Bacterial degradation kinetics of poly(Ɛ-caprolactone) (PCL) film by Aquabacterium sp. CY2-9 isolated from plastic-contaminated landfill.

Despite the identification of numerous bioplastic-degrading bacteria, the inconsistent rate of bioplastic degradation under differing cultivation conditions limits the intercomparison of results on biodegradation kinetics. In this study, we isolated a poly (Ɛ-caprolactone) (PCL)-degrading bacterium from a plastic-contaminated landfill and determined the principle-based biodegradation kinetics in a confined model system of varying cultivation conditions. Bacterial degradation of PCL films synthesized by different polymer number average molecular weights (Mn) and concentrations (% w/v) was investigated using both solid and liquid media at various temperatures. As a result, the most active gram-negative bacterial strain at ambient temperature (28 °C), designated CY2-9, was identified as Aquabacterium sp. Based on 16 S rRNA gene analysis. A clear zone around the bacterial colony was apparently exhibited during solid cultivation, and the diameter sizes increased with incubation time. During biodegradation processes in the PCL film, the thermal stability declined (determined by TGA; weight changes at critical temperature), whereas the crystalline proportion increased (determined by DSC; phase transition with temperature increment), implying preferential degradation of the amorphous region in the polymer structure. The surface morphologies (determined by SEM; electron optical system) were gradually hydrolyzed, creating destruction patterns as well as alterations in functional groups on film surfaces (determined by FT-IR; infrared spectrum of absorption or emission). In the kinetic study based on the weight loss of the PCL film (4.5 × 104 Da, 1% w/v), ∼1.5 (>±0.1) × 10-1 day-1 was obtained from linear regression for both solid and liquid media cultivation at 28 °C. The biodegradation efficiencies increased proportionally by a factor of 2.6-7.9, depending on the lower polymer number average molecular weight and lower concentration. Overall, our results are useful for measuring and/or predicting the degradation rates of PCL films by microorganisms in natural environments.

Horticoccus luteus gen. nov., sp. nov., A Novel Member of the Phylum Verrucomicrobia Isolated from a Dichlorodiphenyltrichloroethane (DDT)-Contaminated Orchard Soil.

Strain KSB-15 T was isolated from an orchard soil that had been contaminated with the insecticide dichlorodiphenyltrichloroethane for about 60 years. The 16S rRNA gene sequence of this strain showed the highest sequence similarities with those of Oleiharenicola alkalitolerans NVTT (95.3%), Opitutus terrae PB90-1 T (94.8%), and Oleiharenicola lentus TWA-58 T (94.7%) among type strains, which are members of the family Opitutaceae within the phylum Verrucomicrobia. Strain KSB-15 T was an obligate aerobe, Gram-negative, non-motile, coccoid or short rod with the cellular dimensions of 0.37-0.62 µm width and 0.43-0.72 µm length. The strain grew at temperatures between 15-37 °C (optimum, 25 °C), at a pH range of 5.0-11.0 (optimum, pH 6.0), and at a NaCl concentration of 0-3% (w/v) (optimum, 0%). It contained menaquinone-7 (MK-7) as the major isoprenoid quinone (94.1%), and iso-C15:0 (34.9%) and anteiso-C15:0 (29.0%) as the two major fatty acids. The genome of strain KSB-15 T was composed of one chromosome with a total size of 4,320,198 bp, a G + C content of 64.3%, 3,393 coding genes (CDS), 14 pseudogenes, and 52 RNA genes. The OrthoANIu values, In silico DDH values and average amino acid identities between strain KSB-15 T and the members of the family Opitutaceae were 71.6 ~ 73.0%, 19.0 ~ 19.9%, and 55.9 ~ 62.0%, respectively. On the basis of our polyphasic taxonomic study, we conclude that strain KSB-15 T should be classified as a novel genus of the family Opitutaceae, for which the name Horticcoccus luteus gen. nov., sp. nov. is proposed.The type strain is KSB-15 T (= KACC 22271 T = DSM 113638 T).

Sweet scents from good bacteria: Case studies on bacterial volatile compounds for plant growth and immunity.

Beneficial bacteria produce diverse chemical compounds that affect the behavior of other organisms including plants. Bacterial volatile compounds (BVCs) contribute to triggering plant immunity and promoting plant growth. Previous studies investigated changes in plant physiology caused by in vitro application of the identified volatile compounds or the BVC-emitting bacteria. This review collates new information on BVC-mediated plant-bacteria airborne interactions, addresses unresolved questions about the biological relevance of BVCs, and summarizes data on recently identified BVCs that improve plant growth or protection. Recent explorations of bacterial metabolic engineering to alter BVC production using heterologous or endogenous genes are introduced. Molecular genetic approaches can expand the BVC repertoire of beneficial bacteria to target additional beneficial effects, or simply boost the production level of naturally occurring BVCs. The effects of direct BVC application in soil are reviewed and evaluated for potential large-scale field and agricultural applications. Our review of recent BVC data indicates that BVCs have great potential to serve as effective biostimulants and bioprotectants even under open-field conditions.

Population Dynamics of Intestinal Enterococcus Modulate Galleria mellonella Metamorphosis.

