Problem 18 - Brock Biology of Microorganisms

Question

Why is the enzyme hydrogenase useful to Desulfovibrio even when it is not grown on \(\mathrm{H}_{2}\) as electron donor? (Section 13.18)

Step-by-Step Solution

Answer

Hydrogenase helps in electron transfer, redox balance, and allows metabolic flexibility for Desulfovibrio.

Step 1: Identify Alternative Electron Donors

Desulfovibrio bacteria can use various electron donors besides \(\text{H}_2\), such as lactate, pyruvate, or ethanol. These molecules can undergo oxidation to release electrons.

Step 2: Role of Hydrogenase in Electron Transfer

The enzyme hydrogenase can facilitate the transfer of electrons from these alternative donors to the electron transport chain, enhancing the bacterial metabolic processes.

Step 3: Maintain Redox Balance

Hydrogenase helps in maintaining the redox balance within the cell by converting protons into \(\text{H}_2\) gas, which can then be either used internally or released into the environment.

Step 4: Flexibility in Metabolism

By possessing hydrogenase, Desulfovibrio can adapt to varying environmental conditions and efficiently utilize different substrates for growth and energy production.

Key Concepts

alternative electron donors

Desulfovibrio bacteria can thrive in various environments because they can utilize different electron donors besides the familiar hydrogen gas (H2). Some common alternative electron donors include lactate, pyruvate, and ethanol.
These molecules are essential because they undergo oxidation, a process in which they lose electrons.
These released electrons are crucial for the bacteria's energy generation and metabolic activities. By using different electron donors, Desulfovibrio shows impressive versatility in their metabolic functions. This flexibility allows them to survive and grow even when hydrogen is not available. This characteristic significantly contributes to their adaptability and resilience in changing environmental conditions.

electron transport chain

The electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions.
In Desulfovibrio, the enzyme hydrogenase plays a critical role in this process. Hydrogenase helps facilitate the transfer of electrons from both hydrogen and alternative donors like lactate or ethanol into the ETC.
This transfer is vital because it drives the creation of a proton gradient across the bacterial cell membrane.
This gradient is then used to produce ATP, the primary energy currency of the cell.
Effective electron transfer through the ETC is indispensable for energy generation and overall cellular function.

redox balance

Maintaining redox balance is paramount for cellular function and survival.
In Desulfovibrio, the enzyme hydrogenase is pivotal in maintaining this balance.
Redox balance refers to the balance between oxidation (loss of electrons) and reduction (gain of electrons) reactions in the cell.
Hydrogenase helps by converting protons into hydrogen gas (H2) when there is an excess of electrons, thus preventing any disruption in the redox state.
The ability to convert excess protons into H2 allows the cell to manage the internal electron flow efficiently.
This process not only avoids the buildup of excess free radicals but also helps in regulating the cell’s oxidative state, ensuring smooth biochemical reactions.

metabolic flexibility

One of the outstanding features of Desulfovibrio is its metabolic flexibility.
This flexibility allows the bacteria to adapt to diverse and changing environmental conditions.
Hydrogenase enhances this adaptability by permitting the bacteria to utilize various substrates as electron donors.
Consequently, Desulfovibrio can switch between different energy sources based on availability.
This metabolic versatility ensures that the bacteria can continue their growth and energy production even when certain nutrients are scarce.
Having an enzyme like hydrogenase provides a competitive advantage in survival and colonization of varied ecological niches.
It optimizes their metabolic pathways, making them efficient and resilient microbial inhabitants.