The production of gibberellin-lilie substances by bacteria and actinomycetes was investigated. Most of the bacterial cultures tested produced a gibberellic acidlilce substance (A3) in ~I~O~I I I~S varying from 1 t o 14 pg/liter. The production of a gibberellin-A9-like colnpound was much more limited, 6 out of 15 cultures yielding small amounts. Six out of 11 actinomycetes showed evidence of A3 synthesis; two produced .A1. Antigibberellin substances co-chromatographing with A3 mere detected in culture filtrates of Bacillz~s poly~nyxa and two actinomycetes. Cultural conditions and concentration of the ingredients of the medium influenced gibberellin synthesis by .4grobactel.iz~tn radiobacbi. Production of these substances was not growth linked and none was detected in stationary cultures. h~Iicrobial slnthesis of the gibberellins was demonstrated also by means of assays with the dwarf maize mutants dl, d?, and dj.A:, added to soil was rapidly inactivated and it was postulated that the plant could derive maximum beneht from microbial synthesis of gibberellins and related substances only a t the root surface--the rhizoplane.
With 1 Figure) Before the development of selective media for lactobacilli, it was almost impossible to determine the numbers of these organisms during the early stages of cheese ripening, when the starter streptococci were dominant. Early workers (i, 2) consequently assumed that the lactobacilli did not reach significant numbers until the streptococci had declined appreciably in numbers. This view is still expressed in recent text-books (3,4). Recent British work (5) however, using a medium which inhibited growth of the starter streptococci, indicates that the lactobacilli grow slowly but steadily from the beginning of the ripening period. This has recently been confirmed by Naylor & Sharped), who made intensive studies of one experimental cheese over a 6-month period.Since 1954 the Dairy Technology Research Unit has been studying the enhancement of flavour in Cheddar cheese made from pasteurized milk. In each series of experiments, representative cheeses have been examined at intervals for the numbers of various groups of bacteria-lactobacilli, enterococci, coliforms, lipolytic and proteolytic-as well as the total viable count. Thus we have accumulated a considerable volume of data. In view of the recent report (7) of erratic fluctuations in counts of lactobacilli it was considered timely to report our quite different findings. MATERIALS AND METHODSIn our experimental cheese-making, samples were taken (a) of the milk in the vat before adding the starter but after other special inocula had been added, and (6) of the cheese after approximately 2-5 days, 2 weeks, 3, 6 and 12 months. The cheeses were customarily ripened at 58° F. for 2 weeks, then at 40° F. for 1 year or longer. Cheese samples of about 10 g. were taken from the 10 lb. cheese with a trier, discarding the surface portion. After grinding with a pestle and mortar, 5 g. were weighed out and added to 95 ml. of 2 % sodium citrate solution tempered at 45° C. After shaking to dissolve and suspend the cheese, further dilutions were made using buffered distilled water (8) and plates poured from appropriate dilutions with Rogosa's(9) medium. Counts were made after 5 days' incubation at 32° C.
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