Microbiota succession influences nematode physiology in a beetle microcosm ecosystem.

Unravelling the multifaceted and bidirectional interactions between microbiota and host physiology represents a major scientific challenge. Here, we utilise the nematode model, Pristionchus pacificus, coupled to a laboratory-simulated decay process of its insect host, to mimic natural microbiota succession and investigate associated tripartite interactions. Metagenomics reveal that during initial decay stages, the population of vitamin B-producing bacteria diminishes, potentially due to a preferential selection by nematodes. As decay progresses to nutrient-depleted stages, bacteria with smaller genomes producing less nutrients become more prevalent. Lipid utilisation and dauer formation, representing key nematode survival strategies, are influenced by microbiota changes. Additionally, horizontally acquired cellulases extend the nematodes' reproductive phase due to more efficient foraging. Lastly, the expressions of Pristionchus species-specific genes are more responsive to natural microbiota compared to conserved genes, suggesting their importance in the organisms' adaptation to its ecological niche. In summary, we show the importance of microbial successions and their reciprocal interaction with nematodes for insect decay in semi-artificial ecosystems.

Relative survival analysis of gynecological cancers in an urban district of Shanghai during 2002-2013.

OBJECTIVE: Appraisal of cancer survival is essential for cancer control, but studies related to gynecological cancer are scarce. Using cancer registration data, we conducted an in-depth survival analysis of cervical, uterine corpus, and ovarian cancers in an urban district of Shanghai during 2002-2013. MATERIALS AND METHODS: The follow-up data of gynecological cancer from the Changning District of Shanghai, China, were used to estimate the 1-5-year observed survival rate (OSR) and relative survival rate (RSR) by time periods and age groups during 2002-2013. Age-standardized relative survival rates estimated by the international cancer survival standards were calculated during 2002-2013 to describe the prognosis of cervical, uterine corpus, and ovarian cancers among women in the district. RESULTS: In total, 1307 gynecological cancer cases were included in the survival analysis in the district during 2002-2013. Among gynecological cancers, the 5-year OSRs and RSRs of uterine corpus cancer were highest (5-year OSR 84.40%, 5-year RSR 87.67%), followed by those of cervical cancer (5-year OSR 73.58%, 5-year RSR 75.91%), and those of ovarian cancer (5-year OSR 53.89%, 5-year RSR 55.90%). After age adjustment, the 5-year relative survival rates of three gynecological cancers were 71.23%, 80.11%, and 43.27%, respectively. CONCLUSION: The 5-year relative survival rate did not show a systematic temporal trend in cervical cancer, uterine cancer, or ovarian cancer. The prognosis in elderly patients was not optimistic, and this needs a more advanced strategy for early diagnosis and treatment. The age structure of gynecological cancer patients in the district tended to be younger than the standardized age, which implies that more attention to the guidance and health education for the younger generation is needed.

Evolution and Diversity of TGF-ß Pathways are Linked with Novel Developmental and Behavioral Traits.

Transforming growth factor-ß (TGF-ß) signaling is essential for numerous biologic functions. It is a highly conserved pathway found in all metazoans including the nematode Caenorhabditis elegans, which has also been pivotal in identifying many components. Utilizing a comparative evolutionary approach, we explored TGF-ß signaling in nine nematode species and revealed striking variability in TGF-ß gene frequency across the lineage. Of the species analyzed, gene duplications in the DAF-7 pathway appear common with the greatest disparity observed in Pristionchus pacificus. Specifically, multiple paralogues of daf-3, daf-4 and daf-7 were detected. To investigate this additional diversity, we induced mutations in 22 TGF-ß components and generated corresponding double, triple, and quadruple mutants revealing both conservation and diversification in function. Although the DBL-1 pathway regulating body morphology appears highly conserved, the DAF-7 pathway exhibits functional divergence, notably in some aspects of dauer formation. Furthermore, the formation of the phenotypically plastic mouth in P. pacificus is partially influenced through TGF-ß with the strongest effect in Ppa-tag-68. This appears important for numerous processes in P. pacificus but has no known function in C. elegans. Finally, we observe behavioral differences in TGF-ß mutants including in chemosensation and the establishment of the P. pacificus kin-recognition signal. Thus, TGF-ß signaling in nematodes represents a stochastic genetic network capable of generating novel functions through the duplication and deletion of associated genes.

Incidence, Mortality Features and Lifetime Risk Estimation of Digestive Tract Cancers in an Urban District of Shanghai, China.

