''Hamiltonella defensa'' (''H. defensa'') is a species of bacteria. It is maternally or sexually transmitted and lives as an

endosymbiont An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within" ...

of whiteflies and

aphid Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A t ...

s, meaning that it lives within a host, protecting its host from attack. It does this through bypassing the host's immune responses by protecting its host against parasitoid wasps. However, ''H. defensa'' is only defensive if infected by a virus. ''H. defensa'' shows a relationship with ''

Photorhabdus ''Photorhabdus'' is a genus of bioluminescent, gram-negative bacilli which lives symbiotically within entomopathogenic nematodes, hence the name ''photo'' (which means light producing) and ''rhabdus'' (rod shape). ''Photorhabdus'' is known to b ...

'' species, together with ''

Regiella insecticola ''Regiella insecticola'' is a species of bacteria, that lives as a symbiont of aphids. It shows a relationship with '' Photorhabdus'' species, together with ''Hamiltonella defensa''. Together with other endosymbionts, it provides aphids protectio ...

''. Together with other endosymbionts, it provides aphids protection against

parasitoids In evolutionary ecology, a parasitoid is an organism that lives in close association with its host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionary strategies within parasitis ...

. It is known to habitate '' Bemisia tabaci''. ''H. defensa'' is a member of the family Enterobacteriaceae. It can be found both extracellularly and intracellulary in ''H. defensa'' itself, and also the bacteriocytes. It is a gram-negative bacteria and has been found to have six distinct secretion systems that mediate the export of protein through the inner and outer membranes. In general, "''

Candidatus In prokaryote nomenclature, ''Candidatus'' (Latin for candidate of Roman office) is used to name prokaryotic phyla that are well characterized but yet-uncultured. Contemporary sequencing approaches, such as 16S sequencing or metagenomics, provide m ...

Hamiltonella defensa's''" functions are relatively unknown, and the ''H. defensa's'' discovery was not specified by a particular person. ''H. defensa's'' draft genome sequence was first discovered in the ''B. tabaci'' complex of the "''Candidatus'' Hamiltonella defensa". This is only found in two invasive

cryptic species In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

: Mediterranean and Middle East-Asia. The ''H. defensa'' is significantly smaller (at 1.84-Mpb) than its bacteria relatives;

Yersinia ''Yersinia'' is a genus of bacteria in the family Yersiniaceae. ''Yersinia'' species are Gram-negative, coccobacilli bacteria, a few micrometers long and fractions of a micrometer in diameter, and are facultative anaerobes. Some members of '' ...

and

Serratia ''Serratia'' is a genus of Gram-negative, facultatively anaerobic, rod-shaped bacteria of the family Yersiniaceae. According to the List of Prokaryotic names with Standing Nomenclature (LPSN), there are currently 19 species of ''Serratia'' that ...

species. It is also dependent on the essential amino acids produced by Buchnera. It is autotrophic for eight out of the ten essential amino acids that Buchnera produces. Although dependent, the ''H. defensa'' genome preserves more genes and pathways for cell structures and processes, than that of obligate symbionts. It also has several abundances: toxin homologs, encoding type-3 secretion systems, and putative pathogenicity loci. Additionally, ''H. defensa'' holds

mobile DNA A transposable element (TE, transposon, or jumping gene) is a nucleic acid sequence in DNA that can change its position within a genome, sometimes creating or reversing mutations and altering the cell's genetic identity and genome size. Transp ...

, like

phage A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bacteri ...

-derived genes,

plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; ho ...

s, and insertion-sequence elements, that feature ''H. defensa's'' dynamicness, and also show the role

horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between unicellular and/or multicellular organisms other than by the ("vertical") transmission of DNA from parent to offspring (reproduction). HG ...

has on shaping it. The ''H. defensa'' genome holds a 2,110,331- bp circular chromosome and a 59,034-bp conjugative plasmid. The chromosome carries a canonical origin of replication. It has notably more cell structure, DNA replication, recombination, and repair of genes than obligate endosymbionts, despite its limited biosynthetic abilities. The proteins present in ''H. defensa'' vary in length significantly. They have a double cycled nonapeptide sequence involved in binding calcium.

Special properties

''H. defensa'' has two types of type-3 secretion systems (T3SS). These translocation systems are typically used by pathogens to occupy host cells and elude immune responses. They are also necessary for the perseverance of certain symbiosis. There have been recent studies done attempting to find ways to manipulate ''H.defensa's'' "self-fighting" qualities, and create a cure for certain illnesses.

References

{{Taxonbar, from=Q2936284 Enterobacteriaceae Bacteria described in 2005