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Lipopolysaccharides from 13 strains of Pseudomonas aeruginosa representing seven serotypes of the Habs scheme have been analysed. The lipid A fractions, obtained by mild acid hydrolysis of the lipopolysaccharides, contained phosphorylated glucosamine residues substituted with dodecanoic, hexadecanoic, 2-hydroxydodecanoic, 3-hydroxydecanoic, and 3-hydroxydodecanoic acids (hexadecanoic acid and 2-hydroxydodecanoic acid were absent from one lipid A). Low-molecular-weight solutes released during the mild hydrolyses included 2-keto-3-deoxyoctonic acid, inorganic orthophosphates and pyrophosphates, ethanolamine mono, pyro and triphosphates. For most strains two polysaccharide fractions, one of which appeared to be the common core polysaccharide, were obtained. The major identifiable components and their approximate proportions in the core polysaccharides were glucose (3 -4), rhamnose (l), galactosamine (l), alanine (1 -1.5), phosphorus (4-6) and heptose (1 -2). Rhamnose was absent from one polysaccharide; another lacked both rhamnose and alanine but contained glucosamine. Small amounts of various amino sugars found in other core polysaccharides could be associated with the presence of higher-molecular-weight material. Such material was isolated from strain NCIB 8626.The high-molecular-weight polysaccharides obtained from ten strains were probably heterogeneous and consisted mainly of amino compounds, though rhamnose was a major component of four polysaccharides and arabinose was present in another. Fucosamine was the most common amino sugar, but quinovosamine, glucosamine, galactosamine, a possible aminohexuronic acid and unidentified amino compounds were also detected.The results of the survey are discussed in terms of the serological classification of the bacteria and of their sensitivity to EDTA.Although studies of bacterial lipopolysaccharides have broadened considerably in recent years, compositional and structural data remain rather fragmentary and superficial for most organisms outside the family Enterobacteriaceae. For various reasons, efforts to rectify this situation for pseudomonads are being made in several laboratories, with the focus of interest being Pseudomonas aeruginosa. Despite the existence for P. aeruginosa of several serological typing schemes based on thermostable antigens (presumptively lipopolysaccharides), the chemical foundations for these schemes are not known. Thus, the elaboration and elucidation of the chemistry of 0-antigens from P. aeruginosa are important objec-

Contrary to previous reports, lipopolysaccharides from Pseudomonas cepacia contain a 3-deoxyoct-2-ulosonic acid (probably a single residue). The lipopolysaccharides contain only two phosphate residues, one of which apparently forms a phosphodiester bridge between 4-amino-4-deoxyarabinose and a glucosamine residue in lipid A. The second, unlocated phosphate residue occurs mainly as a monoester in some lipopolysaccharides, and mainly as a diester in others. All lipopolysaccharides lack pyrophosphate residues. The results support the view that the resistance of P. cepacia to cationic antibiotics stems from ineffective binding to the outer membrane, as a consequence of the low number of phosphate and carboxylate groups in the lipopolysaccharide, and the presence of the protonated aminodeoxypentose.

Cell walls from two EDTA-sensitive and three EDTA-resistant pseudomonads grown in nutrient broth have been analysed. Each wall had a composition broadly characteristic of gramnegative bacteria, although the walls of Pseudomonas pavonacea and P. syncyanea were relatively rich in glycosaminopeptide and loosely-bound lipid, respectively. Phosphatidylglycerol was the only phospholipid common to all species, although phosphatidylethanolamine was absent only from P. diminuta. The latter species contained the distinctive range of glycolipids and a phosphoglucolipid identified previously in cells grown on nutrient agar. However, the glycolipids and an ornithine-containing lipid present in some other species (notably P. rubescens) when grown on nutrient agar were not detected. Except in P. rubescens, the major fatty acids in loosely-bound lipids were CIS, C16:l. and c18:1 acids: in P. rubescens, the major components were CIS, iso-Cl5, and C17:1 acids. Cyclopropane acids occurred in the lipids from P. stutzeri.Components of the lipopolysaccharides were identified and determined. The lipid A fractions contained fatty acids, phosphorus, and (except for P. diminuta) glucosamine. The fatty acids included both hydroxy and non-hydroxy acids. Apart from 2-hydroxydodecanoic acid (present in P. syncyanea), all the hydroxy acids were b-hydroxy acids, and 3-hydroxydodecanoic acid predominated in all species except P. rubescens. Odd-numbered hydroxy acids were minor components in P. diminuta and P. pavonacea and major components (CIS acids) in P. rubescens.The non-hydroxy acids consisted of saturated acids (C12 to C14) and orb-unsaturated acids (dehydration products from the b-hydroxy acids).Unusual features of the polysaccharide fractions from the lipopolysaccharides included the occurrence of non-phosphorylated heptose residues (P. diminuta), the presence of phosphorylated glucose residues and of aspartic acid ( P . pavonacea), the probable absence of 2-keto-3-deoxyoctonic acid and the presence of acid-labile galactose residues (P. rubescens), the virtual absence of glucose ( P . stutzeri), and the presence of alanine ( P . syncyanea). Amino sugars (glucosamine, galactosamine, and quinovosamine) occurred in the polysaccharides from P. stutzeri and P. syncyanea only. Following chromatography of the partly degraded polysaccharides on Sephadex, the distribution of components between possible side chain and core regions of the polysaccharides could be determined. The possible sigdcance of the results for the sensitivity of the organisms to EDTA and for their taxonomy is discussed.Although the cell walls and lipopolysaccharides of gram-negative bacteria have been studied extensively (see [1,2] for recent reviews), relatively little work has been done with pseudomonads other than Pseudomonas aeruginosa. Partly because of its outstanding resistance to many antibacterial agents, this organism has become a pathogen of some importance. It is perhaps surprising, therefore, that the