Contribution of Lysinibacillus sphaericus hemolysin and chitin-binding protein in entomopathogenic activity against insecticide resistant Aedes aegypti

Analyses of the Antibiofilm Activity of o-Phenanthroline Monohydrate against Enterococcus faecalis and Staphylococcus aureus and the Mechanisms Underlying These Effects

Enterococcus faecalis and Staphylococcus aureus exhibit robust biofilm formation capabilities, the formation of which is closely linked to pathogenicity and drug resistance, thereby resulting in host infection and treatment failure. o-Phenanthroline monohydrate (o-Phen) and its derivatives demonstrate a wide range of antibacterial and antifungal activities. In this study, we aimed to explore the antibiofilm activity of o-Phen to E. faecalis and S. aureus and provide insights into the molecular mechanisms for combating biofilm resistance. We demonstrated that o-Phen possesses significant antibacterial and antibiofilm properties against E. faecalis and S. aureus, inducing alterations in bacterial morphology, compromising cell membrane integrity, and exhibiting synergistic effects with β-lactam antibiotics at sub-MIC concentrations. The adhesion ability and automatic condensation capacity of, and synthesis of, extracellular polymers by E. faecalis cells were reduced by o-Phen, resulting in the inhibition of biofilm formation. Importantly, transcriptome analysis revealed 354 upregulated and 456 downregulated genes in o-Phen-treated E. faecalis. Differentially expressed genes were enriched in 11 metabolism-related pathways, including amino acid metabolism, pyrimidine metabolism, and glycolysis/gluconeogenesis. Moreover, the oppA, CeuA, and ZnuB genes involved in the ABC transport system, and the PBP1A penicillin-binding protein-coding genes sarA and mrcA were significantly downregulated. The multidrug efflux pump system and membrane permeability genes mdtG and hlyD, and bacterial adhesion-related genes, including adcA and fss2 were also downregulated, while mraZ and ASP23 were upregulated. Thus, o-Phen is anticipated to be an effective alternative drug for the treatment of E. faecalis and S. aureus biofilm-associated infections.

Rare case of bacteremia due to Lysinibacillus sphaericus in a person living with HIV

Lysinibacillus sphaericus, as an insect pathogen, is a ubiquitous Gram-positive bacterium present in the environment. It is often considered to be contaminating bacteria. L. sphaericus has been reported to cause infectious diseases in humans relatively rarely. We report a rare case of bacteremia due to L. sphaericus in a person living with HIV, which is also the first reported case of bacteremia caused by L. sphaericus in China. L. sphaericus easily causes infection in immunocompromised individuals. We found that L. sphaericus and Lysinibacillus fusiformis could not be distinguished by their 16S ribosomal RNA gene sequence. We performed a genome-wide analysis of the isolated strains of this case and predicted the virulence factors. Finally, L. sphaericus was confirmed. According to antimicrobial susceptibility test, the strain was found to be sensitive to levofloxacin and vancomycin but resistant to penicillin. Greater attention to L. sphaericus infection should be paid and immunocompromised populations should be protected from L. sphaericus infection.

The influence of culture-dependent native microbiota in Zika virus infection in Aedes aegypti

Background

Emerging and re-emerging vector-borne diseases (VBDs) pose a recurring threat to tropical countries, mainly due to the abundance and distribution of the Aedes aegypti mosquito, which is a vector of the Zika, dengue, chikungunya, and yellow fever arboviruses.

Methods

Female 3–5 day-old Ae. aegypti were distributed into two experimental groups: group I—survey of cultivable bacteria; sucrose group: fed only on sucrose, i.e., non-blood-fed (UF); blood-fed group: (i) fed with non-infected blood (BF); (ii) fed with blood infected with the Zika virus (BZIKV); (iii) pretreated with penicillin/streptomycin (pen/strep), and fed with non-infected blood (TBF); (iv) pretreated with pen/strep and fed blood infected with ZIKV, i.e., gravid with developed ovaries, (TGZIKV); group II—experimental co-infections: bacteria genera isolated from the group fed on sucrose, i.e., non-blood-fed (UF).

