GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

7. SYSTEMATICS OF PROKARYOTES

7.5. CHARACTERISTICS OF TAXA ACCORDING TO THE NINTH EDITION OF BERGEY'S MANUAL OF SYSTEMATIC BACTERIOLOGY

7.5.2. Phylum Firmicutes

This group comprises prokaryotes with a Gram-positive Cell wall Structure; the Gram stain reaction is typically (though not always) positive. Cell Morphology can be spherical, rod-shaped, or filamentous, with rods and filaments sometimes exhibiting branching. Reproduction occurs via binary fission. Some species form resting stages as spores (endospores, or spores formed on hyphae or within sporangia). Most species are non-motile; motile forms possess flagella. These are non-photosynthetic organisms, generally chemoheterotrophs, and include aerobes, anaerobes, facultative anaerobes, and microaerophiles. This group encompasses simple asporogenous and spore-forming Bacteria, as well as actinomycetes and related organisms. They are divided into two classes:

Firmibacteria (comprising three sections, nos. 17-19);

Thallobacteria (comprising one section, no. 20).

Class Firmibacteria

Section 17. Gram-Positive Cocci. Chemoorganotrophic, mesophilic, Gram-positive, non-spore-forming cocci, classified as follows:

1) aerobic cocci occurring in pairs, clusters, or tetrads. Catalase-positive. Contain Cytochromes. Cell walls lack Teichoic Acids. Carbohydrate Fermentation is frequently absent or weakly expressed (family Micrococcaceae);

2) facultatively anaerobic or microaerophilic cocci occurring in pairs, chains, clusters, or tetrads. The presence of catalase, cytochromes, and cell-wall teichoic acids is variable (family Streptococcaceae);

3) strictly anaerobic cocci occurring in pairs, chains, tetrads, or cubic packets. Cytochromes are absent. Catalase test results are generally negative, although weak or pseudocatalase activity is occasionally observed (family Peptococcaceae).

Taxonomy. These bacteria are grouped into three families: Micrococcaceae (genera Micrococcus, Staphylococcus, Planococcus); Streptococcaceae (genera Streptococcus, Pediococcus, Aerococcus, Gemella, Leuconostoc); Peptococcaceae (genera Peptococcus, Ruminococcus, Peptostreptococcus, Sarcina). In Bergey's Manual of Determinative Bacteriology (1997), this group consists of 24 genera, more than half of which were not included in Bergey's Manual of Systematic Bacteriology as they were first described after its publication.

Characteristics of Representatives. Bacteria of the family Micrococcaceae are aerobes. They are cocci that divide in more than one plane. Chemoorganoheterotrophs. Motile or non-motile. They inhabit soils, fresh waters, Human and Animal Skin (genus Micrococcus), Skin glands and mucous membranes of warm-blooded animals and humans (genus Staphylococcus), and sea Water (genus Planococcus). They are predominantly Saprophytes, though pathogenic species exist (Staphylococcus aureus causes boils, purulent infections, and even Sepsis).

Classification of the genera within the family Streptococcaceae is based on morphological features and fermentation products: bacteria of the genera Streptococcus, Pediococcus, and Aerococcus ferment glucose with The production of lactic acid, i.e., they are homofermentative. Bacteria of the genus Leuconostoc are heterofermentative, because glucose fermentation yields not only lactic acid but also ethanol, acetic acid, and CO₂. They are found in soils, air, water, milk and dairy products (Streptococcus lactis, Streptococcus cremoris), fermented vegetables, and other food products. They can cause food spoilage (sugar syrup —

Leuconostoc mesenteroides, beer — Pediococcus). They act as parasites of mammals (Gemella, Streptococcus). Streptococci are particularly pathogenic, causing a range of human diseases (lymphadenitis, abscesses, pulmonary and renal infections, etc.).

The family Peptococcaceae comprises anaerobic, non-motile cocci. During fermentation, they produce CO₂, H₂, lower Fatty acids, succinate, and ethanol. Lactic acid is not the primary fermentation product. They are mainly saprophytes and inhabitants of soil (Sarcina), The surface of cereal grains, the Oral Cavity and respiratory tract of humans and animals (Peptococcus), and the rumen of ruminants (Ruminococcus). Pathogenic species also occur (Peptostreptococcus).

Section 18. Endospore-Forming Rods and Cocci. Bacteria capable of forming heat-resistant endospores. The most reliable test for detecting endospores is heating at 70-80°C for 10 min followed by cultivation under favorable conditions. They are most commonly motile rods or filaments, though one genus is represented by motile cocci (arranged in tetrads or cubic packets). Mostly Gram-positive, particularly in young cultures, though members of a single genus are Gram-negative. Obligate aerobes, facultative anaerobes, microaerophiles, or strict anaerobes. Chemoorganotrophs. In one genus of anaerobic bacteria, Anaerobic Respiration utilizes sulfate as the terminal electron acceptor.

