Kingdom Monera

Characteristics, Classification, Microscopy Methods

Overview

Essentially, Monera is a biological kingdom that is made up of prokaryotes (particularly bacteria). As such, it’s composed of single-celled organisms that lack a true nucleus.

Based on previous classifications, kingdom Monera includes organisms known as Archaea (Archaebacteria) in addition to blue-green algae and Schizopyta (bacteria). However, further studies identified unique characteristics of Archaea that allowed them to be separated and identified as a distinct kingdom. 

Apart from some of the earliest modes of classification (e.g. Linnaeus 2 kingdoms (1735) and the Haeckel 3 kingdoms (1866)), kingdom Monera is recognized in most of the other classifications (e.g. two-empire kingdom system, five-kingdom system and the six-kingdom system) in one form or another. 

 

* Archaebacteria is composed of bacteria that are collectively known as extremophiles. This is because they are capable of surviving harsh environmental conditions.

* The term Archaebacteria comes from the Greek words meaning “ancient things/bacteria”.

* The word “Prokaryote” comes from the Greek words “Pro” which means before and “Karyon” that means kernel/nucleus- Before a nucleus.

* The word Monera is derived from the Greek word “Moneres” that means single.

 

Classification and Characteristics of Kingdom Monera

Several systems of classification were suggested between 1866 and 1977.

These include:

 

• Three kingdom classification system by Haeckel (1866)

• Four kingdom classification system by Copeland (1956)

• Five-kingdom classification system by Whittaker (1969)

• Six kingdom classification system by Woese (1977)

 

For this section, however, the five-kingdom classification system will be used.

 

Described in 1969 by Robert H. Whittaker, the 5 kingdom system classification consists of 5 major kingdoms that include:

 

 

* For the most part, the five-kingdom classification system described by Whittaker is based on the nutrition model, the structure of the cell, thallus organization, mode of reproduction as well as their phylogenetic relationships.

 

As the only kingdom that contains bacteria (which are prokaryotic), Monera is the sole prokaryotic kingdom in the five-kingdom classification system.

Generally, within the Whittaker (Five Kingdom Classification) system, kingdom Monera is divided into two major groups (subkingdoms), namely, Archaebacteria and Eubacteria. 

Archaebacteria in Kingdom Monera

As compared to eubacteria, archaebacteria are more primitive being the oldest organisms on earth. While they are also less common in comparison to eubacteria, archaebacteria are capable of surviving such extreme environmental conditions as hot springs and very salty and acidic environments etc.

Within this subkingdom, organisms can be classified/grouped on the basis of the environment in which they reside:

 

Methanogenic bacteria (methanogens) – Bacteria that can be found in the intestinal tract of animals as well as sewage matter. They are capable of producing methane in hypoxic conditions. 

Some examples of methanogenic bacteria include:

• Methanobrevibacter smithii

• Methanococcus maripaludis

• Methanobrevibacter ruminantium

 

Thermoacidophilic bacteria (thermoacidophiles) – These are bacteria that can be found living in hot springs. They are also capable of surviving in environmental conditions with very low pH. Thermoplasma Picrophilus is a good example of a thermoacidophiles.

 

Halophilic bacteria – This includes bacteria that can be found living in extremely salty conditions (e.g. bacteria found in the Dead Sea). 

Examples of halophilic bacteria include:

• Halomonas

• Chromohalobacter

• Halomonas elongata

• Halomonadaceae

 

As compared to other bacteria, Archaebacteria have a unique cell wall structure which allows them to survive harsh environmental conditions. They can also be found in less extreme environments (fresh and ocean waters and soil). 

Cell Structure of Archaea

According to a variety of studies, a majority of archaeal bacteria have been shown to possess flagella used for motility. Compared to the flagella found in other bacteria, archaeal flagella have been found to be more similar to type VI pili of bacteria. In general, they have been described as rotating structures with a filament.

Given that a majority of archaea are either chemotactic or phototactic in nature (or both), these structures, consisting of preproteins, allow them to move from one point to another in their respective environments. 

 

* For a majority of archaea found in extreme environments, glycosylation has been shown to be one of the main components of flagellins. As a result, it has been suggested to contribute to protein stability that allows the organisms to survive. 

