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

The biosynthesis mechanism of bacterioruberin in halophilic archaea revealed by genome and transcriptome analysis

Halophilic archaea are promising microbial cell factories for bacterioruberin (BR) production. BR is a natural product with multi-bioactivities, allowing potential application in many fields. In the previous work, a haloarchaeon Halorubrum sp. HRM-150 with a high proportion of BR (about 85%) was isolated, but the low yield impeded its large-scale production. This work figured out BR synthesis characteristics and mechanisms, and proposed strategies for yield improvement. First, glucose (10 g/L) and tryptone (15 g/L) were tested to be better sources for BR production. Besides, the combination of glucose and starch achieved the diauxic growth, and the biomass and BR productivity increased by 85% and 54% than using glucose. Additionally, this work first proposed the BR synthesis pattern, which differs from that of other carotenoids. As a structural component of cell membranes, the BR synthesis is highly coupled with growth, which was most active in the logarithm phase. Meanwhile, the osmotic down shock at the logarithm phase could increase the BR productivity without sacrificing the biomass. Moreover, the de-novo pathway for BR synthesis with a key gene of lyeJ, and its competitive pathways (notably tetraether lipids and retinal) were revealed through genome, transcriptome, and osmotic down shock. Therefore, the BR yield is expected to be improved through mutant construction, such as the overexpression of key gene lyeJ and the knockout of competitive genes, which need to be further explored. The findings will contribute to a better understanding of the metabolism mechanism in haloarchaea and the development of haloarchaea as microbial cell factories.

IMPORTANCE

Recent studies have revealed that halophilic microorganism is a promising microbial factory for the next-generation industrialization. Among them, halophilic archaea are advantageous as microbial factories due to their low contamination risk and low freshwater consumption. The halophilic archaea usually accumulate long chain C50 carotenoids, which are barely found in other organisms. Bacterioruberin (BR), the major C50 carotenoid, has multi-bioactivities, allowing potential application in food, cosmetic, and biomedical industries. However, the low yield impedes its large-scale application. This work figured out the BR synthesis characteristics and mechanism, and proposed several strategies for BR yield improvement, encouraging halophilic archaea to function as microbial factories for BR production. Meanwhile, the archaea have special evolutionary status and unique characteristics in taxonomy, the revelation of BR biosynthesis mechanism is beneficial for a better understanding of archaea.

Bacterioruberin: Biosynthesis, Antioxidant Activity, and Therapeutic Applications in Cancer and Immune Pathologies

Halophilic archaea, also termed haloarchaea, are a group of moderate and extreme halophilic microorganisms that constitute the major microbial populations in hypersaline environments. In these ecosystems, mainly aquatic, haloarchaea are constantly exposed to ionic and oxidative stress due to saturated salt concentrations and high incidences of UV radiation (mainly in summer). To survive under these harsh conditions, haloarchaea have developed molecular adaptations including hyperpigmentation. Regarding pigmentation, haloarchaeal species mainly synthesise the rare C50 carotenoid called bacterioruberin (BR) and its derivatives, monoanhydrobacterioruberin and bisanhydrobacterioruberin. Due to their colours and extraordinary antioxidant properties, BR and its derivatives have been the aim of research in several research groups all over the world during the last decade. This review aims to summarise the most relevant characteristics of BR and its derivatives as well as describe their reported antitumoral, immunomodulatory, and antioxidant biological activities. Based on their biological activities, these carotenoids can be considered promising natural biomolecules that could be used as tools to design new strategies and/or pharmaceutical formulas to fight against cancer, promote immunomodulation, or preserve skin health, among other potential uses.

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.

Antioxidant Capacity of Carotenoid Extracts from the Haloarchaeon Halorhabdus utahensis

Herein, we report on the production, characterization, and antioxidant power assessment of carotenoids from the haloarchaeon Halorhabdus utahensis. It was grown at 37 °C and 180 rpm agitation in halobacteria medium supplemented with glucose, fructose, and xylose, each at concentrations of 0.2%, 1%, and 2%, and the carotenoid yield and composition were investigated. The microorganism produced the carotenoids under all the conditions tested, and their amount followed the order glucose < xylose < fructose. The highest yield was achieved in 2% fructose growth medium with 550.60 ± 7.91 μg/g dry cell and 2428.15 ± 49.33 μg/L. Separation and identification of the carotenoids were performed by RP-HPLC and HPLC/APCI-ITMSn. Bacterioruberin was the main carotenoid detected and accounted for 60.6%, 56.4%, and 58.9% in 2% glucose, 1% xylose, and 2% fructose extracts, respectively. Several geometric isomers of bacterioruberin were distinguished, and representatives of monoanhydrobacterioruberin, and bisanhydrobacterioruberin were also detected. The assignment to cis-isomers was attempted through analysis of the UV/Vis spectra, intensity of cis peaks, and spectral fine structures. The extracts exhibited superoxide scavenging activity higher than butylhydroxytoluene, ascorbic acid, and Trolox, selected as antioxidant references. The anti-hyaluronidase capacity was investigated, and the 2% fructose extract showed the highest activity reaching 90% enzyme inhibition with 1.5 μg. The overall data confirm that Hrd. utahensis can be regarded as an interesting source of antioxidants that can find applications in the food and cosmetic sectors.