Microbes found in the digestive tracts of insects are known to play an important role in their host's behavior. Although Lepidoptera is one of the most varied insect orders, the link between microbial symbiosis and host development is still poorly understood. In particular, little is known about the role of gut bacteria in metamorphosis. Here, we explored gut microbial biodiversity throughout the life cycle of Galleria mellonella, using amplicon pyrosequencing with the V1 to V3 regions, and found that Enterococcus spp. were abundant in larvae, while Enterobacter spp. were predominant in pupae. Interestingly, eradication of Enterococcus spp. from the digestive system accelerated the larval-to-pupal transition. Furthermore, host transcriptome analysis demonstrated that immune response genes were upregulated in pupae, whereas hormone genes were upregulated in larvae. In particular, regulation of antimicrobial peptide production in the host gut correlated with developmental stage. Certain antimicrobial peptides inhibited the growth of Enterococcus innesii, a dominant bacterial species in the gut of G. mellonella larvae. Our study highlights the importance of gut microbiota dynamics on metamorphosis as a consequence of the active secretion of antimicrobial peptides in the G. mellonella gut. IMPORTANCE First, we demonstrated that the presence of Enterococcus spp. is a driving force for insect metamorphosis. RNA sequencing and peptide production subsequently revealed that antimicrobial peptides targeted against microorganisms in the gut of Galleria mellonella (wax moth) did not kill Enterobacteria species, but did kill Enterococcus species, when the moth was at a certain stage of growth, and this promoted moth pupation.

Genome sequence of the leaf-colonizing Bacterium Bacillus sp. strain 5B6, isolated from a cherry tree.

Plant growth-promoting bacteria colonize various habitats, including the phyllosphere. Here, we present the high-quality draft genome sequence of Bacillus sp. strain 5B6, which was isolated from the leaf of a cherry tree. The 3.9-Mb genome uncovers its potential for understanding the nature of leaf colonization as well as antibiosis against plant pathogens.

Distinct Bacterial and Fungal Communities Colonizing Waste Plastic Films Buried for More Than 20 Years in Four Landfill Sites in Korea.

Plastic pollution has been recognized as a serious environmental problem, and microbial degradation of plastics is a potential, environmentally friendly solution to this. Here, we analyzed and compared microbial communities on waste plastic films (WPFs) buried for long periods at four landfill sites with those in nearby soils to identify microbes with the potential to degrade plastics. Fourier-transform infrared spectroscopy spectra of these WPFs showed that most were polyethylene and had signs of oxidation, such as carbon-carbon double bonds, carbon-oxygen single bonds, or hydrogen-oxygen single bonds, but the presence of carbonyl groups was rare. The species richness and diversity of the bacterial and fungal communities on the films were generally lower than those in nearby soils. Principal coordinate analysis of the bacterial and fungal communities showed that their overall structures were determined by their geographical locations; however, the microbial communities on the films were generally different from those in the soils. For the pulled data from the four landfill sites, the relative abundances of Bradyrhizobiaceae, Pseudarthrobacter, Myxococcales, Sphingomonas, and Spartobacteria were higher on films than in soils at the bacterial genus level. At the species level, operational taxonomic units classified as Bradyrhizobiaceae and Pseudarthrobacter in bacteria and Mortierella in fungi were enriched on the films. PICRUSt analysis showed that the predicted functions related to amino acid and carbohydrate metabolism and xenobiotic degradation were more abundant on films than in soils. These results suggest that specific microbial groups were enriched on the WPFs and may be involved in plastic degradation.

The Galleria mellonella Hologenome Supports Microbiota-Independent Metabolism of Long-Chain Hydrocarbon Beeswax.

The greater wax moth, Galleria mellonella, degrades wax and plastic molecules. Despite much interest, the genetic basis of these hallmark traits remains poorly understood. Herein, we assembled high-quality genome and transcriptome data from G. mellonella to investigate long-chain hydrocarbon wax metabolism strategies. Specific carboxylesterase and lipase and fatty-acid-metabolism-related enzymes in the G. mellonella genome are transcriptionally regulated during feeding on beeswax. Strikingly, G. mellonella lacking intestinal microbiota successfully decomposes long-chain fatty acids following wax metabolism, although the intestinal microbiome performs a supplementary role in short-chain fatty acid degradation. Notably, final wax derivatives were detected by gas chromatography even in the absence of gut microbiota. Our findings provide insight into wax moth adaptation and may assist in the development of unique wax-degradation strategies with a similar metabolic approach for a plastic molecule polyethylene biodegradation using organisms without intestinal microbiota.

Complete Genome Sequences of Enterobacter cancerogenus CR-Eb1 and Enterococcus sp. Strain CR-Ec1, Isolated from the Larval Gut of the Greater Wax Moth, Galleria mellonella.

Enterobacter cancerogenus CR-Eb1 and Enterococcus sp. CR-Ec1 were isolated from the larval gut of Galleria mellonella, the greater wax moth. Here, we report the completed and annotated genome sequences of insect gut-dwelling bacteria.

Combination therapy with polymyxin B and netropsin against clinical isolates of multidrug-resistant Acinetobacter baumannii.

Polymyxins are last-resort antibiotics for treating infections of Gram-negative bacteria. The recent emergence of polymyxin-resistant bacteria, however, urgently demands clinical optimisation of polymyxin use to minimise further evolution of resistance. In this study we developed a novel combination therapy using minimal concentrations of polymyxin B. After large-scale screening of Streptomyces secondary metabolites, we identified a reliable polymixin synergist and confirmed as netropsin using high-pressure liquid chromatography, nuclear magnetic resonance, and mass spectrometry followed by in vitro assays using various Gram-negative pathogenic bacteria. To evaluate the effectiveness of combining polymixin B and netropsin in vivo, we performed survival analysis on greater wax moth Galleria mellonella infected with colistin-resistant clinical Acinetobacter baumannii isolates as well as Escherichia coli, Shigella flexineri, Salmonella typhimuruim, and Pseudomonas aeruginosa. The survival of infected G. mellonella was significantly higher when treated with polymyxin B and netropsin in combination than when treated with polymyxin B or netropsin alone. We propose a netropsin combination therapy that minimises the use of polymyxin B when treating infections with multidrug resistant Gram-negative bacteria.