User:BottsE

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A Microbial Biorealm page on the genus BottsE

Classification

Higher order taxa

Bacteria; Actinobacteria; Actinobacteria; Bifidobacteriales; Bifidobacteriaceae; Bifidobacterium [Others may be used. Use NCBI link to find]

Species

NCBI: Taxonomy

Bifidobacterium longum

Description and significance

Tissier first discovered the genus Bifidobacterium in the feces of breast-fed infants in 1900, even though the name Bifidobacteria did not arise until the early 1960s (1). Bifidobacteria are Gram-positive, non-spore forming, rod-shaped bacteria. Specifically, Bifidobacterium longum are often found clumped together in irregular B or Y shaped branching patterns, although the morphology can vary depending on growth phase (figure 1) (5). Bifidobacteria average about 2.5 mm in diameter, they are non-motile, and anaerobic (except they may tolerate oxygen in the presence of CO2). In terms of metabolic tests, bifidobacteria are catalase negative, benzidine reaction negative, indole negative, and they do not reduce nitrates (3). They are also starch negative and lactose positive (1). They are typically found associated with hosts (primarily mammals), but they have also been found in insect and bird GITs, among other places (5). For humans, they play an extremely important role in forming a stable microbial colony in the GI tract, among other beneficial functions (8).

Currently, there are 25 known species of Bifidobacteria, including B. longum.

Genome structure

The circular genome of B. longum contains 2, 256, 656 base pairs, with 60% of them being G-C pairs. 86% of these genes are thought to be coding (1,730 coding regions), and 22% are specific to B. longum (unless they have yet to be identified in other species). The genome codes for 4 nearly identical rrn operons, 57 tRNAs that code for all 20 amino acids, and 16 intact insertion sequence elements (7). In terms of plasmids, they have been found in 70% of the sequenced B. longum strains, and 7 different types have been identified. Furthermore, some strains harbor defective lysogenic phages, which are dormant plasmids that still contain DNA (1).

The sequence of B. longum subspecies infantis shows a large inverted region (about 1.3 Mb) in the middle of the genome compared to both B. longum strains. This inversion could possibly be a recent evolutionary event (6).

Cell structure and metabolism

In terms of cell wall structure, there is a lot of variety in the genus in terms of peptidoglycan content. Bifidobacteria cell walls do contain a significant amount of polysaccharides (glucose and galactose accompanied by rhamnose) and lipoteichoic acids. The lipoteichoic acid is partly responsible for the hydrophobic nature of the bifidobacterial surface (1).

For carbon sources in the human GI tract, simple sugars are utilized in the upper GI tract and complex carbohydrates are consumed in the distal part. B. longum takes advantage of the complex carbohydrates, whether they are dietary compounds, like cellulose, or host derived compounds, like mucins. To metabolize sugar, Bifidobacteria use a metabolic pathway called the Fructose-6- Phosphate Phosphoketolase pathway, otherwise referred to as the “Bifido shunt” (5). Through this pathway, glucose is fermented primarily into acetic and L (+) lactic acid; no gas is produced. Due to this process, bifidobacteria are able to process a variety of indigestible components (3).

Bifidobacteria use ammonium salts as their sole source of nitrogen, and many strains can synthesize water-soluble vitamins such as thiamine, folic acid, nicotinic acid, pyridoxine, and vitamin B12 (1).

Ecology

Bifidobacteria prefer to live in an environment that is 36-38°C (3). They most commonly live in the alimentary tracts of human adults and infants, where they coexist with many other anaerobes. Bifidobacteria also inhabit other diverse ecological niches, including the rumen of cattle, sewage, the human vagina, dental caries, and honeybee intestines. Bifidobacterium bifidum and B. longum are the most ubiquitous species within the genus (1).

Overall bacterial colonization of the intestine begins at delivery, continues into breastfeeding and weaning, and is complete at the age of 18 months. Aerobic and facultatively anaerobic bacteria, such as enterobacteria, enterococci, and staphylococci, originally colonize the infant GI tract. Once they consume the oxygen present in the intestine, anaerobic bacteria can come, including clostridia, bacteroides, and bifidobacteria. During breastfeeding, various factors in milk help enhance microbial development, including immunoglobulins, lactoferrin, lysozyme, bioactive lipids, leukocytes, and various milk glycans. The specific oligosaccharide glycans are especially important for bifidobacteria growth and are further discussed in the current research section (4).

GI bifidobacteria play the biggest role in infant gut microbiota development through expanding diversity and keeping harmful bacteria in check. As people grow older, the number of bifidobacteria decreases significantly, while the number of other bacteria (including harmful Escherichia coli and clostridia) increases. Bifidobacteria may regulate detrimental bacteria by producing antimicrobial compounds such as organic acids, iron-scavenging compounds, and bacteriocins. Secondly, bifidobacteria can lower the pH in the intestine through production of acetic and lactic acids, which blocks the growth of some harmful bacteria. They also may provide protection against some immune-based disorders by stimulating their host’s innate immune response (6). Specifically, it is hypothesized that bifidobacteria reduce the incidence of GIT diseases such as necrotizing enterocolitis, rotavirus infection, and antibiotic-linked GIT distress (8). Finally, as mentioned above, bifidobacteria might play a role in the production of water-soluble vitamins and the absorption of B complex vitamins (2).

Pathology

How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

Current Research and or Application to Biotechnology

Enter summaries of the most recent research and/or application to biotechnology here--at least three required

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Edited by student of Dr. Lynn M Bedard, DePauw University http://www.depauw.edu