How does a blue transparent bottle affect the growth of micro-organisms?

Hi everyone,

This is my final report about my Winogradsky Columns.

Materials

1. Transparent plastic bottle (1.5 L)
2. Mud from Lake Pamvotis (2/3 of the bottle)
3. Water from Lake Pamvotis (1/3 of the bottle)
4. Carbon source (5 g newspaper in small pieces )
5. Source of sulfur (1 whole boiled egg 70g)

Hypothesis

Since bottle (2) contained 1/3 of the nutritions compared to bottle (1), it would have a slower growth rate (of the organisms it contained) as its metabolic processes would be slowed down .

Bottle (1)                                                     Bottle(2) 
After 60 days 

Summary of Results

The experimental hypothesis was not confirmed as bottle (2) with limited enrichment materials contained greater abundance of microorganisms than bottle (1) with evenly distributed enrichment materials throughout.

It is possible that the color of bottle (1) (transparent blue) affected the light that penetrated it and thus the growth of photosynthetic organisms.

In fact, visible light consists of wavelengths of 400-700 nm. Blue light corresponds to wavelength (λ)= 450 nm, and therefore this λ could not be absorbed by the micro-organisms as it is reflected by the bottle.

In the diagram below you can see the absorption spectra of three basic dyes in photosynthesis:chlorophyll a, chlorophyll b, β-carotene.

All three pigments show a peak for λ ~ 450 nm

Source: khanacademy.org

In particular, all micro-organisms that could be cultured in Winogradsky colums show a peak in their absorption of wavelength λ ~ 450 nm through their pigments.

Source:

Colorful niches of phototrophic microorganisms shaped by vibrations of the water molecule

The ISME Journal 1 p.271-282 (2007) - M. Stomp et. al.

volum1, pageM. Stomp et. 

Especially, purple sulfur bacteria,acorrding to a study (Photosynthetic development of purple sulfur bacteria during illumination with green light-Osnitskaia LK, Chudina VI-1977),use short wavelengths of natural light, blue and green, for CO2 assimilation and biosynthesis of biomass, proteins, and pigments.

Which means that the photosynthetic ability of the micro-organisms in bottle (1) was lowered because their pigments didn't absorb wavelength λ ~ 450 nm. That way, the growth of photosynthetic organisms in bottle (1) was slowed down and in the course of the same time showed lower abundance of micro-organisms than bottle (2).

Christina Diamantopoulou

Department of Biological Applications and Technologies

University of Ioannina-January 2019