Brad Abramson

  • Mar 13, 2018

Date & Location: March 13, 2018, at 12p; Room 168 Plant Biology Building

Subject: Carbon partitioning in engineered cyanobacterium for the study of feedback inhibition of photosynthesis 

Abstract: Photosynthesis evolved in a dynamic environment, and therefore, there are many checks and balances built in that can limit photosynthetic productivity when ample CO2 and light are available. Feedback inhibition occurs when cell metabolism requirements are low and photosynthetically derived sugars accumulate, which limit photosynthetic efficiency and productivity limiting carbon fixation and light use efficiency. This is particularly evident in cyanobacterial bioproduction strains engineered to produce novel compounds, however the molecular mechanisms limiting productivity remain unclear.

To investigate feedback inhibition, we engineered Synechococcus elongatus PCC 7942 to export sucrose by overexpressing sucrose phosphate synthase and sucrose permease. When the cells are exporting sucrose, feedback inhibition of photosynthesis decreases, resulting in an increase in photosystem II’s light use efficiency, a greater relative electron transfer rate and less photosystem I acceptor side limitation. Less PSI acceptor side limitation correlates with an increase in the amount of RbcS-GFP packaged into the carboxysome, suggesting sucrose export leads to greater carbon fixation which is drawing electrons through the photosynthetic electron transport chain. Furthermore, we used this knowledge to reroute carbon from growth to sucrose export, increasing the specific and total productivity of cultures.

Brad Abramson is a graduate student in the lab of Danny Ducat.