 

The flagella of archaea also have the following functions:

 

• Swarming across surfaces

• Formation of biofilm connecting cells to each other: This may play a role in genetic transfer

Cannulae

Apart from flagella, some of the archaea have been shown to contain structures known as cannulae on their surface. These are hollow tubes consisting of various subunits of glycoprotein. Like several components of the flagella, these structures are also highly resistant to such extreme environmental conditions as heat.

For the most part, cannulae have been identified in newly formed cells. Given that no studies have found these structures to penetrate the cell cytoplasm (they have only been shown to enter the periplasmic region of cells), researchers have concluded that by connecting newly formed cells to each other, these structures allow for nutrient and, in some cases, genetic material between the cells. 

Pili

Pili have been identified in many archaea species across the globe. As is the case with flagella, pili of archaea have been shown to be different from those of other bacteria. Depending on the species, they also play a number of functions ranging from aggregation to motility.

For instance, in a study where Sulfolobus cells were exposed to UV light treatment, pili formation allowed for aggregation of the cells before conjugation occurred (the transfer of genetic material from a donor to recipient). 

While archaea and other bacteria share various characteristics with regards to the plasma membrane, the plasma membrane of archaea has a number of unique characteristics that contribute to their general characteristics.

In archaea, the glycerol linkage between the phospholipid head and side-chain has been shown to be of the L-isomeric form which is different from the D-isomeric form found in other bacteria and eukaryotes.

Also, the ether-linkage located between the glycerol and side chain in archaea provide better chemical stability to the membrane of these organisms which also contributes to their overall ability to survive extreme environmental conditions. 

With regards to the plasma membrane, some of the other unique characteristics include:

 

• Contain isoprenoid chains that may contain branching side chains

• Plasma membrane exist as monolayers 

As is the case with other bacteria, the cell wall of archaea also plays an important role in protecting the internal components of the cell from the environment. In addition, the cell wall also serves to withstand turgor pressure exerted against the plasma membrane.

While some archaea lack a cell wall, these structures vary from one species to another depending on their environment. Moreover, they display characteristics that are unique and different from the cell wall of other bacteria.

In some of the species, the cell wall has been shown to contain a proteinaceous S-layer. This, in some species, acts as the sole component of the cell wall. 

Although they lack peptidoglycan found in bacteria, some archaea possess pseudomurein, which has a similar chemical structure. Also, they contain N-acetylalosaminuronic acid that is linked to the N-acetylglucosamine thus increasing the overall strength of the structure.

Some of the other components of the cell wall in archaea include:

 

• Methanochondroitin

  – 

  Lattice structure that forms the protein sheath 

• Plasmids

  – Small DNA molecules consisting of between 5 and 100 genes

• Ribosome – spherical particles involved in protein synthesis
• Cytoskeleton – proteins involved in cell division as well as influencing the shape of the cell

Eubacteria in Kingdom Monera

Commonly referred to as “true bacteria” or simply “bacteria”, eubacteria is the more complex domain (described as a subkingdom in some books) of the kingdom Monera.

As compared to archaebacteria, members of eubacteria are more common and widely distributed in most habitats (water, soil, inside and on extracellular organisms, etc.) across the globe.

As members of the kingdom Monera, eubacteria are prokaryotes and thus do not have membrane-bound organelles. While some species exist as parasites that cause diseases to both plants and animals (including human beings), some bacteria are beneficial and are therefore used for food and drug production among many other uses. 

 

Given that all bacteria (except archaebacteria) fall under the domain/subkingdom eubacteria, they may be grouped into the following categories:

 

Also known as blue-green algae, cyanobacteria contain chlorophyll that allows them to manufacture their own food. As such, they, like plants, are photosynthetic autotrophs.

In nature, they may exist as unicellular, colonial, or filamentous in fresh or marine water. However, they can also be found in terrestrial environments where they use water, carbon dioxide, and solar energy to manufacture their own food. 

While they can manufacture food on their own, some species in this group also form symbiotic relationships with fungi thus forming lichens. In this mutualistic relationship, the bacteria provides organic nutrients that the fungi require while the fungi provides inorganic material as well as protection to the bacteria. 

 

* Cyanobacteria are the only prokaryotes capable of photosynthesis and oxygen production. 

