Adaptive laboratory evolution to hypersaline conditions, of lactic acid bacteria isolated from seaweed

Seaweed biomass has been proposed as a promising alternative carbon source for fermentation processes using microbial factories. However, the high salinity content of seaweed biomass is a limiting factor in large scale fermentation processes. To address this shortcoming, three bacterial species (Pediococcus pentosaceus, Lactobacillus plantarum, and Enterococcus faecium) were isolated from seaweed biomass and evolved to increasing concentrations of NaCl. Following the evolution period, P. pentosaceus reached a plateau at the initial NaCl concentration, whereas L. plantarum, and E. faecium showed a 1.29 and 1.75-fold increase in their salt tolerance, respectively. The impact that salt evolution had on lactic acid production using hypersaline seaweed hydrolysate was investigated. Salinity evolved L. plantarum produced 1.18-fold more lactic acid than the wild type, and salinity evolved E. faecium was able to produce lactic acid, while the wild type could not. No differences in lactic acid production were observed between the P. pentosaceus salinity evolved and wild type strains. Evolved lineages were analyzed for the molecular mechanisms underlying the observed phenotypes. Mutations were observed in genes affecting the ion balance in the cell, the composition of the cell membrane and proteins acting as regulators. This study demonstrates that bacterial isolates from saline niches are promising microbial factories for the fermentation of saline substrates, without the requirement of previous desalination steps, while preserving high final product yields.