Inhibition of nitrogenase by oxygen in marine cyanobacteria controls the global nitrogen and oxygen cycles

International audienceCyanobacterial N2-fixation supplies the vast majority of biologically accessible inorganic nitrogen to nutrient-poor aquatic ecosystems. The process, catalyzed by the heterodimeric protein complex, nitrogenase, is thought to predate that of oxygenic photosynthesis. Remarkably, while the enzyme plays such a critical role in Earth's biogeochemical cycles, the activity of nitrogenase in cyanobacteria is markedly inhibited in vivo at a post-translational level by the concentration of O2 in the contemporary atmosphere leading to metabolic and biogeochemical inefficiency in N2 fixation. We illustrate this crippling effect with data from Trichodesmium spp. an important contributor of "new nitrogen" to the world's subtropical and tropical oceans. The enzymatic inefficiency of nitrogenase imposes a major elemental taxation on diazotrophic cyanobacteria both in the costs of protein synthesis and for scarce trace elements, such as iron. This restriction has, in turn, led to a global limitation of fixed nitrogen in the contemporary oceans and provides a strong biological control on the upper bound of oxygen concentration in Earth's atmosphere

O6-methylguanine-DNA methyltransferase depletion and DNA damage in patients with melanoma treated with temozolomide alone or with lomeguatrib

We evaluated the pharmacodynamic effects of the O6-methylguanine-DNA methyltransferase (MGMT) inactivator lomeguatrib (LM) on patients with melanoma in two clinical trials. Patients received temozolomide (TMZ) for 5 days either alone or with LM for 5, 10 or 14 days. Peripheral blood mononuclear cells (PBMCs) were isolated before treatment and during cycle 1. Where available, tumour biopsies were obtained after the last drug dose in cycle 1. Samples were assayed for MGMT activity, total MGMT protein, and O6-methylguanine (O6-meG) and N7-methylguanine levels in DNA. MGMT was completely inactivated in PBMC from patients receiving LM, but detectable in those on TMZ alone. Tumours biopsied on the last day of treatment showed complete inactivation of MGMT but there was recovery of activity in tumours sampled later. Significantly more O6-meG was present in the PBMC DNA of LM/TMZ patients than those on TMZ alone. LM/TMZ leads to greater MGMT inactivation, and higher levels of O6-meG than TMZ alone. Early recovery of MGMT activity in tumours suggested that more protracted dosing with LM is required. Extended dosing of LM completely inactivated PBMC MGMT, and resulted in persistent levels of O6-meG in PBMC DNA during treatment

Distribution and Genetic Profiles of Campylobacter in Commercial Broiler Production from Breeder to Slaughter in Thailand

Poultry and poultry products are commonly considered as the major vehicle of Campylobacter infection in humans worldwide. To reduce the number of human cases, the epidemiology of Campylobacter in poultry must be better understood. Therefore, the objective of the present study was to determine the distribution and genetic relatedness of Campylobacter in the Thai chicken production industry. During June to October 2012, entire broiler production processes (i.e., breeder flock, hatchery, broiler farm and slaughterhouse) of five broiler production chains were investigated chronologically. Representative isolates of C. jejuni from each production stage were characterized by flaA SVR sequencing and multilocus sequence typing (MLST). Amongst 311 selected isolates, 29 flaA SVR alleles and 17 sequence types (STs) were identified. The common clonal complexes (CCs) found in this study were CC-45, CC-353, CC-354 and CC-574. C. jejuni isolated from breeders were distantly related to those isolated from broilers and chicken carcasses, while C. jejuni isolates from the slaughterhouse environment and meat products were similar to those isolated from broiler flocks. Genotypic identification of C. jejuni in slaughterhouses indicated that broilers were the main source of Campylobacter contamination of chicken meat during processing. To effectively reduce Campylobacter in poultry meat products, control and prevention strategies should be aimed at both farm and slaughterhouse levels

Development and Evaluation of a Novel Single-Nucleotide-Polymorphism Real-Time PCR Assay for Rapid Detection of Fluoroquinolone-Resistant Mycoplasma bovis▿ †

Monitoring of the susceptibility of Mycoplasma bovis field isolates to antibiotics is important for the appropriate choice of treatment. However, in vitro susceptibility testing of mycoplasmas is technically demanding and time-consuming, especially for clinical isolates, and is rarely performed in mycoplasma diagnostic laboratories. Thus, the development of methods allowing rapid real-time detection of resistant strains of M. bovis in clinical samples is a high priority for successful treatment. In this study, a novel TaqMan single-nucleotide-polymorphism (SNP) real-time PCR assay, which enables the rapid identification of M. bovis strains with different susceptibilities to fluoroquinolones, was developed and evaluated. The TaqMan SNP real-time PCR assay is based on the amplification of a 97-bp fragment of the parC quinolone resistance-determining region (QRDR) and allows the specific detection of four possible genotypes: GAC or GAT (susceptible to fluoroquinolones) and AAC or AAT (resistant to fluoroquinolones). Four TaqMan minor groove binder (MGB) probes identifying 1-base mismatches were designed and applied in a dual-probe assay with two reaction tubes. The TaqMan SNP real-time PCRs developed are highly specific for M. bovis, with a detection limit of 5 fg/μl (about 5 M. bovis genomes). In addition, all four SNP real-time PCR tests have almost the same efficiency (97.7% [GAC], 94% [AAC], 99.99% [GAT], and 98% [AAT]). Taken together, the data suggest that this SNP real-time PCR assay has potential as a routine diagnostic test for the detection of decreased susceptibility of M. bovis to fluoroquinolones