[5][6] Unlike plants, algae, and cyanobacteria, purple sulfur bacteria do not use water as their reducing agent, and therefore do not produce oxygen.

If sufficient sulfate is present to support sulfate reduction, the sulfide, produced in the sediments, diffuses upward into the anoxic bottom waters, where purple sulfur bacteria can form dense cell masses, called blooms, usually in association with green phototrophic bacteria.

[10][11] Purple sulfur bacteria are able to affect their environment by contributing to nutrient cycling, and by using their metabolism to alter their surroundings.

[14] Through upwelling of these organisms, phosphorus, a limiting nutrient in the oxic layer of lakes, is recycled and provided to heterotrophic bacteria for use.

For example, in the South Andros Black Hole in the Bahamas, purple sulfur bacteria adopted a new characteristic in which they are able to use their metabolism to radiate heat energy into their surroundings.

By raising the temperature of the surrounding water, they create an ecological niche which supports their own growth, while also allowing them to outcompete other non-thermotolerant organisms.

Due to the large difference in density, the upper and lower layers do not mix, resulting in an anoxic environment below the chemocline.

[17][16] A study done at the Mahoney Lake suggested that purple sulfur bacteria contributes to the recycling of the inorganic nutrient, phosphorus.

[16] Purple sulfur bacteria make conjugated pigments called carotenoids that function in the light harvesting complex.

[18] The authors of the study concluded that, based on the presence of purple sulfur bacteria's biomarker, the Paleoproterozoic ocean must have been anoxic and sulfidic at depth.

Purple sulfur bacteria can contribute to a reduction of environmentally harmful organic compounds and odour emission in manure wastewater lagoons where they are known to grow.