Other Bacterial Groups

Bacteroides and Flavobacterium

Bacteroides and Flavobacterium are both Gram-negative bacteria that can be either motile or non-motile.

Learning Objectives

Describe the role of Bacteroides in the normal flora of the human gastrointestinal tract and the role of Flavobacterium in causing disease in freshwater fish

Key Takeaways

Key Points

  • Bacteroides are characterized by their mutualistic behavior and are typically present in the gastrointestinal tract of mammals to function as normal flora.
  • Bacteroides are capable of breaking down and processing large complex molecules within the intestine.
  • Flavobacterium are found in both soil and fresh water environments. Pathogenic strains of Flavobacterium can infect fish such as salmonids and trouts.

Key Terms

  • mutualistic: Mutually beneficial.
  • normal flora: The aggregate of microorganisms that reside on the surface and in deep layers of skin, in the saliva and oral mucosa, in the conjunctiva, and in the gastrointestinal tracts. Also known as human microbiota.

Bacteroides include a specific genus of gram-negative bacillus bacteria. This genus of bacteria is characterized by their sphingolipid based membranes and are typically non-endospore forming and anaerobic. The bacteroides are further characterized as mutualistic and have been identified in the mammalian gastrointestinal system. The ability of the bacteroides to function in an anaerobic environment allow them to reside in the abdominal cavity in aerotolerant conditions. The presence of bacteroides in the normal flora of mammals is indicative of its role in processing complex molecules to simpler ones that can be utilized by the host. The energy sources for the bacteroides are typically derived from the host. The role of bacteroides in the normal flora extends beyond their ability to breakdown larger complex molecules and can display protective function. The bacteroides are able to benefit the host by preventing infection by potential pathogens that may colonize and infect the gut as well. Due to the abundancy of the bacteroides within the gastrointestinal system, bacteroides constitute a significant portion of the fecal bacterial population.

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Bacteroides biacutus: An image of Bacteroides biacutus, an anaerobic bacterium present within the gastrointestinal tract.

Flavobacterium include a specific genus of gram-negative bacteria that are characterized by their presence in soil and fresh water environments. Flavobacterium can be either non-motile or motile and are rod-shaped. To date, there are 10 established species of flavobacterium and several new proposed species. The flavbacterium are characterized by their ability to cause disease in freshwater fish such as salmon and rainbow trouts. For example, the species Flavobacterium psychrophilum is responsible for causing Bacterial Cold Water Disease (BCWD) on salmonids and Rainbow Trout Fry Disease (RTFS) on rainbow trouts. The species Flavobacterium branchiophilum causes the Bacterial Gill Disease (BGD) on trouts.

Acidobacteria

Acidobacteria are a newly formed phylum of bacteria that are physiologically diverse and abundant in soil environments.

Learning Objectives

Discuss the advantages that Acidobacteria have developed due to their ability to thrive in acidic conditions

Key Takeaways

Key Points

  • Many acidobacteria can be classified as acidophilic organisms because they are able to thrive and reside within highly acidic environments.
  • The acidobacteria that are considered to be acidophilic have developed efficient and effective mechanisms to pump out protons to ensure their intracellular environments remains at a neutral pH.
  • It is hypothesized that acidobacteria play a major role in the ecosystem based on their abundance in soil.

Key Terms

  • acidophilic: Being an acidophile.

Members of Acidobacteria are physiologically diverse. They were first recognized as a novel division in 1997. The members of this phylum are acidophilic, physiologically diverse, and are ubiquitous in soils. The Phylum can be further broken down in Class Acidobacteria with Order Acidobacteriales and Class Solibacteres with Order Solibacterales.

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Acdiobacterium: An image of an Acidobacteria.

Acidophilic organisms are capable of thriving under highly acidic conditions. The ability to thrive under acidic conditions has promoted the evolution of highly efficient and effective mechanisms that lend them protection in these environments. For example, most acidophiles are able to pump protons out of the intracellular space to maintain a neutral pH within the cytoplasm. The mechanisms used to pump protons out are quick and effective. This is advantageous as the intracellular proteins are not required to develop tolerance against highly acidic conditions. However, not all members of this phylum are considered to be acidophilic.

Since they have only recently been discovered and the large majority have not been cultured, the ecology and metabolism of these bacteria is not well understood. However, these bacteria may be an important contributor to ecosystems, since they are particularly abundant within soils. The first species of this phylum, Acidobacterium capsulatum, was discovered in 1991. Other notable species are Holophaga foetida, Geothrix fermentans, Acanthopleuribacter pedis, and Bryobacter aggregatus.

Cytophaga and Relatives

Cytophaga are a type of bacteria characterized as Gram-negative, rod shaped bacteria that utilize a gliding mechanism for locomotion.

Learning Objectives

Describe the unique form of locomotion for Cytophaga

Key Takeaways

Key Points

  • Cytophaga are commonly associated with infections found on fish as a result of abnormal water temperatures that promote growth.
  • Cytophaga columnaris is responsible for columnaris disease in salmonid fish in abnormally high water temperatures and result in lesion and ulcerations on the gill.
  • Cytophaga psychrophila is responsible for the cold water disease in trout and results in skin lesions and occurs in subnormal water temperatures.

