Kiana Sedighi

Home for Two: A Slime Mold Coexistence Experiment

Introduction

For my final DIY BioLab project, I wanted to create an experiment that was both biological and narrative. Instead of only observing the growth of one slime mold, I wanted to place two different slime mold species in the same environment and document what happened when their growing networks approached each other.

The two organisms used in this experiment were Badhamia and Physarum polycephalum. At the beginning, both looked very similar because they were yellowish, which made it difficult to visually separate them during observation. Because of this, I later used a red pigment on the food source of one culture to create a visible contrast.

My final goal was to create a video showing the interaction between the two slime molds. I wanted the project to ask a simple question:

Can two different living organisms share the same space?

Materials

For this experiment I used:

• Badhamia culture
• Physarum polycephalum culture
• Agar-agar
• Water
• Petri dishes
• Oat flakes
• Red pigment / coloring powder
• Laboratory glassware
• Spoon
• Tweezers
• Gloves
• Microscope / camera setup
• Canon DSLR camera
• Python
• Video editing software

Preparing the First Badhamia Culture

Badhamia

At the beginning of the project, I prepared a simple agar medium for the slime mold.

I mixed agar-agar with water, heated it until the agar dissolved, and poured the liquid into a Petri dish. After the agar cooled down and became solid, I transferred Badhamia from the kit that was ordered for me by our lab supervisor Mr. Volpato.

I placed several oat flakes on the agar as food and left the culture to grow. This first step was mainly about keeping the Badhamia alive and giving it enough time to become stronger before using it in the final experiment.

Badhamia kit

Receiving the Second Slime Mold

After the Badhamia culture had started growing, I contacted another student and exchanged slime mold cultures with her. I gave her part of my Badhamia culture, and she gave me Physarum polycephalum.

The Problem of Visibility

Color Physarum polycephalum

At first, both cultures were yellowish and visually very similar. This was a problem because once they started growing on the same agar plate, it would be difficult to tell which slime mold was which.

P1. Food coloring

Because of this, I looked at a previous experiment done by Daria Lukianchuk, who had tested different coloring methods. In her experiment, an unknown red pigment had produced the clearest visible result. I used this information as a practical reference for my own setup.

Instead of repeating the full color-testing process, I decided to use the same red pigment to color the food source of one slime mold. This made the two sides easier to distinguish in the final video. Then I prepared the food as she mentioned.

P2. Food coloring

Preparing the Final Petri Dish

For the final experiment, I prepared new agar plates.

Preparing the Final Petri Dish

I again mixed agar-agar with water, heated the mixture, and poured it into a clean Petri dish. After the agar solidified, I transferred both slime molds onto the same plate.

One side contained Badhamia, and the other side contained Physarum polycephalum. This setup became the central scene of the project: two different organisms, one shared environment.

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Camera Setup

Camera Setup and Recording

To document the experiment, I used a fixed camera setup.

The camera was mounted above the Petri dish and under it a power source so that it could record for several hours without interruption. I configured the camera to take one photo every 10 seconds.

This interval was chosen because it created enough frames for a smooth, while still keeping the number of images manageable.

During the recording session, the camera captured thousands of photographs of the slime molds.

Creating the Video with Python

After the recording session, I transferred the images to my computer.

The folder contained both image files and raw camera files, so I used only the JPG images for the final processing. I wrote a Python program to load the images in order, align them, remove problematic outsider frames when necessary, and combine the sequence into a video.

import cv2
import os
import glob
import numpy as np

# SETTINGS
FPS = 30
OUTPUT = "timelapse_aligned.mp4"
IMAGE_EXT = "*.JPG"

# Read JPG files only
files = sorted(glob.glob(IMAGE_EXT))

if not files:
    raise Exception("No JPG files found in this folder.")

print(f"Found {len(files)} JPG images")

# Use first image as reference
ref = cv2.imread(files[0])
ref = cv2.resize(ref, (1920, 1080))
ref_gray = cv2.cvtColor(ref, cv2.COLOR_BGR2GRAY)

h, w = ref.shape[:2]

video = cv2.VideoWriter(
    OUTPUT,
    cv2.VideoWriter_fourcc(*"mp4v"),
    FPS,
    (w, h)
)

last_good = ref.copy()

for i, file in enumerate(files):
    img = cv2.imread(file)

    if img is None:
        print("Skipped unreadable:", file)
        continue

    # Fix portrait/rotated outsiders automatically
    if img.shape[0] > img.shape[1]:
        img = cv2.rotate(img, cv2.ROTATE_90_CLOCKWISE)

    img = cv2.resize(img, (w, h))
    gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

    # Align image to first image
    warp_matrix = np.eye(2, 3, dtype=np.float32)

    try:
        _, warp_matrix = cv2.findTransformECC(
            ref_gray,
            gray,
            warp_matrix,
            cv2.MOTION_EUCLIDEAN,
            criteria=(cv2.TERM_CRITERIA_EPS | cv2.TERM_CRITERIA_COUNT, 50, 1e-5)
        )

        aligned = cv2.warpAffine(
            img,
            warp_matrix,
            (w, h),
            flags=cv2.INTER_LINEAR + cv2.WARP_INVERSE_MAP
        )

        video.write(aligned)
        last_good = aligned

    except cv2.error:
        # If alignment fails, probably outsider / bad photo
        print("Skipped outsider or badly rotated image:", file)
        continue

    if i % 100 == 0:
        print(f"Processed {i}/{len(files)}")

video.release()
print("Done:", OUTPUT)

The final video was created from the image sequence and exported as an MP4 file. After that, I edited the video further by adding an intro, title cards, music, and an ending message.

