Differential expression of the glucose transporter gene glcH in response to glucose and light in marine picocyanobacteria

Our team discovered that can take up glucose, in a process that changes the transcriptional pattern of several genes involved in glucose metabolization. We have also shown that encodes a very high affinity glucose transporter, and that glucose is taken up by natural populations. We demonstrated that the kinetic parameters of glucose uptake show significant diversity in different and strains. Here, we tested whether the transcriptional response of to several glucose concentrations and light conditions was also different depending on the studied strain. Cultures were grown in the light, supplemented with five different glucose concentrations or subjected to darkness, and cells harvested after 24 h of treatment. qRT-PCR was used to determine expression in four and two strains. In all studied strains was expressed in the absence of glucose, and it increased upon glucose addition to cultures. The changes differed depending on the strain, both in the magnitude and in the way cells responded to the tested glucose concentrations. Unlike the other strains, BL107 showed the maximum glucose uptake at 5 nM glucose. Darkness induced a strong decrease in expression, especially remarkable in MIT9313. Our results suggest that marine picocyanobacteria are actively monitoring the availability of glucose, to upregulate expression in order to exploit the presence of sugars in the environment. The diverse responses observed in different strains suggest that the transcriptional regulation of glucose uptake has been adjusted by evolutive selection. Darkness promotes a strong decrease in expression in all studied strains, which fits with previous results on glucose uptake in . Overall, this work reinforces the importance of mixotrophy for marine picocyanobacteria.