Ocean bacteria bend the rules of photosynthesis

Author:  Iannucci Shandra

Date:  March 2008

Plant biologist Arthur Grossman and colleagues of the Carnegie Institution in Stanford, CA released surprising findings that put a new spin on one of the oldest and most important molecular pathways on earth. Two billion years ago, bacteria evolved that were capable of consuming atmospheric carbon dioxide to produce energy while releasing oxygen gas as a byproduct in a process known as photosynthesis. These photosynthetic bacteria, or cyanobacteria, were responsible for oxygenating the atmosphere of early earth, which paved the way for life on land.

Now, Grossman and his team have discovered at least one type of cyanobacteria that can "cheat" at the game of photosynthesis in order to conserve scarce nutrients. These remarkable findings were published in the March volume of Biochemica et Biophysica Acta and further results are to be published in the May volume of Limnology and Oceanography.

Grossman's team discovered that the cyanobacterium Synechococcus uses a form of photosynthesis that does not require carbon dioxide to produce energy for the cell. The researchers were studying Synechococcus in order to understand how these cyanobacteria can thrive in parts of the ocean where access to iron, a mineral typically necessary for performing photosynthesis, is limited.

The bacteria bypass the stage of photosynthesis that requires iron, which in turn prevents the process from reaching the point at which carbon dioxide is turned into stored energy.

"This discovery represents a paradigm shift in our view of photosynthesis by organisms in the vast, nutrient-starved areas of the open ocean," announced Joe Berry of the Carnegie Institution's Department of Global Ecology. The discovery of a new mechanism of photosynthesis represents a revolutionary new understanding of the vital process.

"We had assumed that like higher plants, the goal was to make carbohydrates from carbon dioxide and store them for later use . We now know that some organisms short-circuit this complicated process, using light in a minimalist way to power cellular processes directly ." Berry explained.

Understanding this new form of photosynthesis will be critical to marine ecologists. Measuring the effect of cyanobacteria that do not produce carbon storage molecules will be essential in determining the net production of carbon compounds from carbon dioxide in open ocean ecosystems, a value that is indicative of the ecosystem's ability to sustain higher organisms.

Written by Shandra Iannucci

Reviewed by Allison Wilkinson

Published by Pooja Ghatalia.