Abstract
Viable but nonculturable (VBNC) bacteria generally inhabit marine environments, especially oligotrophic open ocean, because most marine bacteria which are biologically active can not be cultivated by traditional microbiological protocols. Some researchers argue that VBNC is a temporary state in marine bacteria which are originally cultivated by normal methods, induced by several environmental stresses, for example low temperature, high pressure, and extremely low nutrient concentrations. Other researchers argue that VBNC marine bacteria are novel and unique bacterial groups which have never been isolated by the traditional microbiological techniques. Some phenomenon in marine Vibrio strains support the former and phylogenetic studies on bacterial 16S ribosomal RNA genes directly isolated from seawater samples support the latter view. We introduced here marine oligotrophic bacteria, which were isolated by some low-nutrient media containing only 0.5mg/L of organic nutrients. These bacteria are unculturable in all high-nutrient media containing more than 0.5g/L of organic nutrients, the concentration which is normally used for bacterial cultivation, and their 16S rRNA gene sequences indicate that they are phylogenetically novel.
