Radiation-inducible radioprotective exopolysaccharides of Bacillus siamensis CV5 from irradiated roots of Cistanche violacea to decrease free radical damage produced by ionizing radiation

Abstract

Purpose: To assess exopolysaccharides (EPS) of Bacillus siamensis CV5, isolated from irradiated roots of Cistanche violacea, for their induction by ionizing radiation (IR) and their antioxidant and radioprotective power.

Materials and methods: Isolated bacteria from the roots of C. violacea were screened for EPS production. The most EPS-producing bacterium was selected and the response surface methodology (RSM) was applied to elucidate the IR dose effects on EPS production. Gamma irradiation effects on the morphology and functional groups of EPS were studied using microscopy and Fourier transform infra-red (FT-IR). The radioprotective potential of EPS on the survival of B. siamensis CV5 following IR was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Free radicals scavenging potentialities (FRSP) of non-irradiated and irradiated EPS were evaluated through 2, 2⁻-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid (ABTS) and ferric reducing ability of plasma (FRAP) assays.

Results: Twenty strains, isolated from irradiated roots of C. violacea, were screened for their EPS production. IR-resistant B. siamensis CV5 was the most EPS-producing strain. Its purified EPS contained rhamnose, fructose, mannose and glucose. RSM indicated that EPS of CV5 (CV5-EPS) are radiation inducible. Micrographs of CV5-EPS suggested an increase in the total area and a decrease in the Feret’s statistical diameter following exposure to IR. FT-IR spectra of these EPS revealed an increase of various functional groups. The MTT survival assay demonstrated a positive correlation between the added quantity of CV5-EPS and the viability of irradiated CV5 (p < .01). DPPH, ABTS and FRAP assays indicated that the antioxidant activities of CV5-EPS increased significantly with the irradiation dose (p < .01).

Conclusions: CV5-EPS were demonstrated as radiation-inducible and radioprotective biomolecules. This radioprotective potential of CV5-EPS could be associated with their antioxidant activities. In the future, irradiated EPS could be tested as a gel in cancer radiotherapy for minimizing the damage caused by rays to surrounding healthy tissues.

Graphical Abstract

Keywords:

• Bacillus siamensis
• Cistanche violacea
• exopolysaccharides
• radiation-inducible
• radioprotective

Disclosure statement

The authors declare that they have no competing interests. No conflict of interest declared.

Additional information

Funding

This work was supported by grants from the Tunisian Ministry of Higher Education and Scientific Research; without this generous and strong assistance, this study could not have been undertaken. It was performed under the auspices of the Tunisian National Center for Nuclear Sciences and Technologies (CNSTN) in collaboration with Univ. Manouba, ISBST, BVBGR-LR11ES31, Biotechpole Sidi Thabet (Tunisia).

Notes on contributors

Sihem Guesmi

Sihem Guesmi is an Engineer in Food Industry and Health, she is preparing her PhD in Biology and Environmental Sciences at the National Institute of Agronomy of Tunisia. She is interested in the study of bioactive compounds from microorganisms and plants for multiple applications in biodosimetry and radioprotection.

Habib Chouchane

Habib Chouchane is an Assistant Professor in Microbial Biotechnology. His main research activities focus on microbial biomolecules: biopolymers, biosurfactants and extremozymes with valuable applications in bioremediation and health and on microbial electrochemical systems with potential energy, environmental and industrial applications. Dr. Chouchane has published more than 25 peer-reviewed papers.

Mohamed Neifar

Mohamed Neifar is an Enzymologist. He joined the research laboratory BVBGR at the Biotechnology Department of the Institute of Biotechnology of Sidi Thabet as an Assistant Professor since 2013. His scientific interests focus on microbial catalysts and their applications. Dr. Neifar has published more than 40 peer-reviewed papers.

Faouzi Hosni

Faouzi Hosni is an Associate Professor in Nuclear Physics. His research focused on the effect of gamma irradiation on nuclear material. He is also a specialist in nuclear dosimetry, qualification of irradiation facilities, structural and morphological analysis of organic and oxide materials. He is the author of 48 scientific articles.

Ameur Cherif

Ameur Cherif, PhD in Microbiology in 2001, is a Professor at the ISBST, University of Manouba, and head of the research laboratory “Biotechnology and Bio-Geo Resources valorization”. His current research activities focus on several aspects of microbial resources management, particularly in extreme environments and biotechnological applications of active biomolecules.

Haïtham Sghaier

Dr. Ir. Haïtham Sghaier is an Engineer in Biotechnology and Professor (Associate) of Radiation and Computational Microbiology at the National Center for Nuclear Sciences and Technology (CNSTN) in Tunisia. His research is related to cellular and molecular bioengineering, omics, the study of resistomes, (oxidative) stress tolerance and prokaryotes/eukaryotes interactions.