Epigenetic Regulation of Nostoc punctiforme ATCC 29133 in Response to Nitrogen Availability

Here, we report the restriction modification system of Nostoc punctiforme ATCC 29133, along with its methylated genome sequence, under contrasting nitrate availability. Generated methylation profiles revealed increased methylation for key enzymes of assimilatory nitrate reduction, suggesting that Nostoc punctiforme employs DNA methylation to regulate its nitrogen metabolism.

Impact of Biosynthesized Silver Nanoparticles on Bacterial Growth

Cystic Fibrosis is a genetic disease which causes the production of viscous mucus in airways which limits airflow and creates the perfect conditions for bacterial growth. Unfortunately, deaths due to bacterial infections in Cystic Fibrosis patients have increased as bacterial strains have developed antibiotic resistance. Researchers have found that silver nanoparticles offer a solution to growing antibiotic resistance due to how no resistance has been developed to them in clinical trials. Current research is focusing on the bio-synthesis of silver nanoparticles which does not produce the harmful waste products seen with the industrial production of silver nanoparticles. However, there is a lack of comparative research concerning the effectiveness of silver nanoparticles produced by different microorganisms, which is what the researcher’s work addressed. The researcher’s work primarily focused on determining how effective silver nanoparticles produced by different bacterial species were at inhibiting bacterial growth. Through the collection of nanoparticles via extracellular synthesis, antimicrobial assays were conducted to determine the efficacy of silver nanoparticles produced by different microorganisms. The results indicated that silver nanoparticles produced by B. subtilis were the most effective in inhibiting bacterial growth. This provides a crucial as research in the field should increasingly focus on bacteria which utilize assimilatory nitrate reduction like B. subtilis because of the increased efficacy of silver nanoparticles produced by this method in inhibiting bacterial growth in aerobic conditions. Advances in this area could increase the efficiency of nanoparticle production and make it viable for industrial production.

Genome Analysis of a Marine Bacterium Halomonas sp. and Its Role in Nitrate Reduction under the Influence of Photoelectrons

The solar light response and photoelectrons produced by widespread semiconducting mineral play important roles in biogeochemical cycles on Earth’s surface. To explore the potential influence of photoelectrons generated by semiconducting mineral particles on nitrate-reducing microorganisms in the photic zone, a marine heterotrophic denitrifier Halomonas sp. strain 3727 was isolated from seawater in the photic zone of the Yellow Sea, China. This strain was classified as a Halomonadaceae. Whole-genome analysis indicated that this strain possessed genes encoding the nitrogen metabolism, i.e., narG, nasA, nirBD, norZ, nosB, and nxr, which sustained dissimilatory nitrate reduction, assimilatory nitrate reduction, and nitrite oxidation. This strain also possessed genes related to carbon, sulfur, and other metabolisms, hinting at its substantial metabolic flexibility. A series of microcosm experiments in a simulative photoelectron system was conducted, and the results suggested that this bacterial strain could use simulated photoelectrons with different energy for nitrate reduction. Nitrite, as an intermediate product, was accumulated during the nitrate reduction with limited ammonia residue. The nitrite and ammonia productions differed with or without different energy electron supplies. Nitrite was the main product accounting for 30.03% to 68.40% of the total nitrogen in photoelectron supplement systems, and ammonia accounted for 3.77% to 8.52%. However, in open-circuit systems, nitrite and ammonia proportions were 26.77% and 11.17%, respectively, and nitrogen loss in the liquid was not observed. This study reveals that photoelectrons can serve as electron donors for nitrogen transformation mediated by Halomonas sp. strain 3727, which reveals an underlying impact on the nitrogen biogeochemical cycle in the marine photic zone.

The contribution of the NarB and NarGHI enzymes to nitrate reduction in Mycobacterium smegmatis

Background: Nitrate reduction in bacteria is an essential step in the nitrogen cycle. For this, the reduction of nitrate to nitrite is catalyzed by a variety of nitrate reductase enzymes. In the pathogen Mycobacterium tuberculosis, nitrate reduction is driven by the NarGHI respiratory and assimilatory nitrate reductase. In addition to this enzyme, Mycobacterium smegmatis carries a second putative narB-encoded nitrate reductase and the contribution of this enzyme to nitrate reduction remains unknown. Herein, we set out to investigate this. Results: To assess the relative contribution of NarGHI and NarB, the corresponding gene loci we deleted using two-step allelic replacement, individually and in combination, followed by investigation of nitrate reduction using the Griess assay. However, previous reports demonstrated that this assay was unable to report on nitrate reduction in M. smegmatis, as it yielded no detectable levels of the nitrite product. To address this, we modified the assay through the addition of zinc, which reduces nitrate remaining in the reaction to nitrite thus allowing for assessment of nitrate depletion. This then serves as a surrogate for nitrate reductase activity. The mutant strains lacking narB and/or narGHJI retained the ability to reduce nitrate at levels comparable to the wild type. We further investigated nitrate assimilation and all strains defective for these enzymes were able to grow on nitrate as the sole nitrogen source. Conclusions: Collectively, these data confirm that NarB and NarGHI are individually and collectively dispensable for both respiratory and assimilatory nitrate reduction in M. smegmatis. Furthermore, we identified MSMEG_4206 as a putative, previously unannotated, nitrate reductase in this organism.

The assimilatory nitrate reduction system of the phototrophic bacterium Rhodobacter capsulatus E1F1

The phototrophic bacterium Rhodobacter capsulatus E1F1 assimilates nitrate under anaerobic phototrophic growth conditions. A 17 kb DNA region encoding the nitrate assimilation (nas) system of this bacterium has been cloned and sequenced. This region includes the genes coding for a putative ABC (ATP-binding cassette)-type nitrate transporter (nasFED) and the structural genes for the enzymes nitrate reductase (nasA), nitrite reductase (nasB) and hydroxylamine reductase (hcp). Three genes code for putative regulatory proteins: a nitrite-sensitive repressor (nsrR), a transcription antiterminator (nasT) and a nitrate sensor (nasS). Other genes probably involved in nitrate assimilation are also present in this region. The sequence analysis of these genes and the biochemical properties of the purified nitrate, nitrite and hydroxylamine reductases are reviewed.