Taxonomy. These bacteria are grouped into a single family, Bacillaceae, which comprises five genera (Bacillus, Sporolactobacillus, Clostridium, Sporosarcina, Desulfotomaculum). In Bergey's Manual of Determinative Bacteriology (1997), this group consists of 10 genera, meaning five new genera (Amphibacillus, Oscillospira, Sporohalobacter, Sulfobacillus, Syntrophospora) have been described since the publication of Bergey's Manual of Systematic Bacteriology.

Characteristics of Representatives. This group of bacteria is characterized by a wide diversity of properties. Notable Examples include butyric acid bacteria (Clostridium butyricum), acetone-butanol bacteria (Clostridium acetobutyricum), ureolytic bacteria (Sporosarcina ureae), atmospheric nitrogen fixers (Clostridium pasteurianum), as well as producers of Antibiotics, Enzymes, Amino Acids, and toxins. All of these biologically active compounds are produced by members of the genus Bacillus. The number of antibiotics produced by bacteria of this genus approaches 200, a figure surpassed only by the streptomycetes. The most prolific species is Bacillus subtilis, for which over 70 different antibiotics have been described. Approximately 30 antibiotics are produced by strains of Bacillus brevis. The most important antibiotics include polymyxin, bacitracin, gramicidin S, and subtilin. Bacilli exhibit amylolytic, pectinolytic, lipolytic, cellulolytic, and proteolytic activities. Live cultures of bacilli form The basis of Probiotics—therapeutic and prophylactic biological products endowed with antimicrobial and immunomodulatory properties. It has been established that Bacillus subtilis induces the production of type II interferon. The interferonogenic capacity of bacilli is attributed to their production of extracellular Lectins.

Bacteria of this group inhabit soils, bottom sediments, mud, and fresh and saline water bodies. While predominantly saprophytic, they include parasitic and highly pathogenic species, such as clostridia that cause gas gangrene and botulism.

Section 19. Asenspory Gram-Positive Rod-Shaped Bacteria. Straight or Curved Rods, non-motile (with a few motile exceptions), facultative or obligate anaerobes.

Taxonomy. Bacteria of this group are united into a single family, Lactobacillaceae, represented by the single genus Lactobacillus. The genus Caryophanon, whose systematic position remains uncertain, is also assigned to this family. In Bergey's Manual of Determinative Bacteriology (1997), this bacterial group is significantly expanded and represented by eight genera, which are divided into three main groups based on physiological characteristics.

Characteristics of Representatives. Inhabitants of plants, milk and dairy products, beer, pickles, marinades, and the digestive tract of humans and warm-blooded animals. They are saprophytes, with the exception of those involved in dental caries. Lactic acid is the primary fermentation product, which is why these bacteria are termed "lactic acid bacteria".

Class Thallobacteria

Part 20. Actinomycetes and Related Organisms. Actinomycetes are Gram-positive bacteria that form branched filaments or hyphae resembling a mycelium (both aerial and substrate mycelia). The mycelium may be stable or fragment into rod-shaped and coccoid elements. When the mycelium remains intact, spores are produced for reproduction. These spores can form directly on aerial hyphae (sporophores), from which conidia are abaxialized, or within sporangia. Some representatives produce flagellated (motile) spores. When present, motility in actinomycetes is mediated by flagella. Almost all are aerobes. Actinomycetes derive their name from the first described species, Actinomyces bovis (meaning "ray fungus"), which causes actinomycosis, a disease affecting cattle. They are chemoheterotrophs utilizing diverse Energy Sources, including complex polymers. Genera are distinguished by morphological features as well as the presence or absence of specific cell wall biomarker components. Related organisms include coryneform and propionic acid bacteria.

Taxonomy. The grouping of these bacteria into genera and families is presented in Table 7.2. In the Bergey's Manual of Determinative Bacteriology (1997), information on this bacterial group is significantly expanded. Mycobacteria are classified into a separate group (No. 21). Actinomycetes are represented across eight groups (Nos. 22–29). Data concerning coryneform and propionic acid bacteria are discussed separately (Group No. 20).

Table 7.2.

Part 20. Actinomycetes and Related Organisms

Let us examine the characteristics of these bacterial groups according to this publication.

