Heavy Metal-Tolerant Halophilic Microorganisms from a Hypersaline Lagoon: Promising Candidates for Bioremediation

Halophilic microorganisms are a valuable resource for the bioremediation of saline environments contaminated with heavy metals. This study investigated the microbiota that could be cultured in the hypersaline Laguna Rosa in Torrevieja, Alicante, Spain, by combining an analysis of microbial diversity with an evaluation of tolerance to heavy metals. Water and sediment samples were collected from contrasting microenvironments (salinity 1–40%; pH 7.1–8.1) and subjected to enrichment and selective isolation strategies, yielding 79 isolates: 48 recovered from enrichment cultures and 31 from metal-supplemented media. These isolates represent all three domains of life: Archaea, Bacteria and Eukarya. The dominant taxa included Halorubrum sp., Haloferax sp., Halomonas sp., Marinobacter sp. and Dunaliella sp., as well as cyanobacteria such as Sodalinema sp. and Synechococcus sp. Tolerance assays revealed that haloarchaea exhibited high resistance to lithium, while several bacterial isolates tolerated chromium and arsenite. Dunaliella sp. showed the broadest overall metal tolerance among the photosynthetic isolates. In liquid culture, Halomonas smyrnensis maintained growth at Cr(VI) concentrations up to 25 mM, whereas Halorubrum saccharovorum tolerated up to 4 mM Cr(VI). These findings identify Laguna Rosa as a reservoir of halophilic microorganisms tolerant of heavy metal, with promising potential for the bioremediation of saline and hypersaline environments, including saline industrial wastewater contaminated with toxic metals.