Difference between revisions of "Team:Austin UTexas/Results"

Recapitulation

The process of recapitulations took individual microbes, isolated from kombucha, and recombined these to reform kombucha. This process is essential to create a designer beverage: the microbes that have been taken from kombucha and genetically engineered must be able to be put back together to remake kombucha. The process of recapitulation was repeated multiple times in triplicate. Each trial tested a different growing condition or different combinations of microbes for regenerating kombucha.

The first trials of recapitulations tested the tea media being used to compare the tea that at-home brewers used to see if this would support the microbial growth of isolates. The next trials performed used strictly the microbes isolated from kombucha, the problem with this approach is that not all microbes that occur in kombucha can be isolated away from the symbiotic they exist in, and further they cannot grow on a solid agar plate. Using the previous research on kombucha found in scientific literature, as well as our findings in lab, the most prominent microbes that help to create kombucha were attained (either by isolation from kombucha or by purchasing from a scientific database) to be used in future recapitulations.

After having the essential kombucha microbes, the next set of recapitulations tested what ratios these microbes needed to be in when placed in tea media so they could properly form a SCOBY and recreate kombucha. This process involved multiple trial and error results, but eventually the results included below were found.

Ethanol Reduction

Approach

Two potential ways to reduce ethanol content over the course of the fermentation are to reduce the rate at which yeast produce ethanol or increase the rate at which acetic acid bacteria convert the ethanol to acetic acid. The first of these methods is the most direct approach, and was the first method considered. We considered UV mutagenizing Lachancea fermentati, a yeast our lab has isolated from kombucha, and then screening for ethanol production using a pH indicator, bromothymol blue, in media (Figure 1). Bromothymol blue is blue at basic pH, turns green around pH 7, and turns yellow around pH 6, and has been used previously to screen for fermentation rate among Saccharomyces cerevisiae colonies (Robillard, 2007). During anaerobic respiration, both ethanol and CO2 are produced, and CO2 reacts with water to form carbonic acid, lowering the pH of the plate and changing the color of the indicator. A variety of problems with this approach led us to abandon it. It is likely that L. fermentati produce other acidic metabolic products, so pH would not necessarily correspond to amount of ethanol produced. This assay also relies on distinguishing differences in color in the agar to tell the difference in ethanol production between two colonies, a process that would be somewhat subjective. Additionally, the ethanol produced is necessary for the production of acetic acid, so slowing the rate of ethanol production would likely have slowed the production of the beverage and could have thrown off the flavor. For all these reasons, attempting to decrease the rate of ethanol production by L. fermentati does not seem like a good approach to lowering the ethanol content during the fermentation.

We next considered increasing the rate at which acetic acid bacteria in kombucha convert ethanol to acetic acid. Increasing this rate would utilize more ethanol as it is produced, ideally lowering the ethanol content throughout the course of the fermentation. Two enzymes facilitate steps in this pathway (Mamlouk and Gullo, 2013). An alcohol dehydrogenase (PQQ-ADH) enzyme facilitates the conversion of ethanol to acetaldehyde, and a membrane-bound aldehyde dehydrogenase (ALDH) facilitates the conversion of acetaldehyde to acetic acid. In order to increase the rate at which ethanol is converted into acetic acid, we propose using Golden Gate Assembly to create a genetic construct in which expression of PQQ-ADH and ALDH is governed by a Tac-promoter (pTac), a hybrid promoter which is inhibited except in the presence of allolactose. The construct would be transformed into electrocompetent Escherichia coli and transferred to Gluconacetobacter hansenii via conjugation.

Identifying genes of interest

In order to design a construct increasing expression of PQQ-ADH and ALDH in Ga. hansenii, it was necessary to find the genome of the ATCC strain and identify the coding sequences for these genes. The whole genome shotgun sequence for our organism, ATCC 53582, is published on NCBI (Abbot, 2015) with annotations regarding the functions of specific sequences. Coding sequences are annotated with proposed gene products. Though there are several aldehyde dehydrogenase genes annotated in the genome, there is only one which is described as membrane-bound, matching the description from Mamlouk and Gullo (Mamlouk and Gullo, 2013). There are additionally multiple alcohol dehydrogenases. A known amino acid sequence for a homologous PQQ-ADH in Comamonas testosteroni was compared against sequences in the Ga. hansenii genome using BLAST (Table 1). One ADH enzyme found in the Ga. hansenii genome sequence matches the C. testosteroni sequence with a query cover value of 94% and an E value of 0 (third line of Table 1).

