Rates of infection with hospital-acquired Acinetobacter baumannii have exploded over the past decade due to our inability to limit persistence and effectively treat disease. A. baumannii quickly acquires antibiotic resistance, and its genome encodes mechanisms to tolerate biocides and desiccation, which enhance its persistence in hospital settings. With depleted antibiotic options, new methods to treat A. baumannii infections are desperately needed. A comprehensive understanding detailing A. baumannii cellular factors that contribute to its resiliency at genetic and mechanistic levels is vital to the development of new treatment options. Tools to rapidly dissect the A. baumannii genome will facilitate this goal by quickly advancing our understanding of A. baumannii gene-phenotype relationships. We describe here a recombination-mediated genetic engineering (recombineering) system for targeted genome editing of A. baumannii. We have demonstrated that this system can perform directed mutagenesis on wide-ranging genes and operons and is functional in various strains of A. baumannii, indicating its broad application. We utilized this system to investigate key gene-phenotype relationships in A. baumannii biology important to infection and persistence in hospitals, including oxidative stress protection, biocide resistance mechanisms, and biofilm formation. In addition, we have demonstrated that both the formation and movement of type IV pili play an important role in A. baumannii biofilm.

Over half of adults experience gingivitis, a mild yet treatable form of periodontal disease caused by the overgrowth of oral microbes. Left untreated, gingivitis can progress to a more severe and irreversible disease, most commonly chronic periodontitis. While periodontal diseases are associated with a shift in the oral microbiota composition, it remains unclear how this shift impacts microbiota function early in disease progression. Here, we analyzed the transition from health to gingivitis through both 16S v4-v5 rRNA amplicon and metatranscriptome sequencing of subgingival plaque samples from individuals undergoing an experimental gingivitis treatment. Beta-diversity analysis of 16S rRNA reveals that samples cluster based on disease severity and patient but not by oral hygiene status. Significant shifts in the abundance of several genera occurred during disease transition, suggesting a dysbiosis due to development of gingivitis. Comparing taxonomic abundance with transcriptomic activity revealed concordance of bacterial diversity composition between the two quantification assays in samples originating from both healthy and diseased teeth. Metatranscriptome sequencing analysis indicates that during the early stages of transition to gingivitis, a number of virulence-related transcripts were significantly differentially expressed in individual and across pooled patient samples. Upregulated genes include those involved in proteolytic and nucleolytic processes, while expression levels of those involved in surface structure assembly and other general virulence functions leading to colonization or adaptation within the host are more dynamic. These findings help characterize the transition from health to periodontal disease and identify genes associated with early disease.

Here we implement ultraviolet photodissociation (UVPD) in an online liquid chromatographic tandem mass spectrometry (MS/MS) strategy to support analysis of complex mixtures of lipid A combinatorially modified during development of vaccine adjuvants. UVPD mass spectrometry at 193 nm was utilized to characterize the structures and fragment ion types of lipid A from Escherichia coli, Vibrio cholerae, and Pseudomonas aeruginosa using an Orbitrap mass spectrometer. The fragment ions generated by UVPD were compared to those from collision induced dissociation (CID) and higher energy collision dissociation (HCD) with respect to the precursor charge state. UVPD afforded the widest array of fragment ion types including acyl chain C–O, C–N, and C–C bond cleavages and glycosidic C–O and cross ring cleavages, thus providing the most comprehensive structural analysis of the lipid A. UVPD exhibited virtually no dependence on precursor ion charge state and was best at determining lipid A structure including acyl chain length and composition, giving it an advantage over collision based methods. UVPD was incorporated into an LC–MS/MS methodology for the analysis of a number of structural variants in a complex mixture of combinatorially engineered Escherichia coli lipid A.

Summary Gram-negative bacteria survive harmful environmental stressors by modifying their outer membrane. Much of this protection is afforded upon remodeling of the lipid A region of the major surface molecule lipopolysaccharide (LPS). For example, the addition of cationic substituents, such as 4-amino-4-deoxy-L-arabinose (L-Ara4N) and phosphoehthanolamine (pEtN) at the lipid A phosphate groups is often induced in response to specific environmental flux stabilizing the outer membrane. The work herein represents the first report of pEtN addition to P. aeruginosa lipid A. We have identified the key pEtN transferase which we named EptAPa and characterized its strict activity on only one position of lipid A, contrasting from previously studied EptA enzymes. We further show that transcription of eptAPa is regulated by zinc via the ColRS two-component system instead of the PmrAB system responsible for eptA regulation in E. coli and S. enterica. Further, although L-Ara4N is readily added to the same position of lipid A as pEtN under certain environmental conditions, ColR specifically induces pEtN addition to lipid A in lieu of L-Ara4N when Zn2+ is present. The unique, specific regulation of eptAPa transcription and enzymatic activity described in this work demonstrates the tight yet inducible control over LPS modification in P. aeruginosa.