Interkingdom Gut Microbiome and Resistome of the Cockroach Blattella germanica

Adaptability of the gut microbiota of the German cockroach Blattella germanica to a periodic antibiotic treatment

High-throughput sequencing studies have shown that diet or antimicrobial treatments impact animal gut microbiota equilibrium. However, properties related to the gut microbial ecosystem stability, such as resilience, resistance, or functional redundancy, must be better understood. To shed light on these ecological processes, we combined advanced statistical methods with 16 S rRNA gene sequencing, functional prediction, and fitness analyses in the gut microbiota of the cockroach Blattella germanica subject to three periodic pulses of the antibiotic (AB) kanamycin (n=512). We first confirmed that AB did not significantly affect cockroaches' biological fitness, and gut microbiota changes were not caused by insect physiology alterations. The sex variable was examined for the first time in this species, and no statistical differences in the gut microbiota diversity or composition were found. The comparison of the gut microbiota dynamics in control and treated populations revealed that (1) AB treatment decreases diversity and completely disrupts the co-occurrence networks between bacteria, significantly altering the gut community structure. (2) Although AB also affected the genetic composition, functional redundancy would explain a smaller effect on the functional potential than on the taxonomic composition. (3) As predicted by Taylor's law, AB generally affected the most abundant taxa to a lesser extent than the less abundant taxa. (4) Taxa follow different trends in response to ABs, highlighting "resistant taxa," which could be critical for community restoration. (5) The gut microbiota recovered faster after the three AB pulses, suggesting that gut microbiota adapts to repeated treatments.

Genome reduction and horizontal gene transfer in the evolution of Endomicrobia-rise and fall of an intracellular symbiosis with termite gut flagellates

Bacterial endosymbionts of eukaryotic hosts typically experience massive genome reduction, but the underlying evolutionary processes are often obscured by the lack of free-living relatives. Endomicrobia, a family-level lineage of host-associated bacteria in the phylum Elusimicrobiota that comprises both free-living representatives and endosymbionts of termite gut flagellates, are an excellent model to study evolution of intracellular symbionts. We reconstructed 67 metagenome-assembled genomes (MAGs) of Endomicrobiaceae among more than 1,700 MAGs from the gut microbiota of a wide range of termites. Phylogenomic analysis confirmed a sister position of representatives from termites and ruminants, and allowed to propose eight new genera in the radiation of Endomicrobiaceae. Comparative genome analysis documented progressive genome erosion in the new genus Endomicrobiellum, which comprises all flagellate endosymbionts characterized to date. Massive gene losses were accompanied by the acquisition of new functions by horizontal gene transfer, which led to a shift from a glucose-based energy metabolism to one based on sugar phosphates. The breakdown of glycolysis and many anabolic pathways for amino acids and cofactors in several subgroups was compensated by the independent acquisition of new uptake systems, including an ATP/ADP antiporter, from other gut microbiota. The putative donors are mostly flagellate endosymbionts from other bacterial phyla, including several, hitherto unknown lineages of uncultured Alphaproteobacteria, documenting the importance of horizontal gene transfer in the convergent evolution of these intracellular symbioses. The loss of almost all biosynthetic capacities in some lineages of Endomicrobiellum suggests that their originally mutualistic relationship with flagellates is on its decline.IMPORTANCEUnicellular eukaryotes are frequently colonized by bacterial and archaeal symbionts. A prominent example are the cellulolytic gut flagellates of termites, which harbor diverse but host-specific bacterial symbionts that occur exclusively in termite guts. One of these lineages, the so-called Endomicrobia, comprises both free-living and endosymbiotic representatives, which offers the unique opportunity to study the evolutionary processes underpinning the transition from a free-living to an intracellular lifestyle. Our results revealed a progressive gene loss in energy metabolism and biosynthetic pathways, compensated by the acquisition of new functions via horizontal gene transfer from other gut bacteria, and suggest the eventual breakdown of an initially mutualistic symbiosis. Evidence for convergent evolution of unrelated endosymbionts reflects adaptations to the intracellular environment of termite gut flagellates.

