Effect of carbohydrates on some Myxobacteria.

The nutrition of the myxobacteria has received little attention. Beebe (1943) tested various myxobacteria including Myxococcus fulvus, Polyangium erectum, Myxococcus virescens, ChondroCOCCU8 blastic, and Myxococcus xanthus for their utilization of various carbohydrates. He found that these myxobacteria grew moderately well on unsupplemented 1.5 per cent agar without the addition of any other carbohydrate or a nitrogen source. Using plain mineral salt agar as a base, he added various carbohydrates and, by measuring the size of the myxobacterial swarm after incubation upon the different carbohydrate media, determined which carbohydrates produced the best growth. Beebe sterilized his media by autoclaving the agar solution and the carbohydrate together. He found that the more complex carbon compounds like starch, inulin, cellulose, and dulcitol were utilized readily by the myxobacteria he studied, but that the simpler sugars like pentoses and hexoses were inhibitory. The disaccharides generally had little effect. Stanier (1942) studied the action of a different group of myxobacteria, members of the genus Cytophaga, on certain carbohydrates and discovered that by sterilizing the latter by means of ifitration and then adding them to heat sterilized basal medium, certain simple carbon compounds like glucose and cellobiose promoted growth instead of inhibiting it. In the light of these experiments it was decided to determine what effect carbohydrates steilized by filtration have upon some of the myxobacteria studied by Beebe. The species studied were Myxococcus vire8cens (four strains), Myxococcu8 fulvus (four strains), Myxococcus stipiWus (four strains), and Chondrococcus sp (one strain). The carbon compounds tested were xylose, arabinose, glucose, galactose, fructose, maltose, sucrose, lactose, raffinose, inulin, starch, glycerol, and dulcitol. Three different experiments were conducted. In the first, the method of Beebe (1943) was repeated. Using as a base plain 1.5 per cent agar solution, 1 per cent of the carbon compound was added together with mineral salts. The medium was sterilized in the autoclave. Spore suspensions of the different myxobacteria were inoculated onto the centers of petri plates containing these media. A small inoculating loop was used for uniformity of inoculum, and the inoculated plates were not moved until the inoculum was dry; thus, runninIgof thelatter was prevented. Cultures were incubated at 24 C for 14 days. Growth was determined by measuring the diameter of the swarm. The results are shown in table 1. It can be seen that in general better growth occurred on the more complex carbohydrates; on the simpler carbohydrates growth was either not stimulated or was inhibited. The best growth occurred on the control, with no nitrogen or carbon source added. No visible evidence of agar decomposition occurred. These results are in general agreement with those Beebe obtained. In the second experiment, the carbohydrates were sterilized by filtration through Seitz filters to determine whether any of the simpler carbohydrates such as xylose, arabinose, fructose, and glucose were inhibitory because they were being changed chemically by heating and thus rendered unsuitable for utilization by the microorganisms. Double-strength carbohydrate solutions were prepared, sterilized by passing through Seitz filters, and added to double-strength mineral salts agar base to make one per cent carbohydrate media as before. Starch was sterilized by heating since a solution of Lindner's soluble starch will not pas through a Seitz filter. Plates were poured and inoculations made as before. Incubation was at 24 C for 14 days. The results are shown in table 2. The results of this experiment differ from those of the previous one. First, the simpler carbohydrates no longer inhibit growth. In fact, in certain cases the best growth occurred on the simpler