Lactic acid bacteria
Lactic acid bacteria (LAB) are a group of Gram positive, non-sporulating bacteria that include microorganisms from different genuses such as Leuconostoc, Lactococcus, Lactobacillus, Pedicoccus, and Streptococcus. LAB do not contain LPS attached to the cell membrane. The absence of such endotoxins avoids the possibility of anaphylactic shock when LAB are administered in humans. LAB has a long history of safe use in food production and preservation. It is used to ferment a range of raw materials, such as milk, which is used to produce cheese (species of Lactococcus) and yoghurt (species of Streptococcus and Lactobacillus). Some strains have also been used as probiotic bacteria producers of metabolites and macromolecules that are able to maintain and promote human health. LAB have been classified as food grade microorganisms, which are generally recognized as safe (GRAS) organisms by the US Food and Drug Administration (FDA) and fulfill criteria of the qualified presumption of safety (QPS) according to the European Food Safety Authority (EFSA).
Over the past decade, there has been an increasing interest in the use of LAB as a synthetic biology chassis. For instance, in therapeutics, LAB are used as live delivery vehicles for DNA, peptides, single-chain antibody fragments (ScFvs), antigens, cytokines, enzymes and allergens to treat or prevent infectious diseases, cancer, gastrointestinal tract (GIT) diseases, diabetes, and so on. (Figure 2) In iGEM, several teams have tried to ameliorate LAB to be new chassis in synthetic biology. In 2013, Uppsala-Sweden team designed and tested many promoters, reporter genes, vectors, toxin-antitoxin systems, and signal peptides to make Lactobacillus new probiotic chassis in synthetic biology. They submitted about 70 parts in different series which are subsequently widely used by many iGEM teams. Moreover, many teams have applied LAB in different tracks for different tasks. Lactobacillus bulgaricus was used to build a sustainable and savory drug delivery system (Massachusetts Institute of Technology-USA, 2008). The lycopene and astaxanthin pathway of Lactobacillus casei. was engineered by Uppsala University-Sweden in 2013). Lactococcus lactis was used to create a smart bandage that can heal burn wound and fight against bacterial infections (Groningen University- Netherlands, 2014).
Figure 2 Current applications of lactic acid bacteria