Dietary Inclusion of Halobacterium salinarum Modulates Growth Performances and Immune Responses in Farmed Gilthead Seabream (Sparus aurata L.)

The use of natural immunostimulants is considered the most promising alternative to promote fish health, productive performance and quality, increasing the aquaculture profitability, sustainability and social acceptance. The purpose of this study was to evaluate the effect of the integration of a potential probiotic strain, Halobacterium salinarum, belonging to the Archaea domain, in the formulated diets of farmed gilthead seabream (Sparus aurata L.) in terms of growth performances and immunity responses. The experiment was set up to test two different levels of inclusion of the bacteria in the diet: 0.05% (D1) and 0.1% (D2). The effects on fish growth performances; humoral (peroxidase, protease, antiprotease and IgM levels) and cellular immunity parameters (phagocytosis, respiratory burst and myeloperoxidase), along with bactericidal activity, were evaluated after 15 and 30 days of experimental feeding. The obtained results showed that the inclusion of H. salinarum at the highest concentration (D2 0.1%) improved growth performances, bactericidal activity against Vibrio anguillarum and some parameters related both to the humoral and cellular immune response, suggesting exploring other aspects of welfare in view of future supplementations of this probiotic strain in the diet of S. aurata.

More Than Pigments: The Potential of Astaxanthin and Bacterioruberin-Based Nanomedicines

Carotenoids are natural products regulated by the food sector, currently used as feed dyes and as antioxidants in dietary supplements and composing functional foods for human consumption. Of the nearly one thousand carotenoids described to date, only retinoids, derived from beta carotene, have the status of a drug and are regulated by the pharmaceutical sector. In this review, we address a novel field: the transformation of xanthophylls, particularly the highly marketed astaxanthin and the practically unknown bacterioruberin, in therapeutic agents by altering their pharmacokinetics, biodistribution, and pharmacodynamics through their formulation as nanomedicines. The antioxidant activity of xanthophylls is mediated by routes different from those of the classical oral anti-inflammatory drugs such as corticosteroids and non-steroidal anti-inflammatory drugs (NSAIDs): remarkably, xanthophylls lack therapeutic activity but also lack toxicity. Formulated as nanomedicines, xanthophylls gain therapeutic activity by mechanisms other than increased bioavailability. Loaded into ad hoc tailored nanoparticles to protect their structure throughout storage and during gastrointestinal transit or skin penetration, xanthophylls can be targeted and delivered to selected inflamed cell groups, achieving a massive intracellular concentration after endocytosis of small doses of formulation. Most first reports showing the activities of oral and topical anti-inflammatory xanthophyll-based nanomedicines against chronic diseases such as inflammatory bowel disease, psoriasis, atopic dermatitis, and dry eye disease emerged between 2020 and 2023. Here we discuss in detail their preclinical performance, mostly targeted vesicular and polymeric nanoparticles, on cellular models and in vivo. The results, although preliminary, are auspicious enough to speculate upon their potential use for oral or topical administration in the treatment of chronic inflammatory diseases.

Microalgae, Seaweeds and Aquatic Bacteria, Archaea, and Yeasts: Sources of Carotenoids with Potential Antioxidant and Anti-Inflammatory Health-Promoting Actions in the Sustainability Era

Carotenoids are a large group of health-promoting compounds used in many industrial sectors, such as foods, feeds, pharmaceuticals, cosmetics, nutraceuticals, and colorants. Considering the global population growth and environmental challenges, it is essential to find new sustainable sources of carotenoids beyond those obtained from agriculture. This review focuses on the potential use of marine archaea, bacteria, algae, and yeast as biological factories of carotenoids. A wide variety of carotenoids, including novel ones, were identified in these organisms. The role of carotenoids in marine organisms and their potential health-promoting actions have also been discussed. Marine organisms have a great capacity to synthesize a wide variety of carotenoids, which can be obtained in a renewable manner without depleting natural resources. Thus, it is concluded that they represent a key sustainable source of carotenoids that could help Europe achieve its Green Deal and Recovery Plan. Additionally, the lack of standards, clinical studies, and toxicity analysis reduces the use of marine organisms as sources of traditional and novel carotenoids. Therefore, further research on the processing of marine organisms, the biosynthetic pathways, extraction procedures, and examination of their content is needed to increase carotenoid productivity, document their safety, and decrease costs for their industrial implementation.