Comparative Transcriptomics of Fat Bodies between Symbiotic and Quasi-Aposymbiotic Adult Females of Blattella germanica with Emphasis on the Metabolic Integration with Its Endosymbiont Blattabacterium and Its Immune System

We explored the metabolic integration of Blattella germanica and its obligate endosymbiont Blattabacterium cuenoti by the transcriptomic analysis of the fat body of quasi-aposymbiotic cockroaches, where the endosymbionts were almost entirely removed with rifampicin. Fat bodies from quasi-aposymbiotic insects displayed large differences in gene expression compared to controls. In quasi-aposymbionts, the metabolism of phenylalanine and tyrosine involved in cuticle sclerotization and pigmentation increased drastically to compensate for the deficiency in the biosynthesis of these amino acids by the endosymbionts. On the other hand, the uricolytic pathway and the biosynthesis of uric acid were severely decreased, probably because the reduced population of endosymbionts was unable to metabolize urea to ammonia. Metabolite transporters that could be involved in the endosymbiosis process were identified. Immune system and antimicrobial peptide (AMP) gene expression was also reduced in quasi-aposymbionts, genes encoding peptidoglycan-recognition proteins, which may provide clues for the maintenance of the symbiotic relationship, as well as three AMP genes whose involvement in the symbiotic relationship will require additional analysis. Finally, a search for AMP-like factors that could be involved in controlling the endosymbiont identified two orphan genes encoding proteins smaller than 200 amino acids underexpressed in quasi-aposymbionts, suggesting a role in the host-endosymbiont relationship.

Endosymbiont and gut bacterial communities of the brown-banded cockroach, Supella longipalpa

The brown-banded cockroach (Supella longipalpa) is a widespread nuisance and public health pest. Like the German cockroach (Blattella germanica), this species is adapted to the indoor biome and completes the entirety of its life cycle in human-built structures. Recently, understanding the contributions of commensal and symbiotic microbes to the biology of cockroach pests, as well as the applications of targeting these microbes for pest control, have garnered significant scientific interest. However, relative to B. germanica, the biology of S. longipalpa, including its microbial associations, is understudied. Therefore, the goal of the present study was to quantitatively examine and characterize both the endosymbiont and gut bacterial communities of S. longipalpa for the first time. To do so, bacterial 16S rRNA gene amplicon sequencing was conducted on DNA extracts from whole adult females and males, early instar nymphs, and late instar nymphs. The results demonstrate that the gut microbiome is dominated by two genera of bacteria known to have beneficial probiotic effects in other organisms, namely Lactobacillus and Akkermansia. Furthermore, our data show a significant effect of nymphal development on diversity and variation in the gut microbiome. Lastly, we reveal significant negative correlations between the two intracellular endosymbionts, Blattabacterium and Wolbachia, as well as between Blattabacterium and the gut microbiome, suggesting that Blattabacterium endosymbionts could directly or indirectly influence the composition of other bacterial populations. These findings have implications for understanding the adaptation of S. longipalpa to the indoor biome, its divergence from other indoor cockroach pest species such as B. germanica, the development of novel control approaches that target the microbiome, and fundamental insect-microbe interactions more broadly.

Transmission of antimicrobial resistance in the gut microbiome of gregarious cockroaches: the importance of interaction between antibiotic exposed and non-exposed populations

Antimicrobial resistance (AMR) is a major global health concern, further complicated by its spread via the microbiome bacterial members. While mathematical models discuss AMR transmission through the symbiotic microbiome, experimental studies are scarce. Herein, we used a gregarious cockroach, Pycnoscelus surinamensis, as an in vivo animal model for AMR transmission investigations. We explored whether the effect of antimicrobial treatment is detectable with metagenomic sequencing, and whether AMR genes can be spread and established in unchallenged (not treated with antibiotics) individuals following contact with treated donors, and under various frequencies of interaction. Gut and soil substrate microbiomes were investigated by metagenomic sequencing for bacterial community composition and resistome profiling. We found that tetracycline treatment altered the treated gut microbiome by decreasing bacterial diversity and increasing the abundance of tetracycline resistance genes. Untreated cockroaches that interacted with treated donors also had elevated tetracycline resistance. The levels of resistance differed depending on the magnitude and frequency of donor transfer. Additionally, treated donors showed signs of microbiome recovery due to their interaction with the untreated ones. Similar patterns were also recorded in the soil substrate microbiomes. Our results shed light on how interacting microbiomes facilitate AMR gene transmission to previously unchallenged hosts, a dynamic influenced by the interaction frequencies, using an in vivo model to validate theoretical AMR transmission models.IMPORTANCEAntimicrobial resistance is a rising threat to human and animal health. The spread of resistance through the transmission of the symbiotic gut microbiome is of concern and has been explored in theoretical modeling studies. In this study, we employ gregarious insect populations to examine the emergence and transmission of antimicrobial resistance in vivo and validate modeling hypotheses. We find that antimicrobial treatment increases the levels of resistance in treated populations. Most importantly, we show that resistance increased in untreated populations after interacting with the treated ones. The level of resistance transmission was affected by the magnitude and frequency of population mixing. Our results highlight the importance of microbial transmission in the spread of antimicrobial resistance.

