Insights into the role of extracellular polymeric substances (EPS) in the spread of antibiotic resistance genes

Antibiotic resistance genes (ARG) are prevalent in aquatic environments. Discharge from wastewater treatment plants is an important point source of ARG release into the environment. It has been reported that biological treatment processes may enhance rather than remove ARG because of their presence in sludge. Attenuation of ARG in biotechnological processes has been studied in depth, showing that many microorganisms can secrete complex extracellular polymeric substances (EPS). These EPS can serve as multifunctional elements of microbial communities, involving aspects, such as protection, structure, recognition, adhesion, and physiology. These aspects can influence the interaction between microbial cells and extracellular ARG, as well as the uptake of extracellular ARG by microbial cells, thus changing the transformative capability of extracellular ARG. However, it remains unclear whether EPS can affect horizontal ARG transfer, which is one of the main processes of ARG dissemination. In light of this knowledge gap, this review provides insight into the role of EPS in the transmission of ARGs; furthermore, the mechanism of ARG spread is analyzed, and the molecular compositions and functional properties of EPS are summarized; also, how EPS influence ARG mitigation is addressed, and factors impacting how EPS facilitate ARG during wastewater treatment are summarized. This review provides comprehensive insights into the role of EPS in controlling the transport and fate of ARG during biodegradation processes at the mechanistic level.

Phage tailspike modularity and horizontal gene transfer reveals specificity towards E. coli O-antigen serogroups

BACKGROUND

The interaction between bacteriophages and their hosts is intricate and highly specific. Receptor-binding proteins (RBPs) of phages such as tail fibers and tailspikes initiate the infection process. These RBPs bind to diverse outer membrane structures, including the O-antigen, which is a serogroup-specific sugar-based component of the outer lipopolysaccharide layer of Gram-negative bacteria. Among the most virulent Escherichia coli strains is the Shiga toxin-producing E. coli (STEC) pathotype dominated by a subset of O-antigen serogroups.

METHODS

Extensive phylogenetic and structural analyses were used to identify and validate specificity correlations between phage RBP subtypes and STEC O-antigen serogroups, relying on the principle of horizontal gene transfer as main driver for RBP evolution.

RESULTS

We identified O-antigen specific RBP subtypes for seven out of nine most prevalent STEC serogroups (O26, O45, O103, O104, O111, O145 and O157) and seven additional E. coli serogroups (O2, O8, O16, O18, 4s/O22, O77 and O78). Eight phage genera (Gamaleya-, Justusliebig-, Kaguna-, Kayfuna-, Kutter-, Lederberg-, Nouzilly- and Uetakeviruses) emerged for their high proportion of serogroup-specific RBPs. Additionally, we reveal sequence motifs in the RBP region, potentially serving as recombination hotspots between lytic phages.

CONCLUSION

The results contribute to a better understanding of mosaicism of phage RBPs, but also demonstrate a method to identify and validate new RBP subtypes for current and future emerging serogroups.

The dynamics and transmission of antibiotic resistance associated with plant microbiomes

Antibiotic resistance genes (ARGs) have been widely found and studied in soil and water environments. However, the propagation of ARGs in plant microbiomes has attracted insufficient attention. Plant microbiomes, especially the rhizosphere microorganisms, are closely connected with water, soil, and air, which allows ARGs to spread widely in ecosystems and pose a threat to human health after entering the human body with bacteria. Therefore, it is necessary to deeply understand and explore the dynamics and the transmission of ARGs in rhizosphere microorganisms and endophytes of plants. In this review, the transmission and influencing factors of ARGs in the microorganisms associated with plants, especially the influence of root exudates on plant microbiomes, are analyzed. Notably, the role of intrinsic genes of plants in determining root exudates and their potential effects on ARGs are proposed and analyzed. The important role of phyllosphere microorganisms and endophytes in the transmission of ARGs and co-resistance of antibiotics and other substances are also emphasized. The proliferation and transmission of ARGs associated with plant microbiomes addressed in this review is conducive to revealing the fate of ARGs in plant microorganisms and alleviating ARG pollution.

Plant cultivar determined bacterial community and potential risk of antibiotic resistance gene spread in the phyllosphere

The global increased antibiotic resistance level in pathogenic microbes has posed a significant threat to human health. Fresh vegetables have been recognized to be an important vehicle of antibiotic resistance genes (ARGs) from environments to human beings. Phyllosphere ARGs have been indicated to be changed with plant species, yet the influence of plant cultivar on the phyllospheric resistome is still unclear. Here, we detected the ARGs and bacterial communities in the phyllosphere of two cultivars of cilantros and their corresponding soils using high-throughput quantitative PCR technique and bacterial 16S rRNA gene-based high-throughput sequencing, respectively. We further identified the potential bacterial pathogens and analyzed the effects of plant cultivar on ARGs, mobile genetic elements (MGEs), microbiome and potential bacterial pathogens. The results showed that the cultivars did not affect the ARG abundance and composition, but significantly shaped the abundance of MGEs and the composition structure of bacteria in the phyllosphere. The relative abundance of potential bacterial pathogens was significantly higher in the phyllosphere than that in soils. Mantel test showed that the ARG patterns were significantly correlated to the patterns of potential bacterial pathogens. Our results suggested that the horizontal gene transfer of ARGs in the phyllosphere might be different between the two cultivars of cilantro and highlighted the higher risk of phyllospheric microorganisms compared with those in soils. These findings extend our knowledge on the vegetable microbiomes, ARGs, and potential pathogens, suggesting more agricultural and hygiene protocols are needed to control the risk of foodborne ARGs.

