Bacterial Production Of Hydrogen Sulfide

Hydrogen sulfide or sulfurated hydrogen is a chemical compound, mostly found in biogas, natural gas, and LPG. It is also found in marshy areas, volcanoes, and drainages. Hydrogen sulfide is known by several names such as hydrosulfuric acid, sulfane, sulfurated hydrogen, derived from its various properties. In common parlance it is also called rotten egg gas because of its pungent odor.

Properties

Hydrogen sulfide gas is highly combustible, toxic, odorless, and colorless. H2S is heavier than air, with a vapor density of 1.189 at an auto ignition temperature of 260 degrees Celsius. It forms a weak acid, with its water solubility being 2.9 g per 100 ml at 20 degrees Celsius. It is a highly explosive mixture when it is combined with air or oxygen. It burns with a blue flame to form SO2 and water. It also acts as a reducing agent and reacts with metal ions and alcohol to form metal sulfides and mercaptanes respectively.

Production

Hydrogen sulfide can also be produced by using solid organic compounds to heat sulfur and also by reducing sulfurated organic compounds with the help of hydrogen. Hydrogen sulfide is produced in the lab by heating ferrous sulfide along with a strong acid in a Kipp generator.

Bacterial Breakdown

The bacterial breakdown of organic matter in the absence of oxygen results in the formation of hydrogen sulfide or H2S. H2S can occur at any place where organic material at high temperature comes in contact with sulfur. Sulfate-reducing bacteria, which control the formation of sulfide, is a result of mutant strains of Thiobacillus denitrificans. Anaerobic bacteria of the genera Desulfovibrio and Desulfotomaculum use sulfates under anaerobic conditions to oxidize organic compounds. This reaction results in the production of energy and hydrogen sulfide in the form of a byproduct.

Self-Reducing Bacteria

SRB or self-reducing bacteria are heterotrophic organisms that make use of thiosulphate, sulphate, sulphite, and several other sulphur ions as terminal electron acceptors in their respiratory metabolism. An organic substrate, mostly a small chain acid like pyruvic acid, is formed by the fermentation of anaerobic bacteria acting on other complex organic substrates. This substrate is needed by the bacteria to form acetate.

Other Lifeforms in the Production of Hydrogen Sulfide

Plants and human beings also play a role in the production of hydrogen sulfide although in small quantities. Plants take in sulfate ion through the soil and convert it into plant protein, which in turn is consumed by animals to form animal protein. When these plants and animals die, it leads to decomposition of proteins, which in turn leads to the production of hydrogen sulfide as one of the byproducts. This process also involves a wide variety of actinomycetes, fungi, and bacteria heterotrophy Proteus vulgaris. Bacteria genera such as Chlorobiaceae and Chromtiacceae oxidize hydrogen sulfide photosynthetically into hydrogen sulfate. The human body also produces hydrogen sulfide, though in a meager quantity. It is used by the body as a signaling molecule, but more of it can be fatal and cause death or serious medical hazards. Thus, these are the few ways in which bacterial production of hydrogen sulfide takes place.

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