Proteus mirabilis biofilm expansion microscopy yields over 4-fold magnification for super-resolution of biofilm structure and subcellular DNA organization

Bacterial biofilms form when bacteria attach to surfaces and generate an extracellular matrix that embeds and stabilizes a growing community. Detailed visualization and quantitative analysis of biofilm architecture by optical microscopy are limited by the law of diffraction. Expansion Microscopy (ExM) is a novel Super-Resolution technique where specimens are physically enlarged by a factor of ∼4, prior to observation by conventional fluorescence microscopy. ExM requires homogenization of rigid constituents of biological components by enzymatic digestion. We developed an ExM approach capable of expanding 48-h old Proteus mirabilis biofilms 4.3-fold (termed PmbExM), close to the theoretic maximum expansion factor without gross shape distortions. Our protocol, based on lytic and glycoside-hydrolase enzymatic treatments, degrades rigid components in bacteria and extracellular matrix. Our results prove PmbExM to be a versatile and easy-to-use Super-Resolution approach for enabling studies of P. mirabilis biofilm architecture, assembly, and even intracellular features, such as DNA organization.

Development of lead (Pb) tolerant strain by protoplast technology and their remediation

The lead is poisonous metal and because of its chemical nature it acts as an environmental contaminant through the water or soil and it becomes toxic to humans. The toxicity of Pb occurs as a change in the conformation of nucleic acid and protein, inhibition of enzyme activity, disruption of membrane function and oxidative phosphorylation. For protoplast preparation, the removal of the cell wall and protoplast formation obtained by specific lytic enzyme. In cytoplasmic membrane, the envelope of bacteria consists of overlying cell wall. From hypertonic environment, the complete cell wall removal occurs due to which it maintains the osmotic integrity of the cell and produces the protoplast. In current work, protoplasts were produced by specific lytic enzyme (lysozyme and macerozyme), chemo fused (with the help of Polyethylene Glycol) and regenerated from strains Staphylococcus sp. and Bacillus sp. The fused protoplast was spherical in shape observed under microscopy. Colonies were screened on specific medium supplemented with Pb (Concentration at the rate of 1.5mM). One resistant colony (MICBT-1) was selected and further examined and applied for the transformation of Pb in the broth medium. The strain removed 98% of Pb at 1mM concentration. Next, sucrose containing medium was best which gives maximum protoplast regeneration. From various organisms, fusion technique has been used to combine the genes to create the strains having desired properties. This is a significant technique for engineering of bacterial strains for advantageous applied properties. Further MICBT-1 applied in artificially contaminated soil and removed maximally in exchangeable fraction (remains up to 0.05 mM). An efficient bioremediating agent for lead transformation from soil and water is expected to ease the ever-increasing problem. Further, it is needful to obtain new strain with the help of protoplast technology which can reduce the pollutant. This lead tolerant strain can be applied for bioremediation purposes in the Pb contaminated soil and water environment.

Phenotypic and genotypic characterization of peptidoglycan hydrolases of Lactobacillus sakei

Lactobacillus sakei, a lactic acid bacterium naturally found in fresh meat and sea products, is considered to be one of the most important bacterial species involved in meat fermentation and bio-preservation. Several enzymes of Lb. sakei species contributing to microbial safeguarding and organoleptic properties of fermented-meat were studied. However, the specific autolytic mechanisms and associated enzymes involved in Lb. sakei are not well understood. The autolytic phenotype of 22 Lb. sakei strains isolated from Tunisian meat and seafood products was evaluated under starvation conditions, at pH 6.5 and 8.5, and in the presence of different carbon sources. A higher autolytic rate was observed when cells were grown in the presence of glucose and incubated at pH 6.5. Almost all strains showed high resistance to mutanolysin, indicating a minor role of muramidases in Lb. sakei cell lysis. Using Micrococcus lysodeikticus cells as a substrate in activity gels zymogram, peptidoglycan hydrolase (PGH) patterns for all strains was characterized by two lytic bands of ∼80 (B1) and ∼70 kDa (B2), except for strain BMG.167 which harbored two activity signals at a lower MW. Lytic activity was retained in high salt and in acid/basic conditions and was active toward cells of Lb. sakei, Listeria monocytogenes, Listeria ivanovii and Listeria innocua. Analysis of five putative PGH genes found in the Lb. sakei 23 K model strain genome, indicated that one gene, lsa1437, could encode a PGH (N-acetylmuramoyl-L-alanine amidase) containing B1 and B2 as isoforms. According to this hypothesis, strain BMG.167 showed an allelic version of lsa1437 gene deleted of one of the five LysM domains, leading to a reduction in the MW of lytic bands and the high autolytic rate of this strain. Characterization of autolytic phenotype of Lb. sakei should expand the knowledge of their role in fermentation processes where they represent the dominant species.