Results

Using the cultivable method and the same mosquito colony and ZIKV strain described by in a previous work, our results reveled 11 isolates (Acinetobacter, Aeromonas, Cedecea, Cellulosimicrobium, Elizabethkingia, Enterobacter, Lysinibacillus, Pantoea, Pseudomonas, Serratia, and Staphylococcus). Enterobacter was present in all evaluated groups (i.e., UF, BF, BZIKV, TBF, and TGZIKV), whereas Elizabethkingia was present in the UF, BZIKV, and TBF groups. Pseudomonas was present in the BZIKV and TBF groups, whereas Staphylococcus was present in the TBF and TGZIKV groups. The only genera of bacteria that were found to be present in only one group were Aeromonas, Lysinibacillus, and Serratia (UF); Cedacea, Pantoea and Acinetobacter (BF); and Cellulosimicrobium (BZIKV). The mosquitoes co-infected with ZIKV plus the isolates group fed on sucrose (UF) showed interference in the outcome of infection.

Conclusions

We demonstrate that the distinct feeding aspects assessed herein influence the composition of bacterial diversity. In the co-infection, among ZIKV, Ae. aegypti and the bacterial isolates, the ZIKV/Lysinibacillus–Ae. aegypti had the lowest number of viral copies in the head-SG, which means that it negatively affects vector competence. However, when the saliva was analyzed after forced feeding, no virus was detected in the mosquito groups ZIKV/Lysinibacillus–Lu. longipalpis and Ae. aegypti; the combination of ZIKV/Serratia may interfere in salivation. This indicates that the combinations do not produce viable viruses and may have great potential as a method of biological control.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05160-7.

Assessment of the Synergic Effect between Lysinibacillus sphaericus S-Layer Protein and Glyphosate in the Lethality of the Invasive Arboviral Vector Aedes albopictus

Glyphosate and glyphosate-based herbicides are among the most used chemicals in plant pest control. Both glyphosate and its main by-product Aminomethylphosphonic Acid (AMPA) are highly environmentally persistent and, through several processes (including surface runoff and bioaccumulation), affect species beyond their intended targets, especially in aquatic ecosystems. Aedes albopictus is a novel invasive arboviral vector in Colombia and has spread to much of the national territory in recent years. Strains of the bacterium Lysinibacillus sphaericus have shown the ability to degrade glyphosate into environmentally inert compounds, in addition to having great larvicidal efficiency in different mosquito species through the production of several proteins, including the surface layer (S-Layer) protein. The S-Layer is a bacterial structure consisting of glycoprotein monomers, and its functions are thought to include bacterial interactions, protection from the outside medium and biological control. The study assessed the entomopathogenic activity of L. sphaericus S-Layer protein on Ae. albopictus larvae, and the effects that glyphosate and its by-products have in this process. To that end, bioassays were performed to compare the larval mortality between different treatments with and without S-Layer, glyphosate, and glyphosate derivates. Comparisons were made through Analysis of variance (ANOVA) and Tukey's Honestly Significant Difference (HSD) analyses. Significant differences were found in larval mortality in the treatments, and larval mortality was greater when the S-Layer protein was present, though glyphosate field-doses (1.69 g/L) alone had a notable toxicity as well. An apparent synergic effect on the mortality of larval Ae. albopictus when exposed to mixtures containing 1500 ppm of the S-Layer protein, glyphosate, and/or glyphosate derivates was found. Further studies are needed for the in-depth understanding of this mechanism and its consequences on aquatic ecosystems.

