Physicochemical and Structural Evidence that Bacillus cereus Isolated from the Gut of Waxworms (Galleria mellonella Larvae) Biodegrades Polypropylene Efficiently In Vitro.

Biodegradation of plastic waste using microorganisms has been proposed as one of the solutions to the increasing worldwide plastic waste. Polypropylene (PP) is the second most used plastic used in various industries, and it has been widely used in the production of personal protective equipment such as masks due to the COVID-19 pandemic. Therefore, biodegradation of PP becomes very important. Here, we present results on the physicochemical and structural studies of PP biodegradation by Bacillus cereus isolated from the gut of the waxworms, Galleria mellonella larvae. We also studied the biodegradability of PP by the gut microbiota compared with Bacillus cereus. We analyzed the microbial degradation of the PP surface using scanning electron microscopy and energy - dispersive X-ray spectroscopy and confirmed that the physical and chemical changes were caused by Bacillus cereus and the gut microbiota. The chemical structural changes were further investigated using X-ray photoelectron microscopy and Fourier - transform - infrared spectroscopy, and it was confirmed that the oxidation of the PP surface proceeded with the formation of carbonyl groups (C=O), ester groups (C-O), and hydroxyl groups (-OH) by Bacillus cereus. Additionally, the gut microbiota composed of diverse microbial species showed equal oxidation of PP compared to Bacillus cereus. More importantly, high temperature gel permeation chromatography (HT-GPC) analysis showed that Bacillus cereus exhibited quantitatively a higher biodegradability of PP compared to the gut microbiota. Our results suggest that Bacillus cereus possesses a complete set of enzymes required to initiate the oxidation of the carbon chain of PP and will be used to discover new enzymes and genes that are involved in degrading PP. Supplementary Information: The online version contains supplementary material available at 10.1007/s10924-023-02878-y.

Biodegradability of polyethylene by efficient bacteria from the guts of plastic-eating waxworms and investigation of its degradation mechanism.

Polyethylene (PE) has been regarded as non-biodegradable for decades, and the evidence for its degradation by bacteria remains unclear in the literature. Waxworms have recently gained attention for their ability to degrade natural long-chain polymers and synthetic plastic. This study aims to explore the potential of low-density polyethylene (LDPE)-degrading bacteria from the gut symbionts of lesser waxworm (Achroia grisella) larvae for the effective biodegradation of LEDP. Two bacterial isolates (LDPE-DB1 and LDPE-DB2) exhibited the greatest reduction in tensile strength among all isolates (P < 0.0001), reaching 51.3% and 58.3%, respectively. The bacterial strains LDPE-DB1 and LDPE-DB2 stand for molecularly identified species, Citrobacter freundii and Bacillus sp., respectively. After 5 days of incubation, the cell density of LDPE-DB1 and LDPE-DB2 reached 2.20 × 108 and 1.8 × 108 CFU/mL, respectively. However, after 30 days of incubation, the cell density reached 7.3 × 108 and 5.9 × 108, respectively. The formed cavities indicate the high activity of the isolated bacteria from Achroia grisella larvae where the cavities reach a depth of up to 1.2 µm. The findings of this study demonstrated the presence of LDPE-degrading bacteria in Achroia grisella and provide promising evidence for the biodegradation of plastic waste management in the environment.

Diet and ontogeny drastically alter the larval microbiome of the invertebrate model Galleria mellonella.

Larvae of the greater wax moth (Galleria mellonella) are an emerging animal model to study the innate immune response and biodegradation of plastic polymers. Both of these complex biological processes are likely impacted by the plasticity of host-microbe interactions, which remains understudied in lepidopterans. Consequently, we carried out 16S rRNA sequencing to explore the effect diet (natural, artificial) has on the bacterial assemblages of G. mellonella in different tissues (gut, fat bodies, silk glands) throughout development (eggs, six instar stages, adults). The microbiome was rich in diversity, with Proteobacteria and Firmicutes being the most represented phyla. Contrary to other lepidopterans, G. mellonella appears to possess a resident microbiome dominated by Ralstonia. As larvae progress through development, the bacterial assemblages become increasingly shaped by the caterpillar's diet. In particular, a number of bacteria genera widely associated with the G. mellonella microbiome (e.g., Enterococcus and Enterbacter) were significantly enriched on an artificial diet. Overall, these results indicate that the G. mellonella microbiome is not as simplistic and homogenous as previously described. Rather, its bacterial communities are drastically affected by both diet and ontogeny, which should be taken into consideration in future studies planning to use G. mellonella as model species.

