View source for Snodgrassella alvi wkB2

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[[File:s_mg.jpg|500px|thumb|right|Figure 1: A transmission electron micrograph (TEM) of <i> S. alvi </i> wkB2 cells were found to be approximately 1.0µm long and 0.4 µm wide [4].]]
==Classification==

===Taxonomy===

Domain: Bacteria <br>
Phylum: Proteobacteria <br>
Class: Betaproteobacteria <br>
Order: Neisseriales <br>
Family: Neisseriaceae <br>
Genus: <i> Snodgrassella </i> <br>
Species: <i> alvi </i> <br>
Strain: wkB2 <br>

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===Names===

''Snodgrassella alvi'' wkB2<br>
''Candidatus Snodgrassella alvi'' wkB2 (previously)<br>
''S. alvi'' wkB2 <br>

==Description and Significance==

<i> S. alvi </i> wkB2 is a core member of the western honey bee (<i> Apis mellifera </i>) worker gut microbiota [7]. The cells are short gram negative rods. On agar, <i> S. alvi </i> wkB2 forms smooth white round colonies [4]. It is a is non-motile biofilm former colonizing the ileum of <i> A. mellifera </i> [4]. 

<i> Snodgrassella </i> was so named in honor of Robert Evans Snodgrass was a prominent figure studying insect physiology and had described <i> Apis mellifera </i> [6]. <i> alvi </i> refers to the latin word "alvus" which refers to the bowels or to bees [6]. The strain was described by Waldon Kwong who's initials are "w.k."

Initially, the name "Candidatus" was added to the front of <i> Snodgrassella alvi </i> because its discovery was through gene sequencing and had not been cultivated yet [6].

==Genome Structure==
[[File:S.alvi.jpg|450px|thumb|right|Figure 2: <i> S. alvi </i> genome shown to the right. The protein coding regions are plotted clockwise in solid red (darker red + strand and lighter red - strand). <i> S. alvi </i> wkB2 G+C skew is shown on the outer edge (Kwong 2014).]] 

===Genome===
The genome of <i> S. alvi </i> wkB2 consists of a singular circular chromosome containing 2,527,978 bp (Kwong 2014). The G+C content is 41.3% (Kwong 2014). 

Some pieces of the genome have mutated over time and lost function as <i> S. alvi </i> wkB2 is an obligate symbiont of <i> A. mellifera </i> and is believed to have co-evolved (Kwong 2014). <i> S. alvi </i> wkB2 is also beleived to engage in Horizontal Gene Transfer (HGT) with a proximal gut inhabitant of <i>A. mellifera </i>, <i> Gilliamella apicola </i>. 

====Annotated Genes====

There are 2295 annotated genes and 2193 of them are protein coding, 76 are non-coding, the rest (26) are pseudogenes (Ncbi.nlm.nih.gov). 

A few notable annotated gene functions include genes that code for many pathogen associated functions. One gene codes for nonribosomal peptide synthesis of siderophores (Kwong 2014). The type 6 secretion system (T6SS) (Kwong 2014).

==Cell Structure, Metabolism and Life Cycle==

===Cell Structure===
[[File:S_alvi_metabolism.jpg|570px|thumb|right|Figure 3: The blue image shows <i> S. alvi </i> metabolic pathways predicted from genome sequencing. The solid circles are specific to the <i> S. alvi </i> wkB2 and wkB1 strains. Green lines indicate possible interactions between <i> G. apicola </i> and <i> S. alvi </i> (Kwong 2014).]] 
<i> S. alvi </i> wkB2 is gram negative, non-motile, rod [4]. It displays a type IV pilli structure and YadA-like adhesins which are used to interact with the host gut epithelium which can be seen in figure 3. An TEM of <i> S. alvi </i> wkB2 can be seen in figure 1.

===Metabolism===

<i> S. alvi </i> wkB2 is an obligate aerobe. <i> S. alvi </i> wkB2 has transportation systems for taking up carboxylates like citrate, malate, & α-ketoclutarate (Kwong 2014). These can then be used in the TAC cycle (Kwong 2014). Transportation systems within <i> S. alvi </i> wkB2 can also allow for the uptake of lactate which can be directly converted into pyruvate through the enzyme, lactate dehydrogenase (Kwong 2014). A TCA cycle enzyme, succinyl-CoA synthetase, which catalyzes the interconversion of succinyl-CoA and succinate, is not present in <i> S. alvi </i> yet the pathway is considered to still be functional as no alternative pathways exist to bypass the TCA cycle (Kwong 2014).

<i> S. alvi </i> is able to synthesize purine and pyrimidine nucleotides as well as all 21 proteinogenic amino acids (except selenocysteine). Vitamin B2 and B6 can be synthesized. <i> S. alvi </i> wkB2 specifically can synthesize B3 and its derivatives (NAD+ and NADP+) from aspartate (Kwong 2014). 

====Lost Metabolic Pathways====

Evidence has been found suggesting that <i> S. alvi </i> was able to take up and break down carbohydrates, but has since lost that ability (Kwong 2014). The Glycolosis pathway, Pentose phosphate pathway, & Entner-Doudoroff pathway have all lost essential enzymes (Kwong 2014). These pathways are typically used to convert sugars to pyruvate. 


