C1-alkyl AI-2 analogues do not induce bioluminescence in V. harveyi on their own but enhance the bioluminescence induced by AI-2 in a synergistic fashion. A new facile synthesis of AI-2 facilitates the synthesis of a diverse set of AI-2 analogues and biological screening suggests that receptors that are involved in the synergistic bioluminescence production in V. harveyi are promiscuous.
bBacillus anthracis grows in chains of rod-shaped cells, a trait that contributes to its escape from phagocytic clearance in host tissues. Using a genetic approach to search for determinants of B. anthracis chain length, we identified mutants with insertional lesions in secA2. All isolated secA2 mutants exhibited an exaggerated chain length, whereas the dimensions of individual cells were not changed. Complementation studies revealed that slaP (S-layer assembly protein), a gene immediately downstream of secA2 on the B. anthracis chromosome, is also a determinant of chain length. Both secA2 and slaP are required for the efficient secretion of Sap and EA1 (Eag), the two S-layer proteins of B. anthracis, but not for the secretion of S-layer-associated proteins or of other secreted products. S-layer assembly via secA2 and slaP contributes to the proper positioning of BslO, the S-layer-associated protein, and murein hydrolase, which cleaves septal peptidoglycan to separate chains of bacilli. SlaP was found to be both soluble in the bacterial cytoplasm and associated with the membrane. The purification of soluble SlaP from B. anthracis-cleared lysates did not reveal a specific ligand, and the membrane association of SlaP was not dependent on SecA2, Sap, or EA1. We propose that SecA2 and SlaP promote the efficient secretion of S-layer proteins by modifying the general secretory pathway of B. anthracis to transport large amounts of Sap and EA1. The Gram-positive microbe Bacillus anthracis is the causative agent of anthrax and exists in two forms: vegetative, rodshaped bacilli and small endospores (31). Following uptake into animal or human hosts, spores germinate into vegetative forms that replicate and disseminate into all organ tissues (31). Vegetative forms are thought to evade clearance by host phagocytes through the elaboration of a thick capsule, which is composed of poly-D-␥-glutamic acid (PDGA) tethered to the m-diaminopimelic acid cross bridge of peptidoglycan (7, 51), and through the ability to form elongated chains of bacilli tethered end-to-end at their septal peptidoglycan (47). Chains of bacilli present a physical obstacle for engulfment by immune cells (10, 53).The envelope of B. anthracis is comprised of a plasma membrane and a peptidoglycan layer, which is decorated with the secondary cell wall polysaccharide (SCWP) where ␣-GlcNAc is substituted with ␣-Gal and -Gal at O3 and O4, respectively, and -GlcNAc is substituted with ␣-Gal at O3 (8). The SCWP is tethered via GlcNAc-ManNAc linkage units to the C-6 position of N-acetylmuramic acid (MurNAc) in the repeating MurNAc-GlcNAc disaccharide structure of peptidoglycan (26). The B. anthracis S layer is comprised of the main S-layer proteins Sap and EA1 (14,42,43), which self-assemble into a paracrystalline layer of protein (41). The S layer also harbors B. anthracis S-layer-associated proteins (BSLs) (27), which provide for the uptake of nutrients across the envelope (63), adhesion to host tissues (28), and cell separation within chains of vegetative bac...
The envelope of Bacillus anthracis encompasses a proteinaceous S-layer with two S-layer proteins (Sap and EA1). Protein assembly in the envelope of B. anthracis requires S-layer homology domains (SLH) within S-layer proteins and S-layer-associated proteins (BSLs), which associate with the secondary cell wall polysaccharide (SCWP), an acetylated carbohydrate that is tethered to peptidoglycan. Here, we investigated the contributions of two putative acetyltransferases, PatA1 and PatA2, on SCWP acetylation and S-layer assembly. We show that mutations in patA1 and patA2 affect the chain lengths of B. anthracis vegetative forms and perturb the deposition of the BslO murein hydrolase at cell division septa. The patA1 and patA2 mutants are defective for the assembly of EA1 in the envelope but retain the ability of S-layer formation with Sap. SCWP isolated from the patA1 patA2 mutant lacked acetyl moieties identified in wild-type polysaccharide and failed to associate with the SLH domains of EA1. A model is discussed whereby patA1-and patA2-mediated acetylation of SCWP enables the deposition of EA1 as well as BslO near the septal region of the B. anthracis envelope.
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