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Name: SRRz lysis cassette

Base Pairs: 1650 bp 

Origin: Lambda phage

Properties: Bacterial cell lysis

Implementation and function

Being one of the most widely studied bacterial mechanisms, bacterial cell lysis can be evaluated through the expression of native lyric proteins within the cell. Lysis mechanism could be attained and exploited for designed usages, such as promoting cellular membrane disruption, or acting as an intermediate action to release certain proteins to extracellular solutions. Lysis of bacterial hosts or bacterial walls is deliberately scheduled and regulated, accumulating lysozyme activities. In this basic part, we emphasize the use of the SRRz/Rz1 lambdoid lysis cassette, which consists of a lysin and a holin gene.

At first, the T7 constitutive promoter transcribes and translates β-galactosidase and stores the enzyme in the cell. When testing is about to process, the samples are added to the straining container. The promotor causes the ribosomal binding site to initiate the lysis of the gene, causing the bacterial wall to dissolve and releasing the β-Galactosidase.

SRRz lysis cassette, as well as other lysis gene sequences, are recognized for their importance in cell disruption techniques for attaining specific intracellular proteins. One example of a mechanical technique is cell ultrasonication, which often results in protein denaturation, due to the heat produced during the process. As an alternative to mechanical techniques, chemical techniques including membrane decadence resulting from lysozyme activities, can be considered in use. Lysis systems could be engineered and targeted for the recovery or replacement of intracellularly expressed proteins. 

Procedures to prove our lysis module using copper-sensitive promoter:

Cultivation

Firstly, add liquid LB to a tube or flask and add the appropriate strain to the correct concentration. Then sing a sterile pipette tip to select a single colony from your LB agar plate and loosely cover the culture with a cap. Incubate the E. Coli at 37 degrees Celsius and 200 rpm so that the beta galactocidase to function in its optimal condition. After incubation, use OD600 to measure the density of the culture. When OD600 values equals to 0.3, add different concentrations of arabinose. Measure OD600 values at 0.5h, 1h, 1.5h, 2h, 3h and 4h intervals.

Prove

The results suggested that the lysis circuit works regularly when the concentration of copper ions is above 10^-6 molL. The rapid decline of OD600 at 10^-5 molL indicates lysis of bacterial wall, which proves that our lysis module could function normally and continue to work in a relevant context.

Figure 1 OD600 values of different concentration of copper at various timed intervals

Simialr to the results from the pBad/araC promoter, the graph suggested that the lysis circuit works regularly when the concentration of copper is above 10^-6 mol/L.

Figure 2 Comparison of final OD600 values after 4h、10^-6 mol/L、10^-5 mol/L (copper-sensitive promoter)

Copper promoter +srrz cell lysis gene

Promoter from the copper-sensitive CusR/CusS two component signal system. (E.Coli)

This nucleotide sequence is believed to be able to bind with phosphorylated CusR transcription factor in E.coli. CusR protein is phosphorylated by CusS transmembrane protein in a case of high extracellular concentration of copper ions. After phosphorylation CusR interacts with described DNA sequence and activates the transcription of CusA, CusB, CusC and CusF genes coding the proteins of copper metabolic system.

The SRRz gene codes maybe three protein S,R,Rz.The product of S gene would cause lesions on the cytoplasmic membrane through which the product coded by the R gene escapes to the periplasm and causes murein-degrading, while the Rz gene’s product may be an endopeptidase that can cleave the oligopeptide crosslinks in the peptidoglycan and/or between peptidoglycan and the outer membrane.

Procedures to prove our lysis module using lac promoter:

1. Cultivate E. Coli in LB mediums at 37 degrees Celsius and 200 rpm.

2. When OD600 values equals to 0.4, add different concentrations of copper, three times for each group.

3. Measure OD600 values at 0.5h, 1h, 1.5h, 2h, 3h and 4h intervals.

Figure 1 OD600 values of different concentration of copper at various timed intervals

the graph suggested that the lysis circuit works regularly when the concentration of copper is above 10^-5 mol/L.

Figure 1 Comparison of final OD600 values after 4h、10^-5 mol/L、10^-4 mol/L (copper-sensitive promoter）

Our system is initiated by two components: pBad/araC promoter (BBa_I0500) and copper-sensitive promoter (BBa_I760005). Being two efficient and stable promoters, they induce the expression of lysis genes inserted in the bacterial plasmids productively, guaranteeing the working efficiency of our lysis module.

Procedures to prove our lysis module using pBad/araC promoter:

1. Cultivate E. Coli in LB mediums at 37 degrees Celsius and 200 rpm.

2. When OD600 values equals to 0.3, add different concentrations of arabinose, three times for each group.

3. Measure OD600 values at 0.5h, 1h, 1.5h, 2h, 3h and 4h intervals.

Figure 1 OD600 values of different concentration of arabinose at various timed intervals

The results suggested that the lysis circuit works regularly when the concentration of arabinose is above 10^-6 mol/L. The rapid decline of OD600 at 10^-5 mol/L indicates lysis of bacterial wall, which proves that our lysis module could function normally and continue to work in a relevant context.

Figure 2 Comparison of OD values after 4h、10^-5 mol/L、10^-6 mol/L to control group (pBad/araC promoter)

Procedures to prove our lysis module using copper-sensitive promoter:

1. Cultivate E. Coli in LB mediums at 37 degrees Celsius and 200 rpm.

2. When OD600 values equals to 0.3, add different concentrations of copper, three times for each group.

3. Measure OD600 values at 0.5h, 1h, 1.5h, 2h, 3h and 4h intervals.

srrz cell lysis gene

We used the copper-sensitive CusR/CusS promoter, a two-component signal transduction system that is responsive to copper, coded by Escherichia coli. This nucleotide sequence is believed to be able to bind with phosphorylated CusR transcription factor in E.coli. CusR protein is phosphorylated by CusS transmembrane protein in a case of high extracellular concentration of copper ions. After phosphorylation CusR interacts with described DNA sequence and activates the transcription of CusA, CusB, CusC and CusF genes coding the proteins of the copper metabolic system. This system is initiated by the expression of pcoE, induced by copper ions. pcoE is a gene from the copper-resisting operon pco in. E.coli. Similar to CusR and CusS, PcoR and PcoS from the pco operon are two-component systems, which are also involved in regulating metal-responsive genes.

The SRRz gene codes maybe three proteins: S,R,Rz. The product of S gene would cause lesions on the cytoplasmic membrane through which the product coded by the R gene escapes to the periplasm and causes murein-degrading, while the Rz gene’s product may be an endopeptidase that can cleave the oligopeptide crosslinks in the peptidoglycan and/or between peptidoglycan and the outer membrane.

Sequence and Features