisms that survive in the high salt environment have been shown to be a potential source for metabolites with pharmaceutical importance. In the present study, we have investigated the effect of 5 and 10% (w/v) NaCl on growth, biochemical changes, and metabolite production in seven moderately halophilic bacteria isolated from the salterns/mangrove area of South India. Metabolite production by Bacillus VITPS3 increased by 3.18-fold in the presence of 10% (w/v) NaCl concentration. Total phenolic and flavonoid content increased in Bacillus VITPS5 (11.3-fold) and Planococcus maritimus VITP21 (5.99-fold) whereas β-carotene content was less at higher NaCl concentrations. VITP21 and VITPS5, in response to NaCl, produced metabolites with higher (6.72- and 4.91-fold) DPPH and ABTS radical scavenging activity. UV/visible spectrophotometry of the extracts confirmed the presence of flavonoids, phenolics, and related compounds. ¹H-NMR spectra indicated substantial changes in the metabolite production in response to salt concentration. Principal component analysis (PCA) revealed that VITP21 extracts exhibited the highest antioxidant activity compared with other extracts. The present study presents the first report on the comparative analysis of pigment production by moderate halophilic bacteria, in response to the effect of salt and their relation to radical scavenging property.

Optimization of submerged fermentation process for improved production of β-carotene by Exiguobacterium acetylicum S01

Carotenoids are natural pigments with substantial applications in nutraceutical, pharmaceutical, and food industries. In this study, optimization of the fermentation process for enhancement of β-carotene and biomass production by Exiguobacterium acetylicum S01 was achieved by employing statistical designs including the Placket-Burman design (PBD) and response surface methodology (RSM). Among the seven variables investigated by two levels in PBD, glucose, peptone, pH and temperature were indicated as crucial variables (p < 0.0001) for β-carotene and biomass productivity. Response surface methodology was further applied to evaluate the optimal concentrations of these four variables for maximum β-carotene and biomass productivity. The optimized medium contained glucose 1.4 g/L, peptone 26.5 g/L, pH 8.5, and temperature 30 °C, respectively. A significant increase in β-carotene (40.32 ± 2.55 mg/L) and biomass (2.19 ± 0.10 g/L) productivities in E. acetylicum S01 were achieved by using RSM, which was 3.47-fold and 2.36-fold higher in the optimized medium compared to the un-optimized medium. Further, the optimum fermentation condition in the 5-L bioreactor was achieved a maximal β-carotene yield of 107.22 ± 5.78 mg/L within 96 h. Moreover, the expression levels of carotenoid biosynthetic genes (phytoene desaturase (CrtI) and phytoene synthase (CrtB)) were up-regulated (2.89-fold and 3.71-fold) in E. acetylicum under the optimized medium conditions. Overall, these results suggest that E. acetylicum S01 can be used as a promising microorganism for the commercial production of β-carotene.

Production, characterization and antimicrobial activities of bio-pigments by Aquisalibacillus elongatus MB592, Salinicoccus sesuvii MB597, and Halomonas aquamarina MB598 isolated from Khewra Salt Range, Pakistan

Hypersaline ecosystems offer unique habitats to microbial populations capable of withstanding extreme stress conditions and producing novel metabolites of commercial importance. Herein, we have characterized for the first time the production of bioactive pigments from newly isolated halophilic bacterial species. Halophilic bacteria were isolated from Khewra Salt Range of Pakistan. Three distinctly colored isolates were selected for pigment production. Selected colonies were identified as Aquisalibacillus elongatus MB592, Salinicoccus sesuvii MB597, and Halomonas aquamarina MB598 based on morphological, biochemical, and physiological evidences as well as 16S rRNA analysis. The optimum pigment production observed at mesophilic condition, nearly neutral pH, and moderate salinity was validated using response surface methodology. Different analytical techniques (UV spectroscopy, infrared spectroscopy, and HPLC) characterized these purified pigments as derivatives of bacterioruberin carotenoids. Antioxidant activity of pigments revealed up to 85% free-radical scavenging activity at the concentration of 30 µg ml^-1. Pigments also showed significant antimicrobial activity against Bacillus subtilis, Bacillus pumilus, Enterococcus faecalis, Bacillus cereus, Klebsiella pneumoniae, Alcaligenes faecalis, Pseudomonas geniculata, Enterococcus faecium, Aspergillus fumigatus, Aspergillus flavus, Fusarium solani, and Mucor spp., suggesting potential biomedical applications.

