L-forms, Listeria monocytogenes, cell wall-deficient, gene expression, stress, Science & Technology, Life Sciences & Biomedicine, Biochemistry & Molecular Biology, Microbiology, BACILLUS-SUBTILIS, ESCHERICHIA-COLI, TRANSCRIPTOME ANALYSIS, NUCLEOTIDE-SEQUENCE, VIRULENCE, PROTEIN, BACTERIA, GROWTH, PATHOGENICITY, RECOGNITION, Bacterial Outer Membrane Proteins, Cell Division, Cell Membrane, Cell Wall, Cytoplasmic Vesicles, Gene Expression Profiling, Gene Expression Regulation, Bacterial, L Forms, Microscopy, Electron, Transmission, Oligonucleotide Array Sequence Analysis, RNA, Bacterial, Sequence Analysis, DNA, 06 Biological Sciences, 11 Medical and Health Sciences, 07 Agricultural and Veterinary Sciences
Cell wall-deficient bacteria referred to as L-forms have lost the ability to maintain or build a rigid peptidoglycan envelope. We have generated stable, nonreverting L-form variants of the Gram-positive pathogen Listeria monocytogenes, and studied the cellular and molecular changes associated with this transition. Stable L-form cells can occur as small protoplast-like vesicles and as multinucleated, large bodies. They have lost the thick, multilayered murein sacculus and are surrounded by a cytoplasmic membrane only, although peptidoglycan precursors are still produced. While they lack murein-associated molecules including Internalin A, membrane-anchored proteins such as Internalin B are retained. Surprisingly, L-forms were found to be able to divide and propagate indefinitely without a wall. Time-lapse microscopy of fluorescently labelled L-forms indicated a switch to a novel form of cell division, where genome-containing membrane vesicles are first formed within enlarged L-forms, and subsequently released by collapse of the mother cell. Array-based transcriptomics of parent and L-form cells revealed manifold differences in expression of genes associated with morphological and physiological functions. The L-forms feature downregulated metabolic functions correlating with the dramatic shift in surface to volume ratio, whereas upregulation of stress genes reflects the difficulties in adapting to this unusual, cell wall-deficient lifestyle.