The honeybee gut resistome and its role in antibiotic resistance dissemination

There is now general concern about widespread antibiotic resistance, and growing evidence indicates that gut microbiota is critical in providing antibiotic resistance. Honeybee is an important pollinator; the incidence of antibiotic resistance genes in honeybee gut causes potential risks to not only its own health but also to public and animal health, for its potential disseminator role, thus receiving more attention from the public. Recent analysis results reveal that the gut of honeybee serves as a reservoir of antibiotic resistance genes, probably due to antibiotics application history in beekeeping and horizontal gene transfer from the highly polluted environment. These antibiotic resistance genes accumulate in the honeybee gut and could be transferred to the pathogen, even having the potential to spread during pollination, tending, social interactions, etc. Newly acquired resistance traits may cause fitness reduction in bacteria whereas facilitating adaptive evolution as well. This review outlines the current knowledge about the resistome in honeybee gut and emphasizes its role in antibiotic resistance dissemination.

Evidence of the cooperative response of Blattella germanica gut microbiota to antibiotic treatment

Gut microbiota plays a key role in host health under normal conditions. However, bacterial composition can be altered by external factors such as antibiotic (AB) intake. While there are many descriptive publications about the effects of AB on gut microbiota composition after treatment, the dynamics and interactions among the bacterial taxa are still poorly understood. In this work, we performed a longitudinal study of gut microbiome dynamics in B. germanica treated with kanamycin. The AB was supplied in three separate periods, giving the microbiota time to recover between each antibiotic intake. We applied two new statistical models, not focusing on pair-wise interactions, to more realistically study the interactions between groups of bacterial taxa and how some groups affect a single taxon. The first model provides information on the importance of a given genus, and the rest of the community, to define the abundance of that genus. The second model, on the other hand, provides details about the relationship between groups of bacteria, focusing on which community groups affect the taxa. These models help us to identify which bacteria are community-dependent in stress conditions, which taxa might be better adapted than the rest of the community, and which bacteria might be working together within the community to overcome the antibiotic. In addition, these models enable us to identify different bacterial groups that were separated in control conditions but were found together in treated conditions, suggesting that when the environment is more hostile (as it is under antibiotic treatment), the whole community tends to work together.

Effects of copper and zinc oxide nanoparticles on German cockroach development, indoxacarb resistance, and bacterial load

BACKGROUND

The German cockroach, Blattella germanica, is a ubiquitous and medically significant urban pest. The ongoing development of insecticide resistance in global populations of B. germanica has complicated control efforts and created a need for improved tools. We previously reported that disruption of the gut microbiota by oral administration of the antimicrobial doxycycline reduced resistance in an indoxacarb resistant field strain and also delayed nymphal development and reduced adult fecundity. However, the application of doxycycline for cockroach control in the field is impractical. Here, we sought to determine whether two metal nanoparticles with known antimicrobial properties, copper (Cu) and zinc oxide (ZnO), have similar effects to doxycycline on the physiology of B. germanica and could provide more practical alternatives for control.

RESULTS

We found that dietary exposure to 0.1% Cu nanoparticles, but not ZnO, significantly delays the development of nymphs into adults. However, neither of the nanoparticles altered the fecundity of females, and ZnO surprisingly increased resistance to indoxacarb in a resistant field strain, in contrast to doxycycline. Semi-quantitative polymerase chain reaction (qPCR) further revealed that prolonged dietary exposure (14 days) to Cu or ZnO nanoparticles at the low concentration readily consumed by cockroaches (0.1%) does not reduce the load of the bacterial microbiota, suggesting alternative mechanisms behind their observed effects.

CONCLUSIONS

Together, our results indicate that ingestion of Cu nanoparticles can impact German cockroach development through an undetermined mechanism that does not involve reducing the overall load of the bacterial microbiota. Therefore, Cu may have some applications in cockroach control as a result of this activity but antagonistic effects on insecticide resistance should be considered when evaluating the potential of nanoparticles for cockroach control. © 2023 Society of Chemical Industry.

