The Bacteria Often Mistaken For Mould!

Updated: Sep 26

Gloeocapsa Magma

The black staining on this roof top is Gloeocapsa magma...

Not mould!

Gloeocapsa magma on Colourbond roof

Photo - Customer's home (Condon)

At the majority of quote appointments that we arrive at, the homeowners explain to us that it is only since the 2019 flood in Townsville that the dark growth on their roof or other horizontal surfaces has appeared or grown at an exponential rate.

An ancient photosynthesizing cyanobacterium that converts water into oxygen gas, Gloeocapsa magma (Gleo) is the chloroplast ancestor for all of Earth's plant life.

Video - Customer's home (Alice River)


Gleo thrives in high humidity and low sunlight.

For the Condon home above, it grew only on one side of the roof.

Strange...I first thought...Until my research lead me to understand how perfectly natural it is for this bacteria.


First things first!

How does it grow?

Moisture and calcium carbonate (or limestone), often found in roof shingles, nourish this single-cell organism, which supports colony growth and the gradual accumulation across an entire roof surface over time. Gravity then influences its smear-like stain.

How does it spread?

Small groups of cells (spores) detach from colonies and relocate through wind and animals to continue their life cycle, doing this most successfully where there is low light.

Ah, ha!

Ah, ha!

The affected side of the roof in Condon must receive the least amount of light...

Reduced light allows this bacteria to remain green, resembling algae, but it is not algae!

Gloeocapsa magma is bacteria!

Usually green in the shade and black when protecting itself from UV rays.
Gloeocapsa magma at the base of drainpipe

Photo - Customer's home (Kirwan)

Wait! What?

Wait? What?

Why isn't the roof in Condon totally covered in green then?

To protect itself from high UV exposure, Gleo will develop a dark outer coating, such as seen in the roof at Condon.

This sticky secretion further increases this bacteria's durability, as it effectively affixes itself to a surface, remaining even after its death.

Once the bacteria have become noticeable, the stains and damage the bacteria cause will continue to worsen year to year!


There's more...

Symbiotic, or mutually beneficial, relationships between Gleo and fungi (i.e. mould) often create completely different organisms named lichen. See below, how the edge of the concrete has been deteriorated by these organisms.

Video - Customer's home (Alice River)

Damage to Property

The literature reports agreement between the majority of field experts that Gleo is substantially damaging. As this bacteria holds moisture within roof shingles, left untreated, the materials age prematurely, corrode and lose particles, resulting in a roof's inability to reflect UV rays and shortening its life.


  • Increased air conditioning usage = Higher electricity bills

  • Chronic roof repair / reconstruction

  • Earlier roof replacement

  • Inferior property resale values

  • Insurance companies cancelling policies

Human impact...


ALS (Amyotophic lateral sclerosis) is the subject of latest research connected with people experiencing exposure to significant levels of cyanobacteria toxins such as BMAA (B-Methylamino-l-alanine).

BMAA is a neurotoxin, affecting the brain and its ability to control muscles in all parts of the body.

It can lead to Alzheimer's Disease and death, as the brain and body atrophy (waste away) due to the neurotoxin's degenerative effect on nerve cells.