The Acellular Slime Mold Physarum Polycephalum - Essay Example

?Biology Laboratory Report of Introduction The most species-rich, largest and ecologically significant heterotrophs are composed of distributed networks that do not have specialised centres, as exemplified by the vast mycelial networks of fungi (Dussutour et al. 2010). This fact is a critical information on how distributed systems are able to maintain optimal supply of multiple nutrients which are important to life and reproduction. The acellular slime mold Physarum polycephalum is an extraordinary organism that can make complex nutritional decisions albeit the absence of a coordination centre and only has a vast multi-nucleate cell (Dussutour et al. 2010). It has the ability to detect the shortest route to its food supply (Fenska 2010). It has been studied for cytoplasmic streaming through a network of channels that are driven by pressure gradients where external influences can superimpose slow movement on the whole organism (Kincaid and Mansour 1978; Durham and Ridgway 1976). Studies showed that peristalsis-like waves in Physarum, where it moves like a giant amoeba flowing over that surface as it ingests a matter, move in the direction opposite from the net movement of the organism which is a typical mechanism of chemotaxis (Genome: Physarum polycephalum 2013; Durham and Ridgway 1976). Physarum and other acellular slime molds are made up of syncytial protoplasm mass called plasmodium that lack cell walls in their main vegetative state albeit they can take several microscopic and macroscopic forms. It is the plasmodium that enables Physarum to conduct its peristaltic movement during feeding and to engage its membrane potential using physicochemical mechanism (Genome: Physarum polycephalum 2013, Hato 1979). The objective of this experiment is to investigate on the “food preferences” or chemotaxis behaviour of the species Physarum polycephalum. It aims to observe the movement of the plasmodium as a response to three different substances. Materials and Methods The following methods were applied to observe the ideal environment conducive to the growth of the slime mould, Physarum polycehalum. This method implied the food preference of this slime mould. 1. Two plates of agar block were prepared. These were labelled Plates A and B. Plate A had corn meal agar representing low nutrient levels. Plate B only had water agar representing no nutrient levels. 2. A plug of the slime mould, Physarum polycehalum, was extracted and inoculated in Plates A and B. 3. In Plate A, the area was divided equally into four parts. Two types of fruits and two types of sweets were placed on each of the areas. The plate was left for one day. Data were collected on the second day. 4. In Plate B, the area was divided equally into two parts. The first part was placed with two types of fruits and the second part was placed with two types of sweets. The plate was left for one day. Data were collected on the second day. 5. On the second day, Plates A and B were observed for the growth of Physarum polycehalum within the fruits and sweets placed on the plates. Areas where no growth was observed were also noted. 6. Results of Plates A and B for the whole class were collected. This represented 30 replicates of Plate A (n=30) and 30 replicates of Plate B (n=30). 7. Both the individual and accumulated results were considered for the reporting of this experiment. However, to achieve comprehensiveness of observation of the multicellular properties of Physarum polycehalum, the accumulated results were used for analysis. Growth in different combinations was presented using a bar graph. Results The following results were gathered based on three combinations of substances placed on the agar plates. These combinations included Combination 1 (chocolate and apple), Combination 2 (apple and sugar coated sweet) and Combination 3 (chocolate and sugar coated sweet). Figure 1. Plot of the Number of Growth Observed on Different Types of Combination of Substances Figure 1depicts the specific responses of the slime mould Physarum polycehalum on each of Combinations 1, 2 and 3. These responses are shown according to the number of growth observed on each combination which had 30 replicates. According to Figure 1, Combination 3 with Chocolate had the most number of growth and Combination 1 with Chocolate was second in rank. Conversely, Combination 3 with sugar coated sweets had zero growth and Combination 2 with sugar coated sweets had the least number of growth. Discussion Figure1 above which is a cumulative result for the whole class is congruent with the author’s individual case observations on the slime mould