Helical and linear morphotypes of Arthrospira sp. PCC 8005 display genomic differences and respond differently to ⁶⁰Co gamma irradiation

Figures & data

Figs 1–4. The two representative strains of Arthrospira sp. PCC 8005 under study, displaying: Fig. 1. Helical trichomes (P6); Fig. 2. straight trichomes (P2); Fig. 3. sedimentation (P6) and Fig. 4. surface floating (P2). Figs 1, 2 scale = 32.5 µm.

Fig. 5. Growth curves of Arthrospira sp. PCC 8005 strains P2 and P6 (n = 3); characteristic strain differences are indicated in the panel. Growth rates (GR) were calculated according to formula [1]. Data are mean values, bars = SD.

Fig. 6. Recovery of: a. strain P2 (straight trichomes, floating) and b. strain P6 (helical trichomes, sedimenting) after exposure to three doses of ⁶⁰Co gamma irradiation (mean ± SD, n = 3).

Fig. 7. Antioxidant capacities of Arthrospira sp. PCC 8005 cells before (C = control) and immediately after ⁶⁰Co gamma irradiation at three cumulative doses for the hydrophilic fraction (a, b) and lipophilic fraction (c, d) of strains P2 and P6. Results are expressed in micromoles Trolox-equivalent per mg of fresh weight (µmol TE/mgFW), using mean values, bars = SD.

Fig. 8. Glutathione concentrations for strains P2 and P6 before (C = control) and immediately after exposure to ionizing radiation at three cumulative doses of ⁶⁰Co gamma irradiation. a, b, measured total glutathione concentration [GSH + GSSG] in nmoles per dry weight of pellet; c, d, calculated reduced glutathione concentration in nmoles per dry weight of pellet (GSH) calculated as total glutathione [GSH + GSSG] – 2 × [GSSG]; e, f, GSH/GSSG ratio calculated as ([GSH + GSSG] – 2 × [GSSG])/[GSSG]; and g, h, measured GSSG levels in nmoles per dry weight of pellet. Data are mean values, bars = SD.

Fig 9. Total cellular content of chlorophyll in: a. strain P2 and b. strain P6 before (C = control) and immediately after a given cumulative dose of ⁶⁰Co gamma irradiation. Data are mean values, bars = SD.

Fig. 10. Cellular content of carotenoids in: a. strain P2 and b. strain P6 before (C = control) and after a given cumulative dose of ⁶⁰Co gamma irradiation using the TAC assay and applying formula [4]. Data are mean values, bars = SD.

Fig. 11. Concentrations of: phycocyanin (PC) a. strain P2 and b. strain P6 and allophycocyanin (APC) c. strain P2 and d. strain P6, before (C = control) and after a given cumulative dose of ⁶⁰Co gamma irradiation. Concentrations were measured by the TAC assay using formulas [5] and [6], respectively. Data are mean values, bars = SD.

Fig. 12. Trehalose concentration in cells of: a. strain P2 and b. strain P6 before (C = control) and after a given cumulative dose of ⁶⁰Co gamma irradiation. Data are mean values, bars = SD.

Table 1. Genomic changes in the genomes of strains P2 and P6.

Comparison	SNPs	indels	large insertions
P2 vs Ref	301	310	8
P6 vs Ref	355	314	10
P2/P6 vs Ref	243	288	7
P2 vs P6	168	48	4

Ref is the strain PCC 8005 reference genome (Janssen et al., 2010) (updated version 5 of 15 February 2014, available at NCBI under GenBank assembly accession number GCA_000973065).

Table 2. Affected CDS with known function in strains P2 and P6 based on genome data.

Gene ID	Function	Size (aa)	Strain P2	Strain P6
ARTHROv5_10196	adenylosuccinate synthetase (PurA)	446		C248G
ARTHROv5_10705	Ser/Thr protein kinase	825	E290fs
ARTHROv5_11989	haemolysin-type Ca-binding protein	1261		V592R, L596R, A597D+insPDGPDPEL
ARTHROv5_12033	gas vesicle protein (GvpC)	151		K135D
ARTHROv5_30483	putative Ser/Thr protein phosphatase	360		large insertion
ARTHROv5_30654	nitrilase/cyanide hydratase	269	L21F
ARTHROv5_41442	putative diguanylate cyclase	195	G136R, T172A, C176R
ARTHROv5_60747	signal transduction histidine kinase	790		L443*
ARTHROv5_61039	WD-40 repeat protein	818	A124G	Q100K, T106R, E804G

Janssen, P.J., Morin, N., Mergeay, M., Leroy, B., Wattiez, R., Vallaeys, T., Waleron, K., Waleron, M., Wilmotte, A., Quillardet, P., De Marsac, N.T., Talla, E., Zhang, C.C. & Leys, N. (2010). Genome sequence of the edible cyanobacterium Arthrospira sp. PCC 8005. Journal of Bacteriology, 192: 2465–2466.

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