Microorganisms represent the largest living surface in the marine environment and contain a vast diversity that are mainly undiscovered. Presently it is estimated that less than 1% of the marine microorganism can be cultured by classical cultivation techniques and most of the species have never been described. Several modern conceptual and methodological approaches based on the 16S rRNA culture-independent methods have been developed in the last

Seven strains (Et1, But1, But2, But3, Lac1, Isob1, Benz1) of Gram-negative, mesophilic, nonsporing sulphate-reducing bacteria were isolated from bottom sediments of the Romanian Black Sea coast. Analysis of partial 16S rDNA sequences, obtained from pure cultures of isolated strains by PCR, revealed that all strains belonged to the Delta - subclass of Proteobacteria. Three strains (But1, But3, Lac1) were morphologically and nutritionally similar.