First report on the characterization of pathogenic Rahnella aquatilis KCL-5 from crucian carp: Revealed by genomic and proteomic analyses

Rahnella aquatilis is an important pathogen of several aquatic organisms and is found widely distributed in the freshwater, soil, fish and human clinical samples. Our previously published study reported a novel pathogenic R. aquatilis strain KCL-5 to crucian carp (Carassius auratus). To further investigate the characteristics and pathogenesis caused by R. aquatilis, we here report on the pathological changes, bacterial genomic and proteomic analyses of strain KCL-5. Significantly pathological changes in liver, intestine, spleen and gills were observed in infected fish. The genome consists of one circular chromosome 5,062,299 bp with 52.02% GC content and two plasmids (506,827 bp, 52.16%; 173,433 bp, 50.00%) and predicted 5,653 genes, 77 tRNAs and 22 rRNAs. Some virulence factors were characterized, including outer membrane protein, haemolysin, RTX toxin, chemotaxis and T3SS secretion system. Antimicrobial resistance genes such as EmrAB-TolC, MexABC-OpmB and RosAB efflux pump were found in strain KCL-5. KEGG analysis showed that mainly functional modules were ABC transporters, biosynthesis of amino acids, two-component system, quorum sensing, flagellum assembly and chemotaxis, in which most of them were identified by using 2-DE/MS analyses. To our knowledge, this was first report on the molecular characteristics of R. aquatilis by multi-omics approaches, which will provide insights into the pathogenic mechanism of R. aquatilis infection in fish.

Synergistic effect of Lysinibacillus sphaericus and glyphosate on temephos-resistant larvae of Aedes aegypti

BACKGROUND

Glyphosate-based herbicides are one of the most commonly used compounds to control perennial weeds around the world. This compound is very persistent in the environment and tends to filter into aquatic ecosystems, affecting non-target species such as mosquito larvae. Aedes aegypti mosquitoes are vectors of multiple arboviruses such as dengue and Zika. Glyphosate can be degraded into non-harmful environmental compounds by Lysinibacillus sphaericus, a spore forming bacterium which can also kill Ae. aegypti larvae. In this study, we assessed the effect of glyphosate concentrations, typically used in Colombia, on the entomopathogenic activity of L. sphaericus against Ae. aegypti larvae.

METHODS

Bioassays and toxicity curves were performed to compare the larval mortality between different treatments with and without bacteria and glyphosate (Roundup 747®). Larvae were exposed to both bacteria and glyphosate by adding the compound on chloride-free water. Comparisons were made using both probit regression and ANOVA analysis.

RESULTS

ANOVA showed a significant difference in larval mortality when adding glyphosate and L. sphaericus at the same time. Thus, a positive synergic effect on larval mortality was found when L. sphaericus and glyphosate were mixed. According to probit analysis, median lethal dose (LD50) for bacterial mixture was of 106.23 UFC/ml and for glyphosate was 2.34 g/l.

CONCLUSIONS

A positive synergic effect on the mortality of larval Ae. aegypti when exposed to L. sphaericus mixture and glyphosate was found. Molecular studies focusing on the toxin production of L. sphaericus are required to understand more about this synergistic effect.

Molecular assessment of glyphosate-degradation pathway via sarcosine intermediate in Lysinibacillus sphaericus

The widespread use of glyphosate has permeated not only small- and large-scale agriculture, but also the fight against drug trafficking and illicit crops. Health, alimentary security, and the rights of peasant and indigenous communities have been compromised in countries with intensive use of glyphosate-based herbicides. In 2015, the International Agency for Research on Cancer classified this substance as probably carcinogenic to humans, leading to the suspension of aerial glyphosate spraying the same year in countries like Colombia, where glyphosate has been extensively used in illicit crop eradication. Notwithstanding, according to a study of the U.S. Geological Survey, traces of glyphosate and its main degradation product, AMPA, remain in soil year after year. This underscores the urgency and importance of assessing new technologies to degrade glyphosate present in soils and waterbodies without leaving persistent byproducts. The aim of this study was to evaluate Lysinibacillus sphaericus' glyphosate uptake as a carbon and phosphorous source by a sarcosine-mediated metabolic pathway that releases glycine as final degradation product. To accomplish this, molecular and analytic evidence were collected in vitro from sarcosine oxidase activity, a key enzyme of a degradation pathway which releases byproducts that are easy to incorporate into natural biosynthesis routes.