Fat on plastic: Metabolic consequences of an LDPE diet in the fat body of the greater wax moth larvae (Galleria mellonella).

The caterpillar larvae of the greater wax moth (Galleria mellonella) are avid plastivores, as when provided a diet of low-density polyethylene (LDPE) they actively feed on it. Recent work has highlighted the importance of their microbiome in the putative biodegradation of this plastic polymer, though the impact of plastic metabolism on the insect host is less clear. In the present study, we undertook an integrative approach spanning all levels of biological organization to explore the effects of a plastic diet on the metabolic physiology of this animal model of plastic biodegradation. We demonstrate that an LDPE diet is not sufficient to maintain optimal larval growth and survival. In addition, we confirm that plastic fed waxworms retain their fat body lipid stores in a manner proportional to their individual polyethylene consumption suggesting a direct effect of LDPE biodegradation. At the functional level, the oxidative capacity of the fat body of LDPE-fed larvae is maintained reflecting unaltered metabolic function of the tissue. Finally, metabolomic analyses confirmed fat body lipid stores maintenance in LDPE-fed worms, but uncovered various other nutritional deficiencies. Overall, this work unveils novel insights in the complex interplay between LDPE biodegradation and the metabolic physiology of this model plastivore.

Enhanced Antimicrobial Activity of N-Terminal Derivatives of a Novel Brevinin-1 Peptide from The Skin Secretion of Odorrana schmackeri.

Antimicrobial peptides (AMPs) are promising therapeutic alternatives compared to conventional antibiotics for the treatment of drug-resistant bacterial infections. However, the application of the overwhelming majority of AMPs is limited because of the high toxicity and high manufacturing costs. Amphibian skin secretion has been proven to be a promising source for the discovery and development of novel AMPs. Herein, we discovered a novel AMP from the skin secretion of Odorrana schmackeri, and designed the analogues by altering the key factors, including conformation, net charge and amphipathicity, to generate short AMPs with enhanced therapeutic efficacy. All the peptides were chemically synthesised, followed by evaluating their biological activity, stability and cytotoxicity. OSd, OSe and OSf exhibited broad-spectrum antibacterial effects, especially OSf, which presented the highest therapeutic index for the tested bacteria. Moreover, these peptides displayed good stability. The results from scanning electron microscopy and transmission electron microscopy studies, indicated that brevinin-OS, OSd, OSe and OSf possessed rapid bactericidal ability by disturbing membrane permeability and causing the release of cytoplasmic contents. In addition, OSd, OSe and OSf dramatically decreased the mortality of waxworms acutely infected with MRSA. Taken together, these data suggested that a balance between positive charge, degrees of α-helicity and hydrophobicity, is necessary for maintaining antimicrobial activity, and these data successfully contributed to the design of short AMPs with significant bactericidal activity and cell selectivity.

Role of the intestinal microbiome in low-density polyethylene degradation by caterpillar larvae of the greater wax moth, Galleria mellonella.

Recently, a few insects, including the caterpillar larva of the greater wax moth Galleria mellonella, have been identified as avid 'plastivores'. These caterpillars are able to ingest and metabolize polyethylene at unprecedented rates. While it appears that G. mellonella plays an important role in the biodegradation process, the contribution of its intestinal microbiome remains poorly understood and contested. In a series of experiments, we present strong evidence of an intricate relationship between an intact microbiome, low-density polyethylene (LDPE) biodegradation and the production of glycol as a metabolic by-product. First, we biochemically confirmed that G. mellonella larvae consume and metabolize LDPE, as individual caterpillars fed on polyethylene excreted glycol, but those excretions were reduced by antibiotic treatment. Further, while the gut bacterial communities remained relatively stable regardless of diet, we showed that during the early phases of feeding on LDPE (24-72 h), caterpillars exhibited increased microbial abundance relative to those starved or fed on their natural honeycomb diet. Finally, by isolating and growing gut bacteria with polyethylene as their exclusive carbon source for over 1 year, we identified microorganisms in the genus Acinetobacter that appeared to be involved in this biodegradation process. Taken collectively, our study indicates that during short-term exposure, the intestinal microbiome of G. mellonella is intricately associated with polyethylene biodegradation in vivo.