Artistic Concept

The original concept of the video was Home for Two. I wanted to present the two slime molds almost like two characters sharing one space:

One — Badhamia

Two — Physarum polycephalum

However, after discussing the experiment with our lab supervisor, I realized that my first interpretation was not good. Since both slime molds depend on the same food source, the situation is not simply peaceful coexistence. It is also competition.

In the actual experiment, the two organisms also did not grow as expected. Because of this, the biological part of the project cannot be presented as a successful coexistence experiment. Still, I decided to continue working with the material visually.

For the next attempt, I want to develop the video concept in a more playful direction: not as a peaceful home, but more like a small battlefield, where two organisms compete for space and food.

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Conclusion

This project started as an attempt to create a poetic slime mold film about two different organisms sharing one space. The idea behind Home for Two was to connect biological observation with a wider reflection on difference and coexistence.

However, after the experiment and the feedback discussion, I realized that my original question — whether two different living organisms can share the same space — was too broad. Organisms already share ecosystems in many ways, but my video did not actually show Badhamia and Physarum polycephalum encountering or interacting with each other.

Because of this, the first experiment cannot answer the question I originally asked. The two slime molds did not grow strongly, and the concept of peaceful coexistence was biologically too simplified. Since both organisms use the same food source, their relationship is more likely to involve competition than harmony.

I now see this project as an unfinished first attempt rather than a successful final experiment. Still, I learned how to prepare agar plates, maintain slime mold cultures, exchange biological material, use colored food as a visual marker, build a setup, and turn thousands of photos into a video using Python.

Second Experimental Attempt: A Follow-Up Slime Mold Study

Introduction

After completing the first experiment and discussing the results with our lab supervisor, it became clear that the experiment needed to be repeated. The original setup did not produce the expected interaction between the two slime mold species, and the resulting video did not clearly show their growth or encounter.

For the second attempt, I focused on improving both the biological setup and the recording process. Rather than trying to support a specific artistic interpretation, the goal was simply to document the growth of the two slime molds under improved conditions and observe what would happen when they were placed on the same agar plate.

Recovering the Cultures

After the first experiment, both slime mold cultures developed mold contamination and could no longer be used. Our lab supervisor, Mr. Alessandro Volpato, isolated the cultures to help them recover before the experiment could be repeated.

After several days, the cultures were ready to be used again.

slim mold

Preparing the Agar Plates

As in the first experiment, I prepared a fresh agar medium by mixing agar-agar with water, heating the mixture until the agar dissolved, and pouring it into clean Petri dishes. After the agar solidified, it was ready for the new cultures.

Preparing the Colored Food

To make the growth easier to observe, I again prepared colored oat flakes.

I mixed the unknown red pigment with water, and oat flakes, and allowed them to absorb the color before using them as food for Physarum polycephalum.

Growing the New Culture

A small piece of Physarum polycephalum was transferred onto a fresh Petri dish together with the colored oat flakes. The culture was left to grow for one day so that it became stronger before the final recording.

Preparing the Final Recording Setup

After the culture had recovered, I prepared another fresh agar plate for the final recording.

Badhamia and Physarum polycephalum were placed on opposite sides of the Petri dish, with oat flakes positioned between them to encourage both organisms to grow toward the same area.

Unlike the first experiment, I removed the light source underneath the Petri dish after realizing that it caused noticeable flickering. This resulted in much more stable lighting throughout the recording.

Overnight Recording

The camera was mounted above the Petri dish and connected to an external power source so it could record continuously throughout the night.

For this experiment, the camera captured one photograph every 30 seconds. I started the recording in the evening, checked the setup several times during the night to ensure everything was working correctly, and collected the experiment the following morning.

Creating the Video

After transferring the photographs to my computer, I processed the images using the same Python workflow developed during the first experiment.

Petri dish after two days of growth

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The images were combined into a video, which was then edited by adding titles and music.

Observations

The second experiment produced a different result than expected.

Although both slime molds were placed on the same Petri dish, only Physarum polycephalum showed significant growth throughout the recording. It expanded across the agar surface and eventually occupied much of the available space, while Badhamia remained largely inactive.

An interesting observation was that Physarum polycephalum gradually lost its red coloration as it continued feeding. Because new, uncolored oat flakes were available, the organism slowly returned to its natural yellow appearance during the recording.

As a result, the experiment did not capture the interaction between two actively growing slime molds. Instead, it documented the successful growth of Physarum polycephalum under the improved experimental conditions.