HETEROTROPHIC BACTERIA: CHARACTERISTICS AND EXAMPLES OF SPECIES - BIOLOGY - 2024

The heterotrophic bacteria, also called organotrofas are microorganisms that synthesize their own biomolecules from complex organic compounds carbonaceous but may capture different inorganic elements carbon. Some need to parasitize higher organisms in order to survive.

Heterotrophic bacteria are classified into photoheterotrophs and chemoheterotrophs. Both use organic compounds as a source of carbon, but differ in that the former use light as an energy source and the latter use chemical energy.

Image on the left: cycle of heteotrophic and autotrophic bacteria edited. Image on the right: Illustrative representation of heterotrophic bacteria. Source: Left image: Auto-and_heterotrophs.svg: Mikael Häggströmderivative work: Leptictidium / Right image: Pixabay. com

Heterotrophic bacteria are present in numerous ecosystems, such as soils, water, marine muddy snow, among others, participating in the ecological balance. They can also be found parasitizing higher organisms, such as plants, animals or humans, either as pathogens or as opportunists in a symbiotic relationship.

Characteristics of heterotrophic bacteria

It has been observed in nature that the existence of various types of bacteria makes the life of ecosystems possible, since the products generated by one are used by others in a chain. These bacteria are strategically distributed, almost always stratified.

For example, it has been seen that aerobic heterotrophic bacteria often appear together with cyanobacteria (photoautotrophic bacteria that release oxygen).

In this sense, aerobic heterotrophs and aerobic autotrophs can use oxygen, in turn creating anaerobic conditions in the deeper layers where anaerobic bacteria are found.

Depending on characteristics such as the type of fuel they use to survive, heterotrophic bacteria can be classified into different groups.

Sulforeductase bacteria

They are bacteria that under anaerobic conditions are capable of reducing sulfate (salt or esters of sulfuric acid) without assimilating it. They only use it as the final electron acceptor in the respiratory chain.

These bacteria help in the degradation of organic matter and are found in various ecological niches such as fresh waters, sewer waters, salt waters, hot springs, and geothermal areas. Also in sulfur deposits, oil and gas wells, as well as in the intestines of mammals and insects.

Hydrolase bacteria

They are anaerobic bacteria that break down organic polymers (cellulose and hemicellulose) into small molecules so that they can be absorbed by cell membranes. To do this, they have a system of enzymes called hydrolases (endocellulase, excocellulase and cellobiases).

After hydrolysis, various organic acids are formed such as lactic acid, propionic acid, acetic acid, butanol, ethanol, and acetone. These are then converted into methane gas.

Putrefactive bacteria

They are bacteria that participate in the catabolic degradation of nitrogenous compounds under anaerobic conditions, with the production of compounds with an unpleasant odor, from which their name (putrefactive) arises. This process generates the carbon and nitrogen they need for their development.

Non-sulfur red bacteria of the family

These bacteria are characterized by being straight, motile bacilli with a polar flagellum. They are facultative anaerobes: in anaerobiosis they carry out the photosynthesis process, but in aerobiosis they do not.

These bacteria photoassimilate a great diversity of organic compounds such as sugars, organic acids, amino acids, alcohols, fatty acids and aromatic compounds.

Green non-sulfurous anoxygenic bacteria

They are filamentous bacteria that can develop as photoautotrophs, chemohetrophies, or photoheterotrophs.

Strict aerobic and facultative anaerobic bacteria

Here enter various species that can be part of the usual microbiota of higher organisms, or act as pathogens of these.

Differences from autotrophic bacteria

Lifestyle

Both chemoheterotrophic and chemoautotrophic bacteria use chemical energy to live. However, they differ in that chemoheterotrophs are dependent organisms, since they need to parasitize other higher organisms to obtain the organic compounds necessary for their development.

This characteristic differentiates them from chemoautotrophic bacteria, which are totally free-living organisms (saprophytes), which take simple inorganic compounds from the environment to perform their vital functions.

For their part, photoheterotrophs and photoautotrophs are similar in that both use sunlight to convert it into chemical energy, but they differ in that photoheterotrophs assimilate organic compounds and photoautotrophs do so with inorganic compounds.

