Microbiology of decomposition

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Decomposing pig showing signs of bloat and discoloration, a result of microbial proliferation within the body. Decomp pig.jpg
Decomposing pig showing signs of bloat and discoloration, a result of microbial proliferation within the body.

Microbiology of decomposition is the study of all microorganisms involved in decomposition, the chemical and physical processes during which organic matter is broken down and reduced to its original elements.

Contents

Decomposition microbiology can be divided between two fields of interest, namely the decomposition of plant materials and the decomposition of cadavers and carcasses.

The decomposition of plant materials is commonly studied in order to understand the cycling of carbon within a given environment and to understand the subsequent impacts on soil quality. Plant material decomposition is also often referred to as composting. The decomposition of cadavers and carcasses has become an important field of study within forensic taphonomy.

Decomposition microbiology of plant materials

The breakdown of vegetation is highly dependent on oxygen and moisture levels. During decomposition, microorganisms require oxygen for their respiration. If anaerobic conditions dominate the decomposition environment, microbial activity will be slow and thus decomposition will be slow. Appropriate moisture levels are required for microorganisms to proliferate and to actively decompose organic matter. In arid environments, bacteria and fungi dry out and are unable to take part in decomposition. In wet environments, anaerobic conditions will develop and decomposition can also be considerably slowed down. Decomposing microorganisms also require the appropriate plant substrates in order to achieve good levels of decomposition. This usually translates to having appropriate carbon to nitrogen ratios (C:N). The ideal composting carbon-to-nitrogen ratio is thought to be approximately 30:1. As in any microbial process, the decomposition of plant litter by microorganisms will also be dependent on temperature. For example, leaves on the ground will not undergo decomposition during the winter months where snow cover occurs as temperatures are too low to sustain microbial activities. [1]

Decomposition microbiology of cadavers and carcasses

The decomposition processes of cadavers and carcasses are studied within the field of forensic taphonomy in order to:

Decomposition microbiology as applied to forensic taphonomy can be divided into 2 groups of studies:

Microorganisms in the body

When considering cadavers and carcasses, putrefaction is the proliferation of microorganisms within the body following death and also encompasses the breakdown of tissues brought upon by the growth of bacteria. The first signs of putrefaction are usually the discolorations of the body which can vary between shades of green, blue, red or black depending on 1) where the color changes are observed and 2) how far along within the decomposition process the observation is made. This phenomenon is known as marbling. Discolorations are the results of bile pigments being released following an enzymatic attack of the liver, gallbladder and pancreas and the release of hemoglobin breakdown products. [2] Proliferation of bacteria throughout the body is accompanied with the production of considerable amounts of gases due to their capacities of fermentation. [3] As gases accumulate within the bodily cavities the body appears to swell as it enters the bloat stage of decomposition.

As oxygen is present within a body at the beginning of decomposition, aerobic bacteria flourish during the first stages of the process. As the microbial population increases, an accumulation of gases changes the environment into anaerobic conditions which is consequently followed by a change to anaerobic bacteria. [4] Gastro-intestinal bacteria are thought to be responsible for the majority of the putrefactive processes that occur in cadavers and carcasses. This can be in part attributed to the impressive concentrations of viable gastro-intestinal organisms and the metabolic capacities they possess allowing them to use an array of different nutrient sources. [5] Gastro-intestinal bacteria are also capable of migrating from the gut to any other region of the body by using the lymphatic system and blood vessels. [6] Furthermore, we know that coliform varieties of Staphylococcus are important members of the aerobic putrefactive bacteria and that members of the genus Clostridium make up a large part of anaerobic putrefactive bacteria. [7]

Proposed evolution of microorganisms within the body during decomposition. As oxygen is available at the beginning of decomposition, aerobic microorganisms flourish and quickly deplete the oxygen. Anaerobic bacteria can then proliferate in the body. Later in the decomposition process, fungi and bacteria from the environment will also become involved in the process. Microo scheme.jpg
Proposed evolution of microorganisms within the body during decomposition. As oxygen is available at the beginning of decomposition, aerobic microorganisms flourish and quickly deplete the oxygen. Anaerobic bacteria can then proliferate in the body. Later in the decomposition process, fungi and bacteria from the environment will also become involved in the process.