Exploring Gut Microbial Dynamics and Symbiotic Interaction in Blattella germanica Using Rifampicin

Blattella germanica harbours two cohabiting symbiotic systems: an obligate endosymbiont, Blattabacterium, located inside bacteriocytes and vertically transmitted, which is key in nitrogen metabolism, and abundant and complex gut microbiota acquired horizontally (mainly by coprophagy) that must play an important role in host physiology. In this work, we use rifampicin treatment to deepen the knowledge on the relationship between the host and the two systems. First, we analysed changes in microbiota composition in response to the presence and removal of the antibiotic with and without faeces in one generation. We found that, independently of faeces supply, rifampicin-sensitive bacteria are strongly affected at four days of treatment, and most taxa recover after treatment, although some did not reach control levels. Second, we tried to generate an aposymbiotic population, but individuals that reached the second generation were severely affected and no third generation was possible. Finally, we established a mixed population with quasi-aposymbiotic and control nymphs sharing an environment in a blind experiment. The analysis of the two symbiotic systems in each individual after reaching the adult stage revealed that endosymbiont's load does not affect the composition of the hindgut microbiota, suggesting that there is no interaction between the two symbiotic systems in Blattella germanica.

Cockroaches: a potential source of novel bioactive molecule(s) for the benefit of human health

Cockroaches are one of the hardiest insects that have survived on this planet for millions of years. They thrive in unhygienic environments, are able to survive without food for up to 30 days, without air for around 45 min and being submerged under water for 30 min. Cockroaches are omnivorous and feed on a variety of foods, including cellulose and plastic, to name a few. It is intriguing that cockroaches are able to endure and flourish under conditions that are harmful to Homo sapiens. Given the importance of the gut microbiome on its' host physiology, we postulate that the cockroach gut microbiome and/or its metabolites, may be contributing to their "hardiness", which should be utilized for the discovery of biologically active molecules for the benefit of human health. Herein, we discuss the biology, diet/habitat of cockroaches, composition of gut microbiome, cellular senescence, and resistance to infectious diseases and cancer. Furthermore, current knowledge of the genome and epigenome of these remarkable species is considered. Being one of the most successful and diverse insects, as well as their extensive use in traditional and Chinese medicine, the lysates/extracts and gut microbial metabolites of cockroaches may offer a worthy resource for novel bioactive molecule(s) of therapeutic potential for the benefit of human health and may be potentially used as probiotics.

Wildlife and Antibiotic Resistance

Antibiotic resistance is a major human health problem. While health care facilities are main contributors to the emergence, evolution and spread of antibiotic resistance, other ecosystems are involved in such dissemination. Wastewater, farm animals and pets have been considered important contributors to the development of antibiotic resistance. Herein, we review the impact of wildlife in such problem. Current evidence supports that the presence of antibiotic resistance genes and/or antibiotic resistant bacteria in wild animals is a sign of anthropic pollution more than of selection of resistance. However, once antibiotic resistance is present in the wild, wildlife can contribute to its transmission across different ecosystems. Further, the finding that antibiotic resistance genes, currently causing problems at hospitals, might spread through horizontal gene transfer among the bacteria present in the microbiomes of ubiquitous animals as cockroaches, fleas or rats, supports the possibility that these organisms might be bioreactors for the horizontal transfer of antibiotic resistance genes among human pathogens. The contribution of wildlife in the spread of antibiotic resistance among different hosts and ecosystems occurs at two levels. Firstly, in the case of non-migrating animals, the transfer will take place locally; a One Health problem. Paradigmatic examples are the above mentioned animals that cohabit with humans and can be reservoirs and vehicles for antibiotic resistance dissemination. Secondly, migrating animals, such as gulls, fishes or turtles may participate in the dissemination of antibiotic resistance across different geographic areas, even between different continents, which constitutes a Global Health issue.

Of Cockroaches and Symbionts: Recent Advances in the Characterization of the Relationship between Blattella germanica and Its Dual Symbiotic System

Mutualistic stable symbioses are widespread in all groups of eukaryotes, especially in insects, where symbionts have played an essential role in their evolution. Many insects live in obligate relationship with different ecto- and endosymbiotic bacteria, which are needed to maintain their hosts’ fitness in their natural environment, to the point of even relying on them for survival. The case of cockroaches (Blattodea) is paradigmatic, as both symbiotic systems coexist in the same organism in two separated compartments: an intracellular endosymbiont (Blattabacterium) inside bacteriocytes located in the fat body, and a rich and complex microbiota in the hindgut. The German cockroach Blattella germanica is a good model for the study of symbiotic interactions, as it can be maintained in the laboratory in controlled populations, allowing the perturbations of the two symbiotic systems in order to study the communication and integration of the tripartite organization of the host–endosymbiont–microbiota, and to evaluate the role of symbiotic antimicrobial peptides (AMPs) in host control over their symbionts. The importance of cockroaches as reservoirs and transmission vectors of antibiotic resistance sequences, and their putative interest to search for AMPs to deal with the problem, is also discussed.

