''Liberibacter'' is a genus of
Gram-negative bacteria in the
Rhizobiaceae
The Rhizobiaceae is a family of Pseudomonadota comprising multiple subgroups that enhance and hinder plant development. Some bacteria found in the family are used for plant nutrition and collectively make up the rhizobia. Other bacteria such as ' ...
family. Detection of the liberibacteria is based on PCR amplification of their
16S rRNA gene 16S or 16s may refer to:
* Ribosomal RNAs, in biology:
** prokaryotic 16S ribosomal RNA
** mitochondrial 16S ribosomal RNA
* Myrtle Creek Municipal Airport's FAA identifier
* Fujitsu Micro 16s, a 1983 Business personal computer
*Sulfur
Sulfu ...
with specific primers. Members of the genus are plant pathogens mostly transmitted by
psyllids. The genus was originally spelled ''Liberobacter''.
Most importantly, ''Liberibacter'' is a causative agent of
Huanglongbing disease (HLB) also known as citrus greening disease.
''Liberibacter'' is transmitted by two insects from
Psyllidae family – ''
Diaphorina citri'' in Asia, Brazil and Florida, and ''
Trioza erytreae
The African citrus psyllid (''Trioza erytreae'') is a sap-sucking insect, a hemipteran bug in the family Triozidae. It is an important pest of citrus, being one of only two known vectors of the serious citrus disease, '' huanglongbing'' or citr ...
'' in Africa. The Asian HLB strain, "''Candidatus'' Liberibacter asiaticus" is more heat tolerant, while the African strain, ''Candidatus'' Liberibacter africanus is asymptomatic at temperatures above 30 °C.
Species of ''Liberibacter'', infecting solanaceous plants has been identified and it was carried by another psyllid, a potato pest ''Bactericera cockerelli''.
Pathogenicty
''Liberibacter'' bacteria are carried in the
hemolymph and
salivary glands of psyllids. Since psyllids feed on
sap, this provides bacteria the entry to
phloem of the plant.
They induce significant metabolic and regulatory changes that damage the plants transport system and affects plants defense systems. These impairments have downstream negative effects on citrus microbiome of the infected plants.
Since ''Liberibacter'' cannot be cultivated outside of its vector or host, genetics, bacteria-vector and bacteria-plant interaction have not yet been thoroughly explored. Factors important for adaption and colonization or possible coevolution are not yet understood.
''Liberibacter'' activates salicylic acid pathway in host, likely due to recognition of extracellular molecules such as
lipopolyscacharides or
flagella
A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates.
A microorganism may have f ...
. Pathogen in turn likely mitigates the effects, because it encodes SA hydroxylase, that degrades
salicylic acid
Salicylic acid is an organic compound with the formula HOC6H4CO2H. A colorless, bitter-tasting solid, it is a precursor to and a metabolite of aspirin (acetylsalicylic acid). It is a plant hormone, and has been listed by the EPA Toxic Substance ...
. Liberibacteria were shown to affect the spread of vector, by influencing the flight frequencies and sexual attraction of ''D. citri''. On the other hand, infection with ''Liberibacter'' causes higher mortality of ''D. citri'' adults, but not nymphs.
''Liberibacter'' is a part of the psyllid microbiota and co-existence with other bacteria likely has impact on the overall fitness of the insect, as well as outcome of the disease.
Treatment
Primary strategy for HLB disease management is a vector control. Antimicrobial treatment can suppress ''Liberibacter'' species, however usage of broad spectrum antibiotics is inadvisable due to adverse environmental effects. Alternative treatments, such as heat therapy, ''i.e.'', incubation of plant at temperatures above 40 °C for several days, show varying effects. Another suggested alternatives include the use of compounds that alleviate disease symptoms and boost plants defense systems or reinforcing natural citrus microbiota in order to compete with ''Liberibacter'' species.
Early detection of HLB positive trees and removal from the groves, and extensive control of psyllids are the crucial HLB management strategies.
Species
Named species include:
* "
''Candidatus'' Liberibacter africanus"
corrig. Jagoueix ''et al''. 1994 originated in Africa and is a causal agent of
citrus greening disease
Citrus greening disease (; or HLB) is a disease of citrus caused by a vector-transmitted pathogen. The causative agents are motile bacteria, ''Liberibacter'' spp. The disease is vectored and transmitted by the Asian citrus psyllid, ''Diaphorina ...
, also known as huanglongbing, and vectored by the African citrus psyllid ''
Trioza erytreae
The African citrus psyllid (''Trioza erytreae'') is a sap-sucking insect, a hemipteran bug in the family Triozidae. It is an important pest of citrus, being one of only two known vectors of the serious citrus disease, '' huanglongbing'' or citr ...
''.
* "
''Candidatus'' Liberibacter americanus"
Teixeira ''et al''. 2005 is a novel species from Brazil described in 2005 and associated with huanglongbing and vectored by the Asian citrus psyllid ''
Diaphorina citri''.
* "
''Candidatus'' Liberibacter asiaticus"
corrig. Jagoueix ''et al''. 1994 originated in Asia and is a causal agent of huanglongbing, vectored by the Asian citrus psyllid ''D. citri''.
* "
''Candidatus'' Liberibacter brunswickensis"
Morris ''et al''. 2017 associated with the psyllid ''
Acizzia solanicola'' on eggplant in Australia.
* ''
Liberibacter crescens''
Fagen ''et al''. 2014 was isolated from papaya growing in Puerto Rico.
* "
''Candidatus'' Liberibacter europaeus"
Raddadi ''et al''. 2011 is a novel species described in 2010, found in
pear trees, where it seems to cause no symptoms and is vectored by the
psyllid, ''
Cacopsylla pyri''.
* "
''Candidatus'' Liberibacter solanacearum"
Liefting ''et al''. 2009 is a causal agent of
zebra chip disease in potatoes and vectored by the potato tomato psyllid ''
Bactericera cockerelli''. There are five haplotypes described within this species, designated LsoA and LsoB (from solanaceous plants in North America), and LsoC, LsoD, and LsoE (from carrots and celery in Europe).
** LsoA is also described as a species as "
''Candidatus'' Liberibacter psyllidaureus"
corrig. Hansen ''et al''. 2008 or the misspelling ''Ca.'' L. psyllaurous. It is now considered synonymous as the 16S rRNA genes are identical.
In addition to being a plant pathogen, LsoA also serves as an endosymbiont for the insect vector, by modifying tomato defenses in favor of itself and its vector.
References
Further reading
*
External links
g__Liberibacterin
GTDB
{{Taxonbar, from=Q4262259
Bacterial plant pathogens and diseases
Potato diseases
Rhizobiaceae