*2.3. Comparative Analysis of the Expression of Chitinolytic Enzymes in P. rubra S4059*

A total of twelve chitin utilization associated proteins, including seven GH18s, three GH20s, a GH19, and a LPMO, were identified with a confidence rate of 99% at the peptide and protein levels in the *P. rubra* S4059 global proteome, while a GH19 (A0A5S3UPT5) and an LPMO (A0A5S3V4S2) were not detected (Figure 1C).

All chitinolytic enzymes could be detected in both cells and culture supernatant of S4059, except the enzyme A0A5S3UV09 from the GH20 family, which was not detected in the culture supernatant (Figure 1C). The GH18 chitinase A0A5S3USH6, annotated as ChiC, was the most highly expressed chitinolytic enzyme in both cells and culture supernatant during growth on chitin. Four GH18s (A0A5S3USE2, A0A5S3V6T3 A0A5S3V3K3, and A0A5S3USH6) and two GH20s (A0A5S3V1X9 and A0A5S3UX95) enzymes were significantly upregulated when S4059 was grown on crystalline chitin compared to on mannose (Figure 1). Meanwhile, several chitin-utilization associated proteins were induced and could only be detected when grown on crystalline chitin, including a GH19 chitinase and three GH18 chitinases (A0A5S3V351, A0A5S3V0U4, and A0A5S3V378) (Figure 1C). In addition, an LPMO from the AA10 family was identified under both growth conditions, but with no significant expression difference (Figure 1C).
