Lysis ofEscherichia coli by a Marine Myxobacter MARGARET M. ROPER AND K . C . MARSHALL School of Microbiology, University of New South Wales, Kensington, 2033, New South Wales, Australia The disappearance ofEscherichia coli entering seawater is rapid and is directly proportional to the size of the natural microbial population [6]. The decline has been attributed to predation by Vexillifera [5], parasitism by Bdellovibrio [4], lysis by pseudomonads producing lytic enzymes [4], and in some cases to parasitism by bacteriophage [2]. Physicochemical effects also play a role in the decline [1]. Another predator, identified as a myxobacter of the genus Polyangium [3], has been isolated consistently by the senior author from water samples collected at sewage outfalls on the southeast coast of Australia. The vegetative bacteria of one of these strains (MR45) are large, cylindrical rods with blunt rounded ends (Fig. IA). They are approximately 1/.tm in diameter and vary in length from 2.5 to 4.5/xm. The bacteria produce peach-colored pigments, are flexible, and possess a slime capsule which does not adsorb congo red. The slime capsule results in the formation of slime tracks on solid surfaces (Fig. 1B). Fruiting bodies were prepared for scanning electron microscopy (SEM) by the method of Shimkets and Seale [8] and were found to be sessile sporangia occurring singly or in groups (Fig. 1C). Fruiting bodies are orange in color and contain myxospores which resemble the vegetative bacteria. The mole% GC (determined from the buoyant density in CsCI) is 62.9 which is similar to that reported for Polyangium canicruria [7]. When E. coli M13 and Polyangium MR45 were added to autoclaved natural seawater, E. coli numbers began to decline after twenty-four hours incubation (Fig. 2). The decline ofE. coli was coupled with an increase in the numbers of myxobacters (determined as plaque-forming units). However, the myxobacter population was grossly underestimated because of extensive clumping in the culture. It has not been possible to grow Polyangium MR45 on standard culture media for myxobacters, nor will it grow on host bacteria suspended in diluted seawater. However, the bacterium is able to utilize for growth a wide range of

Microbial Ecology 3, 167-171 (1977) 9 1977 by Springer-VerlagNew York Inc.

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M.M. Roper and D.C. Marshall

Fig. I. Polyangium MR45. (A) Large vegetative forms of myxobacter with some small Escherichia coli (bar = 1 /xm). (B) Slime tracks formed by the myxobacter on an agar surface (bar = 10 p.m). (C) Fruiting bodies with single sporangia (bar = 5/~m).

Lysis ofEscherichia co/i

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hosts including Bacillus cereus, B. megaterium, Corynebacterium sp., Micrococcus lysodeikticus, Staphylococcus aureus, Achromobacter sp., A~otobacter vinlandii, Escherichia coli (4 Strains), Klebsiella aerogenes (3 strains), Pseudomonas denitr~ficans, Pseudomonas sp., and Sahnonella typhimurium. Of the organisms screcned, the myxobacter could not lyse Bacilus subtilis. Streptococcus faecalis, and Lactobacillus plantarum. The wide host range of the myxobacter indicates that it probably feeds on the native marine microbial community to some extent, as well as on high populations of sewage microorganisms. Lack of recognition of myxobacters associated with the control of sewage bacteria in seawater may be due to their inability to grow on ordinary media, and the fact that initially they produce plaques without any obvious colony in the center. After about 10 days incubation, however, a pale growth of Polyangium appears in the center of the plaque. Since these organisms have been isolated from all sites sampled over 1000 km of the southeast coastline of Australia and Tasmania, it is likely that they are very widespread in marine areas polluted by sewage.

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M.M. Roper and D.C. Marshall

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Fig. 2. The lysis of Escherichia coli by myxobacter, o---o, Survival o f E. coil in sterile seawater. -" ~, Survival o f E. coli in sterile seawater inoculated with myxobacter. ~--.a,, Growth o f myxobacter in sterile seawater, m--4, Growth o f m y x o b a c t e r in sterile seawater inoculated with E. coli.

Acknowledgements We thank Dr. Graham Skyring, Baas-Becking Geobiological Laboratories, Canberra, for determining the GC ratios, Dr. Mel Dickson for assistance with the scanning electron microscope, and the Australian Water Resources Council for financial support.

References Carlucei, A. F., anti Pramer, D. 1960. An evaluation of factors affecting the survival of Escherichia coli in seawater. Ill. Antibiotics. Appl. Microbiol. 8:251-254 Carlucci, A. F., and Pramer, D. 1960. An evaluation of factors affecting the survival of Escherichia coil in seawater. IV. Bacteriophages. Appl. Microbiol. 8: 254-256.

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McCurdy, H. D. 1974. The fruiting myxobacteria. In : Bergey's Manual of Determinative Bacteriology, 8th Edition. pp. 76-98. R.E. Buchanan and N.E.Gibbons, editors. Williams and Wilkins, Baltimore.

4.

Mitchell, R. 1968. The effect of water movement on lysis of non-marine microorganisms by marine bacteria. Sarsia 34: 263-266.

5.

Mitchell, R., and Yankofsky, S. 1969. Implication of a marine ameba in the decline Of Escherichia coli in seawater. Environ. Sci. TechnoL 3: 574-576.

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Mitchell, R., ~ankofsky, S., and Jannasch, H. W. 1967. Lysis ofEscherichia coli by marine microorganisms. Nature (London) 215: 891-893.

7.

Normore, W. M. 1973. Guanine-Plus-Cytosine (GC) composition of the DNA of Bacteria, Fungi, Algae and Protozoa, pp. 585-740. In: Handbook of Microbiology, Volume 11. A. I. Laskin and H. A. Lechevalier, editors. Chemical Rubber Company, Ohio. Shimkets, L. and Seale, T. W. 1975. Fruiting-body formation and myxospore differentiation and germination in Myxococcus xanthus viewed by scanning electron microscopy. J. Bacteriol. 121:711-720.