Studies on the identity and activity of saprophytic bacteria on stored barley

1. The epiphytic micro flora of barley seed was investigated to determine the kinds of bacteria present, and the possibility of their growth at low levels of water activity. 2. Identification of the bacteria was based on similarity indices computed for each isolate. 3. On developing grain in the field, yeasts (Rhodotorula) were the first microorganisms to colonize the seed in large numbers. Subsequent growth of bacteria reached a maximum one week before harvest, and then declined somewhat. At the peak of microbial development, it was estimated that 15-20% of the seed surface was occupied by microorganisms. 4. A survey of sack-stored barley showed that the largest single group of bacteria on the grain was composed of Erwinia herbicola. This accounted for 45% of the total isolates. Several other groups formed a heterogeneous collection of gram-variable or gram-positive coryneform bacteria, which together made up a further 38% of the total. Pseudomonades, flavobacteria and cocci were of lesser importance. 5. On stored seed attacked by granary weevils (Sitophilus granarius) there was a decrease in the numbers of bacteria found and, on seed which had previously been sterilized, a corresponding increase in numbers of Aspergillus glaucus. Aspergilli were not found on un-sterilized seed but this was not considered to be the result of antagonism by the saprophytic microflora. 6. Bacteria were shown to multiply on seed kept at atmospheric humilities of 75%, 95% and 100% R.H. Although the rate of increase was inversely proportional to the humidity, the maximum population attained was the same in each case, and once attained it was immediately followed by a drop in numbers. These results were interpreted as indicating that in a physiological sense, xerophytic bacteria do occur on barley, but that this is of no ecological significance because in-the absence of liquid water the growing colony is soon poisoned by its own metabolic wastes