New insight into the relationship between Salmonella Typhimurium and the German cockroach suggests active mechanisms of vector-borne transmission

Diarrheal diseases are among the most common illnesses in the world and the bacterium Salmonella enterica serovar Typhimurium is a leading cause of morbidity and mortality from diarrhea globally. The German cockroach (Blattella germanica) frequently harbors and has been linked to human outbreaks of Salmonella, but the mechanisms of vector-borne transmission are not fully clear. Transmission of S. Typhimurium by cockroaches has been previously described as mechanical. Mechanical transmission is a wholly passive process that involves physical transfer of a pathogen from one location or host to another but lacks bacterial replication in the vector and active bacterial processes that promote vector colonization or transmission. Towards the goal of obtaining novel insight into the mechanisms of S. Typhimurium transmission by cockroaches, here we orally provisioned wild type and mutant strains of the bacteria to adult B. germanica and examined several aspects of colonization and shedding. Our results provide evidence of three previously unappreciated phenomena with significant implications. First, we demonstrate that S. Typhimurium undergoes replication at multiple phases during colonization of the cockroach gut. Second, we show the formation of biofilm-like aggregates by S. Typhimurium in the cockroach foregut. Lastly, we identify two mutant strains of S. Typhimurium that are deficient in colonization and shedding relative to isogenic controls, implicating type III secretion and the formation of fimbriae as two processes that are necessary for interaction with the cockroach vector. Together, our data indicate that transmission of S. Typhimurium by cockroaches is not solely mechanical but may resemble biological transmission by other insect vectors that intake human pathogenic bacteria from infected hosts and are subsequently colonized, enabling active dissemination. Thus, these findings suggest that cockroaches and their control may be more important for infection prevention than is currently appreciated. Additional studies to better understand the cycle and biological mechanisms of vector-borne transmission are warranted.

Gut Microbiota Cannot Compensate the Impact of (quasi) Aposymbiosis in Blattella germanica

Simple Summary

The German cockroach Blattella germanica is a good model to study complex symbiotic relationships because the following two symbiotic systems coexist in a single individual: the endosymbiont Blattabacterium (living inside specialized cells called bacteriocytes) and the gut microbiota. Although the role of the endosymbiont has been fully elucidated, the function of the gut microbiota remains unclear. The study of the gut microbiota will benefit from the availability of insects deprived of Blattabacterium. Our goal is to determine the effect of the removal (or, at least, the reduction) of the endosymbiont population on the cockroach’s fitness, in a normal gut microbiota community. For this purpose, we treated our cockroach population with rifampicin to decrease the amount of endosymbiont in the following generation. As the treatment also affects rifampicin-sensitive gut bacteria, we allowed it to recover for at least 20 days before sampling. We found that after this antibiotic treatment, the endosymbiont population remained extremely reduced and only the microbiota were able to recover, although it could not compensate for the endosymbiont role, and the host’s fitness was drastically affected. This accomplished reduction, however, is not homogenous and requires further study to develop stable quasi-aposymbiotic cockroaches.

Abstract

Blattella germanica presents a very complex symbiotic system, involving the following two kinds of symbionts: the endosymbiont Blattabacterium and the gut microbiota. Although the role of the endosymbiont has been fully elucidated, the function of the gut microbiota remains unclear. The study of the gut microbiota will benefit from the availability of insects deprived of Blattabacterium. Our goal is to determine the effect of the removal (or, at least, the reduction) of the endosymbiont population on the cockroach’s fitness, in a normal gut microbiota community. For this purpose, we treated our cockroach population, over several generations, with rifampicin, an antibiotic that only affects the endosymbiont during its extracellular phase, and decreases its amount in the following generation. As rifampicin also affects gut bacteria that are sensitive to this antibiotic, the treatment was performed during the first 12 days of the adult stage, which is the period when the endosymbiont infects the oocytes and lacks bacteriocyte protection. We found that after this antibiotic treatment, the endosymbiont population remained extremely reduced and only the microbiota was able to recover, although it could not compensate for the endosymbiont role, and the host’s fitness was drastically affected. This accomplished reduction, however, is not homogenous and requires further study to develop stable quasi-aposymbiotic cockroaches.