Physarum polycehalu. It exhibited preference on chocolate as the substance where its growth was highly induced. This is further supported by the number of growth observed in Combinations 1 and 3. Physarum was found to have enormous growth of 77% (Combination 1, n=23) and 90% (Combination 3, n=27) in environments where it has a choice between chocolate against other substance such as apple and sugar coated sweet. In fact, since there was no chocolate in the environment of Combination 2, a low growth of 23% (n=7) and 10% (n=3) were observed between apple and sugar coated sweet, see Figure 1. Preference on chocolate as food by Physarum is moreover supported by the author’s individual case observations. It is noted that growth was only seen on the low level nutrient plate, specifically on the areas with fruits. No growth was seen on areas with sweets and similarly on the plate without nutrients. The consistency of observed results from a total of 180 replicates from both cumulative and individual levels validates the data collected on the preference of the slime mould Physarum. The fact that similar observations stood out from the frequency of repetitions of growth and form of substances demonstrates a good indicator that the perceived outcomes are reliable and stable. Physarum is a protist that inhabits areas that are shady, cool and moist (Dussutour et al. 2010). The slime molds group are key heterotrophs that play important role in decomposing organic matter in temperate and tropical forests. During their vegetative stage, they engulf bacteria and other microbes. They then secrete enzymes that digest the engulfed matter. This must have significantly contributed to the chemotaxis of the plasmodium of Physarum. It could mean that after the incubation period of the plates, the substance that might have possessed the highest concentration of microbes would be the chocolate. Compared to apple and sugar coated sweets, chocolate would have been the most moist and favourable for growth of microbes upon incubation to 20 degrees Celsius temperature for 12 hours. The presence of these microbes then attracted growth of Physarum on the substance, in this case, chocolate. It could be interpreted that the more likely a substance is to decompose, the more microbes will be present and the more slime molds will grow. Conclusion Therefore, in order of environments used in this experiment to find out what is conducive to Physarum’s growth, it can be said that it highly grows on chocolate, apple and sugar coated sweets. Another way of stating this is, chemotaxis in Physarum was found to be of higher concentration in chocolate substance and lower in apple and sugar coated sweet substances. Chocolate substance must have exhibited the nutrient qualities that are of most interest to Physarum. Recommendations Results can be better established in this experiment by duplicating the same methods using longer duration of time. Observations on replicates of 12, 24, 36, 48, etc. hour intervals would likely produce a more robust answer on the chemotaxis behaviour of Physarum using similar setup. Also, external factors have to be considered such as culture care and stage of growth of microplasmodia, substratum used for cell movement, nature of the gradient, effect of salts, pH and temperature, which may contribute on the quality of observed results (Kincaid and Mansour 1978). It will also be interesting to test the nutrient qualities of chocolate compared to other substances that made it most attractive for growth of Physarum. Having this knowledge is important in the understanding of nutrient balancing in distributed systems. References Durnham ACH and Ridgway EB 1976, Control of Chemotaxis in Physarum polycephalum, The Journal of Cell Biology, 69: 218-223. Dussutour A, Latty T, Beekman M and Simpson SJ 2010, Amoeboid organism solves complex nutritional challenges, PNAS, 107(10): 4607-4611, Doi/10.1073/pnas.0912198107. Fenska JE 2010, Slimin’ through the Maze: The Effects of Electromagnetic and Centripetal Forces on Maze solving ability of Physarum polycephalum (Slime mold) (Online), Available: http://oas.uco.edu/06/paper/fenskaje.pdf [25 Feb 2013]. Genome: Physarum polycephalum 2013, Washington University I St. Louis [Online], Available: http://genome.wustl.edu/genomes/detail/physarum-polycephalum/ [25 Feb 2013]. Hato M 1979, Membrane phenomena in chemotaxis in true slime mold Physarum polycephalum, Colloid and Polymer Science [Abstract], 257(4): 397-405. Kincaid RL and Mansour TE 1978, Measurement of chemotaxis in the slime mold Physarum polycephalum, Experimental Cell Research, 116(2): 365-375, http://dx.doi.org/10.1016/0014-4827(78)90460-3. Read More