Comparative genome identification of accessory genes associated with strong biofilm formation in Vibrio parahaemolyticus

Vibrio parahaemolyticus biofilms on the seafood processing plant surfaces are a potential source of seafood contamination and subsequent food poisoning. Strains differ in their ability to form biofilm, but little is known about the genetic characteristics responsible for biofilm development. In this study, pangenome and comparative genome analysis of V. parahaemolyticus strains reveals genetic attributes and gene repertoire that contribute to robust biofilm formation. The study identified 136 accessory genes that were exclusively present in strong biofilm forming strains and these were functionally assigned to the Gene Ontology (GO) pathways of cellulose biosynthesis, rhamnose metabolic and catabolic processes, UDP-glucose processes and O antigen biosynthesis (p < 0.05). Strategies of CRISPR-Cas defence and MSHA pilus-led attachment were implicated via Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation. Higher levels of horizontal gene transfer (HGT) were inferred to confer more putatively novel properties on biofilm-forming V. parahaemolyticus. Furthermore, cellulose biosynthesis, a neglected potential virulence factor, was identified as being acquired from within the order Vibrionales. The cellulose synthase operons in V. parahaemolyticus were examined for their prevalence (22/138, 15.94 %) and were found to consist of the genes bcsG, bcsE, bcsQ, bcsA, bcsB, bcsZ, bcsC. This study provides insights into robust biofilm formation of V. parahaemolyticus at the genomic level and facilitates: identification of key attributes for robust biofilm formation, elucidation of biofilm formation mechanisms and development of potential targets for novel control strategies of persistent V. parahaemolyticus.

Antibiotic and heavy metal resistance genes in sewage sludge survive during aerobic composting

Municipal sewage sludge has been generated in increasing amounts with the acceleration of urbanization and economic development. The nutrient rich sewage sludge can be recycled by composting that has a great potential to produce stabilized organic fertilizer and substrate for plant cultivation. However, little is known about the metals, pathogens and antibiotic resistance transfer risks involved in applying the composted sludge in agriculture. We studied changes in and relationships between heavy metal contents, microbial communities, and antibiotic resistance genes (ARGs), heavy metal resistance genes (HMRGs) and mobile genetic elements (MGEs) in aerobic composting of sewage sludge. The contents of most of the analyzed heavy metals were not lower after composting. The bacterial α-diversity was lower, and the community composition was different after composting. Firmicutes were enriched, and Proteobacteria and potential pathogens in the genera Arcobacter and Acinetobacter were depleted in the composted sludge. The differences in bacteria were possibly due to the high temperature phase during the composting which was likely to affect temperature-sensitive bacteria. The number of detected ARGs, HMRGs and MGEs was lower, and the relative abundances of several resistance genes were lower after composting. However, the abundance of seven ARGs and six HMRGs remained on the same level after composting. Co-occurrence analysis of bacterial taxa and the genes suggested that the ARGs may spread via horizontal gene transfer during composting. In summary, even though aerobic composting is effective for managing sewage sludge and to decrease the relative abundance of potential pathogens, ARGs and HMRGs, it might include a potential risk for the dissemination of ARGs in the environment.

An insight overview on COVID-19 mRNA vaccines: Advantageous, pharmacology, mechanism of action, and prospective considerations

The worldwide spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has urged scientists to present some novel vaccine platforms during this pandemic to provide a rather prolonged immunity against this respiratory viral infection. In spite of many campaigns formed against the administration of mRNA-based vaccines, those platforms were the most novel types, which helped us meet the global demand by developing protection against COVID-19 and reducing the development of severe forms of this respiratory viral infection. Some societies are worry about the COVID-19 mRNA vaccine administration and the potential risk of genetic integration of inoculated mRNA into the human genome. Although the efficacy and long-term safety of mRNA vaccines have not yet been fully clarified, obviously their application has switched the mortality and morbidity of the COVID-19 pandemic. This study describes the structural features and technologies used in producing of COVID-19 mRNA-based vaccines as the most influential factor in controlling this pandemic and a successful pattern for planning to produce other kind of genetic vaccines against infections or cancers.

Evolutionary Overview of Aquaporin Superfamily

Aquaporins (AQPs) are present not only in three domains of life, bacteria, eukaryotes, and archaea, but also in viruses. With the accumulating arrays of AQP superfamily, the evolutional relationship has attracted much attention with multiple publications on "the genome-wide identification and phylogenetic analysis" of AQP superfamily. A pair of NPA boxes forming a pore is highly conserved throughout the evolution and renders key residues for the classification of AQP superfamily into four groups: AQP1-like, AQP3-like, AQP8-like, and AQP11-like. The complexity of AQP family has mostly been achieved in nematodes and subsequent evolution has been directed toward increasing the number of AQPs through whole-genome duplications (WGDs) to extend the tissue specific expression and regulation. The discovery of the intracellular AQP (iAQP: AQP8-like and AQP11-like) and substrate transports by the plasma membrane AQP (pAQP: AQP1-like and AQP3-like) have accelerated the AQP research much more toward the transport of substrates with complex profiles. This evolutionary overview based on a simple classification of AQPs into four subfamilies will provide putative structural, functional, and localization information and insights into the role of AQP as well as clues to understand the complex diversity of AQP superfamily.

