''Eleftheria terrae'' is a recently discovered Gram-negative bacterium. ''E. terrae'' is a temporary name for the organism, as it was only discovered in 2014 and is still undergoing scientific study. It was found to produce a previously unknown antibiotic named

teixobactin Teixobactin () is a depsipeptide, peptide-like secondary metabolite of some species of bacteria, that kills some gram-positive bacteria. It appears to belong to a new Antibiotic classes, class of antibiotics, and harms bacteria by binding to lipid ...

. The discovery of ''E. terrae'' could represent a new age of antibiotics, as teixobactin is the first new antibiotic discovered since the synthetic era of the 1980s. Prior research has indicated that other uncultivable bacteria like ''E. terrae'' have potential in the development of new antimicrobial agents.

Discovery

As of 2015, an estimated 99% of bacterial species are uncultured and require advanced means, such as the iChip, to be isolated. ''E. terrae'' is one such

bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...

affectionately named by scientists "microbial dark matter" cultivated by emerging scientific methods. A team from Novobiotic Pharmaceuticals led by L. Ling discovered ''Eleftheria terrae'' in the fall of 2014 in a field in

Maine Maine () is a state in the New England and Northeastern regions of the United States. It borders New Hampshire to the west, the Gulf of Maine to the southeast, and the Canadian provinces of New Brunswick and Quebec to the northeast and ...

using a technique developed at Northeastern University called the iChip or isolation chip technique. The iChip is a small plastic block that contains 192 holes going through it. The holes are filled with a culture medium that are then inoculated with soil diluted to deposit only one bacterium in each hole. After depositing the bacterium in the holes the iChip is covered on both sides by a semipermeable

membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. ...

and put into a box of the original soil. The

permeable Permeability, permeable, and semipermeable may refer to: Chemistry *Semipermeable membrane, a membrane which will allow certain molecules or ions to pass through it by diffusion *Vascular permeability, the movement of fluids and molecules betwe ...

membranes allow nutrients and growth factors from the soil to diffuse in and allow growth of only one

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

. Ling et al. screened approximately 10,000 iChip growth isolates for prospective antimicrobial activity, and ''E. terrae'' seemed to be hopeful. This technology has potential for discovering even more antibiotics by allowing labs to grow previously "unculturable"

microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

General characteristics

''E. terrae'' is a Gram-negative bacterium which produces several novel antibiotics including

and clovibactin. ''E. terrae'' grows and produces antibacterial activity under many different growth conditions, but optimally in R4 fermentation broth. R4 fermentation broth consists of 10g

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...

, 1g

yeast extract Yeast extracts consist of the cell contents of yeast without the cell walls; they are used as food additives or flavorings, or as nutrients for bacterial culture media. They are often used to create savory flavors and umami taste sensations, ...

, 0.1g casamino acids, 3g proline, 10g MgCl₂·6H₂O, 4g CaCl₂·2H₂O, 0.2g K₂SO₄, 5.6g TES free acid per liter of deionized H₂O at pH 7. ''E. terrae''s

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run c ...

and

ecology Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overl ...

have not yet been extensively documented.

Phylogeny

''E. terrae'' belongs to the class beta-proteobacteria. After sequencing the organism's

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...

it was concluded that ''E. terrae'' is a member of a previously unknown

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

close in genetic makeup to '' Aquabacteria'' based upon its 16S rRNA gene sequencing and DNA-DNA hybridization performed by computer analysis. Organisms of the genus ''Aquabacteria'' had not been known to produce antibiotics until ''E. terrae''´s discovery.

Genomics

Ling and her team sequenced the

of ''E. terrae'' and estimated it to be 6.6 Mbp in length, using an in house pipeline by TUCF Genomics. After the draft genome was assembled it was screened for sequences closely related to adenylation domains.

Contig A contig (from ''contiguous'') is a set of overlapping DNA segments that together represent a consensus region of DNA.Gregory, S. ''Contig Assembly''. Encyclopedia of Life Sciences, 2005. In bottom-up sequencing projects, a contig refers to ov ...

s that were found to code for teixobactin biosynthetic pathways were manually edited and placed in order. This allowed the combination of other contigs that were separately assembled. Any gaps that remained in the genome were filled using bridging fragments developed by PCR and

Sanger sequencing Sanger sequencing is a method of DNA sequencing that involves electrophoresis and is based on the random incorporation of chain-terminating dideoxynucleotides by DNA polymerase during in vitro DNA replication. After first being developed by Fred ...

. The gaps were closed using the same primers used in amplification.

Antibiotic production

''E. terrae''s production of teixobactin is prominent because recent tests have revealed that teixobactin binds differently than most normally used antibiotics which makes it harder for the bacteria being attacked to develop resistance. Experiments performed by Ling et al. have shown teixobactin is capable of binding to lipid precursors of

peptidoglycan Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like peptidoglycan layer outside the plasma membrane, the rigid cell wall (murein sacculus) characteristic of most ba ...

, which makes up part of bacterial cell walls. The results did not show any resistance to teixobactin in the organisms that were studied, including '' Staphylococcus aureus'' and '' Mycobacterium tuberculosis''. These findings indicate that teixobactin's target is not a protein, leading to the belief that the development of bacterial resistance to teixobactin is much less likely. These experiments also showed that teixobactin followed a similar mechanism of action as the antibiotic

vancomycin Vancomycin is a glycopeptide antibiotic medication used to treat a number of bacterial infections. It is recommended intravenously as a treatment for complicated skin infections, bloodstream infections, endocarditis, bone and joint infections, ...

that binds to the

lipid II Lipid II is a precursor molecule in the synthesis of the cell wall of bacteria. It is a peptidoglycan, which is amphipathic and named for its bactoprenol hydrocarbon chain, which acts as a lipid anchor, embedding itself in the bacterial cell me ...

molecule in peptidoglycan precursors but, unlike vancomycin, teixobactin is capable of binding to modified lipid II molecules found in vancomycin resistant bacteria. Teixobactin's inhibition of peptidoglycan synthesis is further explained by Ling's finding of a buildup of undecaprenyl-N-acetylmuramic acid-pentapeptide, a crucial step in the biosynthesis of peptidoglycan. According to Ling's tests, teixobactin is capable of inhibiting peptidoglycan synthesis by binding to either lipid I, lipid II, and undecaprenyl pyrophosphate. Teixobactin also seemed to be specifically involved with peptidoglycan precursors rather than blocking

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

activity.

References

{{Taxonbar, from=Q18759674 Betaproteobacteria Bacteria described in 2015