Snodgrassella alvi wkB2

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Classification

Taxonomy

Domain: Bacteria
Phylum: Proteobacteria
Class: Betaproteobacteria
Order: Neisseriales
Family: Neisseriaceae
Genus: Snodgrassella
Species: alvi
Strain: wkB2

NCBI: Taxonomy

Names

Snodgrassella alvi wkB2
Candidatus Snodgrassella alvi wkB2 (previously)
S. alvi wkB2

Description and Significance

Figure 1: A transmission electron micrograph of S. alvi wkB2 cells were found to be approximately 1.0µm long and 0.4 µm wide. (Kwong 2013).

S. alvi wkB2 is a core member of the western honey bee ( Apis mellifera ) gut microbiota (Kwong, 2012). The cells are short gram negative rods. On agar, S. alvi wkB2 forms smooth white round colonies (Kwong, 2012). It is a is non-motile biofilm former colonizing the ileum of A. mellifera (Kwong 2013).

Snodgrassella was so named in honor of Robert Evans Snodgrass was a prominent figure studying insect physiology and had described Apis mellifera (Martinson, 2012). alvi refers to the latin word "alvus" which refers to the bowels or to bees (Martinson, 2012). The strain was described by Waldon Kwong who's initials are "w.k."

Initially, the name "Candidatus" was added to the front of Snodgrassella alvi because its discovery was through gene sequencing and had not been cultivated yet (Martinson, 2012).

Genome Structure

Figure 2: S. alvi genome shown to the right. The protein coding regions are plotted clockwise in solid red (darker red + strand and lighter red - strand). S. alvi wkB2 G+C skew is shown on the outer edge (Kwong 2014).

Genome

The genome of S. alvi 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 S. alvi wkB2 is an obligate symbiont of A. mellifera and is believed to have co-evolved (Kwong 2014). S. alvi wkB2 is also beleived to engage in Horizontal Gene Transfer (HGT) with a proximal gut inhabitant of A. mellifera , Gilliamella apicola .

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

Figure 3: The blue image shows S. alvi metabolic pathways predicted from genome sequencing. The solid circles are specific to the S. alvi wkB2 and wkB1 strains. Green lines indicate possible interactions between G. apicola and S. alvi (Kwong 2014).

S. alvi wkB2 is gram negative, non-motile, rod (Kwong 2013). It displays a type IV pilli structure and YadA-like adhesins which are used to interact with the host gut epithelium.

Metabolism

S. alvi wkB2 is an obligate aerobe. S. alvi wkB2 has transportation systems for taking up carboxylates like citrate, malate, & α-ketoclutarate. These can then be used in the TAC cycle. Transportation systems within S. alvi wkB2 can also allow for the uptake of lactate which can be directly converted into pyruvate through lactate dehydrogenase.

Lost Metabolic Pathways

Evidence has been found suggesting that S. alvi 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 

 The above data was from the initial cultivation-based characterization of  S. alvi  wkB2 (Kwong, 2012).

Life Cycle

S. alvi wkB2 lives its entire natural life within the gut of A. mellifera worker bees. Cultivation of S. alvi wkB2 in vivo (in A. mellifera) 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 S. alvi wkB2 is typically on Insectargro, Salt-free LB, or R2 Liquid Media (Barrick Lab, 2020).

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

Ecology

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Bee Gut Importance

Within the bee gut, S. alvi wkB2 plays a vital role in O2 consumption keeping the gut of the bee anaerobic (Kwong 2016). S. alvi wkB2 is also a primary biofilm former, forming a layer around the ileum (Kwong 2016).

Ecological Importance

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

A transformed S. alvi 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 S. alvi wkB2 cells can sucessfully colonize A. mellifera in the same part of the ileum that it usually occupies.

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 S. alvi wkB2 cells.

In another experiment, S. alvi 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] 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.

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.

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

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.

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.

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

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

Author

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