Characterization of an Environmental Multidrug-Resistant Acinetobacter seifertii and Comparative Genomic Analysis Reveals Co-occurrence of Antimicrobial Resistance and Metal Tolerance Determinants

Characterization of the diversity of type IV secretion system-encoding plasmids in Acinetobacter

The multi-drug resistant pathogen Acinetobacter baumannii has gained global attention as an important clinical challenge. Owing to its ability to survive on surfaces, its capacity for horizontal gene transfer, and its resistance to front-line antibiotics, A. baumannii has established itself as a successful pathogen. Bacterial conjugation is a central mechanism for pathogen evolution. The epidemic multidrug-resistant A. baumannii ACICU harbours a plasmid encoding a Type IV Secretion System (T4SS) with homology to the E. coli F-plasmid, and plasmids with homologous gene clusters have been identified in several A. baumannii sequence types. However the genetic and host strain diversity, global distribution, and functional ability of this group of plasmids is not fully understood. Using systematic analysis, we show that pACICU2 belongs to a group of almost 120 T4SS-encoding plasmids within four different species of Acinetobacter and one strain of Klebsiella pneumoniae from human and environmental origin, and globally distributed across 20 countries spanning 4 continents. Genetic diversity was observed both outside and within the T4SS-encoding cluster, and 47% of plasmids harboured resistance determinants, with two plasmids harbouring eleven. Conjugation studies with an extensively drug-resistant (XDR) strain showed that the XDR plasmid could be successfully transferred to a more divergent A. baumanii, and transconjugants exhibited the resistance phenotype of the plasmid. Collectively, this demonstrates that these T4SS-encoding plasmids are globally distributed and more widespread among Acinetobacter than previously thought, and that they represent an important potential reservoir for future clinical concern.

Genomic insights into the adaptation of Acinetobacter johnsonii RB2-047 to the heavy metal-contaminated subsurface mine environment

The subsurface mine environments characterized by high levels of toxic metals and low nutrient availability represent an extreme threat to bacterial persistence. In recent study, the genomic analysis of the Acinetobacter johnsonii strain RB2-047 isolated from the Rozália Gold Mine in Slovakia was performed. As expected, the studied isolate showed a high level of heavy metal tolerance (minimum inhibitory concentrations were 500 mg/L for copper and nickel, 1,500 mg/L for lead, and 250 mg/L for zinc). The RB2-047 strain also showed noticeable resistance to several antibiotics (ampicillin, kanamycin, chloramphenicol, tetracycline and ciprofloxacin). The genomic composition analysis demonstrated a low number of antibiotic and metal resistance coding genes, but a high occurrence of efflux transporter genes located on the bacterial chromosome. The experimental inhibition of efflux pumps resulted in decreased tolerance to Zn and Ni (but not to Cu and Pb) and to all antibiotics tested. In addition, the H33342 dye-accumulation assay confirmed the high efflux activity in the RB2-047 isolate. These findings showed the important role of efflux pumps in the adaptation of Acinetobacter johsonii strain RB2-047 to metal polluted mine environment as well as in development of multi-antibiotic resistance.

Genomic analysis of diverse environmental Acinetobacter isolates identifies plasmids, antibiotic resistance genes, and capsular polysaccharides shared with clinical strains

