Sortase-deficient lactobacilli: effect on immunomodulation and gut retention.

Surface proteins of probiotic microbes, including Lactobacillus acidophilus and Lactobacillus gasseri, are believed to promote retention in the gut and mediate host-bacterial communications. Sortase, an enzyme that covalently couples a subset of extracellular proteins containing an LPXTG motif to the cell surface, is of particular interest in characterizing bacterial adherence and communication with the mucosal immune system. A sortase gene, srtA, was identified in L. acidophilus NCFM (LBA1244) and L. gasseri ATCC 33323 (LGAS_0825). Additionally, eight and six intact sortase-dependent proteins were predicted in L. acidophilus and L. gasseri, respectively. Due to the role of sortase in coupling these proteins to the cell wall, ΔsrtA deletion mutants of L. acidophilus and L. gasseri were created using the upp-based counterselective gene replacement system. Inactivation of sortase did not cause significant alteration in growth or survival in simulated gastrointestinal juices. Meanwhile, both ΔsrtA mutants showed decreased adhesion to porcine mucin in vitro. Murine dendritic cells exposed to the ΔsrtA mutant of L. acidophilus or L. gasseri induced lower levels of pro-inflammatory cytokines TNF-α and IL-12, respectively, compared with the parent strains. In vivo co-colonization of the L. acidophilus ΔsrtA mutant and its parent strain in germ-free 129S6/SvEv mice resulted in a significant one-log reduction of the ΔsrtA mutant population. Additionally, a similar reduction of the ΔsrtA mutant was observed in the caecum. This study shows for the first time that sortase-dependent proteins contribute to gut retention of probiotic microbes in the gastrointestinal tract.

Relevance and application of sortase and sortase-dependent proteins in lactic acid bacteria.

Lactic acid bacteria (LAB) are a diverse group of Gram-positive bacteria found in a vast array of environments including dairy products and the human gastrointestinal tract (GIT). In both niches, surface proteins play a crucial role in mediating interactions with the surrounding environment. The sortase enzyme is responsible for covalently coupling a subset of sortase-dependent proteins (SDPs) to the cell wall of Gram-positive organisms through recognition of a conserved C-terminal LPXTG motif. Genomic sequencing of LAB and annotation has allowed for the identification of sortase and SDPs. Historically, sortase and SDPs were predominately investigated for their role in mediating pathogenesis. Identification of these proteins in LAB has shed light on their important roles in mediating nutrient acquisition through proteinase P as well as positive probiotic attributes including adhesion, mucus barrier function, and immune signaling. Furthermore, sortase expression signals in LAB have been exploited as a means to develop oral vaccines targeted to the GIT. In this review, we examine the collection of studies which evaluate sortase and SDPs in select species of dairy-associated and health promoting LAB.

Surface tension-driven self-folding polyhedra.

We discuss finite element simulations and experiments involving the surface tension-driven self-folding of patterned polyhedra. Two-dimensional (2D) photolithographically patterned templates folded spontaneously when solder hinges between adjacent faces were liquefied. Minimization of interfacial free energy of the molten solder with the surrounding fluidic medium caused the solder to ball up, resulting in a torque that rotated adjacent faces and drove folding. The simulations indicate that the folding process can be precisely controlled, has fault tolerance, and can be used to fold polyhedra composed of a variety of materials, ranging in size from the millimeter scale down to the nanometer scale. Experimentally, we have folded metallic, arbitrarily patterned polyhedra ranging in size from 2 mm to 15 microm.