Discovering rare thermophilic Parageobacillus caldoxylosilyticus from hot spring with early plastic-degrading potential revealed from bioassays and gene annotation studies.

The isolate Parageobacillus sp. (isolate W8) (GenBank accession No. PP732525.1), isolated from the Ulu Slim hot spring, showed early indications of potential plastic degrading activity. When tested for the degradation of low-density polyethylene (LDPE) sheets in a 60-day test, viable cell count, weight loss of LDPE sheets, FTIR spectra of LDPE sheets, and enzyme production, all indicate preliminary positive degradation of LDPE sheets. The whole genome sequence and gene annotation was also performed to identify the isolate and further highlight the enzymes responsible for potential plastic degradation, respectively. Results of the 16S rRNA sequence and average nucleotide identity (ANI) identified the isolate as Parageobacillus caldoxylosilyticus. Genome annotation revealed genes encoding for protease and esterase, which supported the protease and esterase assays observed. Several genes encoding for degradation of PE (e.g., glutathione peroxidase, nitrate reductase) were also annotated. P. caldoxylosilyticus (isolate W8) is concluded to have the potential to degrade LDPE based on early trends of sustained viable cell count, gradual weight loss of LDPE, induction of enzyme production when co-incubated with LDPE, and the shifts in functional groups for LDPE. These early observations suggest the potential of P. caldoxylosilyticus as a thermophilic isolate capable of degrading LDPE in high temperature conditions.