Digestive tract cancers are the common cause of cancer deaths in both China and worldwide. This study aimed to describe the burden, recent trends and lifetime risks in the incidence and mortality of digestive tract cancers in an urban district of Shanghai, China. Our study extracted data on stomach, colon, rectum and liver cancers diagnosed in Changning District between 2010 and 2019 from the Shanghai Cancer Registry. We calculated age-standardized incidence and mortality rates, the risks of developing and dying from cancer, and the estimated annual percent changes. Between 2010 and 2019, 8619 new cases and 5775 deaths were registered with digestive tract cancers in the district. The age-standardized incidence rates (ASIRs) of liver cancer decreased steadily, whereas the ASIRs of stomach, colon and rectum cancers remained stable from 2010 to 2019. The age-standardized mortality rates (ASMRs) of stomach and liver cancers showed significant declining changes from 2010 to 2019 in both sexes, but that of colon and rectum cancers remained stable during the entire period. The risks of developing and dying from digestive tract cancers were substantially higher in men than women. The burden of digestive tract cancer and its disparities between sex and age group remain major public health challenges in urban Shanghai. To reduce the burden of digestive tract cancers, the government and researchers should develop and promote a healthy diet, organize a screening, and reduce the prevalence of smoking, alcohol drinking, and hepatitis B virus and hepatitis C virus infections.

EGF/EGFR Promotes Salivary Adenoid Cystic Carcinoma Cell Malignant Neural Invasion via Activation of PI3K/AKT and MEK/ERK Signaling.

BACKGROUND: Salivary adenoid cystic carcinoma (SACC) is one of the most common malignant cancers of the salivary gland, and 32.4-72.0% of SACC cases exhibit neural invasion (NI); however, the molecular mechanism underlying the high invasion potential of SACC remains unclear. METHODS: The present study investigated the role of epidermal growth factor receptor (EGFR) in the AKT inhibition- or mitogen-activated protein kinase kinase (MEK)-induced NI and epithelialmesenchymal transition (EMT) in SACC cells using EGFR, PI3K, and MEK inhibitors. SACC-83 cell viability was assessed using an MTT assay, and a wound healing assay was performed to evaluate cell migration. Immunohistochemical staining with streptavidin peroxidase was used to detect the positive expression rate of EMT, AKT, phosphorylated (p)-AKT, ERK, and p-ERK proteins. The impact of EGFR, PI3K, and MEK inhibitors on tumor growth and NI was examined in a xenograft model in nude mice. RESULTS: EGF and EGFR are effective in increasing cell viability, migration, and invasion. SACC metastasis is affected by the PI3K/AKT and MEK/ERK pathways, both of which are initiated by EGF/EGFR. The EMT and NI are regulated by the EGF/EGFR, PI3K/AKT, and MEK/ERK pathways. The present findings demonstrate the importance of suppressed EGFR/AKT/MEK signaling in NI in SACC by neural-tumor co-culture in vitro. Furthermore, our preclinical experiment provides solid evidence that injection of EGFR, PI3K, and MEK inhibitors suppressed the tumor growth and NI of SACC cells in nude mice. CONCLUSION: It was identified that inhibitors of EGFR, PI3K/AKT or MEK/ERK suppressed the proliferation, migration, and NI of SACC-83 cells via downregulation of the PI3K/AKT or MEK/ERK pathways. It was also demonstrated that inhibition of EGFR abolishes EMT in SACC by inhibiting the signaling of PI3K/AKT and MEK/ERK. The present results suggest the potential effectiveness of targeting multiple oncogenes associated with downstream pathways of EGF/EGFR, as well as potential therapeutic targets to limit NI in SACC by PI3K/AKT or MEK/ERK inhibition.

Synergistic interaction of gut microbiota enhances the growth of nematode through neuroendocrine signaling.

