This project will answer two questions regarding the intrinsic recalcitrance of glycans, (i) which chemical structure motifs resist or slow down microbial enzymatic degradation, and (ii) does primary-produced versus bacterially-transformed organic matter result in glycans of differential intrinsic recalcitrance? Guided by the hypothesis that intrinsically recalcitrant glycans share common chemical structure motifs, B4 LOCK will characterize at molecular resolution chemical structure motifs of intrinsically recalcitrant glycans and thereby contribute to answer one of CONCENTRATE’s central overarching question, i.e., what are the unknown factors of glycan stability and degradation.