Background
Whole cell biosensors provide a simple method for the detection of heavy metals. However, previous designs of them rely primarily on simulation of heavy metal resistance systems of bacteria.
Results
This study proposes a strategy for the rational design of metal detection circuits based on sensor proteins of the MerR family. Our results indicate the expression level of sensor protein can be used as a “rheostat” for tuning detection sensitivity with parabola curves to represent the relationships between the detection slopes and the sensor protein levels. This circuits design strategy (named as “Parabola Principle”), is used as a guide for the discovery of optimum metal detection circuits, and the design of biosensors with specific metal detection characteristics. For example, visible qualitative Hg (II) biosensors with a threshold of 0.05 mg/L are successfully constructed.
Conclusions
These results indicate the feasibility of developing a sensor that is much more tunable than what is presented.
Graphical abstract
Electronic supplementary material
The online version of this article (10.1186/s13036-019-0202-3) contains supplementary material, which is available to authorized users.
Metabolites of serum and milk from genetically modified (GM) cows
and contrast check (CK) cows were comparatively investigated. Serum
and milk were collected from genetically modified (GM) cows and contrast
check (CK) cows, and then, they were analyzed using ultraperformance
liquid chromatography–mass spectrometry (UPLC–MS) and
gas chromatography–mass spectrometry (GC–MS). Although
the level of some blood biochemical indexes for GM cows was shifted
up or down, they were generally in normal physiological condition.
Serum samples from lactoferrin GM cows exhibited reduced levels of
amino acids and elevated levels of indoleacetate, α-keto acids,
long-chain fatty acids, etc. GM milk possessed elevated levels of
pentose and amino sugar metabolites, including arabitol, xylulose,
glucuronate, and N-acetylgalactosamine. Interestingly, some essential
nutrients, such as certain unsaturated fatty acids (e.g., eicosapentaenoic
acid (EPA), docosahexaenoic acid (DHA), and docosapentaenoic acid
(DPA)), and some necessary rare sugars were significantly upregulated.
Compared to the CK group, a Kyoto Encyclopedia of Genes and Genomes
(KEGG) pathway analysis was conducted based on the increased or decreased
metabolites identified in the serum and milk samples of the GM group.
The results showed that the GM cows were in healthy condition and
their milk has improved benefits for customers. The milk from genetically
modified cows was found to be a promising milk source for producing
recombinant human lactoferrin (rhLF) for human beings.
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