ISSN: 1314-6246 Angelova et al. J. BioSci. Biotech. 2014, SE/ONLINE: 67-70 RESEARCH ARTICLE SPECIAL EDITION / ONLINE Section “Microbiology & Biotechnologies” Third Balkan Scientific Conference on Biology, Plovdiv, May 30 – June 1, 2014 67 Ralitsa Angelova 1,2 Michail Iliev 1 Milena Mitova 1 Vasilka Voynova 1 Lyudmila Tasheva 1 Lyubomir Slavov 2 Veneta Groudeva 1 Stefka Antonova-Nikolova 1 Optimization the cultivation of neutrophilic iron bacteria in laboratory conditions Authors’ addresses: 1 Faculty of Biology, Sofia University, 1164 Sofia, Bulgaria. 2 Institute of Electronics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria. Correspondence: Ralitsa Angelova Faculty of Biology, Sofia University, 8 Dragan Tzankov Blvd., 1164 Sofia, Bulgaria. Tel.: +359 896 858 712 e-mail: angelova87@abv.bg ABSTRACT The neutrophilic iron-oxidizing bacteria are different in morphology, physiology and taxonomic status but are united by their ability to oxidize Fe 2+ at neutral pH and to form insoluble ferric oxides/(oxy)hydroxides. The hydroxides formed on their sheaths are of great interest for application in different nanotechnologies, biomedical and bioengineering applications. The bacteria are typical oligocarbophils which makes them a successful indicator for organic pollution of the water. The main problem is connected with the formation of sheaths. The goal of this study is connected with the optimization of the cultivation conditions to obtain sheaths with ferroxides of neutrophilic iron bacteria. The optimization included investigations of the types of cultivation, used of the different nutrient media and the duration of the cultivation.The analysis of the results shows that the isolates grow poorly at 10°С and 37°С. Optimal growth of the cultures was observed at 20 о С under dynamic conditions. The most appropriate for the formation of sheaths was SIGP medium. The formation of the sheaths started after 7 days cultivation period.The analysis of the ferroxides formed shows that the composition of the nutrient medium strongly influences the type of the formed ferroxides. Key words: neutrophilic iron bacteria, sheathed bacteria, Leptothrix, nanotechnologies Introduction The neutrophilic iron-oxidizing bacteria are widely spread in different natural habitats. They are different in morphology, physiology and taxonomic status but are united by their ability to oxidize Fe 2+ at neutral pH and to form insoluble ferric oxides/(oxy)hydroxides. The interest to these bacteria increased in the recent years because many reasons. The hydroxides formed on the their sheaths are of great interest for application in different nanotechnologies and different biomedical and bioengineering applications as magnetic resonance imaging contrast enhancement, tissue repair, immunoassay, detoxification of biological fluids, drug delivery and in cell separation, etc. (Gupta, 2005). On the other side after the intensive growth of the bacteria and the formation of insoluble ferric hydroxides which are environmental pollutants lead to significant economic losses. The bacteria are typical oligocarbophils which makes them a successful indicator for organic pollution of the water. The sheathed bacteria grow as chains of cells in filaments, 0.4-7 μm in width. Gram negative. Filaments grow in a tube