Roseococcus microcysteis sp. nov., isolated from a Microcystis aeruginosa culture sample

Strain NIBR12T (=KACC 22094T=HAMBI 3739T), a novel Gram-stain-negative, obligate aerobic, non-spore-forming, non-motile and coccobacillus-shaped bacterium, was isolated from a cyanobacterial sample culture (Microcysitis aeruginosa NIBRCYC000000452). The newly identified bacterial strain grew optimally in modified Reasoner's 2A medium under the following conditions: 0 % (w/v) NaCl, pH 7.5 and 35 °C. Phylogenetic analysis using the 16S rRNA gene sequence confirmed that strain NIBR12T belongs to the genus Roseococcus , with its closest neighbours being Roseococcus suduntuyensis SHETT (98.8%), Roseococcus thiosulfatophilus RB-3T (97.7%), “Sediminicoccus rosea” R-30T (95.7 %) and Rubritepida flocculans H-8T (95.0 %). Genomic comparison of strain NIBR12T with type species in the genus Roseococcus was conducted using digital DNA–DNA hybridization, average nucleotide identity and average amino acid identity analyses, resulting in values of ≤53.7, ≤93.7 and ≤96.1 %, respectively. The genomic DNA G+C content of strain NIBR12T was 70.9 mol%. The major fatty acids of strain NIBR12T were summed feature 8 (C18 : 1 ω7c and/or C18:1 ω6c) and summed feature 3 (C16 : 1 ω6c/C16 : 1 ω7c). Q-9 was its major respiratory quinone. Moreover, the major polar lipids of strain NIBR12T were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and phosphatidylcholine. Based on our chemotaxonomic, genotypic and phenotype analyses, strain NIBR12T is identified as represeting a novel species of the genus Roseococcus , for which the name Roseococcus microcysteis sp. nov. is proposed.

Bactericidal Activity of a Self-Biodegradable Lysine-Containing Dendrimer against Clinical Isolates of Acinetobacter Genus

The genus Acinetobacter consists of Gram-negative obligate aerobic pathogens, including clinically relevant species, such as A. baumannii, which frequently cause hospital infections, affecting debilitated patients. The growing resistance to antimicrobial therapies shown by A. baumannii is reaching unacceptable levels in clinical practice, and there is growing concern that the serious conditions it causes may soon become incurable. New therapeutic possibilities are, therefore, urgently needed to circumvent this important problem. Synthetic cationic macromolecules, such as cationic antimicrobial peptides (AMPs), which act as membrane disrupters, could find application in these conditions. A lysine-modified cationic polyester-based dendrimer (G5-PDK), capable of electrostatically interacting with bacterial surfaces as AMPs do, has been synthesized and characterized here. Given its chemical structure, similar to that of a fifth-generation lysine containing dendrimer (G5K) with a different core, and previously found inactive against Gram-positive bacterial species and Enterobacteriaceae, the new G5-PDK was also ineffective on the species mentioned above. In contrast, it showed minimum inhibitory concentration values (MICs) lower than reported for several AMPs and other synthetic cationic compounds on Acinetobacter genus (3.2–12.7 µM). Time-kill experiments on A. baumannii, A. pittii, and A. ursingii ascertained the rapid bactericidal effects of G5-PDK, while subsequent bacterial regrowth supported its self-biodegradability.

Bordetella bronchiseptica: a rare cause of meningitis

Background Bordetella bronchiseptica is a gram-negative, obligate aerobic coccobacillus known to cause disease in domesticated animals and pets. In humans, B. bronchiseptica commonly leads to respiratory infections like pneumonia or bronchitis, and animal contact usually precedes the onset of symptoms. Case presentation We report a case of post-traumatic B. bronchiseptica meningitis without recent surgery in the setting of immunosuppression with a monoclonal antibody. Our case concerns a 77-year-old male with ulcerative colitis on infliximab who sustained a mechanical fall and developed a traumatic cerebrospinal fluid leak complicated by meningitis. He received meropenem then ceftazidime during his hospital course, and temporary neurosurgical drain placement was required. His clinical condition improved, and he was discharged at his baseline neurological status. Conclusions B. bronchiseptica is an unusual cause of meningitis that may warrant consideration in immunocompromised hosts with known or suspected animal exposures. To better characterize this rare cause of meningitis, we performed a systematic literature review and summarized all previously reported cases.

