https://orcid.org/0000-0003-0736-2787
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ABSTRACT
Arthrospira are multicellular cyanobacteria that typically reside in alkaline lakes of (sub)tropical regions and are mass cultivated around the globe in a variety of outdoor facilities and photobioreactors for their high nutritional, pharmaceutical and clinical value. Arthrospira sp. strain PCC 8005 was selected by the European Space Agency as an oxygen producer and nutritional end-product in a bioregenerative life support system for long-haul missions. Being highly resistant to ionizing radiation, it is also an ideal candidate for other space applications such as in situ resource utilization and terraformation. During long-term strain maintenance involving continuous subculturing we noted an irreversible morphological change in PCC 8005 subcultures i.e. from only helical to only straight trichomes. These morphotypes displayed differences in growth rate, buoyancy and resistance to gamma radiation. We also found marked differences in antioxidant capacity, pigment content and trehalose concentration, while whole-genome comparison revealed a difference of 168 SNPs, 48 indels and four large insertions affecting, in total, 41 coding regions across both genomes. Although nine of these regions encoded proteins with a known function, no conclusive genotype-phenotype associations could be determined. Nonetheless, genomic changes within the gvpC gene (encoding a gas vesicle protein) and within the regulatory region of the psbD gene (encoding the D2 protein of PSII) provided some clues for the observed differences in buoyancy and growth.
Acknowledgements
We are grateful to Dr M. Mysara of SCK•CEN for performing SNPEff v4.3 analysis, to G. Grousserov of SCK•CEN for his help with sequence variant analysis and statistical analysis of experimental results, and Dr M. Narajczyk of the Electron Microscopy Laboratory – University of Gdansk for providing TEM images. We acknowledge the editor and reviewers of this manuscript for their useful critical appraisal of the original submission.
Disclosure statement
No potential conflict of interest was reported by the authors.
Supplementary information
The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at http://doi.org/10.1080/09670262.2019.1675763
Supplementary file 1: contains all supplementary figures and tables (see below for legends).
Supplementary file 2: contains all computational results of executed genome comparisons.
Supplementary fig. S1: genealogy of strain PCC 8005 and its substrains, with information on genome sequence dates (PCC: Pasteur Culture Collection).
Supplementary fig. S2: Regression line for variables OD750 versus dry weight of P2 cells.
Supplementary fig. S3: Regression line for variables OD750 versus dry weight of P6 cells.
Supplementary figs S4–14: graphs for statistical significance testing of experimental data.
Supplementary fig. S15: ycf4-psbD intergenic region with indicated differences between the genomes of P2 and P6 (see Results and Discussion).
Supplementary figs S16–S18: compilation of TEM images of P2 and P6 cells irradiated with either 2100 Gy or 5000 Gy.
Supplementary tables S1–23: tabulated values for Student’s t-test and obtained significance calls for experimental results using biological triplicates (n = 3) (see also Materials and methods).
Author contributions
A. Yadav: execution and design of experiments, data acquisition and interpretation, manuscript preparation; P. Monsieurs: DNA sequence analysis and genome comparative analysis, manuscript preparation; K. Waleron: selection and analysis of TEM images; A. Misztak: execution of experiments; P. Janssen: original concept, design of experiments, data acquisition and interpretation, manuscript preparation, communications and manuscript management. All authors: manuscript editing and revision.
