|Abstract or Summary
- Most studies of bacteria in water have concerned public health; little attention has been given to organisms which are indigenous to
the aquatic environment. Myxobacteria are known to occur in soil,
in the marine environment, and several have been studied in relation
to diseases of salmonid fishes. However, little information is available
regarding the role of myxobacteria in the freshwater environment.
The major purpose of this research was to obtain data on the
occurrence, distribution, and activities of aquatic myxobacteria in a
As a preliminary step for studying the ecology of myxobacteria
in the freshwater stream, a culture medium and procedure were
developed to provide a means for isolation and enumeration of these
organisms. Enumeration of myxobacteria was based on the morphology
of the colonies growing on the dilute nutrient medium, cytophaga
peptonized milk agar (CPM). The low nutrient concentration of this
medium favored spreading of the myxobacterial colony and the production
of rhizoid edge patterns which are typical of myxobacteria
and distinguishable from eubacterial colonies.
The enumeration method was used to obtain data on the occurrence
and distribution of myxobacteria as compared to the total
bacteria population in Berry Creek. Results of the ecological study
conducted over a two and a half year period indicate that myxobacteria
are present in this aquatic environment all during the year
with highest levels obtained in the fall (October and November) and
lowest levels during the summer (July and August). Seasonal variations
also occurred in the types of myxobacteria comprising the
population of the stream.
It is interesting to note that peaks in the myxobacterial and the
total bacterial populations occurred in advance of the peak in flow
rate. Water temperature and flow rate did not seem to influence the
population levels as might be expected if the myxobacteria were
transient members of the microbial flora.
Additional surveys have shown that the myxobacteria are widespread
in fresh water; they have been found in abundance in bottom
sediments and surface films as well as in the flowing waters. Myxobacteria
also appear to be well adapted to the aquatic environment.
It was shown that they are able to utilize the dilute nutrients present in water for their growth.
In an attempt to determine the possible role myxobacteria play
in the aquatic environment, the predominant myxobacterial types
were isolated and studied morphologically and biochemically. All the
organisms studied corresponded to the classical definition of myxobacterial
cells: gram negative, slender, weakly refractile rodshaped
bacteria which exhibit gliding motility. Colony morphology of
these myxobacteria plated on CPM has been studied in detail and found
to be a constant characteristic of the particular type of myxobacteria
Photographs of several of the predominant forms present in the
stream samples illustrate the distinguishable morphology of the myxobacterial
colonies. Six morphological groups have been arbitrarily
designated on the basis of colony morphology; these morphological
groups also show similarities in their biochemical capabilities. Biochemical
studies on the myxobacterial isolates indicated that most of
the strains were able to utilize simple carbohydrates. All of the
isolates were capable of degrading various macromolecules, such as
chitin, starch, aesculin, caesin, gelatin, and carboxy methyl cellulose.
One of the isolates obtained was strictly proteolytic. The
ability to hydrolyze macromolecules appears to be characteristic of
aquatic isolates as well as of other myxobacteria.
One myxobacterium isolated was believed to be intimately
associated with the sheathed bacterium, Sphaerotilus natans. The
latter organism was abundant in the sucrose and urea enriched section
of Berry Creek. This myxobacterium could not utilize sucrose
or urea and occurred only in the enriched section of the stream when
Sphaerotilus was present.
The fish pathogen, Chondrococcus columnaris was also isolated
from Berry Creek water. This myxobacterium can be distinguished
from the other aquatic myxobacteria on the basis of its unique colony
morphology. This strain of C. columnaris proved to be one of the
common serological types found in the Pacific Northwest.
Based on the results obtained thus far, it is possible to speculate
on the role of myxobacteria in the freshwater environment. All
of the myxobacteria isolated in this study are capable of decomposing
complex materials, it seems likely therefore, that these organisms
may be active in the decomposition of such complex organic compounds,
including the remains of other bacterial cells, which are
present in the aquatic habitat. Since the isolates studied are also
able to utilize the nutrients present at low levels in the stream water,
these myxobacteria are not dependent on macromolecular substrates.
Myxobacteria with these abilities are apparently well adapted to the