 

With over 2,000 species in this division, cyanobacteria come in many shapes and sizes with varying cellular structures. Some of the species produce toxins in water as well as noxious blooms and are thus of significance in water quality management.

Some of the most popular cyanobacteria include:

 

• Mat-formers

• Bloom-formers

• Picocyanobacteria

 

* Apart from photosynthetic autotrophic bacteria, cyanobacteria also includes chemosynthetic autotrophic bacteria that convert inorganic molecules (e.g. nitrates and ammonia etc) to organic substances. As such, they obtain energy from the oxidation of inorganic molecules. 

Heterotrophic

Bacteria 

Heterotrophs are organisms that obtain energy by consuming organic material.

Unlike photosynthetic or chemosynthetic autotrophs, these organisms are unable to manufacture their own food/organic material and thus depend on organic material/food in their environments. Heterotrophic bacteria are abundant in nature with a majority existing as decomposers.

As such, they feed on dead plants and animals in their environment thus breaking them down. This contributes to soil humus that in turn contributes to proper plant development. These types of bacteria are collectively known as saprophytic bacteria.

Apart from heterotrophic bacteria found in the environment (terrestrial habitats etc), some of these bacteria are also part of the normal flora on human skin and do not generally cause harm. However, some are pathogens and cause diseases not only in human beings, but also in plants and animals. A good number of these bacteria depend on the host for their nutrition and thus exist as parasites. 

 

Heterotrophic bacteria may be divided into the following groups:

 

• Spirochetes

• Chlamydias

• Gram-positive bacteria

• Proteobacteria

• Gram-negative bacteria

See more on Gram positive and Gram negative bacteria

General Characteristic of Heterotrophic Bacteria

Although a few bacteria are large enough to be seen with the naked eye (e.g. Epulopiscium fishelsoni bacteria that can grow to about 600um in length), a majority of bacteria are microscopic and can only be observed with the use of a microscope. However, they vary in size, ranging from 100 to 200 nm in diameter.

These bacteria also vary in shape which has allowed them to be classified according to their general appearance. For instance, whereas some species are rod-shaped (bacillus), others are more spherical in shape (coccus). Other bacteria have more complex shapes including spirillum which are spiral-shaped and vibrios that look like curved rods. 

Depending on the species, these bacteria may exist as single cells, pairs or as colonies, etc. For instance, whereas staphylococci are cocci bacteria in clusters, streptobacilli are bacilli bacteria that occur in chain-form. The shape of heterotrophic bacteria also plays an important role in motility.

The shape of spirochaetes and vibrio bacteria (in addition to the presence of flagella) contribute to better mobility of these organisms in their environment. 

Different species of heterotrophic bacteria also depend on certain environmental conditions for their survival. As such, they can only thrive under certain conditions in their environment. These characteristics have also allowed bacteria to be classified on the basis of the conditions they require to grow and reproduce.

Whereas some bacteria need oxygen for normal cellular respiration (Bacillus subtilis and Azotobactor), others like Clostridium tetani thrive in very low oxygen during their vegetative phase.

Some of the other species are capable of switching from aerobic to anaerobic respiration depending on the presence or absence of oxygen in their environment. For instance, whereas facultative anaerobes can produce energy if oxygen is present, they can switch to anaerobic respiration in the absence of oxygen (energy is produced through fermentation). 

 

* While true bacteria are not extreme as is the case with archaebacteria, they are capable of forming spores that are resistant to harsh environmental conditions. This allows them to survive through such conditions.

Cell Surface Structures of Eubacteria

As previously mentioned, there are several differences between the cell surface of archaebacteria and eubacteria. Whereas the glycerol linkage between the phospholipid head and side-chain is of D-isomeric form in eubacteria, it is of L-isomeric form in archaebacteria.

However, eubacteria have ester-linked lipids present between glycerol and side chains compared to the ether-linkage that are found in archaebacteria. As with many other cells, the plasma membrane of eukaryotes (eubacteria) is characterized by lipid bilayers that separate the internal and external environments of the cells. 

A majority of eukaryotes also possess a cell wall. This is a semi-rigid structure that serves to protect and maintain the shape of cells. Typically, the cell wall of eubacteria is characterized by the presence of peptidoglycan that makes it possible to distinguish between Gram-positive and Gram-negative bacteria. 

