auxotrophies

An auxotroph is an organism that cannot synthesize a particular compound required for its growth and must obtain that compound from the environment. This occurs when a mutation disrupts a biosynthetic pathway, rendering the organism unable to produce a specific nutrient such as an amino acid, a nucleotide, a vitamin, or another essential metabolite. By contrast, a prototroph can grow on minimal medium because it can synthesize all needed components from basic nutrients.

Auxotrophies are especially common in microorganisms used for genetic studies. They arise from mutations in genes encoding enzymes of biosynthetic pathways and can be classified by the missing metabolite (for example, amino acid auxotrophs such as histidine, tryptophan, or leucine auxotrophs; nucleotide or vitamin auxotrophs). Some organisms exhibit multiple auxotrophies, while others may be conditional depending on growth conditions.

In research and biotechnology, auxotrophies form useful tools. They enable selection and screening: growth on defined media lacking the missing nutrient requires a genetic complement or a plasmid carrying the functional gene. Auxotrophic markers are used for gene mapping, functional studies, and constructing engineered strains. They also facilitate studies of microbial interactions, such as cross-feeding in communities.

Clinically, auxotrophies have relevance in cancer metabolism and antimicrobial strategies, where exploiting tumor or pathogen nutrient dependencies can inform treatment approaches. Additionally, environmental and industrial applications leverage auxotrophic markers in strain development and quality control.