Bacteria Structure

This article is about microbiology, about bacteria, to be more precise. The brewer is mistaken who thinks only yeasts matter. Bacteria are present in the equipment, in the air, and surely in the beer. It's necessary to understand to effectively control it. I hope you enjoy it, please subscribe to this newsletter for more content!

Bacteria is a single-celled microorganism with sizes ranging from 0,2 – 2 μm in diameter and 2 - 8 μm in length, with rod, spherical, or spiral shape (Bacilli, Cocci,?and?Spirilla).

Cell Structure

They have the following structures:

• Cell Membrane: The cell membrane surrounds the bacterial cell, controlling the entry and exit of substances. Bacteria can be divided into two groups by Gram staining test. We will approach it in a forward article dedicated to it.
• Nucleoid: Non-membranous particle containing the genetic material (circular DNA). Bacteria is a prokaryote, meaning that it has no nuclear membrane.
• Ribosomes: Non-membranous particles responsible for protein synthesis. It is the only organelle present in prokaryote cells.
• Flagella: Used for locomotion. They are long and in few quantity (1 - 10 per cell).
• Pili or Fimbriae: Filamentous for adhesion to surfaces or other cells. They are shorter than flagella but present in greater numbers.

Spores

The bacteria in a vegetative state are active, reproducing, and responding to the environment, but they are sensitive to disinfectant methods. A few bacteria species have the ability to create spores to protect the genetic code. Every time these bacteria are found in harsh conditions, it can trigger the sporulation where a chromosomic copy is involved by a plasmatic membrane forming a endospore. The bacteria create a thick wall around the spore (coat) while the rest of the cell degenerates. By the end, the original cell membrane is broken and releases the endospore.?

When the spore identifies a favorable condition, it hydrates and releases the external wall turning back to a vegetative state. The new bacteria cell starts to reproduce by binary division.

These bacteria represent a challenge for breweries. For example, when a brewer finishes the day by only making a hot water (or alkaline) rinse in a tank and leaving the complete CIP for the next day. The spore-forming bacteria present in the tank will be warned (by the rinse) and enter at spore state. The next day CIP will not be enough to destroy the spores, leading to a contamination focus.

Spore Staining Test

The spore staining test is a laboratory procedure to identify the spore presence in a sample. This test has the following steps:

• The sample is heat-fixed to a glass.
• Cover with green stain (malachite green).
• Heated to facilitate the stain penetration.
• Washed to remove the primary stain.
• Cover with pink contrast (safranin).

The green stain can penetrate both vegetative and spore cells. The wash and the pink stain only penetrate the vegetative cell, leading the vegetative cells pink and the spores green.

Spores are not destroyed by the normal CIP process, only by steam. The effective way to combat spores is to create an atmosphere for spores to enter a vegetative state before the CIP. A good way is to rinse and keep the tank wet for some hours.

Categories

The bacteria can be categorized into groups by temperature, pH, and atmosphere, among others.

Temperature

• Psychrophiles: Bacteria that thrive at very low temperatures, typically below 30 °C.
• Mesophiles: Bacteria grow best at moderate temperatures, between 10 °C and 50 °C.?
• Thermophiles: Bacteria that thrive at high temperatures, usually above 45 °C.It's important to note that bacteria interacting with humans operate within a different temperature range than those that may be present in beer.

pH

• Acidophiles: Bacteria that prefer acidic environments and have an optimal growth range at pH below 5.5.
• Neutrophiles: Bacteria that grow best in environments with near-neutral pH, between 6.5 and 7.5.
• Alkalophiles: Bacteria that prefer alkaline environments and have an optimal growth range at pH above 8.5.Beer has a pH below 4.5, and wort below 5.2.

Atmosphere

• Aerobic: Bacteria that require oxygen for growth.
• Anaerobic: Bacteria that grow in the absence of oxygen.
• Facultative: Bacteria can grow both in the presence and absence of oxygen.

Understanding whether a bacterial colony necessitates oxygen is crucial for assisting brewers in identifying the source of contamination. During aerobic respiration, microorganisms release hydrogen peroxide, necessitating the production of the superoxide dismutase enzyme to prevent cell death. This enzyme is exclusive to aerobic cells.

The catalase test provides a straightforward method to ascertain the presence of this enzyme, determining if the colony is aerobic. The procedure involves introducing hydrogen peroxide into a colony. The emergence of bubbles indicates the presence of the enzyme, signifying an aerobic bacterium.

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