The microbiome of the invertebrate model host Galleria mellonella is dominated by Enterococcus

Camille Nina Allonsius, Wannes Van Beeck, Ilke De Boeck, Stijn Wittouck & Sarah Lebeer
Animal Microbiome

The popularity of Galleria mellonella as invertebrate model is increasing rapidly, because it forms an attractive alternative to study bacterial, fungal and viral infections, toxin biology, and to screen antimicrobial drugs. For a number of vertebrate and invertebrate animal and plant models, it has been established that the microbial communities present on various host surfaces will influence the host’s immune and growth development state and the colonization capacity of newly introduced micro-organisms. The microbial communities of Galleria mellonella larvae have, however, not yet been well characterized.

In this study, we present the bacterial communities that were found on different body sites of G. mellonella larvae. These communities showed very little diversity and were mostly dominated by one Enterococcus taxon. In addition, we found that the production conditions appear to have little impact on the microbiota of the larvae. 

Establishment of the simplicity of the microbiota of G. mellonella larvae underlines the potential of the larvae as a model host system for microbiome-host interactions.

Comparative genome analysis of Lactobacillus mudanjiangensis, an understudied member of the Lactobacillus plantarum group

S. Wuyts, C. Allonsius, S. Wittouck, S. Thys, B. Lievens, S. Weckx, L. De Vuyts and S. Lebeer
Microbial Genomics

The genus Lactobacillusis known to be extremely diverse and consists of different phylogenetic groups. One of the most prominent phylogenetic groups within this genus is the Lactobacillus plantarumgroup, which contains the understudied Lactobacillus mudanjiangensisspecies. Before this study, only one L. mudanjiangensisstrain was described, but without whole-genome analysis. In this study, three strains classified as L. mudanjiangensiswere isolated from three different carrot juice fermentations and their whole-genome sequence was determined, together with the genome sequence of the type strain. The genomes of all four strains were compared with publicly available L. plantarumgroup genome sequences. This analysis showed that L. mudanjiangensisharboured the second largest genome size and gene count of the whole L. plantarumgroup. In addition, all members of this species showed the presence of a gene coding for a cellulose-degrading enzyme. Finally, three of the four L. mudanjiangensisstrains studied showed the presence of pili on scanning electron microscopy (SEM) images.

A genome-based species taxonomy of the Lactobacillus Genus Complex

Stijn Wittouck, Sander Wuyts, Conor J. Meehan, Vera van Noort, Sarah Lebeer

There are more than 200 published species within the Lactobacillus genus complex (LGC), the majority of which have sequenced type strain genomes available. Although genome-based species delimitation cutoffs are accepted as the gold standard by the community, these are seldom actually checked for new or already published species. In addition, the availability of genome data is revealing inconsistencies in the species-level classification of many strains. We constructed a de novo species taxonomy for the LGC based on 2,459 publicly available genomes, using a 94% core nucleotide identity cutoff. We reconciled these de novo species with published species and subspecies names by (i) identifying genomes of type strains and (ii) comparing 16S rRNA genes of the genomes with 16S rRNA genes of type strains. We found that genomes within the LGC could be divided into 239 de novo species that were discontinuous and exclusive. Comparison of these de novo species to published species led to the identification of nine sets of published species that can be merged and one species that can be split. Further, we found at least eight de novo species that constitute new, unpublished species. Finally, we reclassified 74 genomes on the species level and identified for the first time the species of 98 genomes.

Overall, the current state of LGC species taxonomy is largely consistent with genome-based species delimitation cutoffs. There are, however, exceptions that should be resolved to evolve toward a taxonomy where species share a consistent diversity in terms of sequence divergence.

Translating Recent Microbiome Insights in Otitis Media into Probiotic Strategies

Marianne F. L. van den Broek, Ilke De Boeck, Filip Kiekens, An Boudewyns, Olivier M. Vanderveken, Sarah Lebeer
Clinical Microbiology Reviews

The microbiota or bacterial community of the upper respiratory tract (URT) protects us against harmful or pathogenic bacteria via several mechanisms. Different factors, from the environment and/or the human host, can have an impact on the microbiota to an unstable community that predisposes the human body to infection or inflammation. Lactic acid bacteria (LAB) are members of the URT microbiota and associated with healthy conditions. These observations have formed the basis of this review, in which we describe the current knowledge of the molecular and clinical potential of LAB in the URT, which is currently underexplored in microbiome and probiotic research.

Inhibition of Candida Albicans Morphogenesis by Chitinase from Lactobacillus Rhamnosus GG

C. Allonsius, D. Vandenheuvel, E. Oerlemans, M. Petrova, G. Donders, P. Cos, P. Delputte and S. Lebeer
Scientific Reports

Lactobacilli have been evaluated as probiotics against Candida infections in several clinical trials, but with variable results. Understanding the clinical efficacy of Lactobacillus strains is hampered by an overall lack of insights into their modes of action. In this study, we aimed to unravel molecular mechanisms underlying the inhibitory effects of lactobacilli on hyphal morphogenesis, which is a crucial step in C. albicans virulence.

Based on a screening of different Lactobacillus strains, we found that L. rhamnosusL. casei and L. paracasei showed the strongest activity against Candida hyphae formationMsp1 (major peptidoglycan hydrolase) was identified as a key effector molecule, and this was due to its ability to break down chitin, the main polymer in the hyphal cell wall of C. albicans. Our findings will assist in better strain selection and improved application in future clinical trials for Lactobacillus-based Candida-management strategies.

Elastic Recovery of Filler-Binders to Safeguard Viability of Lactobacillus Rhamnosus GG during Direct Compression

E. Byl, S. Lebeer and F. Kiekens
European Journal of Pharmaceutics and Biopharmaceutics

Tablets are increasingly explored as dosage form for oral probiotics. In such tablets, the dry form increases the stability of the product. In addition, the probiotic cells are entrapped in the tablet matrix, which protects them against the environmental factors in the human body. However, the development of a probiotic tablet with an adequate number of viable cells remains a challenge due to the stress of the compression process. The adverse conditions during production can damage the cells, which leads to a loss of viability and a failure of the therapy. This study aimed to investigate the effect of the compression behavior of filler-binders on the survival of Lactobacillus rhamnosus GG during tablet production. The results demonstrated that the elastic recovery of the filler-binder during decompression played a protective role in bacterial survival, reducing the compression stress during manufacturing. Consequently, the bacterial cells were less damaged, which resulted in a higher survival rate and a better stability during long-term storage. In conclusion, the elastic recovery of a filler-binder showed to be an important key in safeguarding probiotic cells during direct compression and storage.