SEARCH FOR THE MOLECULAR-BASIS OF MORPHOLOGICAL VARIATION IN MYCOBACTERIUM-AVIUM

Isolates of Mycobacterium avium exhibit three different colonial varia tions: smooth domed (SmD), smooth transparent (SmT), and rough (Rg). B ecause the discrimination between morphotypes is founded on morphologi cal rather than molecular principles and because of the absence of con sensus over the relevance of morphology to pathogenesis and drug sensi tivity, a comparative study at the protein level was undertaken. By di rect immunization of BALB/c mice with the soluble sonicate of one of t he morphotypes of M. avium serovar 2, eight monoclonal antibodies (MAb s) were identified, of which one was Mi. avium specific. Cross immuniz ation of syngeneic mice with serum-absorbed antigens allowed the gener ation of 15 further MAbs; 11 were M. avium or M. avium complex specifi c, but none of them was morphotype specific. Subcellular fractions ana lyzed by electrophoresis showed similar profiles, with the exception o f a cytosolic protein with a relative molecular mass of ca. 66 kDa (pr otein SmT 66), which was most highly expressed in SmT variants of M. a vium serotypes 2 and 4. Because a well-known, ubiquitous stress-heat s hock protein (hsp65) has a similar molecular mass, protein SmT 66 was compared with hsp65. Western blot (immunoblot) analyses using several cross-reacting MAbs and N-terminal amino acid sequencing established t hat this protein was not the ubiquitous stress protein. Thus, SmT 66 i s the first product to be described which might be associated with the SmT morphotype.