Antibiotic resistant genes in the environment-exploring surveillance methods and sustainable remediation strategies of antibiotics and ARGs

Antibiotic Resistant Genes (ARGs) are an emerging environmental health threat due to the potential change in the human microbiome and selection for the emergence of antibiotic resistant bacteria. The rise of antibiotic resistant bacteria has caused a global health burden. The WHO (world health organization) predicts a rise in deaths due to antibiotic resistant infections. Since bacteria can acquire ARGs through horizontal transmission, it is important to assess the dissemination of antibioticresistant genes from anthropogenic sources. There are several sources of antibiotics, antibiotic resistant bacteria and genes in the environment. These include wastewater treatment plants, landfill leachate, agricultural, animal industrial sources and estuaries. The use of antibiotics is a worldwide practice that has resulted in the evolution of resistance to antibiotics. Our review provides a more comprehensive look into multiple sources of ARG's and antibiotics rather than one. Moreover, we focus on effective surveillance methods of ARGs and antibiotics and sustainable abiotic and biotic remediation strategies for removal and reduction of antibiotics and ARGs from both terrestrial and aquatic environments. Further, we consider the impact on public health as this problem cannot be addressed without a global transdisciplinary effort.

Antimicrobial resistance: new insights and therapeutic implications

Antimicrobial resistance has not been a new phenomenon. Still, the number of resistant organisms, the geographic areas affected by emerging drug resistance, and the magnitude of resistance in a single organism are enormous and mounting. Disease and disease-causing agents formerly thought to be contained by antibiotics are now returning in new forms resistant to existing therapies. Antimicrobial resistance is one of the most severe and complicated health issues globally, driven by interrelated dynamics in humans, animals, and environmental health sectors. Coupled with various epidemiological factors and a limited pipeline for new antimicrobials, all these misappropriations allow the transmission of drug-resistant organisms. The problem is likely to worsen soon. Antimicrobial resistance in general and antibiotic resistance in particular is a shared global problem. Actions taken by any single country can adversely or positively affect the other country. Targeted coordination and prevention strategies are critical in stopping the spread of antibiotic-resistant organisms and hence its overall management. This article has provided in-depth knowledge about various methods that can help mitigate the emergence and spread of antimicrobial resistance globally. KEY POINTS: • Overview of antimicrobial resistance as a global challenge and explain various reasons for its rapid progression. • Brief about the intrinsic and acquired resistance to antimicrobials and development of antibiotic resistance in bacteria. • Systematically organized information is provided on different strategies for tackling antimicrobial resistance for the welfare of human health.

Dormancy induced by oxidative damage during disinfection facilitates conjugation of ARGs through enhancing efflux and oxidative stress: A lagging response

Disinfection is known to greatly alter bacterial characteristics in water, and high horizontal gene transfer (HGT) frequency occurs in eutrophic conditions. Interestingly, these two seemingly irrelevant phenomena were closely linked by a lagging response of the increased conjugation frequency probably via daily water disinfection in this study. Three disinfection methods (UV, chlorine, and UV/chlorine) were selected to investigate the increased frequency of conjugation of ARGs during the stage of continuing culture after disinfection. The results showed that the conjugative transfer frequency was inhibited for all disinfection treatments after 24 h of co-incubation. Unexpectedly, after 3-7 days of co-cultivation, the HGT frequencies were increased by 2.71-5.61-fold and 5.46-13.96-fold in chlorine (30 min) and UV/chlorine (1 min) groups compared to the control, but not in UV-irradiated groups. A neglected lagging response was found for the first time, i.e., oxidative disinfection-induced dormancy promotes conjugative transfer of ARGs. Furthermore, mechanistic insights were gained from (1) membrane permeability, (2) conjugation-regulated system, (3) efflux pump system, and (4) oxidative stress system, suggesting the critical role of enhancing efflux and oxidative stress in the propagation of ARGs. Finally, the known instantaneous effect of oxidation disinfection was compared to address the controversial debate in this research field, proposing that the dormancy level of donor bacteria is the key to evaluating whether it can promote the HGT process. This study has important environmental implications for elucidating the transmission of ARGs after oxidation disinfection.

SDS coated Fe3O4@MoS2 with NIR-enhanced photothermal-photodynamic therapy and antibiotic resistance gene dissemination inhibition functions

Infection caused by antibiotic-resistant bacteria is serious threat for public health, and calls for novel antibacterial agents with versatile functions. In particular, nanomaterial is one of promising candidates to fight the increasing antibiotic resistance crisis. Here, we synthesized distinct Fe₃O₄@MoS₂@SDS nanocomposites by ultrasonication assisted SDS coating on the Fe₃O₄@MoS₂. Photothermal investigation indicated that the Fe₃O₄@MoS₂@SDS showed excellent and stable photothermal performance and could be a NIR-induced photothermal reagent. It also displayed superior disinfection ability of Escherichia coli (E. coli), Methicillin-resistant Staphylococcus aureus (MRSA), and Pseudomonas aeruginosa (P. aeruginosa) and in vivo wound healing ability with the help of NIR irradiation. According to the results of electron paramagnetic resonance (EPR) and radical capture tests, plenty of superoxide, hydroxyl radicals, singlet oxygen and living cell reactive oxygen species can be observed under NIR irradiation. Besides, the synergistic effect Fe₃O₄@MoS₂@SDS and NIR irradiation eradicated almost all the biofilms of MRSA, so this kind of function enhanced the disinfection ability of Fe₃O₄@MoS₂@SDS under NIR irradiation. Furthermore, its inhibition effect on antibiotic resistance gene dissemination was also investigated. As expected, the Fe₃O₄@MoS₂@SDS could efficiently and broadly block the horizontal transfer of antibiotic resistance genes which mediated by conjugative plasmids, and its blocking effect was better than that we have reported Fe₃O₄@MoS₂. Overall, our findings revealed that the Fe₃O₄@MoS₂@SDS could be a potential candidate for photothermal-photodynamic therapy and antibiotic resistance gene dissemination inhibition.

