Abstract:
Interactions between freshwater algae and bacteria were examined
in a natural stream habitat and a laboratory model. Field observations
provided circumstantial evidence, in statistical correlation for syntrophy
between the microbial populations. This relation is probably
subject to control by the temperature and pH of the aquatic environment.
Several species of a pond community were isolated in axenic culture
and tests were performed to determine the nature of mixed species interactions.
Isolation procedures and field studies indicated that selected
strains of Chlorella and Azotobacter were closely associated in their
natural habitat. With the suspected controlling parameters, pH and
temperature, held constant, mixed cultures of algae and bacteria were
compared to axenic cultures of the same organisms, and a mutual
stimulation of growth was observed. A mixed pure culture apparatus was
designed in this laboratory to study the algal-bacterial interaction
and to test the hypothesis that such an interaction may take place
through a diffusable substance or through certain medium-borne conditions,
Azotobacter was found to take up a Chlorella-produced exudate, to
stimulate protein synthesis, to enhance chlorophyll production and to
cause a numerical increase in the interacting Chlorella population. It
is not clear whether control is at the environmental, cellular or
genetic level in these mixed population interactions.
Experimental observations in the model system, taken with field
correlations allow one to state that there may be a direct relationship
governing the population fluctuations of these two organisms in their
natural stream surroundings.
