|Abstract or Summary
- Myxobacteria are known to occur in the aquatic environment,
however, little information is available regarding the taxonomy of
these organisms. This investigation was initiated in an attempt to
classify a group of fresh water cytophagas on the basis of biochemical
and physiological as well as cultural and morphological characteristics.
The 35 isolates used in this investigation were determined to be
myxobacteria on the basis of their cellular morphology. Vegetative
cells were slender, gram negative, weakly refractile rods characterized
by a marked flexibility. Examination of young cells revealed
typical gliding motility. Cells became shorter and thicker with age
and involution forms occurred. The thin, spreading, yellow to yellow-orange
colonies produced by the organisms were typical of myxobacteria.
Fruiting bodies were never observed although microcyst-like
structures were formed by two isolates. As a result these two
organisms are considered to be members of the genus Sporocytophaga.
The remaining 33 isolates can be classified in the genus Cytophaga.
The isolates were non-halophilic mesophiles which grew best
at pH 7.2. All grew anaerobically under defined conditions and most
were moderately thermostable. All but one of the isolates were
resistant to neomycin and most were sensitive to tetracycline,
streptomycin, erythromycin and novobiocin.
The results of the physiological studies showed that the myxobacteria
studied in the present investigation have the capacity to
degrade macromolecules. All of the organisms were lipolytic and
most were proteolytic and amylolytic. Cellulolytic activity as demonstrated
by the utilization of carboxymethyl cellulose was exhibited by
over 70% of the isolates. All of the organisms lysed dead cells of
Aerobacter aerogenes and the majority were capable of lysing dead
cells of a variety of other bacteria and yeast. A small portion also
lysed similar preparations of algal and protozoan cells.
Simple carbohydrates were oxidized by most of the strains,
however, very few of the organisms were able to ferment these substances.
Carbohydrates oxidized by the majority of the isolates include
glucose, galactose, maltose and cellobiose. Of the fermentative
strains, only one required substrate amounts of CO₂ for glucose
fermentation. This isolate may have a metabolic pathway similar
to Cytophaga succinicans, a facultative anaerobic myxobacterium
which carries out a CO₂-dependent fermentation of glucose.
The nutritional requirements of the organisms were relatively simple. The nitrogen requirement could be readily satisfied by either
casein hydrolysate or KNO₃
and starch served as a sole source of
carbon for most of the isolates. However, only 12 of the 35 strains
were able to utilize glucose as a sole source of carbon. Simple
amino acids did not support the growth of any of the isolates when
used as a sole source of carbon,
The DNA base composition and carotenoid pigments of six of the
isolates also were studied. Five of the organisms were found to have
a DNA base composition between 34.88 and 38.54% GC. A value of
53.44% GC was found for one isolate identified as a Sporocytophaga.
The results of the pigment analysis indicated that carotenoid pigments
spectrally similar to lutein, alpha-carotene-5, 6-epoxide and rhodopin
were present in the organisms. It appears from these studies that
pigment analyses of the myxobacteria could contribute significantly
to the taxonomy of this group of organisms.
Based on the results of this investigation, an improved
taxonomic scheme for the genus Cytophaga has been proposed. Unlike
the taxonomic keys which are currently available, the major subdivisions
of this scheme are based on biochemical and physiological
characteristics. Key features for distinguishing members of the
genus Cytophaga according to the proposed scheme include use of
carboxymethyl cellulose, chitin, citrate and carbohydrates as well
as nitrate reduction.