Microorganisms outside the body

Cadavers and carcasses are usually left to decompose in contact with soil whether through burial in a grave or if left to decompose on the soil surface. This allows microorganisms in the soil and air to come in contact with the body and to take part in the decomposition process. Soil microorganism communities also undergo changes as a result of decomposition fluids leaching in the environment. Cadavers and carcasses often show signs of fungal growth suggesting that fungi use the body as a source of nutrients.

The exact impacts that decomposition may have on surrounding soil microbial communities remains unclear as some studies have shown increases in microbial biomass following decomposition whereas other have seen decreases. It is likely that the survival of microorganisms throughout the decomposition process is highly dependent of a multitude of environmental factors including pH, temperature and moisture.

Skeletonized pig carcass showing the production of a cadaver decomposition island surrounding the remains as a result of leaching of decomposition fluids into the surrounding environment. Example of a pig carcass in the dry decay stage of decomposition.jpg
Skeletonized pig carcass showing the production of a cadaver decomposition island surrounding the remains as a result of leaching of decomposition fluids into the surrounding environment.

Decomposition fluids and soil microbiology

Decomposition fluids entering the soil represent an important influx of organic matter and can also contain a large microbial load of organisms from the body. [8] The area where the majority of the decomposition fluid leaches into the soil is often referred to as a cadaver decomposition island (CDI). [9] It has been observed that decomposition can have a favorable influence on the growth of plants due to increased fertility, a useful tool when trying to locate clandestine graves. [10] The changes in the concentration of nutrients can have lasting effects that are still seen years after a body or carcass has completely disappeared. [11] The influence that the surge in nutrients can have on the microorganisms and vegetation of a given site is not well understood but it appears that decomposition initially has an inhibitory effect for an initial stage before entering a second stage of increased growth.

Decomposition fungi

Fungal mycelia (white) on hoof of a deceased pig Fungihoof.JPG
Fungal mycelia (white) on hoof of a deceased pig

It is well known that fungi are heterotrophic for carbon compounds and almost all other nutrients they require. They must obtain these through saprophytic or parasitic associations with their hosts which implicates them in many decomposition processes.

Two major groups of fungi have been identified as being linked to cadaver decomposition:

Ammonia fungi are broken-down into two groups referred to as "early stage fungi" and "late stage fungi." Such a classification is possible due to the successions that are observed between the types of fungi that fruit in or around a burial environment. The progression between the two groups occurs following the release of nitrogenous products from a body in decomposition. Early stage fungi are described as being ascomycetes, deuteromycetes and saprophytic basidiomycetes whereas late stage fungi consisted of ectomycorrhizal basidiomycetes. [12]

Decomposition fungi as PMI estimators

Considering the number of forensic cases in which significant amounts of mycelia are observed is quite high, investigating cadaver associated mycota may prove valuable to the scientific community as they have much forensic potential.

Only one attempt at using fungi as a PMI marker in a forensic case has been published to date. [13] The study reported the presence of two types of fungi (Penicillium and Aspergillus) on a body found in a well in Japan and stated that they could estimate PMI as being approximately ten days based on the known growth cycles of the fungi in question.

See also

Related Research Articles

<span class="mw-page-title-main">Compost</span> Mixture used to improve soil fertility

Compost is a mixture of ingredients used as plant fertilizer and improve soil physical, chemical and biological properties. It is commonly prepared by decomposing plant, food waste, recycling organic materials and manure. The resulting mixture is rich in plant nutrients and beneficial organisms, such as bacteria, protozoa, nematodes and fungi. Compost improves soil fertility in gardens, landscaping, horticulture, urban agriculture, and organic farming, reducing dependency on commercial chemical fertilizers. The benefits of compost include providing nutrients to crops as fertilizer, acting as a soil conditioner, increasing the humus or humic acid contents of the soil, and introducing beneficial microbes of that help to suppress pathogens in the soil and reduce soil-borne diseases.

<span class="mw-page-title-main">Biodegradation</span> Decomposition by living organisms

Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegradation occurs under a specific set of circumstances.

<span class="mw-page-title-main">Mycelium</span> Vegetative part of a fungus

Mycelium is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrates. A typical single spore germinates into a monokaryotic mycelium, which cannot reproduce sexually; when two compatible monokaryotic mycelia join and form a dikaryotic mycelium, that mycelium may form fruiting bodies such as mushrooms. A mycelium may be minute, forming a colony that is too small to see, or may grow to span thousands of acres as in Armillaria.