Key Terms

  • myxobacteria: A type of bacteria known as the “slime bacteria” that reside in soil and feed on insoluble organic matter.
  • columnaris: A disease characterized by the presence of ulcerations on the skin and the development of fungus-like patches on the gill filaments.

Cytophaga represent gram-negative, gliding, rod-shaped bacteria. The bacterial gliding is a form of locomotion utilized by Cytophaga that allows the bacteria to move under its own power. In this specific type of locomotion, the exact mechanisms are unknown, but it is known that this process does not require a flagella. However, a few mechanisms have been partially identified in certain species that utilize the gliding locomotion and these include the use of a type IV pili, the use of focal adhesion complexes distributed through the body, and the use of a polysaccharide slime that is ejected from one the ends of the body. Gliding can also be found in bacteria that are categorized as cyanobacteria and myxobacteria.

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Columnaris disease: An image of a chinook salmon that has been infected with Cytophaga columnaris and has lesions and ulcerations on the gill.

Cytophaga include the following species: Cytophaga columnaris, Cytophaga johnsonae, and Cytophaga psychrophila. The Cytophaga columnaris, also referred to as Flavobacterium columnare or Bacillus columnaris, are responsible for the columnaris disease in salmonid fish. Columnaris disease is characterized by the presence of ulcerations on the skin and the development of fungus-like patches on the gill filaments. This disease is highly contagious and fatal due to the damage of the gills. The Cytophaga johnsonae, or Flavobacterium johnsonae, are associated with false columnaris disease which is similar to columnaris disease and characterized by the presence of damage at the gills. Lastly, the species Cytophaga psychrophila, or Flavobacterium psychrophilum, is responsible for causing bacterial cold water disease (BCWD) in salmonid fish. The disease occurs at subnormal water temperatures and results in lesions on the skin and fins. The Cytophaga species are now referred to as Flavobacterium due to further characterization and change in phylogeny.

Bacteroidetes and Chlorobi

Bacteria categorized under the Phylum Bacteroidetes and Phlyum Chlorobi are closely related base on comparative genomic analysis.

Learning Objectives

Describe the major classes of Bacteroidetes, including: Bacteroidia and Porphyromonas a well as Phlyum Chlorobi

Key Takeaways

Key Points

  • The close relationship between Phylum Bacteroidetes and Phylum Chlorobi are supported by comparative genomic analysis which indicates they are derived from a common ancestor based on unique molecular signatures and common proteins.
  • Phylum Bacteroidetes are composed of three large classes of gram-negative bacteria that are rod-shaped, non-spore forming, and present in anaerobic conditions. Bacteroidetes are found in numerous environments ranging from soils, sediments, sea water, and the guts and skin of animals.
  • Phylum Chlorobi are composed of green sulfur bacteria that are categorized as photolithotrophic oxidizers of sulfur. Chlorobi species are commonly found in symbiotic relationships with colorless, nonphotosynthetic bacteria.

Key Terms

  • photolithotropic: Obtain energy from light and use inorganic electron donors only to fuel biosynthetic reactions.
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Green sulfur bacteria: An image of a green sulfur bacteria which is categorized under the Phlyum Chlorobi and shares a close relationship with bacteria in the Phlyum Bacteroidetes.

The Phylum Bacteroidetes are characterized as rod-shaped, gram-negative bacteria that are non-spore forming and are present in anaerobic environments. Bacteroidetes are capable of thriving in numerous environments that include soil, sediments, sea water, and in the guts and on skin of animal hosts. The Bacteroidetes are classified into three large classes which include the Bacteroidia class and the Porphyromonas class. The Bacteroidia class is the most studied and is present in the gastrointestinal system of mammals which allows it to be abundant in the feces. The Porphyromonas class is characterized by their presence in the oral cavity of humans. The bacteria categorized as bacteroidetes are opportunistic and are rarely pathogenic as they constitute part of the normal flora.

The Phylum Chlorobi are characterized by bacteria that are obligately anaerobic photoautotrophic which includes green sulfur bacteria. The green sulfur bacteria are photolithotropic oxidizers of sulfur and utilize a noncyclic electron transport chain. The green sulfur bacteria are closely related to Bacteroidetes and are non-motile and can be found as sphere, rod, or spiral shaped. The most commonly studied model is Chlorobium tepidum which has had its complete genome sequences. Chlorobium species typically exist in symbiotic relationships with a colorless, nonphotosynthetic bacteria.

The Phlyum Chlorobi is often grouped with the Phlyum Bacteroidetes because their branches are very close together in the phylogenetic tree. By utilizing sequencing techniques such as comparative genomic analysis, there have been three proteins which are unique to all members of the Bacteroidetes and Chlorobi phyla but not to other bacteria indicating a conserved protein signature. Further analysis has identified additional molecular signatures that support the close relationship between these two phyla as well indicating a common ancestor.