Acinetobacter baumannii, an important pathogen known for its widespread antibiotic resistance, has been the focus of extensive research within its genus, primarily involving clinical isolates. Consequently, data on environmental A. baumannii and other Acinetobacter species remain limited. Here, we utilized Illumina and Nanopore sequencing to analyze the genomes of 10 Acinetobacter isolates representing 6 different species sourced from aquatic environments in South Australia. All 10 isolates were phylogenetically distinct compared to clinical and other non-clinical Acinetobacter strains, often tens of thousands of single-nucleotide polymorphisms from their nearest neighbors. Despite the genetic divergence, we identified pdif modules (sections of mobilized DNA) carrying clinically important antimicrobial resistance genes in species other than A. baumannii, including carbapenemase oxa58, tetracycline resistance gene tet(39), and macrolide resistance genes msr(E)-mph(E). These pdif modules were located on plasmids with high sequence identity to those circulating in globally distributed A. baumannii ST1 and ST2 clones. The environmental A. baumannii isolate characterized here (SAAb472; ST350) did not possess any native plasmids; however, it could capture two clinically important plasmids (pRAY and pACICU2) with high transfer frequencies. Furthermore, A. baumannii SAAb472 possessed virulence genes and a capsular polysaccharide type analogous to clinical strains. Our findings highlight the potential for environmental Acinetobacter species to acquire and disseminate clinically important antimicrobial resistance genes, underscoring the need for further research into the ecology and evolution of this important genus.IMPORTANCEAntimicrobial resistance (AMR) is a global threat to human, animal, and environmental health. Studying AMR in environmental bacteria is crucial to understand the emergence and dissemination of resistance genes and pathogens, and to identify potential reservoirs and transmission routes. This study provides novel insights into the genomic diversity and AMR potential of environmental Acinetobacter species. By comparing the genomes of aquatic Acinetobacter isolates with clinical and non-clinical strains, we revealed that they are highly divergent yet carry pdif modules that encode resistance to antibiotics commonly used in clinical settings. We also demonstrated that an environmental A. baumannii isolate can acquire clinically relevant plasmids and carries virulence factors similar to those of hospital-associated strains. These findings suggest that environmental Acinetobacter species may serve as reservoirs and vectors of clinically important genes. Consequently, further research is warranted to comprehensively understand the ecology and evolution of this genus.

Genomic and phenotypic features of Acinetobacter baumannii isolated from oil reservoirs reveal a novel subspecies specialized in degrading hazardous hydrocarbons

The genus Acinetobacter encompasses biotechnologically relevant species and nosocomial pathogens. In this study, nine isolates recovered from different oil reservoir samples showed the ability to grow with petroleum as the only carbon source and possessed the ability to emulsify kerosene. The whole genomes of the nine strains were sequenced and analyzed. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values of all strains were compared to the reference strains, and the results were below the reference values (<97.88 and 82, respectively), suggesting that the isolates belong to a new subspecies of Acinetobacter baumannii. The name Acinetobacter baumannii oleum ficedula is proposed. A comparison of the whole genome repertoire of 290 Acinetobacter species indicated that the strains in this study resemble non-pathogenic Acinetobacter strains. However, the new isolates resemble A. baumannii when comparing virulence factors. The isolates in this study carry many genes involved in hydrocarbon degradation, indicating the potential to degrade most toxic compounds listed by environmental regulatory agencies such as ATSDR, EPA, and CONAMA. In addition, despite the absence of known biosurfactant or bioemulsifier genes, the strains showed emulsifying activity, suggesting the presence of new pathways or genes related to this process. This study investigated the genomic, phenotypic, and biochemical features of the novel environmental subspecies A. baumannii oleum ficedula, revealing their potential to degrade hydrocarbons and to produce biosurfactants or bioemulsifiers. Applying these environmental subspecies in bioaugmentation strategies sheds light on future approaches to bioremediation. The study shows the importance of genomic analysis of environmental strains and their inclusion in metabolic pathways databases, highlighting unique enzymes/alternative pathways for consuming hazardous hydrocarbons.

The evolutionary tale of eight novel plasmids in a colistin-resistant environmental Acinetobacter baumannii isolate

Acinetobacter baumannii is an important opportunistic pathogen known for its high levels of resistance to many antibiotics, particularly those considered last resorts such as colistin and carbapenems. Plasmids of this organism are increasingly associated with the spread of clinically important antibiotic resistance genes. Although A. baumannii is a ubiquitous organism, to date, most of the focus has been on studying strains recovered from clinical samples ignoring those isolated in the environment (soil, water, food, etc.). Here, we analysed the genetic structures of eight novel plasmids carried by an environmental colistin-resistant A. baumannii (strain E-072658) recovered in a recycled fibre pulp in a paper mill in Finland. It was shown that E-072658 carries a new variant of the mcr-4 colistin resistance gene (mcr-4.7) in a novel Tn3-family transposon (called Tn6926) carried by a novel plasmid p8E072658. E-072658 is also resistant to sulphonamide compounds; consistent with this, the sul2 sulphonamide resistance gene was found in a pdif module. E-072658 also carries six additional plasmids with no antibiotic resistance genes, but they contained several pdif modules shared with plasmids carried by clinical strains. Detailed analysis of the genetic structure of all eight plasmids carried by E-072658 showed a complex evolutionary history revealing genetic exchange events within the genus Acinetobacter beyond the clinical or environmental origin of the strains. This work provides evidence that environmental strains might act as a source for some of the clinically significant antibiotic resistance genes.

