SCN3230-ABED_1: Module 8 Lesson 8 - 3 (Lab)

Lesson 8 — Populations and Communities Changing over Time

Microbial Succession Lab

What happens to the population of microorganisms during the process of soybean fermentation? Soy sauce is a commonly used Asian condiment prepared from fermented soy beans and brine. As expected with any fermentation process, soy sauce is colonized by various microorganisms during this process. Observing the data obtained from a six-month study of the microbial succession of soy sauce brine allows a better understanding of the process of microbial succession and the factors that influence the succession.

This lab is based on a study by Sulaiman, Joanita et al, in 2014 on Microbial succession and the functional potential during the fermentation of Chinese soy sauce brine

Problem

What changes in the microbial populations can be observed during soy beans fermentation?

Procedure

Analyze the following results from the study.

Physicochemical changes in the traditional Chinese soy sauce fermentation brine: (A) pH and acidity mean values at various fermentation stages. (B) NaCl and reducing sugar content, (C) ethanol concentration and (D) changes in percentages of total nitrogen content.

Copyright © 2014 Sulaiman, Gan, Yin and Chan.

Analysis

Describe how the microbial communities changed over time. Which microorganisms were most abundant in the beginning, middle, and end of the experiment?
Which interspecific interactions might be responsible for the microbial succession?
How did the environmental factors affect the microbial growth?

Check Your Work.

In the beginning, bacillus, weissella and lactobacillus were most abundant. In the middle of the experiment, klebsiella and candida (yeast) were most abundant. At the end of the experiment, candida (yeast) was the most abundant species in the soy sauce brine.
Competitive exclusion may have reduced the bacterial population.
Bacterial populations that were abundant in the beginning of the experiment turned sugar into lactic acid, lowering the pH of the environment and making it more acidic. This produced a hostile environment for microbes less tolerant of the acidic environment. However, yeast can thrive in low pH and high salinity environment. As the bacterial population reduced competition, yeast and other bacterial populations that can tolerate low pH and high salinity environment emerged. Yeast benefited by using the by-product of bacterial population as a food source. Although the yeast population dominated at the end of fermentation process, the biodiversity of various microbial populations increased and harmful fungal population was wiped out.