Immunostimulant Activity of Bacteria Isolated from Extreme Environments in Baja California Sur, Mexico: A Bioprospecting Approach.

Excessive use of antibiotics has led to an increase of pathogenic bacteria with multiple antibiotic resistance. Hypersaline and hyperthermal environments promote the development of several microorganisms that can potentially act as immunostimulants. Thus, the aim of this study was bioprospecting marine bacteria from these environments using mouse leukocytes as a cell model for assess immunostimulatory activity. Samples were taken from two evaporation ponds with 4 and 8% salinity (p/v) in a marine solar saltern (MSS) at Laguna Ojo de Liebre, Guerrero Negro and a shallow hydrothermal vent (SHV), Bahía Concepción under a mangrove forest both off Baja California Sur, México. From total number of isolates (N = 340), 267 were obtained from the MSS and 73 from the SHV. The 10 isolates that induced nitric oxide (NO) production in mouse splenocytes were identified using the 16S rRNA gene, of which Halomonas elongata, Halomonas sp., Pseudoalteromonas ruthenica, Bacillus subtilis and three Bacillus strains were isolated from the MSS ponds at 8% salinity and three Marinobacter lutaoensis strains from the SHV. Most of the selected bacteria were not cytotoxic for mouse splenocytes and enhanced phagocytic respiratory burst and antioxidant enzyme activities compared to the control immunostimulant (lipopolysaccharide from Escherichia coli). Selected bacteria from 8% salinity ponds in the MSS in Guerrero Negro had immunostimulant activity in vitro in mouse splenocytes. In conclusion, Bacillus subtilis SA4 220, Bacillus sp. SA4 62A, P. ruthenica SA4 40 as well as Halomonas sp. SA4 207 and Halomonas elongata SA8 44 increased several immunological parameters. Further research is needed to evaluate their potential application in preclinical models to fight against infectious diseases. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12088-022-01002-3.