ABSTRACT
The general characteristics of the actinomycetes have been known for a long time. However, during the last few years, it was possible to learn more about their manifold functions in nature. Two genera, Streptomyces and Frankia, were detected in the second half of the 19th century and Micromonospora and Actinoplanes during the fi rst half of the 20th century. In 1875, Cohn illustrated for the fi rst time the typical sporulating hyphae of the genus Streptomyces (Miyadoh et al. 1997). The knowledge of this important soil inhabiting actinomycete was enlarged fundamentally by the taxonomic description of the species Streptomyces scabies, the pathogene of the potato scab (Thaxter 1891). The most typical saprophytic characters of this genus, the life cycle, the physiological requirements and the metabolic activities were studied intensively during the following decades, in which the discovery of antibiotics produced by streptomycetes strains was of
Departamento de Botánica, Centro Regional Universitario Bariloche, Universidad Nacional del Comahue. INIBIOMA-CONICET. Quintral 1250, 8400 S.C. de Bariloche, Río Negro, Argentina. *Corresponding author: marianasolans2005@hotmail.com; msolans@comahue-conicet.gob.ar
prime importance (Waksman 1950). The genus Frankia was described by Brunchorst (1886), as this “fungal-like” microorganism which can cause the production of nodules on young roots of certain trees like Alnus and Hippophae. The hyphal development and formation of small vesicular structures inside the infected cells of the host plant could be presented clearly. Nobbe and Hiltner (1904) were able to prove the symbiotic character and the capacity to fi x atmospheric N2 in situ, but it took many years to obtain pure cultures of Frankia strains (Quispel 1990). The genus name Micromonospora was introduced by Ørskov (1923), emphasizing the type of sporulation with single spores on short sporophores for representatives of those actinomycetes. Micromonospora strains can be isolated commonly from soil; however their predominant incidence seems to be in aquatic ecosystems. They show a high capacity to degrade biopolymers (Vobis 1992). With the methods usually applied for isolating aquatic fungi, Couch (1950) detected the genus Actinoplanes from soil samples. Actinoplanes is closely related to Micromonospora regarding the colonial characteristics; however it is very different in the type of sporulation. It produces sporangia releasing fl agellated spores when immersed in water. The whole life cycle of this saprophytic actinomycete can be described as “aero-aquatic” (Vobis et al. 2012).