====Biochemical Tests====

      Nitrate reductase: Positive 
               Catalase: Positive 
                 Urease: Positive 
   Cytochrome C Oxidase: Negative 
          β-Glucosidase: Negative 
      Indole production: Negative 
             Gelatinase: Negative 
        β-Galactosidase: Negative 
   Arginine dihydrolase: Negative 
         H2S production: Negative 
             Haemolysis: Negative <br>
  The above data was from the initial cultivation-based characterization of <i> S. alvi </i> wkB2 [4].

===Life Cycle===

<i> S. alvi </i> wkB2 lives its entire natural life within the gut of <i> A. mellifera </i> worker bees. Cultivation of <i> S. alvi </i> wkB2 in vivo (in <i> A. mellifera</i>) needs no substrate or assistance outside of the bee's regular diet. It is primarily passed on through the fecal-oral route (Martinson 2014).

This strain can also be cultivated in vitro on the following agars: Heart Infusion, Heart Infusion supplemented with Sheep's Blood, Columbia supplemented with Sheep's Blood (CBA), & R2 Agar (Barrick Lab, 2020). Liquid cultivation of <i> S. alvi </i> wkB2 is typically on Insectargro, Salt-free LB, or R2 Liquid Media (Barrick Lab, 2020). 

On solid or liquid media, in vitro cultivation of <i> S. alvi </i> wkB2 is typically at 35°C and 5% CO2 (Barrick Lab, 2020).

==Ecology==
[[File:gut_location.jpg|450px|thumb|right|Figure 4: The composition of the typical adult worker bee based on 16S rRNA gene amplicons from whole guts. The localization was determined based on fluorescence in situ hybridization and qPCR studeies. <i> S. alvi </i> is shown in green (Kwong 2016).]] 
===Bee Gut Importance===
Within the bee gut, <i> S. alvi </i> wkB2 plays a vital role in O2 consumption keeping the gut of the bee anaerobic (Kwong 2016). <i> S. alvi </i> wkB2 is also a primary biofilm former, forming a layer around the ileum (Kwong 2016).

===Ecological Importance===

For <i> A. mellifera </i> two pests that have been attributed to the large decline in honey bee populations are, the Varroa mite (<i>Varroa destructor</i>) and the Deformed Wing Virus (DWV).

A transformed <i> S. alvi </i> wkB2 cells using RNAi have been proposed as a solution to the decreasing honey bee population (Leonard 2020). It has been shown that these synthetic <i> S. alvi </i> wkB2 cells can sucessfully colonize <i> A. mellifera </i> in the same part of the ileum that it usually occupies. <br>

This engineered microbe was transformed with a plasmid coding for double stranded RNA (dsRNA) targeting an essential mRNA on the deformed wing virus which plagues the western honey bee. Leonard et al. were able to show an increase in bee survival for bees incoulated with the DWV and had sucessful colonizations of transformed <i> S. alvi </i> wkB2 cells. <br>

In another experiment, <i> S. alvi </i> wkB2 was transformed with a plasmid which coded for dsRNA which targeted 14 essential Varroa mite genes. They were also able to show a decrease in survival rates for the Varroa mites feeding on these bees.

==References==
[Sample reference] [http://ijs.sgmjournals.org/cgi/reprint/50/2/489 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.]

[1] Barricklab.org. 2020. Barrick Lab :: Protocolsculturingsnodgrassellaalvi. [online] Available at: <https://barricklab.org/twiki/bin/view/Lab/ProtocolsCulturingSnodgrassellaAlvi> [Accessed 29 April 2020].

[2] Leonard, S., Powell, J., Perutka, J., Geng, P., Heckmann, L., Horak, R., Davies, B., Ellington, A., Barrick, J. and Moran, N., 2020. Engineered symbionts activate honey bee immunity and limit pathogens. Science, 367(6477), pp.573-576.

[3] Kwong, W., Engel, P., Koch, H. and Moran, N., 2014. Genomics and host specialization of honey bee and bumble bee gut symbionts. Proceedings of the National Academy of Sciences, 111(31), pp.11509-11514.

[4] Kwong, W. and Moran, N., 2012. Cultivation and characterization of the gut symbionts of honey bees and bumble bees: description of Snodgrassella alvi gen. nov., sp. nov., a member of the family Neisseriaceae of the Betaproteobacteria, and Gilliamella apicola gen. nov., sp. nov., a member of Orbaceae fam. nov., Orbales ord. nov., a sister taxon to the order 'Enterobacteriales' of the Gammaproteobacteria. INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY, 63(Pt 6), pp.2008-2018.

[5] Kwong, W. and Moran, N., 2016. Gut microbial communities of social bees. Nature Reviews Microbiology, 14(6), pp.374-384.

[6] Martinson, V., Moy, J. and Moran, N., 2012. Establishment of Characteristic Gut Bacteria during Development of the Honeybee Worker. Applied and Environmental Microbiology, 78(8), pp.2830-2840.

[7] Moran, N., Hansen, A., Powell, J. and Sabree, Z., 2012. Distinctive Gut Microbiota of Honey Bees Assessed Using Deep Sampling from Individual Worker Bees. PLoS ONE, 7(4), p.e36393.

[8] Ncbi.nlm.nih.gov. 2020. Home - Gene - NCBI. [online] Available at: <https://www.ncbi.nlm.nih.gov/gene> [Accessed 29 April 2020].

==Author==
Page authored by Samantha Worthington, student of Prof. Jay Lennon at Indiana University.

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