Creation of Golden Gate parts

In order to assemble the construct, the coding sequences for the genes of interest must be amplified from the Ga. hansenii genome and edited such that they have the correct Golden Gate overhangs and no internal BsaI or BsmBI restriction sites. The sequences were uploaded to Benchling for analysis and planning. The coding sequence for the membrane-bound ALDH contains a BsaI restriction site near the middle of the gene (Figure 2), and the PQQ-ADH coding sequence contains a BsmBI restriction site near the end of the gene (Figure 3). To eliminate the BsaI site in ALDH, primers were designed that would introduce a point mutation at the restriction site. One set of primers, igem2016_KOM_EtOH_01 and igem2016_KOM_EtOH_02, amplifies the sequence upstream of the restriction site, adding a type 3 Golden Gate prefix and removing the restriction site. Another set, igem2016_KOM_EtOH_03 and igem2016_KOM_EtOH_04, amplifies the region downstream of the restriction site, introducing a mutation to the site and adding a type 3 Golden Gate suffix to the end of the gene. These two products will be used in an overlap PCR reaction to create a final product with no BsaI restriction sites and the correct prefix and suffix for assembly. To remove the BsmBI site from the PQQ-ADH coding sequence, a set of primers (igem2016_KOM_EtOH_05 and igem2016_KOM_EtOH_06) was designed to amplify the region upstream of the restriction site and add a Golden Gate type 3 prefix to the beginning of the sequence. The reverse primer additionally adds a mutation to existing BsmBI restriction site and creates a new BsmBI restriction site that will be used to join the piece to a double-stranded DNA, igem2016_KOM_EtOH_07, containing the rest of the gene’s coding sequence appended with a Golden Gate type 3 suffix. The assembly of the PQQ-ADH part will therefore take place in two reactions: one reaction in which the upstream piece of DNA is created, and one reaction in which it is ligated to the gBlock. Table 2 contains more information about each of these oligonucleotides. All were ordered from IDT.

pH Sensors

During the kombucha brewing process, the beverage becomes more acidic. Additionally, it is unclear if or how the microbial community changes within the beverage over time. Thus, our team decided to find pH sensitive promoters that could be used to track not only the pH of the maturing beverage, but also the presence of the various microbes within the kombucha over time. We successfully created a neutral range reporter, attempted to create acidic and basic range reporters, and found three putative acidic range reporters that are endogenous to one of our kombucha bacteria, Gluconobacter oxydans

Though an acidic sensor was what was required for our kombucha analysis, the identification of sensors in other areas of the pH spectrum were explored as well. Three sequences were identified, the CadC operon for the acidic range, CpxA-CpxR complex for the neutral range, and the P-atp2 promoter from the BioBrick Registry (BBa_K1675021) for the basic range. Each sequence was paired with a unique corresponding reporter sequence so that if each pH sensitive plasmid were in the same environment, the specific pH of the system could be seen. The reporters used were, BBa_E1010 for the CadC construct, BBa_K1033916 for the CpxA-CpxR complex, and BBa_K592009 for the P-atp2 promoter.

CpxA-CpxR

Figure 1. Testing the CpxR Construct in pH 6-9. From left to right is control pH 6-9 and then experimental pH 6-9. These are showing the gradient change in expression accordingly with the change of pH due to a pH-dependent promotor compared to consistent expression accordingly with a promoter that is always "on". Credit: Sofia Chinea

CpxA-CpxR is a two-component mechanism that is activated at pH 7.4 and repressed at pH 6.0. CpxA is an intermembrane protein that autophosphorylates at a certain external pH, CpxR (a kinase) then gets phosphorylated by CpxA and acts as a transcription factor. This system originally is a transcription factor for the virF gene, but virF was replaced with a reporter. The original sequence was found in Shigella sonnei, but E. coli has a homolog of these proteins so all that is required on the construct is the appropriate prefix/suffix and CpxR binding site (Nakayama and Watanabe, 1995; Nakayama and Watanabe, 1998).

Figure 3. amajLime expressed in E. coli in liquid LB. Credit: Sofia Chinea

Figure 2. Normalized fluorescent values from CpxR construct vs control (YGCP). The fluorescence per cell count stayed generally the same throughout the range of pH while the CpxR has a clear increase in fluorescence per cell. Credit: Sofia Chinea

The order from left to right in figure 1 is control pH 6-9 and then Experimental pH 6-9. These are showing the gradient change in expression accordingly with the change of pH due to a pH-dependent promotor compared to consistent expression accordingly with a promoter that is always "on". The main point is that the control at pH 6 has more expression of the yellow-green chromoprotein than the Experimental at pH 6. The pH-dependent promoter of the experimental group is down-regulated at pH 6 whereas the control is not. Also, there is an increase in YGCP expression between the experiment pH 7 and pH 8 that is not seen in the control between pH 7 and pH 8. The normalized data in figure 2 shows the relative expression of YGCP. The CpxA-CpxR construct can be found on the iGEM registry as: BBa_K2097000, while the construct utilized as a control can be found on the iGEM registry as BBa_K2097002 as well as in figure 3.

CadC

The CadC operon is a native pathway in E. coli, involved in the cadaverine synthesis pathway. The protein CadC protein on the operon is produced and activates segments downstream of the operon on the CadBA receptors. The CadC protein is pH sensitive to an external pH 5.5 and below, as well as lysine dependent. A point mutation on codon 265, in which argenine is converted to cystine, causes the CadC protein to become lysine independent (Kuper and Jung, 2005).