Structure of mycobacterial ATP synthase with the TB drug bedaquiline

SummaryTuberculosis (TB), the leading cause of death by infectious disease worldwide, is increasingly resistant to first line antibiotics. Developed from a screen against Mycobacterium smegmatis, bedaquiline can sterilize even latent M. tuberculosis infections that may otherwise persist for decades and has become a cornerstone of treatment for multidrug resistant and extensively-drug resistant TB. Bedaquiline targets mycobacterial ATP synthase, an essential enzyme in the obligate aerobic Mycobacterium genus. However, how the drug binds the intact enzyme is unknown. We determined the structure of M. smegmatis ATP synthase with and without bedaquiline. The drug-free structure reveals hook-like extensions from the enzyme’s α subunits that inhibit ATP hydrolysis in low-energy conditions, such as during latent infections. Bedaquiline binding induces global conformational changes in ATP synthase, creating tight binding pockets at the interface of subunits a and c. These binding sites explain the drug’s structure-activity relationship and its potency as an antibiotic for TB.

Complete Genome Sequence of Methylomonas denitrificans Strain FJG1, an Obligate Aerobic Methanotroph That Can Couple Methane Oxidation with Denitrification

ABSTRACT Methylomonas denitrificans strain FJG1 is a member of the gammaproteobacterial methanotrophs. The sequenced genome of FJG1 reveals the presence of genes that encode methane, methanol, formaldehyde, and formate oxidation. It also contains genes that encode enzymes for nitrate reduction to nitrous oxide, consistent with the ability of FJG1 to couple denitrification with methane oxidation.

Nitrous Oxide Reduction by an Obligate Aerobic Bacterium, Gemmatimonas aurantiaca Strain T-27

ABSTRACT N2O-reducing organisms with nitrous oxide reductases (NosZ) are known as the only biological sink of N2O in the environment. Among the most abundant nosZ genes found in the environment are nosZ genes affiliated with the understudied Gemmatimonadetes phylum. In this study, a unique regulatory mechanism of N2O reduction in Gemmatimonas aurantiaca strain T-27, an isolate affiliated with the Gemmatimonadetes phylum, was examined. Strain T-27 was incubated with N2O and/or O2 as the electron acceptor. Significant N2O reduction was observed only when O2 was initially present. When batch cultures of strain T-27 were amended with O2 and N2O, N2O reduction commenced after O2 was depleted. In a long-term incubation with the addition of N2O upon depletion, the N2O reduction rate decreased over time and came to an eventual stop. Spiking of the culture with O2 resulted in the resuscitation of N2O reduction activity, supporting the hypothesis that N2O reduction by strain T-27 required the transient presence of O2. The highest level of nosZ transcription (8.97 nosZ transcripts/recA transcript) was observed immediately after O2 depletion, and transcription decreased ∼25-fold within 85 h, supporting the observed phenotype. The observed difference between responses of strain T-27 cultures amended with and without N2O to O2 starvation suggested that N2O helped sustain the viability of strain T-27 during temporary anoxia, although N2O reduction was not coupled to growth. The findings in this study suggest that obligate aerobic microorganisms with nosZ genes may utilize N2O as a temporary surrogate for O2 to survive periodic anoxia. IMPORTANCE Emission of N2O, a potent greenhouse gas and ozone depletion agent, from the soil environment is largely determined by microbial sources and sinks. N2O reduction by organisms with N2O reductases (NosZ) is the only known biological sink of N2O at environmentally relevant concentrations (up to ∼1,000 parts per million by volume [ppmv]). Although a large fraction of nosZ genes recovered from soil is affiliated with nosZ found in the genomes of the obligate aerobic phylum Gemmatimonadetes, N2O reduction has not yet been confirmed in any of these organisms. This study demonstrates that N2O is reduced by an obligate aerobic bacterium, Gemmatimonas aurantiaca strain T-27, and suggests a novel regulation mechanism for N2O reduction in this organism, which may also be applicable to other obligate aerobic organisms possessing nosZ genes. We expect that these findings will significantly advance the understanding of N2O dynamics in environments with frequent transitions between oxic and anoxic conditions.