The Chemotactic Response of Plasmodia of the Myxomycete Physarum polycephalum to Sugars and Related Compounds

Abstract

A new technique, the double strip method, for studying the chemotaxis of myxomycete plasmodia is described. Physarum polycephalum was attracted by the aldohexoses D-glucose, D-galactose and D-mannose and their derivatives 2-deoxy-~-glucose and maltose, thresholds ranging from 0.25 mM (D-glucose) to 5 mM (D-mannose). These sugars competed with each other, a uniform background of one of them inhibiting taxis to the others. Other attractants were N-acetyl-D-glucosamine and mannitol, with thresholds at 1 mM, and fucose (6-deoxy-~-galactose). Although in general only those carbohydrates which could support growth were attractants, there were exceptions such as 2-deoxy-~-glucose ; hence metabolism of a compound was not necessary for attraction. In addition, some compounds, such as fructose, could be metabolized but did not attract. At high concentrations (about 100 mM) all the compounds tested, including attractants, could under appropriate conditions cause repulsion, probably through osmotic effects. I N T R O D U C T I O NCarlile (1970) found that plasmodia of the myxomycete Physarum polycephalum Schweinitz were attracted by (i.e. showed positive chemotaxis to) glucose, maltose, mannose and galactose but not by sucrose, fructose or ribose. Each of the former group of sugars supported growth in shaken liquid culture when present as the sole carbohydrate, but the latter group did not. I t was tentatively concluded that with P. polycephalurn there was a parallel between the chemotactic effectiveness of sugars and their ability to support growth .However, studies on chemotaxis with Escherichiu coli have established that although most nutrients are attractants, some compounds are metabolized but do not attract, and others are not metabolized but are strong attractants (Adler, 1975). This conclusion suggests that the chemotactic responses of P. polycephalum to a wider range of sugars should be examined, and compared with the ability of the sugars to support growth and influence migration. Studies on growth and migration were reported in the preceding paper (Knowles & Carlile, 1978); studies on chemotaxis are described here.

Slime mold uses an externalized spatial “memory” to navigate in complex environments

“…The set-up (Fig. 3) consisted of a Petri dish with an acetate U-shaped trap placed between the plasmodium and a well in the agar containing food: an attractive 2% (wt/vol) glucose solution, the "goal" (16)(17)(18). The diffusing glucose solution produced an attraction gradient through the agar, drawing the plasmodium toward the glucose source and into the U-shaped trap.…”

Amoeboid organism solves complex nutritional challenges

“…A second consequence of high nutrient concentrations was that the higher the concentration of carbohydrate in the medium, the higher was the incidence of mortality. This may be related to the sensitivity of slime molds to high osmotic pressure (11,30,31). The osmotic effects of high sugar concentrations have been suggested to cause both reduced migration rate (31, 32) and negative chemotaxis (11,33).…”

“…A recent study showed that P. polycephalum increases allocation toward exploratory growth when its current food resource is diluted (22). On substrates with higher nutrient concentrations, the plasmodia in the present study grew more compactly, with slime molds on high-protein diets producing a veinless structure, indicating that media able to support rapid growth depress migration, allowing the organism to remain at a site until nutrients are exhausted (11,23).This result has strong parallels with observations in other distributed systems, such as bacterial and fungal colonies, in which the overall pattern of growth is influenced by varying the concentration of nutrient (20,24). The ratio of protein and carbohydrate in the diet also had a strong influence on migration distance.…”

“…This may be related to the sensitivity of slime molds to high osmotic pressure (11,30,31). The osmotic effects of high sugar concentrations have been suggested to cause both reduced migration rate (31, 32) and negative chemotaxis (11,33). Glucose has been shown to be repellent at high concentration (56 g·L −1 ) (33); here, we found that none of the slime molds survived when glucose concentration exceeded 60 g·L −1 .…”

Habituation in non-neural organisms: evidence from slime moulds

“…Here we designed a protocol to investigate habituation phenomena in slime moulds using chemotaxis as the behavioural response under scrutiny. Chemotaxis is the directed motion of an organism towards favourable chemicals (attractants) and away from unfavourable ones (repellents) [19,20]. To test whether slime moulds are capable of habituation, individuals were repeatedly exposed to quinine or caffeine, known repellents for P. Polycephalum [21,22] and their behavioural responses were recorded.…”