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In bacteria, chromosomal DNA spends most of its time floating in the cytoplasm without ever needing to venture across a membrane barrier. But when cells mate, or are about to [...]

A genomic and bioactivity informed analysis of the metabolome of the extremophile Amycolatopsis sp. DEM30355 has allowed for the discovery and isolation of the polyketide antibiotic tatiomicin. Identification of the biosynthetic gene cluster was confirmed by heterologous expression in Streptomyces coelicolor M1152. Structural elucidation, including absolute stereochemical assignment, was performed using complementary crystallographic, spectroscopic and computational methods. Tatiomicin shows antibiotic activity against Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). Cytological profiling experiments suggest a putative antibiotic mode-of-action, involving membrane depolarisation and chromosomal decondensation of the target bacteria., (© 2022. The Author(s).)

The peptidoglycan cell wall is an essential structure for the growth of most bacteria. However, many are capable of switching into a wall-deficient L-form state in which they are resistant to antibiotics that target cell wall synthesis under osmoprotective conditions, including host environments. L-form cells may have an important role in chronic or recurrent infections. The cellular pathways involved in switching to and from the L-form state remain poorly understood. This work shows that the lack of a cell wall, or blocking its synthesis with β-lactam antibiotics, results in an increased flux through glycolysis. This leads to the production of reactive oxygen species from the respiratory chain, which prevents L-form growth. Compensating for the metabolic imbalance by slowing down glycolysis, activating gluconeogenesis or depleting oxygen enables L-form growth in Bacillus subtilis, Listeria monocytogenes and Staphylococcus aureus. These effects do not occur in Enterococcus faecium, which lacks the respiratory chain pathway. Our results collectively show that when cell wall synthesis is blocked under aerobic and glycolytic conditions, perturbation of cellular metabolism causes cell death. We provide a mechanistic framework for many anecdotal descriptions of the optimal conditions for L-form growth and non-lytic killing by β-lactam antibiotics.

The bacterial cell wall is a highly conserved essential component of most bacterial groups. It is the target for our most frequently used antibiotics and provides important small molecules that trigger powerful innate immune responses. The wall is composed of glycan strands crosslinked by short peptides. For many years, the penicillin-binding proteins were thought to be the key enzymes required for wall synthesis. RodA and possibly other proteins in the wider SEDS (shape, elongation, division and sporulation) family have now emerged as a previously unknown class of essential glycosyltranferase enzymes, which play key morphogenetic roles in bacterial cell wall synthesis. We provide evidence in support of this role and the discovery of small natural product molecules that probably target these enzymes. The SEDS proteins have exceptional potential as targets for new antibacterial therapeutic agents.

The peptidoglycan cell wall is a major protective external sheath in bacteria and a key target for antibiotics(1). Peptidoglycan is present in virtually all bacteria, suggesting that it was probably present in the last bacterial common ancestor(2). Cell wall expansion is orchestrated by cytoskeletal proteins related to actin (MreB) and tubulin (FtsZ)(3). FtsZ is a key essential player in a highly organized division machine that directs an invaginating annulus of cell wall peptidoglycan. The recent discovery that cell-wall-less bacteria (L-forms) can grow and divide independently of FtsZ(4,5), provided a means of generating an ftsZ null mutant of Escherichia coli. Remarkably, we have been able to isolate variants of E. coli that lack FtsZ but are capable of efficient growth in a walled state. Genetic analysis reveals that a combination of mutations is needed for this phenotype. Importantly, the suppressive mutations lead to a major cell shape change, from the normal cylindrical shape to a branched and bulging, ramified shape, which we call 'coli-flower'. The results highlight the versatility of bacterial cells and illustrate possible evolutionary routes leading to the emergence of specialized bacteria, such as pathogenic Chlamydia or aquatic Planctomycetes, that lack FtsZ but retain the cell wall(6-8).