JACK LEECH PITTSBURGH CENTRAL CATHOLIC HIGH SCHOOL GRADE Pesticide Effects on Yeast Survivorship

Pesticides Pesticides include any chemical, antibacterial, biological agent, or other similar substance used to kill or repel unwanted species. Grouped in other categories, such as bactericides, fungicides, herbicides, rodenticides, and insecticides. Insecticides are then grouped under other titles such as ovicides, larvicides, and adulticides.

Concern Insect Killing Soap Main ingredients include potassium salts of fatty acids which pierce the cell membrane, causing the contents to leak out and dehydrate. Works by penetrating and destroying the outer shells of soft-bodied insect pests, resulting in dehydration and death within hours of contact. Concentration of 3.5oz per gallon of water.

Ortho Rose Pride This insecticide uses acephate as its main active ingredients. Acephate prevents the neurotransmitter acetylcholine from being degraded and destroys the nervous system.

Safer Brand Yard and Garden Contains pyrethrins and also potassium salts of fatty acids. Pyrethrins attack the insect’s nervous system by depolarizing a normally negatively charged cell, causing the nerve cell to constantly trigger action potentials and keep firing. Potassium salts weaken the insect’s protective outer shell.

Yeast Saccharomyces cerevisiae. Easy to manipulate in the laboratory. Most commonly studied cell. Very similar in structure and biochemistry to more complex eukaryotes, including human cells. Buds in single colonies, can be easily counted.

Purpose Determine if any of the pesticides will have a significant effect on the survivorship of yeast.

Hypothesis Null-the pesticides used will have no significant effect on yeast survivorship. Alternative-the pesticides will have a significant effect on yeast survivorship.

Materials YEPD agar plates (1% yeast extract, 2% glucose, 1.5% agar) YEPD media (1% yeast extract, 2% peptone, 2% glucose) Sterile capped test tube sterile dilution fluid (SDF) (10 mM KH 2 PO4, 10 mM K 2 HPO 4, 1 mM MgSO 4, 0.1 mM CaCl 2, 100 mM NaCl) Concern Insect Killing Soap Ortho Rose Pride Insecticide Safer Brand Yard and Garden Spray Micropipette Permanent marker Plate spreader Ethanol Bunsen Burner Klett Spectrophotometer Incubator Sidearm flask

Procedure (Continuous Contact Exposure) S.c. yeast was grown overnight in sterile YEPD media. A sample of the overnight culture was added to fresh media in a sterile sidearm flask. The culture was placed in a incubator (30 C) until a density of 50 Klett spectrophotometer units was reached. This represents a cell density of approximately 10 7 cells/mL. 0.1 mL of each variable at concentration of 1X was pipetted onto five plates per variable. The plates were labeled and the agar was allowed to absorb the variable for thirty minutes. After vortexing to evenly suspend cells, 0.1mL aliquots were removed from the tubes and spread on YEPD plates. The cell culture was diluted in sterile dilution fluid to a concentration of approximately 10 3 cells/mL. The plates were incubated at 30 C for 48 hours. The resulting colonies were counted. Each colony is assumed to have risen from one cell.

Procedure (Pulse Exposure) S.c. yeast was grown overnight in sterile YEPD media. A sample of the overnight culture was added to fresh media in a sterile sidearm flask. The culture was placed in a incubator (30 C) until a density of 50 Klett spectrophotometer units was reached. This represents a cell density of approximately 10 7 cells/mL. The cell culture was diluted in sterile dilution fluid to a concentration of approximately 10 3 cells/mL. After vortexing to evenly suspend cells, 0.1mL aliquots were removed from the tubes and spread on YEPD plates. 0.1 mL of each variable at concentration of 1X was pipetted onto five plates per variable. The plates were incubated at 30 C for 48 hours. The resulting colonies were counted. Each colony is assumed to have risen from one cell.

Yeast Survivorship After Indirect Exposure p=7.65 ^-10 Resulting Colonies Groups of Variables Standard cut-off: p =.05

Yeast Survivorship After Direct Exposure P=3.39 ^-11 Resulting Colonies Groups of Variables Standard cut-off: p =.05

Dunnett’s Test If p-value is < than.05, significant variation. If t-value is > than the t-critical (3.29), significant variation.

Dunnett’s Tests Results for Indirect Exposure Variables UsedResults Concern Soap Ortho Rose Pride Safer Brand p<.05 (Significant) p<.05 (Significant) p<.05 (Significant) t-value(9.25)>3.48 (Significant) t-value(14.32)>3.48 (Significant) t-value(3.49)>3.48 (Significant) Not significant if cut-off of.01 is used. (t-critical of 4.98)

Dunnett’s Tests Results for Direct Exposure Variables UsedResults Concern Soap Ortho Rose Pride Safer Brand p<.05 (Significant) p<.05 (Significant) p<.05 (Significant) t-value(13.14)>3.48 (Significant) t-value(18.44)>3.48 (Significant) t-value(9.58)>3.48 (Significant)

Interpretation Direct exposure appeared to have a more significant effect on yeast survivorship when compared to the indirect exposure based upon the statistical analysis. The indirect exposure of Safer Brand resulted in a significant effect on survivorship when the t-critical in the Dunnett’s test was 3.48, but not These t- critical values represent.05 and the more stringent cut-off of.01, respectively.

Conclusions Null hypothesis rejected for all trials in both the direct and indirect exposures. However, the result found in the Safer Brand indirect trial, although insignificant with a statistical analysis value of.05, the result would not be significant with the more rigid value of.01.

Limitations and Inconsistencies The plates were open during the trials, therefore environmental contamination could have been a factor. Other methods of destruction from the pesticides could have effected the yeast growth aside of the main active ingredients.

Continuations Use a wider range of pesticides in addition to insecticides. Test the specific ingredients of the pesticide instead of the entire product. Test different concentrations of each variable instead of the listed recommended concentration.

Works Cited