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The author comments on a study published within the isse which argues that the activation of CpxRA actually helps bacteria resist aminoglycoside and hydroxyurea lethality. He believes that the common pathway model for antibiotic lethality links broad areas of bacterial physiology and accounts for large sets of genome-scale data. The author finds that the model was thus a plausible working hypothesis with experimentally testable predictions.

To characterize the consequences of eliminating essential functions needed for peptidoglycan synthesis, we generated deletion mutations of Acinetobacter baylyi by natural transformation and visualized the resulting microcolonies of dead cells. We found that loss of genes required for peptidoglycan precursor synthesis or polymerization led to the formation of polymorphic giant cells with diameters that could exceed ten times normal. Treatment with antibiotics targeting early or late steps of peptidoglycan synthesis also produced giant cells. The giant cells eventually lysed, although they were partially stabilized by osmotic protection. Genome-scale transposon mutant screening (Tn-seq) identified mutations that blocked or accelerated giant cell formation. Among the mutations that blocked the process were those inactivating a function predicted to cleave murein glycan chains (the MltD murein lytic transglycosylase), suggesting that giant cell formation requires MltD hydrolysis of existing peptidoglycan. Among the mutations that accelerated giant cell formation after ß-lactam treatment were those inactivating an enzyme that produces unusual 3->3 peptide cross-links in peptidoglycan (the LdtG L,D-transpeptidase). The mutations may weaken the sacculus and make it more vulnerable to further disruption. Although the study focused on A. baylyi, we found that a pathogenic relative (A. baumannii) also produced giant cells with genetic dependencies overlapping those of A. baylyi. Overall, the analysis defines genetic pathway for giant cell formation conserved in Acinetobacter species in which independent initiating branches converge to create the unusual cells. [ABSTRACT FROM AUTHOR]

Teredinibacter turnerae is an intracellular bacterial symbiont in the gills of wood-eating shipworms, where it is proposed to use antibiotics to defend itself and its animal host. Several biosynthetic gene clusters are conserved in T. turnerae and their host shipworms around the world, implying that they encode defensive compounds. Here, we describe turnercyclamycins, lipopeptide antibiotics encoded in the genomes of all sequenced T. turnerae strains. Turnercyclamycins are bactericidal against challenging Gram-negative pathogens, including colistin-resistant Acinetobacter baumannii. Phenotypic screening identified the outer membrane as the likely target. Turnercyclamycins and colistin operate by similar cellular, although not necessarily molecular, mechanisms, but turnercyclamycins kill colistin-resistant A. baumannii , potentially filling an urgent clinical need. Thus, by exploring environments that select for the properties we require, we harvested the fruits of evolution to discover compounds with potential to target unmet health needs. Investigating the symbionts of shipworms is a powerful example of this principle. [Display omitted] • Microbial competition in a symbiosis leading to antibiotics • Group of lipopeptide antibiotics that targets drug-resistant Acinetobacter The symbiotic bacteria associated with marine shipworms are prolific producers of bioactive metabolites. Miller et al. use an ecology-guided approach to isolate the turnercyclamycins, proposed to be important for this association. Turnercyclamycins are described as a group of lipopeptide antibiotics with selective activity against Gram-negative pathogens, including drug-resistant Acinetobacter. [ABSTRACT FROM AUTHOR]