Extremophilic microbial isolates and metagenomic analysis of Greek and Hungarian bauxite residues

Bauxite residue (BR) is an extreme environment for microorganisms. The aim of the work was to isolate extremophilic microorganisms for further biotechnological applications, such as bioleaching or waste rehabilitation. At the same time, metagenomic analysis was performed to monitor short-term changes in deposited BR. We isolated and identified alkaliphilic and extreme halotolerant strains of Nesterenkonia massiliensis, N. natronophila, Micrococcus luteus, Aspergillus iizukae, Gibellulopsis serrae, and G. nigrescens from Greek and Hungarian BRs. Most strains were siderophore producers, cellulose degraders and produced oxalic and acetic acids. Metagenomic analysis revealed a shift in the most abundant bacterial classes from the freshly produced BR during 1 month and 3 months of storage: from Gammaproteobacteria (29% relative abundance), to Actinomycetes (31%) and Gammaproteobacteria (39%), respectively. Metagenomic analysis showed the presence of Nesterenkonia species. These results highlight the diverse microbiome of BR and underscore its potential as a valuable reservoir of extremophilic microorganisms.