Structural Investigations on Cell Walls of Nocardia sp.

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 C 16–18 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 C 58 H 110 O 3 —C 66 H 124 O 3 the nocardones as tri‐and tetra‐unsaturated ketones C 57 H 106 O—C 63 H 1180 O, and the main carotenoid pigment as phlei‐xantophylle palmitate. Esters of glycerol with C 14 , C 16 , C 18 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 arabino galactan 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 )‐A 2 pm‐( d )‐NH 2 tripeptides and diamidated l ‐Ala‐ d ‐αGln‐( l )‐A 2 pm‐( d )‐NH 2 ‐( l )‐ d ‐Ala tetrapeptides, where A 2 pm is meso ‐diaminopimelic acid. Crosslinking between some of the peptide units is mediated through d ‐Ala‐( d )‐A 2 pm linkages (peptidoglycan of chemotype I).