Animals are associated with a diverse bacterial community that impacts host physiology. It is well known that nutrients and enzymes synthesized by bacteria largely expand host metabolic capacity. Bacteria also impact a wide range of animal physiology that solely depends on host genetics through direct interaction. However, studying the synergistic effects of the bacterial community remains challenging due to its complexity. The omnivorous nematode Pristionchus pacificus has limited digestive efficiency on bacteria. Therefore, we established a bacterial collection that represents the natural gut microbiota that are resistant to digestion. Using this collection, we show that the bacterium Lysinibacillus xylanilyticus by itself provides limited nutritional value, but in combination with Escherichia coli, it significantly promotes life-history traits of P. pacificus by regulating the neuroendocrine peptide in sensory neurons. This gut-to-brain communication depends on undigested L. xylanilyticus providing Pristionchus nematodes a specific fitness advantage to compete with nematodes that rupture bacteria efficiently. Using RNA-seq and CRISPR-induced mutants, we show that 1-h exposure to L. xylanilyticus is sufficient to stimulate the expression of daf-7-type TGF-ß signaling ligands, which induce a global transcriptome change. In addition, several effects of L. xylanilyticus depend on TGF-ß signaling, including olfaction, body size regulation, and a switch of energy allocation from lipid storage to reproduction. Our results reveal the beneficial effects of a gut bacterium to modify life-history traits and maximize nematode survival in natural habitats.

Vitamin B12 and predatory behavior in nematodes.

The round worms or nematodes are the largest phylum of animals with an estimated species number of more than one million. Nematodes have invaded all ecosystems and are known from all continents including Antarctica. Parasitic species infest plants, animals and humans often with high host-specificity. Free-living species are known from marine, fresh water and soil systems, the latter of which contain many culturable species. This includes Caenorhabditis elegans, a species that was developed as one of the most prominent model systems in modern biology since the 1960ies. Pristionchus pacificus is a second nematode model organism that can easily be cultured in the laboratory. This species shows a number of complex traits including omnivorous feeding and the capability of predation on other nematodes. Predation depends on the formation of teeth-like denticles in the mouth of P. pacificus, structures unknown from C. elegans and most other nematodes. Here, we review the current knowledge about the role of vitamin B12 for the predatory behavior in P. pacificus and correlate its role with that on the physiology and development in C. elegans.

Horizontally Acquired Cellulases Assist the Expansion of Dietary Range in Pristionchus Nematodes.

Horizontal gene transfer (HGT) enables the acquisition of novel traits via non-Mendelian inheritance of genetic material. HGT plays a prominent role in the evolution of prokaryotes, whereas in animals, HGT is rare and its functional significance is often uncertain. Here, we investigate horizontally acquired cellulase genes in the free-living nematode model organism Pristionchus pacificus. We show that these cellulase genes 1) are likely of eukaryotic origin, 2) are expressed, 3) have protein products that are secreted and functional, and 4) result in endo-cellulase activity. Using CRISPR/Cas9, we generated an octuple cellulase mutant, which lacks all eight cellulase genes and cellulase activity altogether. Nonetheless, this cellulase-null mutant is viable and therefore allows a detailed analysis of a gene family that was horizontally acquired. We show that the octuple cellulase mutant has associated fitness costs with reduced fecundity and slower developmental speed. Furthermore, by using various Escherichia coli K-12 strains as a model for cellulosic biofilms, we demonstrate that cellulases facilitate the procurement of nutrients from bacterial biofilms. Together, our analysis of cellulases in Pristionchus provides comprehensive evidence from biochemistry, genetics, and phylogeny, which supports the integration of horizontally acquired genes into the complex life history strategy of this soil nematode.

Host-associated microbe PCR (hamPCR) enables convenient measurement of both microbial load and community composition.

The ratio of microbial population size relative to the amount of host tissue, or 'microbial load', is a fundamental metric of colonization and infection, but it cannot be directly deduced from microbial amplicon data such as 16S rRNA gene counts. Because existing methods to determine load, such as serial dilution plating, quantitative PCR, and whole metagenome sequencing add substantial cost and/or experimental burden, they are only rarely paired with amplicon sequencing. We introduce host-associated microbe PCR (hamPCR), a robust strategy to both quantify microbial load and describe interkingdom microbial community composition in a single amplicon library. We demonstrate its accuracy across multiple study systems, including nematodes and major crops, and further present a cost-saving technique to reduce host overrepresentation in the library prior to sequencing. Because hamPCR provides an accessible experimental solution to the well-known limitations and statistical challenges of compositional data, it has far-reaching potential in culture-independent microbiology.

Nematode biphasic 'boom and bust' dynamics are dependent on host bacterial load while linking dauer and mouth-form polyphenisms.

