Saturated fatty acids as bacterial antimetabolites

The interaction between dietary lipids and fibre in the sheep 2. Digestibility studies

Digestibility studies were carried out to establish the inter-relationship between crude fibre and total lipid digestibility in the presence of added calcium or non-ionic detergents. Three levels of calcium, corresponding to daily intakes of 2·3, 4·8 and 22·9 g per sheep, were used in a predominantly ground barley diet (65 to 73%) to which was added 8% beef tallow or maize oil. Two non-ionic detergents were used at 0·1% of the diet: nonyl phenol ethylene oxide and fatty alcohol combined with 3 molecules of ethylene oxide.

With a daily intake of 2·3 or 4·8 g calcium per sheep, supplementation with fat resulted in a reduced fibre digestibility. When the intake was increased to 22·9 g, there was a significant improvement (P<0·05) only for the maize-oil-supplemented diet. Increasing calcium intake, associated with increased calcium digestibility, significantly (P<0·05) depressed total lipid digestibility. Intake of 4·8 g calcium per day was associated with the highest calcium digestibility of 33% digestibility units and the total lipid digestibility of 94%. Maize oil was better digested than beef tallow with the lower level of calcium; the position was reversed with the higher level of calcium supplementation. No advantages were found for crude fibre and total lipid digestibility when detergents were added.

A possible mechanism by which the physical wetting of dietary lipids causes decreased digestibility of the fibre component is discussed.

Inhibition of Methanogenesis from Acetate in Granular Sludge by Long-Chain Fatty Acids

The effect of four saturated long-chain fatty acids (caprylic, capric, lauric, and myristic) and one unsaturated long-chain fatty acid (oleic) on the microbial formation of methane from acetate was investigated in batch anaerobic toxicity assays. The tests were carried out with granular sludge from an upflow anaerobic sludge bed reactor. In this sludge, Methanothrix spp. are the predominant acetoclastic methanogens. Lauric acid appeared to be the most versatile inhibitor: inhibition started at 1.6 mM, and at 4.3 mM the maximum specific acetoclastic methanogenic activity had been reduced to 50%. Caprylic acid appeared to be only slightly inhibitory. Oleic acid was almost as inhibitory as lauric acid. Although adsorption of the inhibitor on the cell wall might play an important role in the mechanism of inhibition, the inhibition was found to be correlated with concentration rather than with the amount per unit of biomass. In practical situations, as in anaerobic waste treatment processes, synergism can be expected to enhance the inhibition of methanogenesis. In the present research a background concentration of lauric acid below its MIC strongly enhanced the toxicity of capric acid and (to an even greater extent) myristic acid.

Microthrix parvicella, a filamentous bacterium isolated from activated sludge: cultivation in a chemically defined medium

A large number of media have been tested for cultivating Microthris parvicella, a filamentous microorganism often present in the activated sludge of oxidation ditches. The bacterium was found to utilize oleic acid (preferably as Tween 80) as the sole source of carbon and energy. Sulfur is required in the reduced form. The tested media vary from a complex to a chemically defined medium. Growth yields of 1.3 to 1.5 g/liter were obtained on media containing Tween 80 (4 g/liter), reduced nitrogen and reduced sulfur compounds, calcium and magnesium salts, phosphate buffer, trace elements, thiamin, and cyanocobalamin. The optimum temperature for growing the organism is approximately 25 degrees C, and the pH of the nutrient medium should be above 7.

GROWTH RESPONSE OF CHLAMYDOMONAS AND HAEMATOCOCCUS TO THE VOLATILE FATTY ACIDS

The first five straight-chain saturated fatty acids were tested to determine their effect on cell division of phytoflagellates. Chlamydomonas reinhardti Danseard and Haematococcus pluvialis Flotow were selected for measurement because of information available from similar studies of the long-chain acids. Cultures were grown at five concentrations of the sodium salt within the range of 0.5 to 10.0 mmoles/liter.Acetate stimulated the rate of cell division, while butyrate, the other acid with an even number of carbons, produced an inconsistent although negligible effect.The fatty acids with an odd number of carbons inhibited division of cells, with propionate being most and valerate least effective. Inhibition in these tests, in which initial pH was kept constant, was proportional to the initial concentration of the acid salt. Additional tests showed propionate inhibition to be approximately proportional to a calculated amount of undissociated acid in the medium. H. pluvialis was 9–12 times more sensitive than was C. reinhardti.The possibility of propionic acid inhibition of algae in acid lakes is discussed.