Isolation and characterization of halophilic bacteria producing exopolymers with emulsifuing and antioxidant activities

Halophilic bacteria are considered a great source of new strains producing novel exopolymers with functional properties. In this work we isolated ten halophilic strains producing exopolymers from different hypersaline environments in Morocco. Phenotypic characterization showed that the strains were moderately halophilic, mesophilic and neutrophilic with the ability to produce some hydrolytic enzymes. Strains identification based on 16S rRNA gene sequences comparison showed that nine strains, designed as N1, N2, N5, N7, N8, N9, N10, N11 and N12 belong to Halomonas genus and one strain, designed as N4, to Marinobacter genus. The majority of the strains showed high levels of exopolymer production. The study of emulsifying and antioxidant activities revealed that all the polymers have an interesting emulsifying and antioxidant activities with the polymer from Marinobacter sp. N4 forming the highest and most stable emulsions and exhibiting the best antioxidant activity in comparison with other exopolymers produced by Halomonas strains. The obtained results demonstrate the great potential of exopolymers from halophilic bacteria to be applied as emulsifying and antioxidant agents in food, cosmetics and oil industries

Marinobacter maroccanus sp. nov., a moderately halophilic bacterium isolated from a saline soil.

During the taxonomic investigation of exopolymer producing halophilic bacteria, a rod shaped, motile, Gram-stain-negative, aerobic, halophilic bacterium, designated strain N4T, was isolated from a natural saline soil located in the northern Morocco. The optimal growth of the isolate was at 30-37 ºC and at pH 6.0-9.0, in the presence of 5-7% (w/v) NaCl. Useful tests for the phenotypic differentiation of strain N4T from other Marinobacter species included α-chymotrypsin and α-glucosidase activities and the carbohydrate assimilation profile. The major fatty acids detected in strain N4T were C18:1 ω9c, C16:0, and C16:1 ω7c/C15:0 iso 2-OH. Sequence analysis of the 16S rRNA indicated that strain N4T belonged to the genus Marinobacter and was closely related to Marinobacter adhaerens NC17506T (99.04%), Marinobacter salsuginis SD-14BT (98.97%), and Marinobacter flavimaris SW-145T (98.36%). Phylogenetic analysis of the rpoD gene sequence also showed that the nearest neighbours of strain N4T were M. adhaerens (90.63%) and M. salsuginis (91.13%). Strain N4T showed 87.98% similarity in the average nucleotide identity (ANI) with M. flavimaris and M. salsuginis, and 87.47% with M. adhaerens. In the in-silico genome-to-genome distance (GGD), strain N4T showed DNA-DNA hybridization (DDH) values of 33.30% with M. adhaerens, 34.60% with M. flavimaris and 34.70% with M. salsuginis. DNA G+C content of N4T was 57.3 mol%. Based on the results of phenotypic characterization, phylogenetic analysis and genome comparison, strain N4T represents a novel species of the genus Marinobacter, for which the name Marinobacter maroccanus sp. nov. is proposed. The type strain is N4T (=CECT 9525T=LMG 30466T)