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Proteobacteria: diversity, characteristics, ecological and medical roles

Proteobacteria are a large, diverse phylum of Gram-negative bacteria defined by rRNA sequences; they include major environmental players, symbionts, and many human pathogens.

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Overview

Proteobacteria form one of the largest and most varied phyla of Bacteria. Members are united primarily by molecular criteria (ribosomal RNA sequence relationships) rather than a single morphological trait. They are all Gram-negative in the classical staining sense, and the group includes free-living microbes, plant and animal symbionts, and numerous human and animal pathogens.

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Key characteristics

Despite their diversity, many Proteobacteria share structural and biochemical features that are useful for identification and classification:

  • Cell envelope: a double-membrane structure with an outer membrane containing lipopolysaccharide (LPS), a thin peptidoglycan layer, and a periplasmic space—explaining the typical Gram-negative staining outcome.
  • Metabolic versatility: species display a wide range of lifestyles including heterotrophy, chemoautotrophy, lithotrophy, and in some groups phototrophy; many are facultative or obligate aerobes or anaerobes depending on niche.
  • Genetic markers: classification relies largely on conserved rRNA gene sequences and other molecular phylogenetic methods instead of older phenotype-only systems.

Major subdivisions

The phylum is commonly divided into several classes whose names reflect their prefix: Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria and Epsilonproteobacteria. Each class contains groups with distinct ecologies: for example, Alphaproteobacteria include many marine planktonic lineages and intracellular symbionts; Gammaproteobacteria include familiar enteric bacteria; Deltaproteobacteria contain many sulfate-reducers and predatory forms.

Ecological roles and human relevance

Proteobacteria are central to numerous global processes. Several fix atmospheric nitrogen in symbiosis with plants (e.g., rhizobia), others drive sulfur, nitrogen and carbon cycling in soils and oceans. Some Alphaproteobacteria such as members of the SAR11 clade are extremely abundant in the open ocean. Many genera are clinically important: Escherichia, Salmonella, Vibrio, Helicobacter, Campylobacter, Neisseria and others cause disease in humans and animals, while other strains are exploited in bioremediation, agriculture and biotechnology.

History and notable facts

The name Proteobacteria alludes to Proteus, a shape-changing figure in Greek mythology, chosen to reflect the group's great diversity. Molecular systematics in the late 20th century reorganized bacterial taxonomy and established Proteobacteria as a coherent phylum defined by rRNA phylogenies. Some researchers propose that the bacterial ancestor of mitochondria belongs to or is related to Alphaproteobacteria, a hypothesis supported by multiple lines of molecular evidence but still refined by ongoing research.

Further reading and resources

Systematics

The following are some important orders, families, and genera of the eight classes of Proteobacteria. The article Systematics of bacteria is considered a reference in Wikipedia and contains a larger selection of taxa in the phylum Proteobacteria.

Acidithiobacillia

·         Order I. Acidithiobacillales

·         Acidithiobacillaceae family

·         genus Acidithiobacillus

·         Thermithiobacillaceae family

·         genus Thermithiobacillus

Alphaproteobacteria

·         Order I. Rhodospirillales

·         Family I. Rhodospirillaceae (non-sulfur-processing purple bacteria)

·         Family II Acetobacteraceae; triv. acetic acid bacteria (vinegar)

·         Order II Rickettsiales

·         Order VI Rhizobiales

·         Family I. Rhizobiaceae

·         Genus I. Rhizobium

·         Family II. Bartonellaceae

·         Family III Brucellaceae

and other taxa

Betaproteobacteria

·         Order I. Burkholderial

·         Order IV Neisseriales

·         Family I. Neisseriaceae

·         Genus I. Neisseria

·         Genus IX Kingella

and other taxa

Gammaproteobacteria

·         Order I. Chromatiales

·         Family I. Chromatiaceae (triv. sulfur purple bacteria)

·         Family II. Ectothiorhodospiraceae

·         Order II "Xanthomonadales".

