Feb. io, 1923 
A Bacterial Leaf spot of T obacco 
489 
Resistance to desiccation. —The organism dried on cover slips in 
sterile Petri dishes did not lose its power of growth until after 14 days. 
Relation TO oxygen. —No growth in atmosphere freed from oxygen 
by pyrogallol-KOH method. Some growth in closed arm of fermenta¬ 
tion tubes with saccarose and dextrose. 
Effect of sunlight. —Fifteen minutes’ exposure of plates on ice to 
sunlight killed a few organisms, and practically all were killed on 30 to 
60 minutes’ exposure. 
Vitality and virulence. —The organism can be kept in culture and 
maintain its virulence for at least three years. It may lose its virulence, 
however, upon certain media while still giving normal growth in culture 
or it may die out rapidly on presumably favorable cultural media for 
reasons not definitely understood. 
Group number. —221.3333633. The name Bacterium melleum , n. sp., 
is suggested for this organism, basing the specific name on the honeylike 
color imparted to potato dextrose agar. 
TECHNICAL DESCRIPTION 
Bacterium melleum, n. sp. 5 
A short rod with rounded ends, occurring singly, in pairs, or in chains. Average 
size 0.6 by 1.8 microns. Motile by a tuft of polar flagella usually two to three in number, 
but ranging from one to seven, and three to five times as long as the body of the organism. 
No spores or involution forms have been observed. Capsules are present. It is Gram¬ 
negative and not acid-fast. The organism is pale or orange yellow on most media, 
particularly on potato-dextrose agar, to which it imparts a honeylike pigment. Growth 
on potatoe agar stroke is abundant, echinulate, raised, glistening, smooth, and viscid; 
agar colonies grow rapidly, are circular, smooth, and convex. On nutrient broth the 
surface growth is slight or none, clouding strong, and sediment somewhat flaky, more 
amorphous, and moderate in amount. In gelatin stabs growth is best at top with 
liquefaction, beginning in 3 days and complete in about 20 days. The coagulation of 
milk is prompt, coagulum slowly peptonized. Alkaline reaction with litmus milk, 
with prompt reduction. Good growth in Fermi’s and Cohn’s solution. No indol or 
ammonia produced. Nitrate in nitrate broth not reduced. Optimum temperature 
for growth about 26° to 28° C., maximum 35 0 to 36°. Thermal death point 57 0 . 
Optimum reaction for growth in broth -|-io Fuller’s scale. Pathogenic on Nicotiana 
tabacum, causing a leafspot with or without a chlorotic halo around the point of infec¬ 
tion, usually followed by browning of affected tissue. 
COMPARISON WITH OTHER BACTERIAL LEAFSPOTS OF TOBACCO 
It is evident from the description of the causal organism that the 
Wisconsin leafspot differs from that of the previously described Ameri¬ 
can tobacco leafspots, namely, wildfire and angular leafspot. The 
most striking difference is that of the color of the pathogenes, which 
is white in both of the latter diseases but yellow in the Wisconsin leaf- 
spot. As far as symptoms themselves are concerned, one could not 
with certainty distinguish between wildfire and Wisconsin leafspot, 
though the former is the more destructive and widespread and under 
field conditions usually possesses the most marked chlorotic halo. 
The Wisconsin leafspot disease is not so readily distinguishable from 
the Sumatran disease described as black rust by Honing (4). Neither 
specimens of this disease nor the causal organism have been seen. There¬ 
fore Honing’s description offers the only basis for comparison. 
3 According to the elas 1 ifLation of the American Society of Bacteriologists the combination would be 
Psuedomonas tnellea n. sp. 
