Novel halotolerant microbial system enhanced by gamma irradiation for advanced multimetal bioremediation

Saline industrial effluents are difficult to treat because elevated ionic strength can inhibit biological treatment and alter metal speciation. This study evaluated two moderately halotolerant microorganisms recovered from seawater and shark-associated samples and examined whether gamma selection altered the performance of the more radioresistant isolate.

The isolates were identified as Serratia proteamaculans PX875896 and Rhodotorula mucilaginosa PX876763 by 16 S and 18 S rRNA gene sequencing, respectively. Both grew at 3-5% (w/v) NaCl but not at 10% or higher. In synthetic saline medium, S. proteamaculans showed the highest removal after 72 h for Cd (50.71%), Mo (42.56%), Cu (34.13%), and Co (25.26%); no net Cr removal was detected. S. proteamaculans was not recovered after 0.5 kGy, whereas R. mucilaginosa survived exposure up to 4 kGy. Relative to the wild yeast, gamma-selected yeast derivatives showed higher removal for several metals, including Co (22.61% at 48 h) and Cu (12.34% at 72 h) by the 4 kGy derivative and Mo (14.73% at 72 h) by the 3 kGy derivative. The 4 kGy derivative also contained more total carotenoids (67.30 µg/mL) than the wild strain (44.40 µg/mL). In textile wastewater, the 4 kGy derivative yielded the greatest removal of Mo (93.05%), Cr (77.88%),Co ( 60.80%) and Cd (51.42%), whereas S. proteamaculans yielded the greatest removal of Mo ( 58.43 %, Cr 57. 14 %, Fe (52.17%) and V (74.68%).

Saline-derived Serratia proteamaculans PX875896 showed greater metal removal in synthetic saline medium, while Rhodotorula mucilaginosa PX876763 exhibited broader metal tolerance and greater gamma resistance.The 4 kGy yeast derivative improved multimetal removal from textile wastewater, coinciding with a more carotenoid-rich phenotype.These findings highlight the value of moderate halotolerance, gamma-assisted selection, and complementary bacterial-yeast approaches, while showing that tolerance alone does not predict removal efficiency. l.