Cross-kingdom interactions involve dynamic processes that shape terrestrial ecosystems and represent striking examples of co-evolution. The multifaceted relationships of entomopathogenic nematodes with their insect hosts and symbiotic bacteria are well-studied cases of co-evolution and pathogenicity. In contrast, microbial interactions in soil after the natural death of insects and other invertebrates are minimally understood. In particular, the turnover and succession of nematodes and bacteria during insect decay have not been well documented - although it represents a rich ecological niche with multiple species interactions. Here, we utilize developmentally plastic nematode Pristionchus pacificus and its associated scarab beetles as models. On La Réunion Island, we collected rhinoceros beetle Oryctes borbonicus, induced death, and placed carcasses in cages both on the island and in a mock-natural environment in the laboratory controlling for high spatial and temporal resolution. Investigating nematode population density and dispersal dynamics, we were able to connect two imperative plasticities, dauer and mouth form. We observed a biphasic 'boom and bust' dispersal dynamic of dauer larvae that corresponds to bacterial load on carcasses but not bacterial type. Strikingly, all post-dauer adults have the predatory mouth form, demonstrating novel intricate interactions on decaying insect hosts. Thus, ecologically relevant survival strategies incorporate critical plastic traits.

Determining the level of extra-pair paternity in yellow-bellied prinias, a socially monogamous passerine.

Previous work based on molecular evidence has shown that most socially monogamous birds follow a genetic polyandrous mating system. However, our knowledge about avian mating systems is heavily biased toward the north temperate zone, with data on tropical birds remaining relatively scarce. This uneven distribution of both phylogenetic and spatial sampling has hampered our understanding and interpretation of results. In this study, we investigated the frequency of extra-pair paternity (EPP) in a tropical population of yellow-bellied prinias ( Prinia flaviventris) in Guangxi, southern China. A total of 129 individuals belonging to 24 nests were sampled, among which 12 out of 83 chicks (14.46%) in seven nests were found to be EPP offspring. In nests in which all nestlings were sampled, only five out of 56 chicks were EPP offspring, accounting for an unbiased EPP rate of 8.93%. This rate is below the average rate of EPP in the family Sylviidae. The possible causes of EPP in prinias and the occurrence of EPP in birds with high resource investment and intensive parental care are discussed. This study highlights the value of genome-wide markers in determining relatedness in a wild bird species without a reference genome.

Comparative study of confirmed and suspected undiagnosed cases of COVID-19 in Changning District， Shanghai / 上海预防医学

Objective:To analyze and compare the differences between the epidemiological data and clinical indicators of confirmed and suspected undiagnosed cases of COVID-19 in Changning District， Shanghai. Methods:A retrospective comparative study was conducted. We included 20 confirmed and 34 suspected but undiagnosed COVID-19 cases from January 20 to February 29， 2020. We analyzed the differences in epidemiological history， early clinical symptoms， blood routine indicators， and clinical imaging characteristics between the two groups. Results:The epidemic status of COVID-19 in Changning District of Shanghai was mainly imported， and most cases were promptly confirmed. Early clinical symptoms of confirmed and suspected undiagnosed cases often manifested as respiratory symptoms such as fever and dry cough. Compared with the confirmed cases， the cell counts of leukocytes， eosinophils， and neutrophils in suspected undiagnosed cases were significantly higher. Also， the concentration of serum C-reactive protein in suspected cases was higher than that in confirmed cases （P=0.230）. The clinical imaging manifestations of confirmed cases were mainly ground glass opacity （GGO） scattered in both lung leaves， while the suspected undiagnosed cases mainly manifested as plain patch opacity， and the distribution of GGO was more irregular. Conclusion:There exists significant difference in blood routine indicators and clinical imaging features between confirmed and suspected cases of COVID-19.

Avian phenotypic convergence is subject to low genetic constraints based on genomic evidence.

