Carotegenic Virgibacillus halodenitrificans from Wadi El-Natrun Salt Lakes: Isolation, Optimization, Characterization and Biological Activities of Carotenoids

Abstract

Carotenoids, as phytonutrient pigments, are signified by their unique beneficial features that serve human health and the surrounding ecosystem. Haloalkaliphiles from soda lakes produce different natural bioactive molecules; however, their ability to produce carotenoids has been limited. Therefore, this study focused on the screening and isolation of carotenoid-producing haloalkaliphilic microbes. Out of 10 isolates, a powerful carotigenic bacterium was isolated, characterized phenotypically and identified on the molecular level as Virgibacillus halodenitrificans. By employing statistical approaches like Plackett–Burman design and central composite design, the influence of significant nutritional variables on carotenoids production was screened and optimized. Predictive modeling manifested that carotenoid yield was 36.42 mg/mL, a 2.12-fold enhancement compared to the basal conditions through inoculating 1.8% of bacterial biomass on optimized medium containing yeast extract (2 g/mL), peptone (10 g/mL) and NaCl (233.6 g/mL). The carotenoids content was confirmed by UV-Vis spectrum which detected a characteristic unique peak with left and right shoulders at 461 nm, 490 and 522 nm. However, FTIR and Raman spectroscopy showed the presence of several functional groups. Meanwhile, LC–MS confirmed that the examined carotenoids were composed of β-carotene, lutein and β-Apo-8′-carotenal mixture. As a bioactive agent, the carotenoids of V. halodenitrificans DASH showed characteristic antagonistic potency against a wide spectrum of Gram-positive and Gram-negative pathogens. Interestingly, a potent antifungal capacity was observed against Candida albicans, reflecting promising mycocidal efficacy against COVID-19 white fungal post-infections. Furthermore, carotenoids (20 μg/mL) inhibited the biofilm formation of P. aeruginosa and S. aureus by 54.01 ± 3.97% and 80.082 ± 0.895%, respectively. Our results proposed that haloalkaliphiles of Wadi El-Natrun lakes are promising sources of carotenoids that exhibited efficiency as safe, biocompatible and natural bioactive agents for environmental, medical and industrial applications.

Sun protection and antibacterial activities of carotenoids from the soft coral Sinularia sp. symbiotic bacteria from Panjang Island, North Java Sea

“…8 , Table 7 ). The spectra profile was different from that of the carotenoids isolated from Virgibacillus halodenitrificans from Wadi El-Natrun Salt Lakes ( Fayez et al, 2022 ).

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“…Also, the HPLC analysis of carotenoids from the bacteria symbiont 19. PP.Sc.13 revealed three peaks at the retention’s times (Rt) of 2.59, 2.75, and 4.62 with maximum absorbance at λ range of 450 – 490 nm, strongly suggesting the absorbance of carotenoids ( Fayez et al, 2022 , Finkel’shtein, 2016 , Scott, 2001 ) ( Table 6 , Fig. 7 ).…”

“…Many carotenoids produced from soft coral symbiotic bacteria have shown pronounced potential as a commercial commodity due to their biological activities ( Galasso et al, 2017 , Vílchez et al, 2011 ), including antioxidant ( Kusmita et al, 2021b , Kusmita et al, 2017 , Mutiara et al, 2017 ), anti-aging ( Kusmita et al, 2021a ), and antibacterial activities ( Kusmita et al, 2021b , Murti et al, 2016a ). ( Fayez et al, 2022 ) recently reported the carotenoids produced by Virgibacillus halodenitrificans bacteria with biological activity. Another study reported the anticancer and antiviral activities of the carotenoids of Natrialba sp.…”

Genome analysis of a halophilic Virgibacillus halodenitrificans ASH15 revealed salt adaptation, plant growth promotion, and isoprenoid biosynthetic machinery

“…Among the various bacterial genera inhabiting various extreme environments, the morphologically, biochemically, and genetically diverse genus Virgibacillus is widely recognized as an important model group for agriculture and industrial applications (Sánchez-Porro et al, 2014 ; Fayez et al, 2022 ). A wide range of different species of Virgibacillus have been reported globally from various saline environments, such as seawater, marine sediments, lakes, soil, and fermented seafoods (Montriwong et al, 2012 ; Amziane et al, 2013 ; Xu et al, 2018 ; Mechri et al, 2019 ; Bhatt and Singh, 2022 ).…”

“…To date, 39 validated and 381 non-validated species in the Virgibacillus genus have been published in the NCBI database (Chen et al, 2018 ), whereas six complete genomic sequences of Virgibacillus species are available in the NCBI database (2017) (Chen et al, 2018 ). Virgibacillus halodenitrificans is one of such bacteria whose potential is less explored (Lee et al, 2012 ; Kumaunang et al, 2019 ; Fayez et al, 2022 ). In 1989, the first report of a halophilic denitrifier, Bacillus halodenitrificans , from a solar saltern was reported by Denariaz et al ( 1989 ).…”