Bioevaluation of Ranatuerin-2Pb from the Frog Skin Secretion of Rana pipiens and its Truncated Analogues.

Antimicrobial peptides (AMPs) are considered as a promising agent to overcome the drug-resistance of bacteria. Large numbers of AMPs have been identified from the skin secretion of Rana pipiens, including brevinins, ranatuerins, temporins and esculentins. In this study, the cDNA precursor of a broad-spectrum antimicrobial peptide, ranatuerin-2Pb, was cloned and identified. Additionally, two truncated analogues, RPa and RPb, were synthesised to investigate the structure-activity relationship of ranatuerin-2Pb. RPa lost antimicrobial activity against Candida albicans, MRSA, Enterococcus faecalis and Pseudomonas aeruginosa, while RPb retained its broad-spectrum antimicrobial activity. Additionally, ranatuerin-2Pb, RPa and RPb demonstrated inhibition and eradication effects against Staphylococcusaureus biofilm. RPb showed a rapid bacterial killing manner via membrane permeabilization without damaging the cell membrane of erythrocytes. Moreover, RPb decreased the mortality of S. aureus infected Galleria mellonella larvae. Collectively, our results suggested that RPb may pave a novel way for natural antimicrobial drug design.

Efficient biodegradation of polyethylene (HDPE) waste by the plastic-eating lesser waxworm (Achroia grisella).

Polyethylene (PE) is one of the major persistent plastic that is not biodegradable at considerable rates in most environments, and is the major source of unceasing environmental pollution. Recently, biodegradation of plastic wastes through waxworms and mealworms were reported. The present study focuses on the high-density polyethylene (HDPE) degradation capabilities of the larvae of Achroia grisella (lesser waxworm) and its ability to complete its life cycle when fed with HDPE. Effects of added nutrition on PE degradation were assessed, providing wax comb as co-feed (PE-WC). The egested frass of the waxworm fed on waxcomb (WC), PE, and PE-WC were studied by analyzing the changes in physiochemical properties through FTIR and 1H NMR techniques in addition to weight loss percentage of PE and survival rates of the tested lesser waxworms. The post-degradation studies of WC and PE showed 90.5 ± 1.2% and 43.3 ± 1.6% weight loss, respectively, by a group of 100 lesser waxworms. Over an 8-day period, PE consumption increased with an ingestion of 1.83 mg of PE per day per larvae. Supplementing the PE feed of lesser waxworms with WC facilitated enhanced PE degradation showing 69.6 ± 3.2% weight loss. Twenty-eight day survival rates for lesser waxworms fed on WC, PE, and PE-WC were 91.3 ± 1.01%, 74.6 ± 2.9%, and 86 ± 1.4%, respectively. The FTIR and 1H NMR analysis of egested frass indicated formation of new functional organic groups, supporting biodegradation of PE in lesser waxworms. The frass of the lesser waxworm fed on PE samples shows the presence of new carbonyl and alcoholic groups with increase in unsaturated hydrocarbon indicating formation of biodegraded intermediates. Lesser waxworms fed with WC, PE, and PE-WC completed all life cycle stages (larvae, pupae, moth, and egg) developing into a second generation. The second generation of PE-WC fed larvae of A. grisella efficiently degrades PE at par with first generation counterparts.

Target-Specificity in Scorpions; Comparing Lethality of Scorpion Venoms across Arthropods and Vertebrates.

Scorpions use their venom in defensive situations as well as for subduing prey. Since some species of scorpion use their venom more in defensive situations than others, this may have led to selection for differences in effectiveness in defensive situations. Here, we compared the LD50 of the venom of 10 species of scorpions on five different species of target organisms; two insects and three vertebrates. We found little correlation between the target species in the efficacy of the different scorpion venoms. Only the two insects showed a positive correlation, indicating that they responded similarly to the panel of scorpion venoms. We discuss the lack of positive correlation between the vertebrate target species in the light of their evolution and development. When comparing the responses of the target systems to individual scorpion venoms pairwise, we found that closely related scorpion species tend to elicit a similar response pattern across the target species. This was further reflected in a significant phylogenetic signal across the scorpion phylogeny for the LD50 in mice and in zebrafish. We also provide the first mouse LD50 value for Grosphusgrandidieri.