A project undertaken at the University of Technology Sydney, and supervised by Katherina Petrou
Photosynthesis is one of the most important biological processes on Earth. It produces the oxygen we breathe and underpins almost all ecosystems. Most photosynthetic organisms rely on visible sunlight, but some remarkable microorganisms can survive and grow using near-infrared light – light that is invisible to the human eye and present only in very dim environments.
These near-infrared photosynthetic microorganisms live at the limits of light availability, in places such as caves, dense microbial mats, ancient stromatolites and even within coral reef organisms. Because these organisms are microscopic and because their near-infrared–emitting photosynthetic pigments are largely invisible to conventional instruments used to study cyanobacteria, they have been difficult to detect. Combined with the fact that they often inhabit environments that are hard to access and study, their diversity and ecological importance have long been overlooked.
This project investigates these hidden photosynthetic systems across a range of Australian environments, including the Great Barrier Reef, coastal mangroves in New South Wales, limestone caves in the Blue Mountains and the ancient stromatolites of Shark Bay in Western Australia that form one of the oldest living ecosystems on Earth. The research combines fieldwork in remote and extreme environments with advanced microscopy techniques that allow scientists to see how photosynthesis works inside living cells. Many of these microorganisms naturally emit a faint glow when illuminated, and by measuring this glow across different colours of light, the research team can identify organisms that are specially adapted to use near-infrared light.
A major focus of the project is understanding how these organisms organise their photosynthetic machinery to survive in very low-light conditions. This includes growing newly discovered microorganisms in the laboratory under carefully controlled lighting, so their growth, physiology and adaptations can be studied in detail.
One of the most exciting outcomes so far has been the discovery of near-infrared photosynthetic bacteria living within a coral-like reef animal on the Great Barrier Reef. This is the first time such organisms have been identified in this type of coral-associated system, revealing a previously unknown way that photosynthesis may support reef ecosystems in shaded or light-filtered environments.
The project also builds on detailed work in Shark Bay, where layered microbial communities form living stromatolites similar to those that dominated Earth billions of years ago. By studying how light penetrates these structures and how different microorganisms specialise at different depths, the research provides new insight into how early photosynthetic life may have functioned on the young Earth.
Our team is comprised of marine photobiologist and ecophysiologist, Associate Professor Katherina Petrou (project supervisor), with scientific direction and research delivery led by Dr Anya Salih, an Adjunct researcher at UTS with expertise in reef field-work, far red cyanobacterial diversity and advanced microscopy, working in collaboration with Professor Anthony Larkum, one of the original discoverers of chlorophyll D and chlorophyll F photosynthetic organisms, whose long-standing expertise in Shark Bay microbial biofilms has been central to advancing this field of research.
Together, this work is uncovering a hidden layer of Australia’s biodiversity and reshaping our understanding of how photosynthesis operates in some of the most extreme and light-limited environments on the planet.