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Part A MetabolbmResults of earlier work on the carbohydrate metabolism have been summarized (Rodwell, 1960). The observation that glucose is not metabolized anaerobically by cell suspensions, although lactate is the major produce of glucose breakdown during growth in nonaerated cultures, was puzzling.It was suggested that glycerol oxidation might proceed by a flavoproteincatalyzed oxidation of L-glycerol-3-phosphate (GP) . Because glycerol is an essential nutrient and glucose is not fermented by cell suspensions, it was postulated that this pathway must be essentially irreversible, and that no other freely reversible NAD-linked pathway exists from hexose to GP. It has since been found that, when glycerol is the growth-limiting nutrient, glycerol carbon is diluted with carbon derived from glucose (Plackett, unpublished). The nature of the terminal respiratory system catalyzing the transfer of electrons from reduced nicotinamide adenine dinucleotide (NADH) to oxygen was not investigated, although no cytochrome system could be found (Rodwell and Rodwell, 1954a).The carbohydrate and oxidative metabolism was therefore reexamined. The aims were to explain why glucose is fermented during growth in nonaerated cultures but not by washed cell suspensions, how glucose carbon enters glycerol compounds and to determine the nature of the terminal respiratory system. METHODSOrganisms. Strain V5 of M. mycoides and a goat mycoplasma (strain Y, Laws, 1956) were used. Strain Y (referred to as strain G Y in earlier publications) is closely related serologically and biochemically to M. mycoides. It differs from strain V5 in that it grows almost as well in nonaerated cultures as in aerated ones, but no differences have been observed in its fermentative or respiratory activities under the two conditions. Cultural Conditions. The growth medium was devised by Buttery (unpublished). Its composition in amounts per 1 is: "Panmede" (Paines and Byrne Ltd., Greenford, England) 30 g; Na2HP04 (anh) 10 g; glucose 4 g; ox serum 100 ml; adenine 12.5 mg; guanine 12.5 mg; sodium oleate 0.1 m-mole; sodium palmitate 0.1 m-mole and glycerol 1.7 m-mole. The pH is adjusted to 7.9 with sodium hydroxide and the medium sterilized by Seitz filtration. Cultures were grown in 500 ml Florence flasks containing 100 ml medium and rotated at 100 rpm during incubation (rotated flask cultures) or in 150 ml Erlenmayer flasks containing 100 ml medium and incubated without rotation (static cultures). The inoculum was 1 .O ml and the flasks were incubated for 16-1 8 hr for strain Y and for 20-24 hr for the slower-growing strain V5. Glucose is oxidized to acetate and carbon dioxide in rotated flask cultures, lactate is the major product of glucose breakdown in static cultures.

SUMMARY : Bacteria possessing active amino-acid decarboxylases, isolated from horse-stomach and sheep-rumen contents, were classified within the genus Lactobacillus. One strain, studied in detail, was a homolactic fermenter, the lactic acid formed being optically inactive; lactose was not fermented. Of twenty-six named strains belonging to eight species of the genus, only two possessed amino-acid decarboxylases, namely, one strain of L. pentoaceticus and one strain of L. b@dUs.The occurrence and distribution of amino-acid decarboxylases among strains of bacteria belonging to many species have been the subject of extensive studies by Gale ( 1 9 4 0~~ b, 194l), but strains of the genus Lactobacillus were not included. With the exception of two strains of L. arabinosus examined by Eggerth (1939) which did not produce histamine under the conditions of cultivation used, lactobacilli have not been examined for amine production by earlier workers. Of thirty-nine strains of lactobacilli isolated from the human mouth which were examined by Lagerborg & Clapper (1952), a number were shown to possess amino-acid decarboxylases. Two named strains examined, a strain of L. casei and one of L. arabinosus, showed no decarboxylase activity. The present paper records the examination of strains of Lactobacillus spp. isolated from horse stomach and sheep rumen and twenty-six named strains, for amino-acid decarboxylases. MATERIALS AND METHODSGrowth media Wheat-mush medium. Wheat-mash medium was prepared by adding 15 ml. of 10 yo (w/v) pepsin solution, sterilized by Seitz filtration, to 5 g. sterile ground wheat (autoclaved at 25 lb./sq.in. for 1 hr.). The pH value of the mash was then adjusted to 3*5-4.0 by the aseptic addition of hydrochloric acid.Wheat-digest histidine broth. One 1. distilled water and 100 ml. of 10 yo (w/v) pepsin solution were added to 200 g. ground wheat, the pH value adjusted to 3.0 and the mixture incubated at 37" for 4-5 days under toluene, with occasional shaking. The supernatant liquid was collected by decantation and centrifugation, heated to 100°, filtered, and to the filtrate 1 yo (w/v) Bactopeptone (Difco), 1 % (w/v) glucose and 0.1 % (w/v) L-histidine hydrochloride were added. The pH value was adjusted to 6.0 and the medium autoclaved at 10 lb./sq.in. for 20 min. For solid media, 3 % (w/v) Bacto-agar was added before autoclaving.

In a defined medium for Mycoplasma strain Y, a mixture of the diacetoxysuccinoyl esters of monoolein and monopalmitin replaced unesterified fatty acids and serum protein fractions, enabling the minimal growth requirements to be determined. Other Mycoplasma strains did not grow in media in which these esters replaced fatty acids and protein fractions.Good growth of Mycoplasma strain Y was obtained in a medium containing defatted bovine serum albumin to bind fatty acids and a heat-stable serum protein fraction to disperse cholesterol (medium C 2, Rodwell, I 969). The amino acid, peptide and growth factor requirements of strain Y were determined in a protein free medium (medium D, Rodwell, 1967) in which fatty acids were added in growth limiting concentrations. Growth in medium D was poor and might have been limited by nutrients other than fatty acids, while the protein supplements might have contributed unrecognised nutrients in medium C2. A completely defined medium giving good growth of strain Y is described in this paper. Some observations on the nutrition of other strains are also reported. M E T H O D SOrganisms. Strain Y, isolated from a goat (Laws, I 956), resembles Mycoplasma mycoides in its nutrition and metabolism (Rodwell, 1960(Rodwell, , 1967, but differs in that its growth is not improved by aeration. The following strains were also used: v5, GLADYSDALE and KH,J of M . mycoides; the CHU strain of M . mycoides var. Capri; strains ~2 9 and ~2 9 1 7 , isolated from bovine arthritis, and s6 ( M . galzisepticum). Growth assays. These were performed as described previously (Rodwell, 1969). Cultures of strain Y were incubated vertically without agitation at 37'; cultures of the other strains were incubated in the same way and also in an inclined rack which was rotated at 10 rev./min. (rotated tube cultures).Growth was measured by turbidity at 660 mp; by the incorporation of 3H thymidine (Rodwell, 1969), or by protein determination, by the method of Lowry, Rosebrough, Farr & Randall (1951) with crystalline bovine serum albumin dried to constant weight as standard, in cells washed in 0.25 M-sodium chloride+0.02 M-sodium phosphate (pH 7.4) + 0.01 M-magnesium sulphate.In some cases, an accumulation of pyruvate during growth suggested a defect in the pyruvate oxidase system, and cells were then examined manometrically for pyru-