Cellular acclimation strategies of a minimal picocyanobacterium to phosphate stress

Abstract

The proteomic response of Prochlorococcus marinus MED4, subjected to extended phosphate (P) starvation, was measured utilizing the quantitative technique isobaric tags for relative and absolute quantitation. Seventeen proteins were identified as significantly more abundant in MED4 cultures grown under P-stressed conditions than the nonstressed cultures, while 14 proteins were observed to be significantly less abundant. Proteins involved in P acquisition, and membrane-associated functions such as protein folding, export and recycling as well as a protein putatively associated with maintaining DNA integrity were found to be higher in abundance than the nonstressed cultures. The effect of P starvation was also noticeable on the photosynthetic apparatus, whereby important proteins involved with light harvesting were reduced in abundance directly affecting the metabolism. This is expected, as the cell is starved of an essential nutrient; however, proteins involved in maintaining structural integrity in the photosystems are more abundant, which was not expected. We conclude that MED4 is capable of acclimating to long periods of P deprivation through a suite of processes including activating P transport and acquisition mechanisms, general stress responses, reduction of energy-related metabolic processes and importantly maintaining structural integrity in vital cell mechanisms.