The emergence of antibiotic resistant bacteria is a major health concern worldwide in recent years. The objective of this study is to establish the larvae of the silk moth (commonly known as silkworm), Bombyx mori as an infection model to study antibacterial effect of antibiotics against Klebsiella pneumoniae. In this study, the pathogenicity of a K. pneumoniae strain isolated from food to silkworm larvae was examined. Within 72 h of bacterial injection, all silkworm larvae were killed in a dose-dependent manner with their body color turning into black due to increased melanization. Bacterial numbers in the larval hemolymph (blood) significantly increased after 9 h of infection with a decrease in viable circulatory hemocytes in hemolymph. When presented with bacteria laden leaves, larvae did not eat but injection of bacteria directly into the midgut killed larvae within 12 h with a higher load required in comparison to that required for the killing by hemolymph injection. Administration of four different antibiotics into larval hemolymph showed therapeutic effect at different doses with varying efficacies against hemolymph-injected K. pneumoniae. These results indicate that the silkworm larvae can be used as an infection model not only to study the pathogenicity of K. pneumoniae but also to perform rapid screening for the identification of antibiotics effective against multidrug-resistant strains of K. pneumoniae.

Sludges from pulp and paper mills represent a major ecological and environmental cost, and anaerobic digestion represents a method of waste reduction and energy recovery for these mills. This study compared methane production potential and microbial communities across 11 primary- and biosludges from five pulp and paper mills using various mill processes. We measured methane production from sludges in anaerobic batch reactor experiments over 64 days. Sludges were incubated with and without added substrate to test for organic substrate limitation versus inhibition of methanogens. Initial microbial communities and changes to community composition were determined using Illumina MiSeq for metabarcoding of bacterial and archaeal 16S rRNA genes. Mean methane production potential varied greatly between sludges (0.002-79 mL CH4 g-1 TS). Among primary sludges, kraft mill sludge produced more methane than other mill types. For these other mills, biosludge produced more methane than primary sludge, which had evidence of methanogen inhibition. Microbial communities and diversity were influenced by the initial community composition, and high methane production was only seen in sludges with high diversity. A number of sludges innately produced substantial methane and may be targets for further modelling and larger scale testing of anaerobic digestion.

Per- and polyfluoroalkyl substances (PFAS) such as perfluorooctanoic acid (PFOA) have received recent heightened attention as emerging contaminants. Due to widespread application in household products and aqueous film-forming foams, PFAS are globally distributed in the environment, and bioaccumulate in the blood and tissues of mammals including humans. The microbially driven Fenton reaction, a hybrid biotic/abiotic hydroxyl radical (HO•)-generating system, previously degraded a wide variety of persistant organic pollutants. In the present study, the microbially driven Fenton reaction was employed to attempt degradation of PFOA. Batch cultures of the facultatively anaerobic bacteria Shewanella oneidensis were amended with PFOA and Fe(III)-citrate. Under aerobic conditions, S. oneidensis reduced oxygen to hydrogen peroxide (H2O2), while under anaerobic conditions, S. oneidensis reduced Fe(III) to Fe(II). During aerobic-to-anaerobic transition periods, Fe(II) and H2O2 interacted chemically via the Fenton reaction to produce HO• radicals, which in turn interacted with PFOA. Batch reactors were cycled between aerobic and anaerobic phases for four cycles, residual PFOA was extracted via liquid-liquid extraction and analyzed by liquid chromatography combined with tandem mass spectrometry. Unlike degradation of other organic pollutants, PFOA concentrations remained unchanged, which indicated that PFOA was resistant to degradation by the microbially-driven Fenton reaction. Similar to abiotic (purely chemical) Fenton reaction systems, these results most likely reflect the inability of HO• radicals to oxidatively degrade PFOA.

Antibiotic-exposed bacteria acquire genetic mutations and emerge as antibiotic-resistant clones that thwart treatment of bacterial diseases. Genome-wide mutations are inflicted by the reactive oxygen species (ROS), hydroxyl radical, formed in most of the antibiotic-exposed bacteria. Hydroxyl radical is generated through the Fenton reaction of Fe (II) with H2O2, which is formed by the dismutation of superoxide. This implied that antibiotic-exposed bacteria would contain these three ROS, promoting resister generation. In the present study, we examined Escherichia coli exposed independently to gentamicin and moxifloxacin for the presence of the three ROS and consequential emergence of genetic resisters to the antibiotics. Here we show that the three ROS are formed in E. coli exposed independently to bactericidal concentrations of gentamicin and moxifloxacin for a prolonged duration. Resisters to these antibiotics were found to emerge from the respective antibiotic-surviving population. The antibiotic-unexposed cultures did not show these responses. The Gram-positive ESKAPE pathogen, Staphylococcus aureus, also showed a response similar to that of E. coli upon prolonged exposure to bactericidal concentrations of rifampicin and moxifloxacin. The similar responses of E. coli and S. aureus to antibiotics indicated a common mechanism of ROS generation in the emergence of resisters against antibiotics.

The structure of the microbial community during sand crab juice fermentation was analyzed using culture-based methods and high-throughput 16S rRNA gene sequencing. Additionally, the changes in amino acid nitrogen (AAN) and total volatile basic nitrogen (TVB-N) were evaluated. Staphylococcus equorum, Staphylococcus arlettae, Staphylococcus saprophyticus, Salinicoccus amylolyticus and Bacillus cereus were isolated by traditional culture isolation technique. The Good's coverage obtained by high-throughput sequencing was over 99.5%, and the Chao1 and Simpson indices showed small fluctuations, indicating that the species abundance and diversity did not change significantly during the fermentation process, although the abundance decreased. Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria were the dominant bacterial phyla observed during fermentation, whereas Aquabacterium, Roseovarius, Muribaculaceae, and Silicimonas were the dominant bacterial genera. The AAN content increased from 0.15 to 0.43 g/100 mL during the 15-day fermentation, indicating the production of small peptides and amino acids during fermentation. The TVB-N content (25.2 mg/100 mL) on day 15 indicated slight spoilage of sand crab juice, although the freshness conformed to the production standard. These results provide a theoretical basis for improving the quality and optimizing the production process of sand crab juice.

CoQ10, which has been widely applied in medicine by dietary supplement, possesses important functions in antioxidant process and bioenergy generation. Iterative mutagenesis introduced by atmospheric and room temperature plasma (ARTP) treatment was studied to improve the coenzyme Q10 (CoQ10) production of Rhodobacter sphaeroides (R. sphaeroides), and multiple selection pressures including vitamin K3 (VK3), Na2S and benzoic acid (BA) were adopted for the first time. After two rounds of mutation and screening, a mutant strain R.S 17 was obtained, and the product titer was increased by 80.37%. The CoQ10 titer and cell density reached 236.7 mg L-1 and 57.09 g L-1, respectively, in the fed-batch fermentation, and the CoQ10 content was 22.1% higher than that of the parent strain. In addition, the spectral scanning results indicated the metabolic flux improvement contributing to the CoQ10 production in R.S 17, and the genetic stability was validated. Based on the iterative mutagenesis introduced by ARTP under multiple selection pressures, the promotion of CoQ10 production by R. sphaeroides was achieved. The significant improvement in fermentation performances and the good genetic stability of R.S 17 indicate a potential way for the efficient biosynthesis of CoQ10.