Screening of Moderately Halophilic Bacteria Producing Ectoine Resulting in the Selection of Virgibacillus salarius BHTA19.

Research background: Ectoine is a desirable molecule with high application potential, particularly in the cosmetics and pharmaceutical industries. The current production method uses microorganisms that require high salinity. Therefore, purification of the product is expensive, complex and requires appropriate equipment. To overcome these obstacles, we were looking for new moderately halophilic, ectoine-producing bacteria.

Experimental approach: The bacteria were isolated from high-salinity environments: in the vicinity of Tyrawa spring, in Złockie near the Na Mokradłach spring and in Rajcza, all in Poland. Their ability to biosynthesise ectoine and additionally hydroxyectoine in a 10 % premixed seawater environment was assessed semiquantitatively using mass spectrometry (MS). The growth of the bacteria was also compared under these conditions. The most promising strains were then identified based on 16S rDNA sequence and their morphological, biochemical and physiological properties were described. The ectoine was biosynthesised based on the collected data and the preferences of individual strains. The concentrations of the final product were determined by HPLC. After the screening process, the most suitable strain was identified.

Results and conclusions: Fifty-six bacterial strains were isolated. Most strains produced insignificant amounts of ectoine or hydroxyectoine in the presence of 10 % salt. However, ten strains, all isolated from the Tyrawa spring, showed promising properties and were used in further studies. Based on the 16S rDNA sequence, four were identified as Halobacillus sp., two as Virgibacillus sp. and one as Bacillus sp., Pseudalkalibacillus sp., Salimicrobium sp. and Thalassobacillus sp. The basic biochemical and physiological properties as well as the ability to grow in the presence of NaCl, KCl, (NH₄)₂SO₄ and MgSO₄ were described. Ectoine was biosynthesised following the best parameters estimated for each strain. Based on the results, Virgibacillus salarius BHTA19 was identified as a new potential producer of ectoine.

Novelty and scientific contribution: We isolated a promising ectoine producer, moderately halophilic bacterium - Virgibacillus salarius BHTA19. BHTA19 is a wild-type strain that produces significant amounts of ectoine in environments with moderate salt concentrations. It has great potential and the possibility of industrial application.