Structural investigations on cell walls of Nocardia sp. The wall lipid and peptidoglycan moieties of Nocardia kirovani

The walls of Nocardia kirovani are composed of three main constituents: the peptidoglycan matrix, a polysaccharide polymer and a variety of free and bound lipids. The free lipids represent 17.5% (dry weight) of the walls and consist for the major part of C16–18 fatty acids and nocardic acids, and for the minor part, of nocardones, triglycerides and carotenoid pigments. The nocardic acids were identified as tri- and tetra-unsaturated, α-branched, β-hydroxylated compounds C58H110O3—C66H124O3 the nocardones as tri-and tetra-unsaturated ketones C57H106O—C63H1180O, and the main carotenoid pigment as phlei-xantophylle palmitate. Esters of glycerol with C14, C16, C18 fatty acids and, for some of them, with odd numbered poly-unsaturated acids containing 35 to 45 carbon atoms, were also identified. Bound lipids represent about 20% (dry weight) of the walls and consist mainly of nocardic acids probably ester-linked to an arabinogalactan polymer. The peptidoglycan (about 40% dry weight) is composed of β-1,4-N-acetylglucosaminyl-N-glycolylmuramic acid disaccharide units that are substituted by diamidated L-Ala-D-αGln-(L)-A2pm-(D)-NH2 tripeptides and diamidated l-Ala-d-αGln-(L)-A2pm-(D)-NH2-(L)-d-Ala tetrapeptides, where A2pm is meso-diaminopimelic acid. Crosslinking between some of the peptide units is mediated through D-Ala-(D)-A2pm linkages (peptidoglycan of chemotype I).