Reconstructing the Last Common Ancestor: Epistemological and Empirical Challenges

Reconstructing the genetic traits of the Last Common Ancestor (LCA) and the Tree of Life (TOL) are two examples of the reaches of contemporary molecular phylogenetics. Nevertheless, the whole enterprise has led to paradoxical results. The presence of Lateral Gene Transfer poses epistemic and empirical challenges to meet these goals; the discussion around this subject has been enriched by arguments from philosophers and historians of science. At the same time, a few but influential research groups have aimed to reconstruct the LCA with rich-in-detail hypotheses and high-resolution gene catalogs and metabolic traits. We argue that LGT poses insurmountable challenges for detailed and rich in details reconstructions and propose, instead, a middle-ground position with the reconstruction of a slim LCA based on traits under strong pressures of Negative Natural Selection, and for the need of consilience with evidence from organismal biology and geochemistry. We defend a cautionary perspective that goes beyond the statistical analysis of gene similarities and assumes the broader consequences of evolving empirical data and epistemic pluralism in the reconstruction of early life.

Electrochemical flow-through disinfection reduces antibiotic resistance genes and horizontal transfer risk across bacterial species

Antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs), as emerging pollutants, are released into environment, increasing the risk of horizontal gene transfer (HGT). However, a limited number of studies quantified the effects of ARB disinfection on the HGT risk. This study investigated the inactivation of E. coli 10667 (sul) and the release and removal of ARGs using an electrochemical flow-through reactor (EFTR). Furthermore, the transfer frequencies and potential mechanisms of HGT after disinfection were explored using non-resistant E. coli GMCC 13373 as the recipient and E. coli DH5α carrying plasmid RP4 as the donor. A threshold of current density (0.25 mA/cm²) was observed to destroy cells and release intracellular ARGs (iARGs) to increase extracellular ARGs (eARGs) concentration. The further increase in the current density to 1 mA/cm² resulted in the decline of eARGs concentration due to the higher degradation rate of eARGs than the release rate of iARGs. The performance of ARGs degradation and HGT frequency by EFTR were compared with those of conventional disinfection processes, including chlorination and ultraviolet radiation (UV). A higher ARGs degradation (83.46%) was observed by EFTR compared with that under chlorination (10.23%) and UV (27.07%). Accordingly, EFTR reduced the HGT frequency (0.69) of released ARGs into the recipient (Forward transfer), and the value was lower than that by chlorination (2.69) and UV (1.73). Meanwhile, the surviving injured E. coli 10667 (sul) with increased cell permeability was transferred by plasmid RP4 from the donor (Reverse transfer) with a higher frequency of 0.33 by EFTR compared with that under chlorination (0.26) and UV (0.16). In addition, the sul3 gene was the least resistant to EFTR than sul1 and sul2 gene. These findings provide important insights into the mechanism of HGT between the injured E. coli 10667 (sul) and environmental bacteria. EFTR is a promising disinfection technology for preventing the spread of antibiotic resistance.

A review of the bioelectrochemical system as an emerging versatile technology for reduction of antibiotic resistance genes

Antibiotic contamination and the resulting resistance genes have attracted worldwide attention because of the extensive overuse and abuse of antibiotics, which seriously affects the environment as well as human health. Bioelectrochemical system (BES), a potential avenue to be explored, can alleviate antibiotic pollution and reduce antibiotic resistance genes (ARGs). This review mainly focuses on analyzing the possible reasons for the good performance of ARG reduction by BESs and potential ways to improve its performance on the basis of revealing the generation and transmission of ARGs in BES. This system reduces ARGs through two pathways: (1) the contribution of BES to the low selection pressure of ARGs caused by the efficient removal of antibiotics, and (2) inhibition of ARG transmission caused by low sludge yield. To promote the reduction of ARGs, incorporating additives, improving the removal rate of antibiotics by adjusting the environmental conditions, and controlling the microbial community in BES are proposed. Furthermore, this review also provides an overview of bioelectrochemical coupling systems including the BES coupled with the Fenton system, BES coupled with constructed wetland, and BES coupled with photocatalysis, which demonstrates that this method is applicable in different situations and conditions and provides inspiration to improve these systems to control ARGs. Finally, the challenges and outlooks are addressed, which is constructive for the development of technologies for antibiotic and ARG contamination remediation and blocking risk migration.

