PSYCHROTROPHIC BACTERIA | Arthrobacter spp.

The genus Arthrobacter belongs to the class Actinobacteria, family Micrococcaceae, which includes microorganisms that live in soil, subterranean cave silts, sea, glacier silts, sewage, water sludge, aerial surfaces of plants, vegetables, and various animal species. Phylogenetically, it is a member of the high-GC Actinomycetes and includes a group of Gram-positive microorganisms, which, initially, grow as rods, subsequently becoming shorter taking on the appearance of large cocci. In aged cultures, cells may have entirely coccoid conformations, but mixed rod–coccus types are often seen. Arthrobacter atrocyaneus, A. aurescens, A. citreus, A. crystallopoietes, A. globiformis, A. histidinolovorans, A. ilicis, A. nicotianae, A. oxydans, A. pascens, A. protophormiae, A. ramosus, A. sulfureus, A. ureafaciens, and A. uratoxydans are the main species, but every year new species are proposed. Arthrobacters contaminate meat and meat products, fish and fish products, fruit, vegetables, and milk and dairy products. Because of their great nutritional versatility, they rapidly develop on the food surfaces and produce colored smears, in coculture with coryneforms, micrococci, staphylococci, and yeasts. In cheese, they are responsible for either spoilage or ripening. Being strictly aerobic, they produce colored smears and low-molecular-weight compounds on the surface of the cheese that are responsible for the product’s typical aroma.