Differential expression of phosphorus acquisition genes in response to phosphorus stress in two Raphidiopsis raciborskii strains |
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| Affiliation: | 1. Australian Rivers Institute, Griffith University, Nathan, 4111 Queensland, Australia;2. Department of Earth and Environmental Sciences, and the Lamont-Doherty Earth Observatory, Columbia University, Palisades NY, 10964, USA;1. Australian Rivers Institute, Griffith University, QLD, Australia;2. School of Biotechnology and Biomolecular Sciences, University of New South Wales, NSW, Australia;3. School of Environmental and Life Sciences, The University of Newcastle, NSW, Australia;4. Faculty of Veterinary and Agricultural Sciences, University of Melbourne, VIC, Australia;5. Population Health and Immunity Division, Walter and Eliza Hall Institute of Medical Research, Melbourne, VIC, Australia;1. Australian Rivers Institute, Griffith University, 170 Kessels Road, Nathan, Queensland 4111, Australia;2. School of Environment, Griffith University, 170 Kessels Road, Nathan, Queensland 4111, Australia;1. Australian Rivers Institute, Griffith University, Nathan Queensland 4111, Australia;2. Seqwater, Ipswich, Queensland 4305, Australia;3. School of Biological Sciences, Monash University, Clayton Victoria 3800, Australia;1. Australian Rivers Institute, Griffith University, 170 Kessels Road, Nathan 4111, QLD, Australia;2. School of Chemical Engineering, The University of Queensland, St Lucia 4072, QLD, Australia;3. Seqwater, 117 Brisbane Street, Ipswich 4305, QLD, Australia |
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| Abstract: | The cyanobacterium Raphidiopsis raciborskii is a nuisance in freshwater ecosystems. Strains vary in their physiological responses to environmental drivers, thus a greater understanding of the magnitude of strain variation is required to characterize the species. In this study, two strains of R. raciborskii isolated from a tropical Australian water reservoir were grown with and without phosphorus (P) to determine any relative response to P stress. The strains had the same growth rates and under P free conditions, cells grew at the same rate as P replete conditions until day 9 when cell growth ceased. There was no difference in the alkaline phosphatase activity per cell for the P replete and P free conditions, but the level of activity per cell was greater in CS-505 than CS-506. P acquisition genes were identified from the sequenced genomes; both strains contained the same genes, but with differences in copy number of phoA (7 and 6), phnK (3 and 1) and phnH (2 and 1) between CS-505 and CS-506 (respectively). The expression of P acquisition genes under P stress was measured throughout the experiment and shown to vary in magnitude and timing across strains, and in P replete versus P free cultures. In strain CS-505, upregulation of the pstS1 and phoA genes occurred late in the growth phase and into senescence. These genes are involved in phosphate uptake and use of various forms of organic P. For strain CS-506, there was upregulation of the phosphate uptake gene, pit, and organic P utilization genes, phoA, phoU, phnD and phnK, commencing late in the growth phase. Our study shows that despite the fact that these two strains were isolated from the same waterbody, they differed markedly in their gene expression response to P free conditions. This capacity of R. raciborskii to vary in strain responses to P conditions gives the organism flexibility in responding to environmental change, particularly P stress conditions. |
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| Keywords: | Cyanobacteria Ecotypes Phosphorus metabolic pathways Alkaline phosphatase Gene expression |
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