<span class="mw-page-title-main">Decomposition</span> Process in which organic substances are broken down into simpler organic matter

Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is essential for recycling the finite matter that occupies physical space in the biosphere. Bodies of living organisms begin to decompose shortly after death. Animals, such as worms, also help decompose the organic materials. Organisms that do this are known as decomposers or detritivores. Although no two organisms decompose in the same way, they all undergo the same sequential stages of decomposition. The science which studies decomposition is generally referred to as taphonomy from the Greek word taphos, meaning tomb. Decomposition can also be a gradual process for organisms that have extended periods of dormancy.

<span class="mw-page-title-main">Taphonomy</span> Study of decomposition and fossilization of organisms

Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term taphonomy was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov to describe the study of the transition of remains, parts, or products of organisms from the biosphere to the lithosphere.

Putrefaction is the fifth stage of death, following pallor mortis, algor mortis, rigor mortis, and livor mortis. This process references the breaking down of a body of an animal, such as a human, post-mortem. In broad terms, it can be viewed as the decomposition of proteins, and the eventual breakdown of the cohesiveness between tissues, and the liquefaction of most organs. This is caused by the decomposition of organic matter by bacterial or fungal digestion, which causes the release of gases that infiltrate the body's tissues, and leads to the deterioration of the tissues and organs. The approximate time it takes putrefaction to occur is dependent on various factors. Internal factors that affect the rate of putrefaction include the age at which death has occurred, the overall structure and condition of the body, the cause of death, and external injuries arising before or after death. External factors include environmental temperature, moisture and air exposure, clothing, burial factors, and light exposure.

<span class="mw-page-title-main">Bioremediation</span> Process used to treat contaminated media such as water and soil

Bioremediation broadly refers to any process wherein a biological system, living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluents etc., in natural or artificial settings. The natural ability of organisms to adsorb, accumulate, and degrade common and emerging pollutants has attracted the use of biological resources in treatment of contaminated environment. In comparison to conventional physiochemical treatment methods which suffer serious drawbacks, bioremediation is sustainable, eco-friendly, cheap, and scalable. Most bioremediation is inadvertent, involving native organisms. Research on bioremediation is heavily focused on stimulating the process by inoculation of a polluted site with organisms or supplying nutrients to promote the growth. In principle, bioremediation could be used to reduce the impact of byproducts created from anthropogenic activities, such as industrialization and agricultural processes. Bioremediation could prove less expensive and more sustainable than other remediation alternatives.

<span class="mw-page-title-main">Post-mortem interval</span> Time that has elapsed since a person has died

The post-mortem interval (PMI) is the time that has elapsed since an individual's death. When the time of death is not known, the interval may be estimated, and so an approximate time of death established. Postmortem interval estimations can range from hours, to days or even years depending on the type of evidence present. There are standard medical and scientific techniques supporting such an estimation.

Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have come from the feces and remains of organisms such as plants and animals. Organic molecules can also be made by chemical reactions that do not involve life. Basic structures are created from cellulose, tannin, cutin, and lignin, along with other various proteins, lipids, and carbohydrates. Organic matter is very important in the movement of nutrients in the environment and plays a role in water retention on the surface of the planet.

An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments. Oligotrophs are characterized by slow growth, low rates of metabolism, and generally low population density. Oligotrophic environments are those that offer little to sustain life. These environments include deep oceanic sediments, caves, glacial and polar ice, deep subsurface soil, aquifers, ocean waters, and leached soils.

<span class="mw-page-title-main">Detritus</span> Dead particulate organic material

In biology, detritus is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts communities of microorganisms that colonize and decompose it. In terrestrial ecosystems it is present as leaf litter and other organic matter that is intermixed with soil, which is denominated "soil organic matter". The detritus of aquatic ecosystems is organic material that is suspended in the water and accumulates in depositions on the floor of the body of water; when this floor is a seabed, such a deposition is denominated "marine snow".

<span class="mw-page-title-main">Soil biology</span>

Soil biology is the study of microbial and faunal activity and ecology in soil. Soil life, soil biota, soil fauna, or edaphon is a collective term that encompasses all organisms that spend a significant portion of their life cycle within a soil profile, or at the soil-litter interface. These organisms include earthworms, nematodes, protozoa, fungi, bacteria, different arthropods, as well as some reptiles, and species of burrowing mammals like gophers, moles and prairie dogs. Soil biology plays a vital role in determining many soil characteristics. The decomposition of organic matter by soil organisms has an immense influence on soil fertility, plant growth, soil structure, and carbon storage. As a relatively new science, much remains unknown about soil biology and its effect on soil ecosystems.

