photoauxotrophic

Photoauxotrophic is an adjective used in microbiology to describe a strain or organism that exhibits an auxotrophy tied to light dependence. In this sense, growth or survival hinges on exposure to light because certain biosynthetic steps or energy-generating processes require light-activated reactions. The term is not universally standardized, and its use varies across the literature. Some authors employ photoauxotrophy to denote strains that cannot synthesize specific essential compounds in the dark due to defects in light-dependent pathways, making light exposure or the provision of a photosensitized cofactor necessary for growth. It is distinct from photoautotrophy, in which an organism uses light as an energy source and fixes carbon dioxide, and from general phototrophy, which describes energy acquisition from light without implying auxotrophic growth requirements.

Possible mechanisms for photoauxotrophy include mutations that affect the function or regulation of light-activated enzymes, or a requirement for light to activate a cofactor necessary for metabolism. In practice, photoauxotrophy can complicate experimental growth conditions by requiring precise light exposure regimens, and it may be exploited as a selectable phenotype in mutagenesis, screening, or metabolic studies.

Because the term is infrequently used and its exact meaning can vary, authors describing photoauxotrophic strains should specify the observed growth requirements and the biosynthetic pathways or compounds implicated. Related concepts include auxotrophy, phototrophy, and photoautotrophy.