Actinomycetes are fungi-like bacteria. They form branching hyphae (tubular structures) both on surfaces and within solid substrates. Their hyphae generally have cross-walls and are multinucleated. Reproduction is often asexual and is achieved by sporulation. Most actinomycetes are sessile, but species capable of motility derive their locomotion from flagellated spores. In many places in the Arctic, species of Actinomyces are primary soil inhabitants. They are widely distributed and key to the mineralization of organic matter. Actinomycetes have the ability to degrade a wide variety of organic compounds and, as such, play a pivotal role in the nutrient cycling of arctic terrestrial ecosystems. Although most actinomycetes are free living, some species are pathogenic, such as Actinomyces bovis.
Actinomyces bovis causes actinomycosis or "lumpy jaw" in caribou. This bacterium is a normal part of the mouth flora, but when it invades lesions in the oral cavity, it can become problematic. During teething, or when the animal's food source is particularly abrasive, tears in the mouth tissue can become infected with A. bovis. Bony lumps develop that can become as large as a tennis ball in just a few months. Respiration and chewing become problematic, which leads to weight loss. Other than the swellings in the mouth, infected animals appear healthy. Fortunately, this is one disease which is not transmissible to humans.