Genomic plasticity and adaptive capacity of the quaternary alkyl-ammonium compound and copper tolerant Acinetobacter bohemicus strain QAC-21b isolated from pig manure

Here, we present the genomic characterization of an Acinetobacter bohemicus strain QAC-21b which was isolated in the presence of a quaternary alky-ammonium compound (QAAC) from manure of a conventional German pig farm. The genetic determinants for QAAC, heavy metal and antibiotic resistances are reported based of the whole genome shotgun sequence and physiological growth tests. A. bohemicus QAC-21b grew in a species typical manner well at environmental temperatures but not at 37 °C. The strain showed tolerance to QAACs and copper but was susceptible to antibiotics relevant for Acinetobacter treatments. The genome of QAC-21b contained several Acinetobacter typical QAAC and heavy metal transporting efflux pumps coding genes, but no key genes for acquired antimicrobial resistances. The high genomic content of transferable genetic elements indicates that this bacterium can be involved in the transmission of antimicrobial resistances, if it is released with manure as organic fertilizer on agricultural fields. The genetic content of the strain was compared to that of two other A. bohemicus strains, the type strain ANC 3994^T, isolated from forest soil, and KCTC 42081, originally described as A. pakistanensis, a metal resistant strain isolated from a wastewater treatment pond. In contrast to the forest soil strain, both strains from anthropogenically impacted sources showed genetic features indicating their evolutionary adaptation to the anthropogenically impacted environments. Strain QAC-21b will be used as model strain to study the transmission of antimicrobial resistance to environmentally adapted Acinetobacter in agricultural environments receiving high content of pollutants with organic fertilizers from livestock husbandry.

Occurrence of clinically relevant antimicrobial resistance genes, including mcr-3 and mcr-7.1, in soil and water from a recreation club

We researched clinically relevant antimicrobial resistance genes (ARGs) and mobile genetic elements (MGEs) in environmental samples from a recreation club in Brazil. A total of 172 amplicons (105 from soil and 67 from water) of 26 ARGs (20 among the soil and water samples; four only in soil samples; two only in water samples) were detected. Nine MGEs were detected, including plasmids and class 1 integron. The absolute abundance of the mcr-3 gene ranged from 1.12 × 10² to 1.81 × 10³ copies/mL^-1 in water samples. The rapid spread of mcr-like genes in several sources has generated a huge concern to public health. Accordingly, understanding of antimicrobial resistance, carry out surveillance studies may contribute to tackle antimicrobial resistance. As the environmental samples were collected from a popular recreation club in Brazil, this study points out to the risk and exposure to clinically relevant ARGs, especially to mcr-3 and mcr-7.1 genes.

Comparative phylo-pangenomics reveals generalist lifestyles in representative Acinetobacter species and proposes candidate gene markers for species identification

Acinetobacter species have the potential to invade and colonize immunocompromised patients, therefore being well-known as opportunistic pathogens. Among these bacteria, the species of the Acinetobacter calcoaceticus-Acinetobacter baumannii "complex" (Acb members) emerge as the main often isolated bacteria in clinical specimens. The unequivocal taxonomy is crucial to correctly identify these species and associated with comparative genomic analyses aids to understand their life-styles as well. In this study, all publicly available Acinetobacter species at the date of this study preparation were analyzed. The results revealed that the Acb members are in fact a complex when phenotypic methods are confronted, while for comparative and phylogenomics analyses this term is misleading, since they composed a monophyletic group instead. Nine best gene markers (response regulator, recJ, recG, phosphomannomutase, pepSY, monovalent cation/H + antiporter subunit D, mnmE, glnE, and bamA) were selected for identification of Acinetobacter species. Moreover, representative strains of each species were split according their isolation sources in the categories: environmental, human, insect and non-human vertebrate. Neither niche-specific genome signature nor niche-associated functional and pathogenic potential were associated with their isolation source, meaning it is not the main force acting on Acinetobacter adaptation in a given niche and corroborating that their ubiquitous distribution is a reflex of their generalist life-styles.

