Strains belonging to the yeast species Kluyveromyces marxianus have been 
isolated from a great variety of habitats, which results in a high metabolic 
diversity and a substantial degree of intraspecific polymorphism. As a 
consequence, several different biotechnological applications have been 
investigated with this yeast: production of enzymes (beta-galactosidase, 
beta-glucosidase, inulinase, and polygalacturonases, among others), of 
single-cell protein, of aroma compounds, and of ethanol (including 
high-temperature and simultaneous saccharification-fermentation processes); 
reduction of lactose content in food products; production of bioingredients from 
cheese-whey; bioremediation; as an anticholesterolemic agent; and as a host for 
heterologous protein production. Compared to its congener and model organism, 
Kluyveromyces lactis, the accumulated knowledge on K. marxianus is much smaller 
and spread over a number of different strains. Although there is no publicly 
available genome sequence for this species, 20% of the CBS 712 strain genome was 
randomly sequenced (Llorente et al. in FEBS Lett 487:71-75, 2000). In spite of 
these facts, K. marxianus can envisage a great biotechnological future because 
of some of its qualities, such as a broad substrate spectrum, thermotolerance, 
high growth rates, and less tendency to ferment when exposed to sugar excess, 
when compared to K. lactis. To increase our knowledge on the biology of this 
species and to enable the potential applications to be converted into industrial 
practice, a more systematic approach, including the careful choice of (a) 
reference strain(s) by the scientific community, would certainly be of great 
value.