To observe and study members of the Kingdom Monera, a number of microscopic techniques can be used. Whereas some of the techniques are used to study and differentiate the genetic material found in these organisms, some are simply used to study general morphology which also makes it possible to differentiate the different members of the kingdom. 

 

FISH (Fluorescent in Situ Hybridization)

Unlike microscopy techniques used to observe the general morphology of different types of bacteria, FISH is a molecular technique that can be used to detect the presence of given genetic elements of an organism making it possible to differentiate between various species. Generally, the technique largely depends on the hybridization of a probe with a fluorescent tag that is complementary to a given DNA sequence.

Here, the probe is applied to the sample under favorable conditions to allow for the attachment of the probe to the sequence of interest. The sample is then observed under the microscope (fluorescent microscope). Using this technique, it’s possible to differentiate the different species or archaebacteria as well as eubacteria based on their genetic material. 

 

* In fluorescence microscopy, fluorescent dyes are also used to identify given cellular components. For instance, using phalloidin, it is possible to identify the actin filaments of bacteria.

Thermo-Microscope (Phase-Contrast Microscope inside a Plexiglas Housing)

This is a technique that has been used to observe the swimming behavior of archaea. First, cells in a sample were transferred into glass capillaries (rectangular in shape). The capillaries were then sealed (both sides) and placed on an electrically heated stage on the microscope table. The thermo-microscope was then used for the purposes of analyzing the swimming behavior of the archaea.

 

* For this technique, heating the stage provided favorable conditions for M. thermoautotrophicus.

For bacteria referred to as “true bacteria” a variety of microscopic techniques can be used.

These include:

 

 

Return to Unicellular Organisms 

Return to Prokaryotes main page

Return to Bacteria main page 

Return from Monera to MicroscopeMaster home

References

Gina Hamilton. (2006). Kingdoms of Life: Monera. 

Johannes P. Schneider and Marek Basler. (2016). Shedding light on biology of bacterial cells. ncbi. 

Sandy Y. M. Ng, Behnam Zolghadr, Arnold J. M. Driessen, Sonja-Verena Albers, Ken F. Jarrell. (2008). Cell Surface Structures of Archaea. Journal of Bacteriology. 

 

 

Links

 

https://serc.carleton.edu/microbelife/research_methods/microscopy/fish.html

https://www.researchgate.net/publication/316617126_Difference_Between_Archaebacteria_and_Eubacteria

 

Te explicamos qué es el reino monera, el origen del término, sus características y clasificación. Cómo es su taxonomía y ejemplos.

¿Qué es el reino monera?

El reino monera es uno de los grandes grupos en que la biología clasifica a los seres vivos, como el reino animal, vegetal o fungi. Comprende las formas de vida más simples y primitivas que se conocen, que pueden ser muy diversas en su naturaleza, aunque presentan características celulares comunes: son unicelulares y procariotas.

El reino monera es anterior a todos los demás que existen pero aún hoy existen muchos interrogantes con respecto a la aparición en la Tierra de las células eucariótas, un hito clave en el desarrollo de los seres pluricelulares. Una de las ideas más aceptadas es la llamada Teoría de la endosimbiosis seriada, desarrollada por la bióloga estadounidense Lynn Margulis en 1967. Esta teoría propone que un par de organismos unicelulares pertenecientes al reino monera habrían desarrollado una simbiosis muy estrecha, que llevó a uno a formar parte del cuerpo mismo del otro, ocupándose de algunas funciones internas.

Hoy el término monera está en desuso. Se prefieren otros modelos de clasificación, como el propuesto por Carl Woese en los años 1970, que distingue tres dominios: Eukarya (que incluye a todos los organismos eucariotas), Archaea (arqueobacterias) y Bacteria (bacterias), siendo estos últimos dos lo que anteriormente formaban el reino monera, y los que agrupan entre ambos a todos los organismos procariotas.

Ver además: Célula animal

Origen del término monera

El término “monera” tiene sus raíces en el vocablo griego moneres (“simple”), y se ha usado a lo largo del tiempo, cambiado su significado específico. En principio fue propuesto por el naturalista y filósofo alemán Ernst Haeckel en 1866, que fue el primero en proponer una clasificación de la vida basada en el evolucionismo. Distinguió tres reinos: animal, vegetal y protista, reuniendo en el último a todas las formas de vida “simples” o “primitivas”, que no parecían tener un parentesco específico con los animales y las plantas, considerados “superiores”. Haeckel colocó a las microscópicas moneras o moneres en la base del árbol evolutivo y las clasificó dentro del reino protista.