Monitoring antibiotic resistance genes in wastewater treatment: Current strategies and future challenges

Antimicrobial resistance (AMR) is a growing threat to human and animal health. Progress in molecular biology has revealed new and significant challenges for AMR mitigation given the immense diversity of antibiotic resistance genes (ARGs), the complexity of ARG transfer, and the broad range of omnipresent factors contributing to AMR. Municipal, hospital and abattoir wastewater are collected and treated in wastewater treatment plants (WWTPs), where the presence of diverse selection pressures together with a highly concentrated consortium of pathogenic/commensal microbes create favourable conditions for the transfer of ARGs and proliferation of antibiotic resistant bacteria (ARB). The rapid emergence of antibiotic resistant pathogens of clinical and veterinary significance over the past 80 years has re-defined the role of WWTPs as a focal point in the fight against AMR. By reviewing the occurrence of ARGs in wastewater and sludge and the current technologies used to quantify ARGs and identify ARB, this paper provides a research roadmap to address existing challenges in AMR control via wastewater treatment. Wastewater treatment is a double-edged sword that can act as either a pathway for AMR spread or as a barrier to reduce the environmental release of anthropogenic AMR. State of the art ARB identification technologies, such as metagenomic sequencing and fluorescence-activated cell sorting, have enriched ARG/ARB databases, unveiled keystone species in AMR networks, and improved the resolution of AMR dissemination models. Data and information provided in this review highlight significant knowledge gaps. These include inconsistencies in ARG reporting units, lack of ARG/ARB monitoring surrogates, lack of a standardised protocol for determining ARG removal via wastewater treatments, and the inability to support appropriate risk assessment. This is due to a lack of standard monitoring targets and agreed threshold values, and paucity of information on the ARG-pathogen host relationship and risk management. These research gaps need to be addressed and research findings need to be transformed into practical guidance for WWTP operators to enable effective progress towards mitigating the evolution and spread of AMR.

The Origin(s) of Cell(s): Pre-Darwinian Evolution from FUCAs to LUCA : To Carl Woese (1928-2012), for his Conceptual Breakthrough of Cellular Evolution

The coming of the Last Universal Cellular Ancestor (LUCA) was the singular watershed event in the making of the biotic world. If the coming of LUCA marked the crossing of the "Darwinian Threshold", then pre-LUCA evolution must have been Pre-Darwinian and at least partly non-Darwinian. But how did Pre-Darwinian evolution before LUCA actually operate? I broaden our understanding of the central mechanism of biological evolution (i.e., variation-selection-inheritance) and then extend this broadened understanding to its natural starting point: the origin(s) of the First Universal Cellular Ancestors (FUCAs) before LUCA. My hypothesis centers upon vesicles' making-and-remaking as variation and competition as selection. More specifically, I argue that vesicles' acquisition and merger, via breaking-and-repacking, proto-endocytosis, proto-endosymbiosis, and other similar processes had been a central force of both variation and selection in the pre-Darwinian epoch. These new perspectives shed important new light upon the origin of FUCAs and their subsequent evolution into LUCA.

Microbial community characterization of shrimp survivors to AHPND challenge test treated with an effective shrimp probiotic (Vibrio diabolicus)

BACKGROUND

Acute hepatopancreatic necrosis disease (AHPND) is an important shrimp bacterial disease caused by some Vibrio species. The severity of the impact of this disease on aquaculture worldwide has made it necessary to develop alternatives to prophylactic antibiotics use, such as the application of probiotics. To assess the potential to use probiotics in order to limit the detrimental effects of AHNPD, we evaluated the effect of the ILI strain, a Vibrio sp. bacterium and efficient shrimp probiotic, using metabarcoding (16S rRNA gene) on the gastrointestinal microbiota of shrimp after being challenged with AHPND-causing V. parahaemolyticus.

RESULTS

We showed how the gastrointestinal microbiome of shrimp varied between healthy and infected organisms. Nevertheless, a challenge of working with AHPND-causing Vibrio pathogens and Vibrio-related bacteria as probiotics is the potential risk of the probiotic strain becoming pathogenic. Consequently, we evaluated whether ILI strain can acquire the plasmid pV-AHPND via horizontal transfer and further cause the disease in shrimp. Conjugation assays were performed resulting in a high frequency (70%) of colonies harboring the pv-AHPND. However, no shrimp mortality was observed when transconjugant colonies of the ILI strain were used in a challenge test using healthy shrimp. We sequenced the genome of the ILI strain and performed comparative genomics analyses using AHPND and non-AHPND Vibrio isolates. Using available phylogenetic and phylogenomics analyses, we reclassified the ILI strain as Vibrio diabolicus. In summary, this work represents an effort to study the role that probiotics play in the normal gastrointestinal shrimp microbiome and in AHPND-infected shrimp, showing that the ILI probiotic was able to control pathogenic bacterial populations in the host's gastrointestinal tract and stimulate the shrimp's survival. The identification of probiotic bacterial species that are effective in the host's colonization is important to promote animal health and prevent disease.

CONCLUSIONS

This study describes probiotic bacteria capable of controlling pathogenic populations of bacteria in the shrimp gastrointestinal tract. Our work provides new insights into the complex dynamics between shrimp and the changes in the microbiota. It also addresses the practical application of probiotics to solve problems with pathogens that cause high mortality-rate in shrimp farming around the world. Video Abstract.

Can mobile genetic elements rescue genes from extinction?

Bacteria and other prokaryotes evolve primarily through rapid changes in their gene content by quickly losing and gaining genes whenever an ecological opportunity emerges. As gene loss and horizontal gene transfer (HGT) appear to be the most common events across the prokaryotic tree of life, we need to think beyond gradual sequence evolution if we wish to understand the microbial world. Especially genes that reside on mobile genetic elements (MGEs) may spread much more rapidly through a microbial population than genes that reside on the bacterial chromosome. This raises the question: why are some genes associated with MGEs, while others are not? Here, I briefly review a recently proposed class of genes for which we have coined the term "rescuable genes". The fitness effect of carrying these genes is so small, either constantly or on average, that they are prone to be lost from a microbial population. I argue that HGT, even when costly to the individual cells, may play an important role in maintaining these rescuable genes in microbial communities.

