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Publication Abstract from PubMed

Microbial glycan degradation is essential to global carbon cycling. The marine bacterium Salegentibacter sp. Hel_I_6 (Bacteroidota) isolated from seawater off Helgoland island (North Sea) contains an alpha-mannan inducible gene cluster with a GH76 family endo-alpha-1,6-mannanase (ShGH76). This cluster is related to genetic loci employed by human gut bacteria to digest fungal alpha-mannan. Metagenomes from the Hel_I_6 isolation site revealed increasing GH76 gene frequencies in free-living bacteria during microalgae blooms, suggesting degradation of alpha-1,6-mannans from fungi. Recombinant ShGH76 protein activity assays with yeast alpha-mannan and synthetic oligomannans showed endo-alpha-1,6-mannanase activity. Resolved structures of apo-ShGH76 (2.0 A) and of mutants co-crystalized with fungal mannan-mimicking alpha-1,6-mannotetrose (1.90 A) and alpha-1,6-mannotriose (1.47 A) retained the canonical (alpha/alpha)6 fold, despite low identities with sequences of known GH76 structures (GH76s from gut bacteria: <27%). The apo-form active site differed from those known from gut bacteria, and co-crystallizations revealed a kinked oligomannan conformation. Co-crystallizations also revealed precise molecular-scale interactions of ShGH76 with fungal mannan-mimicking oligomannans, indicating adaptation to this particular type of substrate. Our data hence suggest presence of yet unknown fungal alpha-1,6-mannans in marine ecosystems, in particular during microalgal blooms.

Glycoside hydrolase from the GH76 family indicates that marine Salegentibacter sp. Hel_I_6 consumes alpha-mannan from fungi.,Solanki V, Kruger K, Crawford CJ, Pardo-Vargas A, Danglad-Flores J, Hoang KLM, Klassen L, Abbott DW, Seeberger PH, Amann RI, Teeling H, Hehemann JH ISME J. 2022 Apr 12. pii: 10.1038/s41396-022-01223-w. doi:, 10.1038/s41396-022-01223-w. PMID:35414716^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.