Comparative analysis of phosphorus uptake and transport pathway genes between toxic and non-toxic Cylindrospermopsis raciborskii and their responses to low phosphorus
The molecular basis for cyanobacteria to adapt to environmental phosphorus fluctuations is to have complete phosphorus uptake and transport pathway genes(Pho regulon).Currently,little is known about the response and expression pattern of these genes in Cylindrospermopsis raciborskii.Based on our previous study on the non-toxic C.raciborskii N8,Pho regulon genes in the CYN-producing strain QDH7 were further analyzed,and compared the growth,alkaline phosphatase(ALP)activity,and temporal ex-pression of eight Pho regulon genes of the two strains under high and low phosphorus(P)conditions.The results showed that the Pho regulon genes of both strains were relatively complete,with some differences in arrangement and copy number of several genes.Under low P concentration,the growth of both strains was significantly inhibited,and the ALP activity significantly increased between days 14 to 18.The growth trend of toxic and non-toxic strains was almost consistent under the same P concentration.Both strains sig-nificantly increased the expression of two component regulatory system genes phoB and phoR during days 4 to 6 and 14 to 16,while only one of the two high affinity inorganic P binding protein genes pstS1 showed a significantly increased expression.Among the two ALP genes,the expression of phoA1 was synchronized with an increase in ALP activity.These findings indicated that the pstS1 and phoA1 genes played a crucial role in the response to low P.The upregulation of the low affinity inorganic P transport system pit during days 16 to 18 may be an indication of extreme P deficiency in the strain QDH7 and N8.We found that the maximal relative expression levels of six genes of toxic QDH7 under low P were higher than those of non-toxic N8.This difference may affect the competition for phosphorus and the formation of relative advantage between the two genotype strains coexisting in natural water bodies in phosphorus deficient environments.
Cylindrospermopsis raciborskiitoxic and non-toxic strainsphosphorus uptake and transport pathway genesalkaline phosphatasegene expression
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