Evolutionary history of dimethylsulfoniopropionate (DMSP) demethylation enzyme DmdA in marine bacteria

Dimethylsulfoniopropionate (DMSP), an osmolyte produced by oceanic phytoplankton and bacteria, is primarily degraded by bacteria belonging to the Roseobacter lineage and other marine Alphaproteobacteria via DMSP-dependent demethylase A protein (DmdA). To date, the evolutionary history of DmdA gene family is unclear. Some studies indicate a common ancestry between DmdA and GcvT gene families and a co-evolution between Roseobacter and the DMSP-producing-phytoplankton around 250 million years ago (Mya). In this work, we analyzed the evolution of DmdA under three possible evolutionary scenarios: (1) a recent common ancestor of DmdA and GcvT, (2) a coevolution between Roseobacter and the DMSP-producing-phytoplankton, and (3) an enzymatic adaptation for utilizing DMSP in marine bacteria prior to Roseobacter origin. Our analyses indicate that DmdA is a new gene family originated from GcvT genes by duplication and functional divergence driven by positive selection before a coevolution between Roseobacter and phytoplankton. Our data suggest that Roseobacter acquired dmdA by horizontal gene transfer prior to an environment with higher DMSP. Here, we propose that the ancestor that carried the DMSP demethylation pathway genes evolved in the Archean, and was exposed to a higher concentration of DMSP in a sulfur-rich atmosphere and anoxic ocean, compared to recent Roseobacter eco-orthologs (orthologs performing the same function under different conditions), which should be adapted to lower concentrations of DMSP.

Desiccation does not drastically increase the accessibility of exogenous DNA to nuclear genomes: evidence from the frequency of endosymbiotic DNA transfer

Background

Although horizontal gene transfer (HGT) is a widely accepted force in the evolution of prokaryotic genomes, its role in the evolution of eukaryotic genomes remains hotly debated. Some bdelloid rotifers that are resistant to extreme desiccation and radiation undergo a very high level of HGT, whereas in another desiccation-resistant invertebrate, the tardigrade, the pattern does not exist. Overall, the DNA double-strand breaks (DSBs) induced by prolonged desiccation have been postulated to open a gateway to the nuclear genome for exogenous DNA integration and thus to facilitate the HGT process, thereby enhancing the rate of endosymbiotic DNA transfer (EDT).

Results

We first surveyed the abundance of nuclear mitochondrial DNAs (NUMTs) and nuclear plastid DNAs (NUPTs) in five eukaryotes that are highly resistant to desiccation: the bdelloid rotifers Adineta vaga and Adineta ricciae, the tardigrade Ramazzottius varieornatus, and the resurrection plants Dorcoceras hygrometricum and Selaginella tamariscina. Excessive NUMTs or NUPTs were not detected. Furthermore, we compared 24 groups of desiccation-tolerant organisms with their relatively less desiccation-tolerant relatives but did not find a significant difference in NUMT/NUPT contents.

Conclusions

Desiccation may induce DSBs, but it is unlikely to dramatically increase the frequency of exogenous sequence integration in most eukaryotes. The capture of exogenous DNA sequences is possible only when DSBs are repaired through a subtype of non-homologous end joining, named alternative end joining (alt-EJ). Due to the deleterious effects of the resulting insertion mutations, alt-EJ is less frequently initiated than other mechanisms.

Occurrence of integrons and antibiotic resistance genes in cryoconite and ice of Svalbard, Greenland, and the Caucasus glaciers

The prevalence of integrons and antibiotic resistance genes (ARGs) is a serious threat for public health in the new millennium. Although commonly detected in sites affected by strong anthropogenic pressure, in remote areas their occurrence, dissemination, and transfer to other ecosystems is poorly recognized. Remote sites are considered as a benchmark for human-induced contamination on Earth. For years glaciers were considered pristine, now they are regarded as reservoirs of contaminants, thus studies on contamination of glaciers, which may be released to other ecosystems, are highly needed. Therefore, in this study we evaluated the occurrence and frequency of clinically relevant ARGs and resistance integrons in the genomes of culturable bacteria and class 1 integron-integrase gene copy number in the metagenome of cryoconite, ice and supraglacial gravel collected on two Arctic (South-West Greenland and Svalbard) and two High Mountain (the Caucasus) glaciers. Altogether, 36 strains with intI1 integron-integrase gene were isolated. Presence of class 1 integron-integrase gene was also recorded in metagenomic DNA from all sampling localities. The mean values of relative abundance of intI1 gene varied among samples and ranged from 0.7% in cryoconite from Adishi Glacier (the Caucasus) to 16.3% in cryoconite from Greenland. Moreover, antibiotic-resistant strains were isolated from all regions. Genes conferring resistance to β-lactams (bla_SHV, bla_TEM, bla_OXA, bla_CMY), fluoroquinolones (qepA, qnrC), and chloramphenicol (cat, cmr) were detected in the genomes of bacterial isolates.