Coryneforms (Group 20). Coryneform bacteria are Gram-positive, rod-shaped forms prone to morphological variation, producing club-shaped, slightly branched Cells that often arrange at angles to form V- or Y-like configurations. They may also appear as irregular rods transitioning into coccoid forms (exhibiting a characteristic coccus–rod–coccus cycle). Most are non-motile, non-acid-fast chemoorganoheterotrophs, predominantly obligate aerobes, though facultative anaerobes do exist. Bacteria of the genus Corynebacterium are aerobic organotrophs. They inhabit soil, water, and air, and several species are pathogens of plants, animals, and humans (for example, the CAUSATIVE AGENT OF diphtheria, Corynebacterium diphtheriae). Arthrobacters inhabit soil, where they participate in ammonification, nitrification, and MOLECULAR Nitrogen Fixation, and degrade plastics, herbicides, fungicides, and mercury-containing compounds. Bacteria of the genus Cellulomonas degrade Cellulose; their cell walls lack both meso-diaminopimelic acid and arabinose.

Anaerobic microorganisms in this group are represented by organotrophic, non-spore-forming bacteria: butyric acid-producing Eubacterium and Butyrivibrio, homoacetogenic Acetobacterium, lactic acid-producing Bifidobacterium, propionic acid-producing Propionibacterium, and thermophilic Thermoanaerobacter, all of which carry out various Types of fermentation accompanied by H₂ evolution and the production of diverse fatty acids.

Mycobacteria (Group 21). This group comprises acid-fast, aerobic, non-motile, organotrophic rods of the genus Mycobacterium that do not form spores. They are characterized by slow growth (from 2 to 40 days) and acid-fastness (upon staining, they resist decolorization by acidified alcohol or strong mineral acids). Acid-fastness is attributed to the presence of mycolic acids containing 78–95 carbon atoms in their cell walls. Only long-chain mycolic acids impart acid-fastness to the cells. It should be noted that mycolic acids are also present in The Cell walls of coryneforms (genus Corynebacterium) and nocardiae (genus Nocardia), but their carbon chains are shorter (coryneform mycolic acids contain 32–36 carbon atoms, and those of nocardiae contain 48–58), rendering these bacteria non-acid-fast. They stain poorly with the Gram stain. Occasionally, they form branching filaments. An aerial mycelium is not formed. Most are saprophytes, but some are human pathogens (such as the tuberculosis bacterium). They inhabit soil, water, and animal Tissues.

Nocardioforms (Group 22). This group includes Gram-positive bacteria prone to forming branched structures and a poorly developed mycelium. A typical genus of the group is Nocardia. Despite their name, organotrophic bacteria of the genus Rhodococcus have nothing in common with purple non-sulfur bacteria. They are relatively slow-growing aerobes capable of efficiently utilizing petroleum Hydrocarbons.

Geodermatophilaceae and Frankiae (Group 23). These are regarded as actinomycetes that do not form a mycelium. Genera include Dermatophilus, Geodermatophilus, and Frankia. They are aerobic organotrophs. Frankia is a nitrogen-fixing symbiont of alder that forms ROOT nodules (similar to rhizobia). They are characterized by the presence of a typical aerial mycelium bearing sporangia divided into numerous spores.

Actinoplanes (Group 24). These are aquatic actinomycetes that form well-developed substrate and aerial mycelia. Spores are produced within sac-like sporangia, where they tolerate desiccation. Upon rehydration, however, the spores are released as motile, flagellated cells. Genera include Actinoplanes and Dactylosporangium.

Streptomycetes (Group 25). These are the organisms to which the common name "actinomycetes" originally became attached. They form a well-developed mycelium and reproduce via conidia. They share a structural Organization similar to that of Fungi, but with thinner prokaryotic hyphae containing multiple nucleoids that are not always partitioned into distinct cells. Primarily soil organisms, they are adapted to relatively arid conditions. They exhibit high hydrolytic activity toward various polymers. Many streptomycetes assimilate cellulose, Chitin, and other recalcitrant natural substances. The mycelium is differentiated into a substrate mycelium and an aerial mycelium, which serves a reproductive function. Conidiospores act simultaneously as reproductive Organs and resting stages. Streptomycetes are notable producers of antibiotics (such as streptomycin, chloromycetin, aureomycin, and Tetracyclines). Genera include Streptomyces (over 500 species), Streptoverticillium, Intrasporangium, Kineosporia, and Sporichthya.

Maduromycetes or oligosporous actinomycetes (Group 26). These share the same mycelial structure as other actinomycetes, but, unlike them, produce a low number of conidia.

The genera are distinguished primarily by the shape of their conidiophores. Genera include Actinomadura, Microbispora, Planomonospora, Microtetraspora, Spirillospora, and Streptosporangium.

Thermoactinomycetes (Groups 27 and 28). Distinguished by their moderate thermophily. Genera include Thermoactinomyces, Thermomonospora, Actinosynnema, Nocardiopsis, and Streptoalloteichus.

Other genera (Group 29). These form an aerial mycelium bearing spore chains. Genera include Glycomyces, Kitasatosporia, and Saccharothrix.