Which of the following bacteria are gram-negative, filamentous anoxygenic phototrophs, which use reduced sulphur compound for phototrophy, and also show 3-hydroxypropionate CO₂ assimilatory pathway, with one of its species specially used for the study of evolution of photosynthesis?

Choroflexus are gram-negative filamentous anoxygenic phototrophic (FAP) organism that do not produce oxygen as a byproduct of photosynthesis, in contrast to oxygenic phototrophs like cyanobacteria. It uses reduced sulphur compounds such as thiosulphate or elemental sulphur.

Instead of using the Calvin-Benson-Bassham Cycle typical of plants, Chloroflexus aurantiacus has been demonstrated to use a novel autotrophic pathway known as the 3-hydroxypropionate pathway.

Chloroflexus aurantiacus that can survive using either respiration or photosynthesis are of interest in on-going attempts to trace the evolution of photosynthesis.