Despite several attempts, we have been unable to grow the modified CadC operon on pSB1C3 in E. coli suggesting some form of cell toxicity. Specifically, all plasmids isolated have contained additional point mutations that appear to inactivate the expression of CadC. Due to this apparent toxicity, no data regarding the lysine-independent CadC could be collected. Alternative acidic range pH sensor candidates have been identified and are discussed below.

P-atp2

The P-atp2 promoter, native to the bacterium Corynebacterium glutamicum is reportedly induced at pH 7, to pH 9 (BIT-China-2015 and BBa_K1675021). Utilizing the blue chromoprotein (BBa_K592009), a test was designed in which a plasmid containing the P-atp2 promoter with the blue chromoprotein was grown alongside an E. coli line that contained a plasmid with just the blue chromoprotein. We expected to see constant blue chromoprotein production in the control series (those that lacked P-atp2) and a visual increase in blue chromoprotein as the pH was raised from 6 to 9 in the cells that contained the P-atp2 construct. The construct utilized as a control can be found on the iGEM registry BBa_K2097001 as as in figure 5.

However, as seen in figure 4, no clear change in color expression appears in the experimental trials, suggesting a lack of sensitivity of the P-atp2 promoter.

Figure 5. amilCP expressed in E. coli and in liquid LB. Credit: Riya Sreenivasan

Figure 4. Spun down P-atp2 constructs compared to controls in pH6-9. There is no clear gradient change in color expression. Credit: Ian Overman and Alex Alario

GOX Sequences as Putative Promoters

Three endogenous upstream regions of loci on the Gluconobacter oxydans chromosome were reported to show increased mRNA synthesis as pH decreased, were isolated and obtained, as seen in table 1 (Hanke, et al., 2012). Using Golden Gate assembly, these putative promoters have been placed on the Golden Gate entry vector pYTK001 for later use. By utilizing these pH-sensitive promoters with different reporters and transforming them into multiple organisms in kombucha, the visualization of the microbes and their location in kombucha would be possible (Lee, et al., 2015). This will serve as a stepping stone into further understanding how the microbiome of kombucha changes as it brews as well as determining organism concentration specific times during the brewing process.

Gellan Gum

Figure 1. Our plate protocol developed from multiple references and trial and error. The bacteria are first inoculated into rich media for cell multiplication over a span 24 hours before being inoculated with a 1 to 10 dilution into Gellan-production minimal media to maximize the concentration of Gellan in the culture. After 48-96 hours, the culture is then autoclaved or microwaved. Immediately after sterilization, concentrated, sterilized media is added and the plates are poured before the Gellan can solidify. After 5-10 minutes, the plates can be streaked with microbes and placed in an incubator. Credit: Jenna McGuffey

The do-it-yourself (DIY) movement is focused on making science more accessible to the public. Because many consumers brew their own kombucha, we have developed a set of DIY instructions that would allow an average person to analyze their home-brew and identify their kombucha’s species outside of a lab setting. This procedure is possible because of Gellan Gum, produced by the halobacterium Sphingomonas pauci-mobilis.

Figure 2. An LB-Gellan plate streaked with E. coli and incubated for 24 hours at 37°C. Credit: Jenna McGuffey

Figure 3. A YPD-Gellan plate streaked with S. cerevisiae and incubated for 48 hours at 30°C. Credit: Jenna McGuffey

Gellan Gum is produced through aerobic fermentation (Kang et al. 1982). This exopolysaccharide is a “high-molecular-mass, anionic polysaccharide which consists of a tetrasaccharide structure with 20% glucuronic acid, 60%glucose, and 20% rhamnose” (Wang et. al. 2006). The advantages of using Gellan in place of agar include: requiring half of the quantity, a consistent production, more clarity than agar, a reduced plate preparation time along with a faster setting time, stability at high temperatures, and lack of contamination factors found in agar that are toxic to some organisms (Ioannis et. al. 2007).

This protocol involves creating media from every-day grocery store items, autoclaving or microwaving a culture of S. paucimobilis for sterilization, then pouring them into plates which can be streaked with microbes. Figure 1 denotes each of the steps of the protocol. An S. paucimobilis colony is initially grown in conditions that focus the cell’s metabolism on multiplication. This maximizes the number of cells producing Gellan when inoculated into minimal media (Wu et. al. 2014).

We tested this protocol by growing Escherichia coli on LB-Gellan plates and by growing Saccharomyces cerevisiae on YPD-Gellan plates. Both microbes successfully grew on Gellan plates as in Figure 2 and Figure 3. We then confirmed the viability of Gellan-tea media plates to be used for kombucha by streaking various strains that we isolated from Kombucha.

In addition to being usable in this DIY procedure, Gellan Gum is environmentally and socially conscious. Currently there is an agar shortage in the world, because of several threats to its origin, red algae (Calloway 2015).