Pyruvate metabolism in Lactobacillus brevis

The pyruvate metabolism of LactobaciUus plan- tarum and Latobacillus arabino8su, which accord- ing to Bergey (1948) are identical organisms, has been studied by Rowatt (1951) and Nossal (1952).Both these homofermentative lactobacilli were shown to form 3-hydroxybutan-2-one (acetoin) as the main product of their pyruvate metabolism.No one appears to have studied the metabolism of pyruvate by any of the heterofermentative lacto- bacilli, of which Lactobacillus breisq is a typical example.This species frequently occurs in cheddar cheese, in the ripening of which it may play a significant part.It was considered of interest therefore to compare the pyruvate metabolism of L. brevis with that of the homofermentative species. MATERIALS AND METHODSGrowth of cells.The organism used throughout these studies was L. brevis strain 1.2, originally isolated from New Zealand cheddar cheese by Sherwood (1939).Throughout this work stock cultures were maintained in sterile skim milk containing 0-2 % of yeast extract (Oxoid, Oxo Ltd.).Cells for experimental use were grown in the lactose-yeastphosphate broth of Hunter (1946) for 48 hr. at 300.After centrifuging, the cells were washed twice and finally re- suspended in sterile 1% (w/v) KCI.Individual cell crops showed random variation in yield and activity; a similar phenomenon was reported by Nossal (1952) with L.arabinosus.This fact, together with the slow growth rate of L. brevis, made it difficult to obtain exactly reproducible quantitative results; for example, the final yields of CO0 sometimes fell short of the theoretical quantity by amounts between 10 and 20%.The overall qualitative picture, however, was not affected.Reagents.Pyruvic acid and 2-oxobutyric acid were re- distilled in vacuo.Solutions of their sodium salts were prepared by suitable dilution and neutralization (with NaOH).Lithium lactate (British Drug Houses Ltd., Poole, Dorset, England) was purified by dissolving in a minimum of hot water, filtering, precipitating with ethanol and drying over CaCl.Other compounds were commercial products.