Habitat

On the other hand, chemoheterotrophic bacteria differ from chemoautotrophs in the habitat where they develop.

Chemoheterotrophic bacteria generally parasitize higher organisms to live. On the other hand, chemoautotrophic bacteria can withstand extreme environmental conditions.

In these environments, chemoautotrophic bacteria get the inorganic elements they need to live, substances that are generally toxic to other microorganisms. These bacteria oxidize these compounds and turn them into more environmentally friendly substances.

Nutrition

Heterotrophic bacteria only assimilate complex organic compounds already preformed to be able to synthesize the biomolecules necessary for their development. One of the carbon sources most used by these bacteria is glucose.

In contrast, autotrophic bacteria simply need water, inorganic salts, and carbon dioxide to get their nutrients. That is, from simple inorganic compounds they can synthesize organic compounds.

However, although heterotrophic bacteria do not use carbon dioxide as a carbon source, nor as the last electron acceptor, on some occasions they can use it in small amounts to carry out carboxylations in certain anabolic and catabolic pathways.

Microscopic study

In some ecosystems, samples can be taken to study the population of photoautotrophic and photoheterotrophic bacteria. For this, the technique of microscopy based on epifluorescence is used: Fluorochrome such as primulin and excitation filters for blue and ultraviolet light are used.

Heterotrophic bacteria do not stain with this technique, while autotrophs take on a bright whitish blue color, also showing the auto-fluorescence of the bacteriochlorophyll. The heterotrophic count is obtained by subtracting the total count of bacteria minus the autotrophs.

Disease production

In this sense, the bacteria that cause diseases in humans, animals and plants belong to the group of chemoheterotrophic bacteria.

Autotrophic bacteria are saprophytic and do not cause disease in humans, because they do not need to parasitize higher organisms to live.

Examples of heterotrophic bacteria species

Photoheterotrophs

The bacteria belonging to this group are always photosynthetic, since the rest of the microorganisms that share this classification are eukaryotic algae.

Sulfur bacteria are generally photoautotrophic, but can sometimes grow photoheterotrophically. However, they will always require small amounts of inorganic material (H ₂ S), whereas non-sulfurous ones are photoheterotrophic.

Among the photoheterotrophic bacteria we find the non-sulphorous red bacteria, such as the bacteria of the Bradyrhizobiaceae family, genus Rhodopseudomonas.

On the other hand, there are non-sulfurous green bacteria, as well as heliobacteria.

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They are facultative chemoautotrophs, that is, they normally use molecular hydrogen as an energy source to produce organic matter, but they are also capable of using a certain number of organic compounds for the same purpose.

Chemoheterotrophs

Chemoheterotrophic bacteria involved in nitrogen fixation

Bacteria of the family Frankiaceae, group Rhizobiaceae and the genera Azotobacter, Enterobacter, Klebsiella and Clostridium. These microorganisms participate in the fixation of elemental nitrogen.

Most can do this independently, but some need to establish symbiotic relationships with rhizobiaceae and legumes.

This process helps soil renewal, converting elemental nitrogen into nitrates and ammonia, which are beneficial as long as the latter are in low concentrations in the soil.

Nitrate and ammonium can then be absorbed by plants, such that these bacteria are extremely important in nature. Rhizobia are the bacteria most used in agriculture, and are part of biofertilizers.

Chemoheterotrophic bacteria that participate in the hydrolysis and acidogenesis processes of organic matter

Putrefactive Chemoheterotrophic Bacteria

In this category are species of the genus Clostridium: C. botulinum, C. perfringens, C. sporongenes, C. tetani and C. tetanomorphum. Likewise, some species of the genera Fusobacterium, Streptococcus, Micrococcus and Proteus are also putrefactive.

Facultative aerobic and anaerobic chemoheterotrophic bacteria

Here are found all the bacteria that cause infectious diseases in man and animals. Also those that are part of the usual microbiota.

Examples: Streptococaceae, Staphylococaceae, Enterobacteriaceae, Mycobacteriaceae, Pasteurellaceae, Neisseriaceae, Pseudomonadaceae families, among many others.

References

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