Engineering Haloferax mediterranei as an Efficient Platform for High Level Production of Lycopene

Lycopene attracts increasing interests in the pharmaceutical, food, and cosmetic industries due to its anti-oxidative and anti-cancer properties. Compared with other lycopene production methods, such as chemical synthesis or direct extraction from plants, the biosynthesis approach using microbes is more economical and sustainable. In this work, we engineered Haloferax mediterranei, a halophilic archaeon, as a new lycopene producer. H. mediterranei has the de novo synthetic pathway for lycopene but cannot accumulate this compound. To address this issue, we reinforced the lycopene synthesis pathway, blocked its flux to other carotenoids and disrupted its competitive pathways. The reaction from geranylgeranyl-PP to phytoene catalyzed by phytoene synthase (CrtB) was identified as the rate-limiting step in H. mediterranei. Insertion of a strong promoter P_phaR immediately upstream of the crtB gene, or overexpression of the heterologous CrtB and phytoene desaturase (CrtI) led to a higher yield of lycopene. In addition, blocking bacterioruberin biosynthesis increased the purity and yield of lycopene. Knock-out of the key genes, responsible for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) biosynthesis, diverted more carbon flux into lycopene synthesis, and thus further enhanced lycopene production. The metabolic engineered H. mediterranei strain produced lycopene at 119.25 ± 0.55 mg per gram of dry cell weight in shake flask fermentation. The obtained yield was superior compared to the lycopene production observed in most of the engineered Escherichia coli or yeast even when they were cultivated in pilot scale bioreactors. Collectively, this work offers insights into the mechanism involved in carotenoid biosynthesis in haloarchaea and demonstrates the potential of using haloarchaea for the production of lycopene or other carotenoids.

Exploring the Valuable Carotenoids for the Large-Scale Production by Marine Microorganisms

Carotenoids are among the most abundant natural pigments available in nature. These pigments have received considerable attention because of their biotechnological applications and, more importantly, due to their potential beneficial uses in human healthcare, food processing, pharmaceuticals and cosmetics. These bioactive compounds are in high demand throughout the world; Europe and the USA are the markets where the demand for carotenoids is the highest. The in vitro synthesis of carotenoids has sustained their large-scale production so far. However, the emerging modern standards for a healthy lifestyle and environment-friendly practices have given rise to a search for natural biocompounds as alternatives to synthetic ones. Therefore, nowadays, biomass (vegetables, fruits, yeast and microorganisms) is being used to obtain naturally-available carotenoids with high antioxidant capacity and strong color, on a large scale. This is an alternative to the in vitro synthesis of carotenoids, which is expensive and generates a large number of residues, and the compounds synthesized are sometimes not active biologically. In this context, marine biomass has recently emerged as a natural source for both common and uncommon valuable carotenoids. Besides, the cultivation of marine microorganisms, as well as the downstream processes, which are used to isolate the carotenoids from these microorganisms, offer several advantages over the other approaches that have been explored previously. This review summarizes the general properties of the most-abundant carotenoids produced by marine microorganisms, focusing on the genuine/rare carotenoids that exhibit interesting features useful for potential applications in biotechnology, pharmaceuticals, cosmetics and medicine.

DNA Repair and Photoprotection: Mechanisms of Overcoming Environmental Ultraviolet Radiation Exposure in Halophilic Archaea

Halophilic archaea push the limits of life at several extremes. In particular, they are noted for their biochemical strategies in dealing with osmotic stress, low water activity and cycles of desiccation in their hypersaline environments. Another feature common to their habitats is intense ultraviolet (UV) radiation, which is a challenge that microorganisms must overcome. The consequences of high UV exposure include DNA lesions arising directly from bond rearrangement of adjacent bipyrimidines, or indirectly from oxidative damage, which may ultimately result in mutation and cell death. As such, these microorganisms have evolved a number of strategies to navigate the threat of DNA damage, which we differentiate into two categories: DNA repair and photoprotection. Photoprotection encompasses damage avoidance strategies that serve as a "first line of defense," and in halophilic archaea include pigmentation by carotenoids, mechanisms of oxidative damage avoidance, polyploidy, and genomic signatures that make DNA less susceptible to photodamage. Photolesions that do arise are addressed by a number of DNA repair mechanisms that halophilic archaea efficiently utilize, which include photoreactivation, nucleotide excision repair, base excision repair, and homologous recombination. This review seeks to place DNA damage, repair, and photoprotection in the context of halophilic archaea and the solar radiation of their hypersaline environments. We also provide new insight into the breadth of strategies and how they may work together to produce remarkable UV-resistance for these microorganisms.

