The significant increase in economic concern and environmental restrictions has resulted in increasing interest in biotechnological solutions. The application of acidophilic, sulfur-oxidizing microorganisms in biomining and in the treatment of waste matrices has been extensively explored. However, to surmount the current challenges encountered by the industrial use of acidophiles, there is an opportunity for neutrophilic and alkaliphilic microorganisms to be comprehensively considered for the biooxidation of refractory sulfide materials. This review, for the first time, provides a detailed study of neutrophiles and alkaliphiles that have potential for oxidizing sulfur-containing wastes and sulfide refractory ores to recover entrapped metals especially gold in a sustainable manner. The study illustrates the applicability of neutrophilic and alkaliphilic microorganisms to provide better and sustainable alternatives for the recovery of metals from wastes from various sources as well as refractory materials. The microorganisms summarized in this review have been successfully used in oxidizing different sulfide sources by achieving high oxidizing efficiencies (>80%) in numerous technologies. The fundamentals of biooxidation along with possible mechanisms involved in the biooxidation have been discussed in detail.
Keywords: acidophile; alkaliphile; chemolithotroph; metal sulfide; neutrophile.