·         Family I. "Xanthomonadaceae"

·         Genus I. Xanthomonas

·         Genus VII Stenotrophomonas

Within the LPSN (List of Prokaryotic names with Standing in Nomenclature), an important listing of the systematics of bacteria, the order Xanthomonadales is no longer listed. This order and the single family Xanthomonadaceae that was added were dissolved due to recent research. Many of the genera are now placed in the order Lysobacterales, others are not yet assigned to any specific order. However, the old system is still in use and is, for example, still used in the taxonomy database of the NCBI (National Center for Biotechnology Information), an important source of information on bacteria.

·         Order IV Thiotrichales

·         Family I. Thiotrichaceae

·         Genus VII Thiomargarita

·         Order VIII Pseudomonales

·         Family I. Pseudomonaceae

·         Genus I. Pseudomonas

·         Family II. Moraxellaceae

·         Genus I. Moraxella

·         Genus II Acinetobacter

·         Order X. "Vibrionales"

·         Family I. Vibrionaceae

·         Genus I. Vibrio

·         Order XII. Enterobacterales, previously referred to as order "Enterobacteriales

·         Budviciaceae family

·         Enterobacteriaceae family

·         Erwiniaceae family

·         Hafniaceae family

·         Morganellaceae family

·         Pectobacteriaceae family

·         Thorselliaceae family

·         Yersiniaceae family

·         Order XIII Pasteurellales

·         Family I. Pasteurellaceae

·         Genus I. Pasteurella

·         Genus III. Haemophilus

·         Order XIV Oceanospirillales

·         Family I. Alcanivoracaceae

·         Family II. Hahellaceae

·         Family III. Halomonadaceae

·         Genus I Halomonas

·         Family IV. Litoricolaceae

·         Family V. Oceanospirillacae

·         Family VI. Oleiphilaceae

·         Family VII "Saccharospirillaceae"

and other taxa

Hydrogenophilalia

·         Order I. Hydrogenophilic

·         Family Hydrogenophilaceae

with only one genus, Hydrogenophilus

Deltaproteobacteria

·         Order I. Desulfovibrionales

·         Family I. Desulfovibrionaceae

·         genus Desulfovibrio

·         Order II Myxococcales (Myxobacteria)

·         Myxococcaceae family

·         Order Bdellovibrionales

·         Family Bdellovibrionaceae

·         genus Bdellovibrio

and other taxa

Epsilonproteobacteria

·         Order Campylobacterales

·         Campylobacteraceae family

·         genus Campylobacter

·         Helicobacteraceae family

·         helicobacter genus

·         Order Nautiliales

·         Family Nautiliaceae

·         nautile genus

and other taxa

Oligoflexia

·         Order I. Oligoflexal

·         Oligoflexaceae family

·         Oligoflexus genus

·         Order II Silvanigrellales

·         Silvanigrellalaceae

·         genus Silvanigrella

"Zetaproteobacteria"

·         family "Mariprofundaceae", with the only genus Mariprofundus

Questions and answers

Q: What are Proteobacteria?

A: Proteobacteria are a major phylum of bacteria.

Q: Are Proteobacteria gram-negative or gram-positive bacteria?

A: Proteobacteria are gram-negative bacteria.

Q: What is the Gram staining protocol?

A: The Gram staining protocol is a test used to classify two distinct types of bacteria based on the structural differences of their cell walls.

Q: How does the Gram staining protocol differentiate between gram-negative and gram-positive bacteria?

A: Gram-negative bacteria do not retain the violet dye in the Gram staining protocol, and a counterstain (commonly safranin) is added after the crystal violet, colouring all gram-negative bacteria with a pink colour.

Q: What are some notable examples of pathogens that belong to the Proteobacteria phylum?

A: Some notable examples of pathogens that belong to the Proteobacteria phylum include Escherichia coli, Salmonella, Vibrio, and Helicobacter.

Q: Are all Proteobacteria bacteria pathogens?

A: No, not all Proteobacteria are bacteria pathogens. Others are free-living, and include many of the bacteria responsible for nitrogen fixation.

Q: What are alphaproteobacteria and where can they be found?

A: Alphaproteobacteria are a group of Proteobacteria that are widely found in marine plankton, and may constitute over 10% of the open ocean microbial community.

Related articles

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AlegsaOnline.com Proteobacteria: diversity, characteristics, ecological and medical roles

URL: https://en.alegsaonline.com/art/79519

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