Identification and characterization of parvalbumin-like protein in Trichophyton violaceum

Parvalbumins play crucial physiological roles in neuromuscular systems of vertebrates, such as cell-cycle, development of neurons, contraction of muscles, and regulation of intracellular calcium. To perform these neuromuscular functions, parvalbumin may be in associated with other proteins including calbindin, carbonic anhydrase, and cytochrome oxidase. Humans may show an IgE-specific hypersensitivity to parvalbumins after consumption of some distinct fish species. While this protein is abundant in fish muscles, literature review of publications related to fish parvalbumins, do not point to the presence of parvalbumins in eukaryotic microbes. In this study, we propose that distantly related parvalbumins may be found in some non-fish species. Bioinformatics studies such as multiple sequence alignment (MSA), phylogenetic analysis as well as molecular-based experiments indicate that, at least two parvalbumins sequences (UniProt IDs: A0A178F775 and A0A178F7E4) with EF-hand domains and Ca²⁺-binding sites could be identified in Trichophyton violaceum, a pathogenic fungal species. It was determined that both genes consisted of a single exon and encoded for parvalbumin proteins possessing conserved amino acid motifs. Antigenicity prediction revealed antigenic sites located in both sides of the Ca²⁺-binding site of the first EF-hand domain. Our phylogenetic analysis revealed that one of parvalbumins (UniProt ID: 0A178F775) can be evolved to other parvalbumins in T. violaceum (UniProt ID: A0A178F7E4) and fish species through evolutionary phenomenon. To confirm our in-silico findings, we designed three primer pairs to detect one of the T. violaceum parvalbumins (UniProt ID: A0A178F7E4) by polymerase chain reaction (PCR); one primer pair showed a strong and specific band in agarose gel electrophoresis. To evaluate the specificity of the method, the primers were tested on extracted DNA from Trichophyton rubrum and T. mentagrophytes. The results demonstrated that the evaluated parvalbumin gene (UniProt ID: A0A178F7E4) was T. violaceum-specific and this pathogenic fungus can be differentiated from T. rubrum and T. mentagrophytes through identification of parvalbumin genes. Further studies are necessary to unravel the biochemical and physiological functions of parvalbumins in T. violaceum.

Methods to Quantify DNA Transfer in Enterococcus

DNA uptake in Enterococcus normally occurs by conjugation, a natural process that is replicated in biomedical research to assess the transferability of different mobile genetic elements and chromosomal regions as well as to study the host range of plasmids and other conjugative elements. More efficient artificial methods to transform cells with foreign DNA as chemotransformation and electroporation are widely used in molecular genetics. Here, we described conjugation protocols to quantify DNA transfer among Enterococcus and revise current perspectives and lab strains. Protocols of electrotransformation have been previously described in this series.

Methods for the Analysis and Characterization of Defense Mechanisms Against Horizontal Gene Transfer: CRISPR Systems

CRISPR-Cas systems provide RNA-guided adaptive immunity to the majority of archaea and many bacteria. They are able to capture pieces of invading genetic elements in the form of novel spacers in an array of repeats. These elements can then be used as a memory to destroy incoming DNA through the action of RNA-guided nucleases. This chapter describes general procedures to determine the ability of CRISPR-Cas systems to capture novel sequences and to use them to block phages and horizontal gene transfer. All protocols are performed in Staphylococcus aureus using Type II-A CRISPR-Cas systems. Nonetheless, the protocols provided can be adapted to work with other bacteria and other types of CRISPR-Cas systems.

Arsenic-resistance mechanisms in bacterium Leclercia adecarboxylata strain As3-1: Biochemical and genomic analyses

Microbial arsenic transformation is important in As biogeochemical cycles in the environment. In this study, a new As-resistant bacterial strain Leclercia adecarboxylata As3-1 was isolated and its associated mechanisms in As resistance and detoxification were evaluated based on genome sequencing and gene annotations. After subjecting strain As3-1 to medium containing arsenate (AsV), AsV reduction occurred and an AsV-enhanced bacterial growth was observed. Strain As3-1 lacked arsenite (AsIII) oxidation ability and displayed lower AsIII resistance than AsV, probably due to its higher AsIII accumulation. Polymerase chain reaction and phylogenetic analysis showed that strain As3-1 harbored a typical AsV reductase gene (arsC) on the plasmids. Genome sequencing and gene annotations identified four operons phoUpstBACS, arsHRBC, arsCRDABC and ttrRSBCA, with 8 additional genes outside the operons that might have involved in As resistance and detoxification in strain As3-1. These included 5 arsC genes explaining why strain As3-1 tolerated high AsV concentrations. Besides ArsC, TtrB, TtrC and TtrA proteins could also be involved in AsV reduction and consequent energy acquisition for bacterial growth. Our data provided a new example of diverse As-regulating systems and AsV-enhanced growth without ArrA in bacteria. The information helps to understand the role of As in selecting microbial systems that can transform and utilize As.

Pan-genome analysis of Riemerella anatipestifer reveals its genomic diversity and acquired antibiotic resistance associated with genomic islands

Riemerella anatipestifer is a gram-negative bacterium that leads to severe contagious septicemia in ducks, turkeys, chickens, and wild waterfowl. Here, a pan-genome with 32 R. anatipestifer genomes is re-established, and the mathematical model is calculated to evaluate the expansion of R. anatipestifer genomes, which were determined to be open. Average nucleotide identity (ANI) and phylogenetic analysis preliminarily clarify intraspecies variation and distance. Comparative genomic analysis of R. anatipestifer found that horizontal gene transfer events, which provide an expressway for the recruitment of novel functionalities and facilitate genetic diversity in microbial genomes, play a key role in the process of acquiring and transmitting antibiotic-resistance genes in R. anatipestifer. Furthermore, a new antibiotic-resistance gene cluster was identified in the same loci in 14 genomes. The uneven distribution of virulence factors was also confirmed by our results. Our study suggests that the ability to acquire foreign genes (such as antibiotic-resistance genes) increases the adaptability of R. anatipestifer, and the virulence genes with little mobility are highly conserved in R. anatipestifer.