BACKGROUND: Phenotypic convergence between distinct species provides an opportunity to examine the predictability of genetic evolution. Unrelated species sharing genetic underpinnings for phenotypic convergence suggests strong genetic constraints, and thus high predictability of evolution. However, there is no clear big picture of the genomic constraints on convergent evolution. Genome-based phylogenies have confirmed many cases of phenotypic convergence in birds, making them a good system for examining genetic constraints in phenotypic convergence. In this study, we used hierarchical genomic approaches to estimate genetic constraints in three convergent avian traits: nocturnality, raptorial behavior and foot-propelled diving. RESULTS: Phylogeny-based hypothesis tests and positive selection tests were applied to compare 16 avian genomes, representing 14 orders, and identify genes with strong convergence signals. We found 43 adaptively convergent genes (ACGs) associated with the three phenotypic convergence cases and assessed genetic constraints in all three cases, from (amino acid) site mutations to genetic pathways. We found that the avian orders shared few site mutations in the ACGs that contributed to the convergent phenotypes, and that these ACGs were not enriched in any genetic pathways. In addition, different pairs of orders with convergent foot-propelled diving or raptorial behaviors shared few ACGs. We also found that closely related orders that shared foot-propelled diving behavior did not share more ACGs than did distinct orders, suggesting that convergence among these orders could not be explained by their initial genomic backgrounds. CONCLUSIONS: Our analyses of three avian convergence events suggest low constraints for phenotypic convergence across multiple genetic levels, implying that genetic evolution is unpredictable at the phylogenetic level of avian order. Ours is one of first studies to apply hierarchical genomic examination to multiple avian convergent cases to assess the genetic constraints in life history trait evolution.

Improving Transgenesis Efficiency and CRISPR-Associated Tools Through Codon Optimization and Native Intron Addition in Pristionchus Nematodes.

A lack of appropriate molecular tools is one obstacle that prevents in-depth mechanistic studies in many organisms. Transgenesis, clustered regularly interspaced short palindromic repeats (CRISPR)-associated engineering, and related tools are fundamental in the modern life sciences, but their applications are still limited to a few model organisms. In the phylum Nematoda, transgenesis can only be performed in a handful of species other than Caenorhabditis elegans, and additionally, other species suffer from significantly lower transgenesis efficiencies. We hypothesized that this may in part be due to incompatibilities of transgenes in the recipient organisms. Therefore, we investigated the genomic features of 10 nematode species from three of the major clades representing all different lifestyles. We found that these species show drastically different codon usage bias and intron composition. With these findings, we used the species Pristionchus pacificus as a proof of concept for codon optimization and native intron addition. Indeed, we were able to significantly improve transgenesis efficiency, a principle that may be usable in other nematode species. In addition, with the improved transgenes, we developed a fluorescent co-injection marker in P. pacificus for the detection of CRISPR-edited individuals, which helps considerably to reduce associated time and costs.

Correction: Bacterial vitamin B12 production enhances nematode predatory behavior.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Long-term liver cancer incidence and mortality trends in the Changning District of Shanghai, China.

OBJECTIVE: To evaluate the trends and estimate the long-term effects of age, period and birth cohort on the incidence and mortality rates of liver cancer (LC) in an urban district of Shanghai, China. METHODS: Crude and age-standardized rates of the incidence and mortality of LC were calculated from 1973 to 2013 annually by sex, and the direction and magnitude of the trends were estimated by the average annual percentage change (AAPC) using the Joinpoint Regression Model. An age-period-cohort (APC) model was also used to evaluate the non-linear effects of calendar time and birth cohort on LC incidence and mortality. RESULTS: In 1973-1977 and 2008-2013 the age-standardized rates of LC incidence and mortality (per 100 000) were 24.27 and 22.60 in men, and 7.50 and 7.26 in women, respectively. Declining trends of LC incidence and mortality rates were observed for both sexes (AAPC; P < 0.05 for both). The APC models indicated that the rates of LC incidence and mortality were significantly influenced both by calendar time and birth cohort effects. CONCLUSIONS: The incidence and mortality rates of LC have decreased in both sexes in the Changning District of Shanghai over the past four decades. Although obvious descending trends of LC incidence and mortality were detected, attention should also be paid to the LC burden for a long time in the future because of huge population size in China and the continuity of population aging.

Bacterial vitamin B12 production enhances nematode predatory behavior.

Although the microbiota is known to affect host development, metabolism, and immunity, its impact on host behavior is only beginning to be understood. In order to better characterize behavior modulation by host-associated microorganisms, we investigated how bacteria modulate complex behaviors in the nematode model organism Pristionchus pacificus. This nematode is a predator that feeds on the larvae of other nematodes, including Caenorhabditis elegans. By growing P. pacificus on different bacteria and testing their ability to kill C. elegans, we reveal large differences in killing efficiencies, with a Novosphingobium species showing the strongest enhancement. This enhanced killing was not accompanied by an increase in feeding, which is a phenomenon known as surplus killing, whereby predators kill more prey than necessary for sustenance. Our RNA-seq data demonstrate widespread metabolic rewiring upon exposure to Novosphingobium, which facilitated screening of bacterial mutants with altered transcriptional responses. We identified bacterial production of vitamin B12 as an important cause of such enhanced predatory behavior. Although vitamin B12 is an essential cofactor for detoxification and metabolite biosynthesis, shown previously to accelerate development in C. elegans, supplementation with this enzyme cofactor amplified surplus killing in P. pacificus, whereas mutants in vitamin B12-dependent pathways reduced surplus killing. By demonstrating that production of vitamin B12 by host-associated microbiota can affect complex host behaviors, we reveal new connections between animal diet, microbiota, and nervous system.