Effective microorganisms (EM) are various blends of common predominantly anaerobic microorganisms in a carbohydrate-rich liquid carrier substrate of EM Research Organization, Inc.,

<span class="mw-page-title-main">Phototrophic biofilm</span> Microbial communities including microorganisms which use light as their energy source


Phototrophic biofilms are microbial communities generally comprising both phototrophic microorganisms, which use light as their energy source, and chemoheterotrophs. Thick laminated multilayered phototrophic biofilms are usually referred to as microbial mats or phototrophic mats. These organisms, which can be prokaryotic or eukaryotic organisms like bacteria, cyanobacteria, fungi, and microalgae, make up diverse microbial communities that are affixed in a mucous matrix, or film. These biofilms occur on contact surfaces in a range of terrestrial and aquatic environments. The formation of biofilms is a complex process and is dependent upon the availability of light as well as the relationships between the microorganisms. Biofilms serve a variety of roles in aquatic, terrestrial, and extreme environments; these roles include functions which are both beneficial and detrimental to the environment. In addition to these natural roles, phototrophic biofilms have also been adapted for applications such as crop production and protection, bioremediation, and wastewater treatment.

Forensic entomological decomposition is how insects decompose and what that means for timing and information in criminal investigations. Medicolegal entomology is a branch of forensic entomology that applies the study of insects to criminal investigations, and is commonly used in death investigations for estimating the post-mortem interval (PMI). One method of obtaining this estimate uses the time and pattern of arthropod colonization. This method will provide an estimation of the period of insect activity, which may or may not correlate exactly with the time of death. While insect successional data may not provide as accurate an estimate during the early stages of decomposition as developmental data, it is applicable for later decompositional stages and can be accurate for periods up to a few years.

<span class="mw-page-title-main">Carrion insects</span>

Carrion insects are those insects associated with decomposing remains. The processes of decomposition begin within a few minutes of death. Decomposing remains offer a temporary, changing site of concentrated resources which are exploited by a wide range of organisms, of which arthropods are often the first to arrive and the predominant exploitive group. However, not all arthropods found on or near decomposing remains will have an active role in the decay process.

Decomposition in animals is a process that begins immediately after death and involves the destruction of soft tissue, leaving behind skeletonized remains. The chemical process of decomposition is complex and involves the breakdown of soft tissue, as the body passes through the sequential stages of decomposition. Autolysis and putrefaction also play major roles in the disintegration of cells and tissues.

<span class="mw-page-title-main">Bokashi (horticulture)</span> Food waste processing technique involving fermentation

Bokashi is a process that converts food waste and similar organic matter into a soil amendment which adds nutrients and improves soil texture. It differs from traditional composting methods in several respects. The most important are:

The necrobiome has been defined as the community of species associated with decaying corpse remains. The process of decomposition is complex. Microbes decompose cadavers, but other organisms including fungi, nematodes, insects, and larger scavenger animals also contribute. Once the immune system is no longer active, microbes colonizing the intestines and lungs decompose their respective tissues and then travel throughout the body via the blood and lymphatic systems to break down other tissue and bone. During this process, gases are released as a by-product and accumulate, causing bloating. Eventually, the gases seep through the body's wounds and natural openings, providing a way for some microbes to exit from the inside of the cadaver and inhabit the outside. The microbial communities colonizing the internal organs of a cadaver are referred to as the thanatomicrobiome. The region outside of the cadaver that is exposed to the external environment is referred to as the epinecrotic portion of the necrobiome, and is especially important when determining the time and location of death for an individual. Different microbes play specific roles during each stage of the decomposition process. The microbes that will colonize the cadaver and the rate of their activity are determined by the cadaver itself and the cadaver's surrounding environmental conditions.

<span class="mw-page-title-main">Corpse decomposition</span>

Decomposition is the process in which the organs and complex molecules of animal and human bodies break down into simple organic matter over time. In vertebrates, five stages of decomposition are typically recognized: fresh, bloat, active decay, advanced decay, and dry/skeletonized. Knowing the different stages of decomposition can help investigators in determining the Post Mortem Interval (PMI). The rate of decomposition of human remains can vary due to environmental factors and other factors. Environmental factors include temperature, burning, humidity, and the availability of oxygen. Other factors include body size, clothing, and the cause of death.

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