Prokaryotic Information Games: How and When to Take up and Secrete DNA

Besides transduction via bacteriophages natural transformation and bacterial conjugation are the most important mechanisms driving bacterial evolution and horizontal gene spread. Conjugation systems have evolved in eubacteria and archaea. In Gram-positive and Gram-negative bacteria, cell-to-cell DNA transport is typically facilitated by a type IV secretion system (T4SS). T4SSs also mediate uptake of free DNA in Helicobacter pylori, while most transformable bacteria use a type II secretion/type IV pilus system. In this chapter, we focus on how and when bacteria "decide" that such a DNA transport apparatus is to be expressed and assembled in a cell that becomes competent. Development of DNA uptake competence and DNA transfer competence is driven by a variety of stimuli and often involves intricate regulatory networks leading to dramatic changes in gene expression patterns and bacterial physiology. In both cases, genetically homogeneous populations generate a distinct subpopulation that is competent for DNA uptake or DNA transfer or might uniformly switch into competent state. Phenotypic conversion from one state to the other can rely on bistable genetic networks that are activated stochastically with the integration of external signaling molecules. In addition, we discuss principles of DNA uptake processes in naturally transformable bacteria and intend to understand the exceptional use of a T4SS for DNA import in the gastric pathogen H. pylori. Realizing the events that trigger developmental transformation into competence within a bacterial population will eventually help to create novel and effective therapies against the transmission of antibiotic resistances among pathogens.

Microfluidics-Based Analysis of Contact-dependent Bacterial Interactions

Bacteria in nature live in complex communities with multiple cell types and spatially-dependent interactions. Studying cells in well-mixed environments such as shaking culture tubes or flasks cannot capture these spatial dynamics, but cells growing in full-fledged biofilms are difficult to observe in real time. We present here a protocol for observing time-resolved, multi-species interactions at single-cell resolution. The protocol involves growing bacterial cells in a near monolayer in a microfluidic device. As a demonstration, we describe in particular observing the dynamic interactions between E. coli and Acinetobacter baylyi. In this case, the protocol is capable of observing both contact-dependent lysis of E. coli by A. baylyi via the Type VI Secretion System (T6SS) and subsequent functional horizontal gene transfer (HGT) of genes from E. coli to A. baylyi.

Monitoring plasmid-mediated horizontal gene transfer in microbiomes: recent advances and future perspectives

The emergence of antimicrobial resistant bacteria constitutes an increasing global health concern. Although it is well recognized that the cornerstone underlying this phenomenon is the dissemination of antimicrobial resistance via plasmids and other mobile genetic elements, the antimicrobial resistance transfer routes remain largely uncharted. In this review, we describe different methods for assessing the transfer frequency and host ranges of plasmids within complex microbiomes. The discussion is centered around the critical evaluation of recent advances for monitoring the fate of fluorescently tagged plasmids in bacterial communities through the coupling of fluorescence activated cell sorting and next generation sequencing techniques. We argue that this approach constitutes an exceptional tool for obtaining quantitative data regarding the extent of plasmid transfer, key disseminating taxa, and possible propagation routes. The integration of this information will provide valuable insights on how to develop alternative avenues for fighting the rise of antimicrobial resistant pathogens, as well as the means for constructing more comprehensive risk assessment models.

Genome analysis of the freshwater planktonic Vulcanococcus limneticus sp. nov. reveals horizontal transfer of nitrogenase operon and alternative pathways of nitrogen utilization

BACKGROUND

Many cyanobacteria are capable of fixing atmospheric nitrogen, playing a crucial role in biogeochemical cycling. Little is known about freshwater unicellular cyanobacteria Synechococcus spp. at the genomic level, despite being recognised of considerable ecological importance in aquatic ecosystems. So far, it has not been shown whether these unicellular picocyanobacteria have the potential for nitrogen fixation. Here, we present the draft-genome of the new pink-pigmented Synechococcus-like strain Vulcanococcus limneticus. sp. nov., isolated from the volcanic Lake Albano (Central Italy).

RESULTS

The novel species Vulcanococcus limneticus sp. nov. falls inside the sub-cluster 5.2, close to the estuarine/marine strains in a maximum-likelihood phylogenetic tree generated with 259 marker genes with representatives from marine, brackish, euryhaline and freshwater habitats. V.limneticus sp. nov. possesses a complete nitrogenase and nif operon. In an experimental setup under nitrogen limiting and non-limiting conditions, growth was observed in both cases. However, the nitrogenase genes (nifHDK) were not transcribed, i.e., V.limneticus sp. nov. did not fix nitrogen, but instead degraded the phycobilisomes to produce sufficient amounts of ammonia. Moreover, the strain encoded many other pathways to incorporate ammonia, nitrate and sulphate, which are energetically less expensive for the cell than fixing nitrogen. The association of the nif operon to a genomic island, the relatively high amount of mobile genetic elements (52 transposases) and the lower observed GC content of V.limneticus sp. nov. nif operon (60.54%) compared to the average of the strain (68.35%) support the theory that this planktonic strain may have obtained, at some point of its evolution, the nif operon by horizontal gene transfer (HGT) from a filamentous or heterocystous cyanobacterium.

CONCLUSIONS

In this study, we describe the novel species Vulcanococcus limneticus sp. nov., which possesses a complete nif operon for nitrogen fixation. The finding that in our experimental conditions V.limneticus sp. nov. did not express the nifHDK genes led us to reconsider the actual ecological meaning of these accessory genes located in genomic island that have possibly been acquired via HGT.