NOTE Studies of the Biological Characteristics of Some Halophilic and Halotolerant Actinomycetes Isolated from Saline and Alkaline Soils

Microorganisms found in extreme environments have attracted a great deal of attention, due to the production by such microorganisms of various natural compounds and their specialized mechanisms for adaption to extreme environments1-4). But relatively little research work has been done on actinomycetes found in extreme environments5). For example, the nutritional requirements of actinomycetes under extreme environments (including halophilic actinomycetes) remain unknown. It is also not known whether halophilic actinomycetes are similar to bacteria in their mechanisms for adapting to high salt conditions. In short, our current understanding and ability to use halophilic Actinomycetes is greatly circumscribed. Nevertheless, a study of such physiological problems is essential for achieving an overall understanding of halophilic Actinomycetes. Scientists have known that halophilic bacteria could endure and grow at high salt concentrations. However, they were unaware of the existence of halophilic actinomycetes until the 1970s. Gochnauer6) first discovered a strain of halophilic actinomycetes from a contaminated plate and named it Actinopolyspora halophila. Thereafter, research efforts focused on finding new halophilic actinomycetes. However, in contrast to halophilic bacteria, there are very few reports in the literature on halophilic actinomycetes. We still do not understand the physiological mechanisms that provide tolerance to high concentrations of NaCl, whether having addiction with different ions, how pH and nutrition material of medium affect its growth and metabolic product. Answers to these problems would advance efforts to isolate, classify, and apply halophilic actinomycetes. Halophilic bacteria and actinomycetes have been grouped according to salinity requirements by microbiologists such as Kushner (1978)6), Lasern (1986)7), Vreeland (1987)8), RamosCormenzana (1989)9). Among these methods, the method of classification proposed by Kushner (1978)6) (see Table 1) appears to be the most popular. But, in fact, NaCl is not the only salt found in high salt environments such as saline soils and seawater. For example, most saline soils in Xinjiang10) and Inner Mongolia11), China, also have high concentrations of Na+, K+, Mg2+, Ca2+. Accordingly, studies of halophilic actinomycetes focusing only on NaCl concentrations are inadequate for gaining an overall understanding of these actinomycetes. This paper reports on studies of the biological characteristics of 43 actinomycete strains isolated from Xinjiang, Hebei and Qinghai provinces, P. R. China, and of strains representative of four genera, including Prauserell rugosa (DSM43194T), Saccharomonospora halophila (DSM44411T), Nocardiopsis kunsanensis (KCTC9831T), Nocardiopsis halotolerans (DSM44410T), in environments of varying pH levels and varying concentrations of the salts Na+, K+, Mg2+, and Ca2+.