High carotenoid production by a halotolerant bacterium, Kocuria sp. strain QWT-12 and anticancer activity of its carotenoid

Halophilic prokaryotes are extremophile microorganisms that grow optimally in media containing salts and almost appeared pigmented. Many of them contain high concentrations of carotenoids. Amongst 15 strains of halophilic prokaryotes isolated from industrial tannery wastewater in Qom, a Gram-stain-positive coccoid, aerobic, non-endospore-forming, halotolerant bacterium designated as strain QWT-12 showed high capacity in the production of carotenoids in a wide range of culture medium factors. 16S rRNA gene analysis showed that this strain belongs to the genus Kocuria. Carotenoids from this strain were extracted by methanol. MTT assay for extracted carotenoid was carried out against seven cancer cell lines belonging to breast, lung and prostate cancer with negative control of fibroblast cell line through six concentration levels to find out IC₅₀. Based on statistical analysis of data from MTT assay, IC₅₀ of 1, 4 and 8 mg/ml for MCF-7, (A549 and MDA-MB-468) and MDA-MB-231 respectively. Additionally, qualitative carotenoid determination was carried out using spectrophotometric method in 300-600 nm and thin layer chromatography, respectively. According to the obtained results from mass spectrophotometry, absorption spectrum of strain QWT-12 is similar to the absorption spectrum of the carotenoid neurosporene.

Carotenoids from Haloarchaea and Their Potential in Biotechnology

The production of pigments by halophilic archaea has been analysed during the last half a century. The main reasons that sustains this research are: (i) many haloarchaeal species possess high carotenoids production availability; (ii) downstream processes related to carotenoid isolation from haloarchaea is relatively quick, easy and cheap; (iii) carotenoids production by haloarchaea can be improved by genetic modification or even by modifying several cultivation aspects such as nutrition, growth pH, temperature, etc.; (iv) carotenoids are needed to support plant and animal life and human well-being; and (v) carotenoids are compounds highly demanded by pharmaceutical, cosmetic and food markets. Several studies about carotenoid production by haloarchaea have been reported so far, most of them focused on pigments isolation or carotenoids production under different culture conditions. However, the understanding of carotenoid metabolism, regulation, and roles of carotenoid derivatives in this group of extreme microorganisms remains mostly unrevealed. The uses of those haloarchaeal pigments have also been poorly explored. This work summarises what has been described so far about carotenoids production by haloarchaea and their potential uses in biotechnology and biomedicine. In particular, new scientific evidence of improved carotenoid production by one of the better known haloarchaeon (Haloferax mediterranei) is also discussed.

Integration of poly-3-(hydroxybutyrate-co-hydroxyvalerate) production by Haloferax mediterranei through utilization of stillage from rice-based ethanol manufacture in India and its techno-economic analysis

Haloferax mediterranei has potential for economical industrial-scale production of polyhydroxyalkanoate (PHA) as it can utilize cheap carbon sources, has capacity for nonsterile cultivation and allows simple product recovery. Molasses-based Indian distilleries are converting themselves to cereal-based distilleries. Waste stillage (14 l) of rice-based ethanol industry was used for the production of PHA by H. mediterranei in the simple plug-flow reactor configuration of the activated sludge process. Cells utilized stillage and accumulated 63 ± 3 % PHA of dry cell weight and produced 13.12 ± 0.05 g PHA/l. The product yield coefficient was 0.27 while 0.14 g/l h volumetric productivity was reached. Simultaneous lowering of 5-day biochemical oxygen demand and chemical oxygen demand values of stillage by 82 % was attained. The biopolymer was characterized as poly-3-(hydroxybutyrate-co-17.9 mol%-hydroxyvalerate) (PHBV). Directional properties of decanoic acid jointly with temperature-dependent water solubility in decanoic acid were employed for two-step desalination of the spent stillage medium in a cylindrical baffled-tank with an immersed heater and a stirrer holding axial and radial impellers. 99.3 % of the medium salts were recovered and re-used for PHA production. The cost of PHBV was estimated as US$2.05/kg when the annual production was simulated as 1890 tons. Desalination contributed maximally to the overall cost. Technology and cost-analysis demonstrate that PHA production integrated with ethanol manufacture is feasible in India. This study could be the basis for construction of a pilot plant.

Draft Genome Sequence of Haloferax sp. Strain ATB1, Isolated from a Semi-Arid Region in the Brazilian Caatinga

Organisms in the Haloferax genus are extreme halophiles that grow in environments with pH values between 4 and 12, and temperatures between 0°C and 60°C. In the present study, a draft of the first Haloferax sp. strain ATB1 genome isolated from the region of Cariri (in Paraíba State, Brazil) is presented.