Changes in Effective Compounds and Anti-fatigue Activity Before and After Compatibility of Ginseng Radix et Rhizoma Rubra and Rhodiolae Crenulate Radix et Rhizoma / 中国实验方剂学杂志

Objective:To preliminarily interpret the compatibility of Ginseng Radix et Rhizoma Rubra and Rhodiolae Crenulate Radix et Rhizoma in chemical and pharmacodynamic levels，and provide theoretical basis for its clinical application.Method:Rapid resolution liquid chromatography coupled with quadrupole-time-of-flight tandem mass spectrometry（RRLC-Q-TOF-MS） was applied to identify and analyze the changes in chemical components of the Ginseng Radix et Rhizoma Rubra and Rhodiolae Crenulate Radix et Rhizoma before and after compatibility. The anti-fatigue activity before and after compatibility of Ginseng Radix et Rhizoma Rubra and Rhodiolae Crenulate Radix et Rhizoma was detected by weight-loading swimming experiment and determination of levels of serum urea，blood lactic acid and hepatic glycogen.Result:A total of 51 compounds were identified in mixture decoction of Ginseng Radix et Rhizoma Rubra and Rhodiolae Crenulate Radix et Rhizoma. Malonyl ginsenoside mRg1，mRb1，mRb2，mRb3 and mRd contents were significantly decreased，while ginsenoside Rb1，Rb2，Rb3，Rd，F2 and Rg3 contents were significantly increased in the compatibility mixture. According to pharmacodynamics study，as compared with those in the blank control group，swimming time of mice was significantly prolonged in all other groups （P<0.01），serum urea nitrogen（P<0.05，P<0.01） and lactic acid（P<0.05，P<0.001） levels of mice in the combined decoction and the single decoction groups were significantly lowered，while liver glycogen levels were significantly elevated（P<0.05，P<0.01）. The anti-fatigue ability of the combined decoction of Ginseng Radix et Rhizoma Rubra and Rhodiolae Crenulate Radix et Rhizoma was higher than that of the single decoctions.Conclusion:In this article, the effect enhancing mechanism of compatibility of Ginseng Radix et Rhizoma Rubra with Rhodiolae Crenulate Radix et Rhizoma was revealed based on the chemical changes, providing theoretical reference for the clinical application and development of products.

Convergent Evolution among Ruminant-Pathogenic Mycoplasma Involved Extensive Gene Content Changes.

Convergent evolution, a process by which organisms evolved independently to have similar traits, provides opportunities to understand adaptation. The bacterial genus Mycoplasma contains multiple species that evolved independently to become ruminant pathogens, which represents an interesting study system for investigating the process. In this work, we determined the genome sequences of 11 Entomoplasma/Mesoplasma species. This new data set, together with the other available Mollicutes genomes, provided comprehensive taxon sampling for inferring the gene content evolution that led to the emergence of Mycoplasma Mycoides cluster. Our results indicated that the most recent common ancestor (MRCA) of the Mycoides-Entomoplasmataceae clade lost ∼15% of the core genes when it diverged from the Spiroplasma Apis clade. After this initial wave of genome reduction, relatively few gene gains or losses were inferred until the emergence of the Mycoides cluster. Compared with those Entomoplasmataceae lineages that maintained the association with insects, the MRCA of the Mycoides cluster experienced a second wave of gene losses, as well as acquiring >100 novel genes through horizontal gene transfer. These gene acquisitions involved many with the Mycoplasma Hominis/Pneumoniae lineages as the putative donors, suggesting that gene exchanges among these vertebrate symbionts with distinct phylogenetic affiliations may be important in the emergence of the Mycoides cluster. These findings demonstrated that the gene content of bacterial genomes could be exceedingly dynamic, even for those symbionts with highly reduced genomes. Moreover, the emergence of novel pathogens may involve extensive remodeling of gene content, rather than acquisition of few virulence genes.