Haloarchaeal carotenoids exert an in vitro antiproliferative effect on human breast cancer cell lines

Oxidative stress has been linked to the onset and progression of different neoplasia. Antioxidants might help prevent it by modulating biochemical processes involved in cell proliferation. Here, the aim was to evaluate the in vitro cytotoxic effect of Haloferax mediterranei bacterioruberin-rich carotenoid extracts (BRCE) (0-100 µg/ml) in six BC cell lines, representative of the intrinsic phenotypes and a healthy mammary epithelium cell line. Cell index values were obtained using xCELLigence RTCA System. Furthermore, cell diameter, viability, and concentration were measured at 12 h, 24 h, and 30 h. We found that BC cells were selectively affected by BRCE (SI > 1, p < 0.005). After 30 h, the population of BC cells exposed to 100 µg/ml was 11.7-64.6% of the control (p = 0.0001-0.0009). Triple-negative cells were significantly affected [MDA-MB-231 (IC₅₀ 51.8 µg/ml, p < 0.0001) and MDA-MB-468 (IC₅₀ 63.9 µg/ml, p < 0.0001)]. Cell size was also reduced after 30 h treatment in 3.8 (± 0.1) µm and 3.3 (± 0.02) µm for SK-BR-3 (p < 0.0001) and MDA-MB-468 (p < 0.0001), respectively. In conclusion, Hfx. mediterranei BRCE exerts a cytotoxic effect on BC cell lines representative of all studied intrinsic subtypes. Furthermore, results obtained for MDA-MB-231 and MDA-MB-468 are very promising, considering the aggressive behaviour of the triple-negative BC subtype.

Identification and Functional Analysis of Two Novel Genes-Geranylgeranyl Pyrophosphate Synthase Gene (AlGGPPS) and Isopentenyl Pyrophosphate Isomerase Gene (AlIDI)-from Aurantiochytrium limacinum Significantly Enhance De Novo β-Carotene Biosynthesis in Escherichia coli

Precursor regulation has been an effective strategy to improve carotenoid production and the availability of novel precursor synthases facilitates engineering improvements. In this work, the putative geranylgeranyl pyrophosphate synthase encoding gene (AlGGPPS) and isopentenyl pyrophosphate isomerase encoding gene (AlIDI) from Aurantiochytrium limacinum MYA-1381 were isolated. We applied the excavated AlGGPPS and AlIDI to the de novo β-carotene biosynthetic pathway in Escherichia coli for functional identification and engineering application. Results showed that the two novel genes both functioned in the synthesis of β-carotene. Furthermore, AlGGPPS and AlIDI performed better than the original or endogenous one, with 39.7% and 80.9% increases in β-carotene production, respectively. Due to the coordinated expression of the 2 functional genes, β-carotene content of the modified carotenoid-producing E. coli accumulated a 2.99-fold yield of the initial EBIY strain in 12 h, reaching 10.99 mg/L in flask culture. This study helped to broaden current understanding of the carotenoid biosynthetic pathway in Aurantiochytrium and provided novel functional elements for carotenoid engineering improvements.

Bioactive molecules from haloarchaea: Scope and prospects for industrial and therapeutic applications

Marine environments and salty inland ecosystems encompass various environmental conditions, such as extremes of temperature, salinity, pH, pressure, altitude, dry conditions, and nutrient scarcity. The extremely halophilic archaea (also called haloarchaea) are a group of microorganisms requiring high salt concentrations (2–6 M NaCl) for optimal growth. Haloarchaea have different metabolic adaptations to withstand these extreme conditions. Among the adaptations, several vesicles, granules, primary and secondary metabolites are produced that are highly significant in biotechnology, such as carotenoids, halocins, enzymes, and granules of polyhydroxyalkanoates (PHAs). Among halophilic enzymes, reductases play a significant role in the textile industry and the degradation of hydrocarbon compounds. Enzymes like dehydrogenases, glycosyl hydrolases, lipases, esterases, and proteases can also be used in several industrial procedures. More recently, several studies stated that carotenoids, gas vacuoles, and liposomes produced by haloarchaea have specific applications in medicine and pharmacy. Additionally, the production of biodegradable and biocompatible polymers by haloarchaea to store carbon makes them potent candidates to be used as cell factories in the industrial production of bioplastics. Furthermore, some haloarchaeal species can synthesize nanoparticles during heavy metal detoxification, thus shedding light on a new approach to producing nanoparticles on a large scale. Recent studies also highlight that exopolysaccharides from haloarchaea can bind the SARS-CoV-2 spike protein. This review explores the potential of haloarchaea in the industry and biotechnology as cellular factories to upscale the production of diverse bioactive compounds.