Fusobacteria

Fusobacterium are anaerobic, non-spore forming, gram-negative bacteria that are associated with periodontal disease and Lemierre’s syndrome.

Learning Objectives

Describe the role of Fusobacterium in Lemierre’s syndrome

Key Takeaways

Key Points

  • Fusobacterium flourish in anaerobic conditions.
  • Fucosbacterium necrophorum are responsible for causing Lemierre’s syndrome which is characterized by thrombophlebitis.
  • Identification of Fusobacterium within the laboratory is difficult due to their asaccharolytic nature; however, advancements in molecular technology has resulted in identification of numerous species.

Key Terms

  • periodontal disease: disease surrounding a tooth
  • asaccharolytic: incapable of metabolizing carbohydrates
  • septicemia: presence of pathogenic organisms in the bloodstream leading to sepsis

Fusobacteria are a genus of bacteria categorized as gram-negative with similarities to Bacteroides. Fusobacteria are rod-shaped bacilli capable of thriving in anaerobic conditions. However, in contrast to Bacteroides, Fusobacterium have a potent lipopolysaccharide that can function as an endotoxin. The Fusobacterium are associated with infection and disease including periodontal diseases, topical skin ulcers and Lemierres’s syndrome. Fusobacterium are difficult to identify in the laboratory due to their asaccharolytic nature. However, the use of novel molecular biology techniques has allowed for the the identification of new species that are included in Fusobacterium. The diseases attributed to Fusobacterium infection involve symptoms that include tissue necrosis, septicemia, intra-amniotic infections and ulcers.

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Fusobacterium novum: Image of a Fusobacterium cultured in a specific medium.

A specific disease caused by Fusobacteria includes Lemierres’s syndrome. Lemierres’s syndrome is also known as postanginal sepsis and is a form of thrombophlebitis. Thrombophlebitis is inflammation caused by a blood clot. In individuals infected with Fusobacterium necrophorum and additonal Fusobacterium as well, a sore develops in the throat due to infection by a bacterium of the Streptococcus genus. Once this sore develops into a peritonsillar abscess, the pocket is filled with pus and bacteria in close proximity to the tonsils. At this point, bacteria which are capable of thriving in anaerobic conditions, such as Fusobacterium necrophorum can flourish deep in the abscess. At this point, the bacteria are able to pass into the neighboring jugular vein and cause an infected clot to form. The bacteria are then able to circulate throughout the body via the bloodstream and pieces of the blood clot will dissociate from the original site and travel to the lungs. The pieces of the clot will settle in the lungs and block branches of the pulmonary artery, resulting in shortness of breath, chest pain and pneumonia. Fusobacteria are normal flora within the oropharyngeal and can clearly result in disease if conditions are optimal.

Spirochaetes

Spirochaetes are characterized by the presence of a double-membrane and long, spiral-shaped cells that are chemoheterotrophic.

Learning Objectives

Outline the characteristics associated with spirochaetes and the associated diseases

Key Takeaways

Key Points

  • Spirochaetes are chemoheterotrophic in nature and capable of thriving in anaerobic conditions.
  • The spirochaetes are categorized by the presence of axial filaments which run lengthwise between the inner and outer membranes in periplasmic space.
  • Spirochaetes are capable of causing diseases including leptospirosis, Lyme disease, relapsing fever and syphilis.

Key Terms

  • periplasmic: surrounding the plasma of a bacterium

The spirochaetes belong to a phylum of distinctive double-membrane bacteria that are characterized by their long, spiral-shaped cells. The spirochaetes are chemoheterotrophic in nature, free-living and capable of thriving in anaerobic environments. They are often distinguished from other bacterial phyla by the location of their flagella. The flagella, in spirochaetes, runs lengthwise between the inner and outer membranes in the periplasmic space. Often referred to as axial filaments, there is a twisting motion that occurs which allows the spirochaete to move. During reproduction, the spirochaete is capable of undergoing asexual reproduction via binary fission. The binary fission allows for production of two separate spirochaetes.

The spirochaetes can be divided into three families which include: Brachyspiraceae, Leptospiraceae, and Spirochaetaceae. These families are all categorized under a single order, Spirochaetales. There are specific species of spirochaetes that are considered to be pathogenic. Some of the pathogenic species include:

  • Leptospira, the cause of leptospirosis – leptospirosis is transmitted to humans from animals and a common form of transmission is by allowing contaminated water to come in contact with unhealed breaks in the skin, eyes and mucous membranes. The water becomes contaminated by coming into contact with the urine of an infected animal.
  • Borrelia burgdorferi, Borrelia garinii, Borrelia afzelii, the cause of lyme-disease
  • Borrelia recurrentis, the cause of relapsing fever
  • Treponema pallidum, subspecies pallidum, the cause of syphilis
  • Treponema pallidum, subspecies pertenue, the cause of yaws (tropical infection of the skin, bones and joints)
  • Brachyspira pilosicoli and Brachyspira aalborgi, the cause of intestinal spirochetosis