Posteriormente, en los años 1920, el naturalista francés Édouard Pierre Chatton descubrió que las bacterias no poseen núcleo celular y, en función de este hallazgo, propuso la distinción y el uso de los términos procariontes y eucariontes en el mismo sentido que se utilizan actualmente, es decir, organismos sin y con núcleo celular respectivamente. A raíz de ello, en 1939, Fred Alexander Barkley empleó el término monera para referirse a un nuevo reino formado por el conjunto de todos los organismos procariotas, y que se dividía entre arqueófitos o Archeophyta (actuales cianobacterias) y esquizófitos o Schizophyta (bacterias).

Más adelante en la historia, en 1956, el biólogo estadounidense Herbert Copeland reorganizó los reinos de la vida en cuatro categorías: animales, plantas, protoctistas (donde estaban los eucariontes unicelulares y los de organización simple) y moneras (donde estaban los procariotas). A esta clasificación añadió el ecólogo estadounidense Robert Whittaker en 1969 el reino de los hongos (Fungi) y es esta última versión de cinco reinos, revisada en 2000, la que hoy en día aún figura en muchos textos de y cursos de Biología.

Sin embargo, si bien esta clasificación sigue siendo popularmente utilizada, el término monera ha desaparecido de la literatura técnica, luego de los cambios propuestos por el microbiólogo estadounidense Carl Woese, conocido como el creador de la nueva taxonomía molecular. En los años 1970, este científico descubrió que los procariontes encajaban en dos grupos distintos en función de su estructura, composición y genética molecular. Así, Woese propuso la reorganización de este grupo de organismos en dos taxones distintos, Archaea (o arqueas) y Bacteria (también llamadas Eubacterias), con la categoría nueva de dominio. El otro dominio, Eukarya, lo forman todos los organismos eucariontes, divididos en los cuatro reinos que ya se habían descrito: Protista, Animalia, Fungi y Plantae.

Características del reino monera

Las especies del reino monera pueden ser muy diversas en su morfología y hábitos de vida, pero tienen características mínimas de simpleza evolutiva y biológica que las unifican, tales como:

• Miden de 3 a 5 micrómetros. Se trata de los seres vivientes más pequeños que existen en el planeta.
• Son unicelulares y procariotas. Se trata de organismos unicelulares, o sea, células autónomas que no forman tejidos, ni colonias, ni organismos más complejos, y que además carecen de núcleo celular en donde repose su ADN.
• Sin orgánulos de ningún tipo. A diferencia de las células eucariotas, mucho más grandes y complejas a lo interior, las moneras son células sin “órganos internos” como mitocondrias o plastos, aunque sí poseen estructuras simples que cumplen procesos internos.
• Reproducción asexual. Los procesos de reproducción de las moneras no involucran la meiosis o producción de gametos (células sexuales), sino que implican la fusión binaria y otros procesos en que un individuo da origen a dos idénticos.
• ADN circular. El ADN de estas especies se encuentra suelto en el citoplasma y tiene circular en vez de doble hélice, siendo mucho más simple y pequeño.
• Nutrición. Muchas moneras son heterótrofas (saprófitas, parásitas o simbióticas), o sea, se alimentan de materia orgánica del medio ambiente; pero también pueden ser autótrofas (fotosintéticas o quimiosintéticas), aprovechando la luz solar o las reacciones químicas del entorno para fabricar su propio alimento.

Clasificación del reino monera

Las moneras abarcan tres grandes grupos, que son:

• Eubacterias. Su nombre significa “bacterias verdaderas” y representan las formas de vida celular más simples conocidas sobre la Tierra. Este grupo de organismos procariotas posee un único cromosoma y una pared celular rígida compuesta de peptidoglicano. Algunas bacterias son móviles y cuentan con flagelos que utilizan para desplazarse. Pueden presentar diversas formas y en función de este criterio pueden clasificarse en bacilos (forma de bastón), cocos (forma redonda), espirilos (forma de tirabuzón) y vibrios (forma de coma).
• Arqueobacterias. Este grupo de microorganismos procariontes comparten algunas características con las bacterias, como la falta de núcleo, pero sus diferencias, como la composición de su pared celular, las ubican en un taxón aparte. Las arqueobacterias se caracterizan por vivir en condiciones que imposibilitan la vida de otros seres vivos. Así, se las encuentra en hábitats extremos, donde sobreviven aprovechando los recursos químicos del medio: salinidad, calor, pH, etc. Se cree que son tan numerosas que componen el 20% de la biomasa terrestre.
• Cianobacterias. Conocidas como algas verde-azuladas, son los únicos organismos procariotas capaces de realizar la fotosíntesis oxigénica, aunque de una manera ligeramente distinta a la de las plantas. Son los seres procariotas de mayor tamaño: pueden alcanzar dimensiones de hasta 60 micrómetros. Su presencia en la mayoría de los hábitats les permite formar relaciones simbióticas con otras especies.

Taxonomía del reino monera

Este reino se subdividía inicialmente en dos: bacterias y arqueas, cada una con su propia subclasificación. Pero tras el descubrimiento del ADN ribosómico en los años 1980, se pudo establecer una nueva clasificación basada en cuatro grupos distintos:

• Mendosicutes, Arqueas o arqueobacterias. Arqueas significa “antiguas”, ya que inicialmente se suponían una especie de protobacterias. Es difícil clasificarlas ya que son realmente muy pequeñas, pero presentan rutas metabólicas y procesos internos mucho más semejantes a los eucariotas que a los demás procariotas tradicionales.
• Mollicutes, Tenericutes o micoplasmas. Son un tipo de bacterias mayormente parásitas, cuyo rasgo notorio es que carecen de la pared celular presente en la mayoría de las bacterias y que tienen una forma y un código genético de los más simples conocidos.
• Gracilicutes o bacterias gram negativas. Son un supergrupo de bacterias que integran los grupos Spirochaetes, Proteobacteria, Planctobacteria y Sphingobacteria. Se caracterizan por tener una pared celular muy delgada (que a veces incluso está ausente) compuesta de mureína y una doble membrana plasmática. Las características de su pared celular hacen que no sean susceptibles a la tinción de Gram, y de ahí su nombre.
• Firmicutes o bacterias gram positivas. Llamadas endobacterias, poseen una pared celular muy gruesa y forma de bacilo o de coco. En este grupo se hallan las bacterias gram positivas, que responden a la tintura de Gram adquiriendo color azul o violeta.

Importancia del reino monera

Los integrantes del reino monera fueron los primeros organismos que existieron cuando la vida se originó de un modo u otro en el planeta. Su simpleza les permitió surgir y sobrevivir en las hostiles condiciones iniciales de la Tierra, y aún hoy es posible hallar representantes de este grupo en hábitats donde otras formas de vida no pueden adaptarse ni subsistir. Desde este enfoque, estudiar a las moneras es intentar profundizar en el conocimiento sobre el origen mismo de la vida.

En la actualidad, se conoce una enorme cantidad de organismos pertenecientes al reino monera, incluyendo varios que pueden alojarse en animales, humanos y plantas. Dentro de este grupo, muchos son agentes infecciosos del ser humano, cuya comprensión permitirá combatir mejor enfermedades y salvar vidas. Por otra parte, muchos microorganismos clasificados en este reino son utilizados por los seres humanos en distintas industrias, como la farmaceútica (para producir antibióticos) o la alimenticia (en la producción de productos lácteos).

Finalmente, cabe mencionar la importancia del reino monera en el medio ambiente, en relación con su rol en las cadenas y redes tróficas. Muchas bacterias son descomponedoras y, por lo tanto, permiten que se complete el ciclo del carbono, devolviendo este elemento a su forma inorgánica. También existen otras fijadoras de nitrógeno o de oxígeno.

Ejemplos de moneras

Algunos ejemplos de integrantes del reino monera son las diversas bacterias conocidas por la humanidad, como la Escherichia coli, un bacilo gramnegativo que a menudo parasita el tracto digestivo humano, o el Clostridium tetani, una bacteria muy común en el suelo y en el tracto digestivo de los animales, que puede causar en el ser humano el tétano, una enfermedad letal, al ingresar a la sangre.

Puede servirte: Virus

Referencias