Cadmium and antibiotic-resistant Acinetobacter calcoaceticus strain STP14 reported from sewage treatment plant

A bacterium designated as strain STP14 was isolated from a sewage treatment plant and identified as Acinetobacter calcoaceticus based on 16S ribosomal RNA gene sequencing. Strain STP14 exhibited resistance to several metals such as mercury, cobalt, copper, nickel, lead, and cadmium. Among these metals, the bacterium showed maximum resistance to cadmium in concentration up to 1200 mg/L. The antimicrobial susceptibility test of A. calcoaceticus strain STP14 showed coresistance to all tested antibiotics except tigecycline and chloramphenicol for which 16 ± 1- and 15 ± 1-mm zone of inhibition was observed, respectively. The protein pattern of the crude cellular extract revealed substantial differences in protein bands of untreated control and cadmium treated A. calcoaceticus strain STP14 suggesting variable protein expression under cadmium stress. Metals and antibiotic resistance are increasing phenomenon and universal concern of public health. This study improves our understanding regarding the bacterial coresistance against metals and antibiotics and the possible emergence of multidrug resistance due to selective pressure and coselection in the metal polluted sewage sludge.

The Biocontrol Agent and Insect Pathogen Photorhabdus luminescens Interacts with Plant Roots

The number of sustainable agriculture techniques to improve pest management and environmental safety is rising, as biological control agents are used to enhance disease resistance and abiotic stress tolerance in crops. Here, we investigated the capacity of the Photorhabdus luminescens secondary variant to react to plant root exudates and their behavior toward microorganisms in the rhizosphere. P. luminescens is known to live in symbiosis with entomopathogenic nematodes (EPNs) and to be highly pathogenic toward insects. The P. luminescens-EPN relationship has been widely studied, and this combination has been used as a biological control agent; however, not much attention has been paid to the putative lifestyle of P. luminescens in the rhizosphere. We performed transcriptome analysis to show how P. luminescens responds to plant root exudates. The analysis highlighted genes involved in chitin degradation, biofilm regulation, formation of flagella, and type VI secretion system. Furthermore, we provide evidence that P. luminescens can inhibit growth of phytopathogenic fungi. Finally, we demonstrated a specific interaction of P. luminescens with plant roots. Understanding the role and the function of this bacterium in the rhizosphere might accelerate the progress in biocontrol manipulation and elucidate the peculiar mechanisms adopted by plant growth-promoting rhizobacteria in plant root interactions.IMPORTANCE Insect-pathogenic Photorhabdus luminescens bacteria are widely used in biocontrol strategies against pests. Very little is known about the life of these bacteria in the rhizosphere. Here, we show that P. luminescens can specifically react to and interact with plant roots. Understanding the adaptation of P. luminescens in the rhizosphere is highly important for the biotechnological application of entomopathogenic bacteria and could improve future sustainable pest management in agriculture.

Interest of bacterial pangenome analyses in clinical microbiology

Thanks to the progress and decreasing costs in genome sequencing technologies, more than 250,000 bacterial genomes are currently available in public databases, covering most, if not all, of the major human-associated phylogenetic groups of these microorganisms, pathogenic or not. In addition, for many of them, sequences from several strains of a given species are available, thus enabling to evaluate their genetic diversity and study their evolution. In addition, the significant cost reduction of bacterial whole genome sequencing as well as the rapid increase in the number of available bacterial genomes have prompted the development of pangenomic software tools. The study of bacterial pangenome has many applications in clinical microbiology. It can unveil the pathogenic potential and ability of bacteria to resist antimicrobials as well identify specific sequences and predict antigenic epitopes that allow molecular or serologic assays and vaccines to be designed. Bacterial pangenome constitutes a powerful method for understanding the history of human bacteria and relating these findings to diagnosis in clinical microbiology laboratories in order to optimize patient management.

Azolla filiculoides L. as a source of metal-tolerant microorganisms

The metal hyperaccumulator Azolla filiculoides is accompanied by a microbiome potentially supporting plant during exposition to heavy metals. We hypothesized that the microbiome exposition to selected heavy metals will reveal metal tolerant strains. We used Next Generation Sequencing technique to identify possible metal tolerant strains isolated from the metal-treated plant (Pb, Cd, Cr(VI), Ni, Au, Ag). The main dominants were Cyanobacteria and Proteobacteria constituting together more than 97% of all reads. Metal treatment led to changes in the composition of the microbiome and showed significantly higher richness in the Pb-, Cd- and Cr-treated plant in comparison with other (95–105 versus 36–44). In these treatments the share of subdominant Actinobacteria (0.4–0.8%), Firmicutes (0.5–0.9%) and Bacteroidetes (0.2–0.9%) were higher than in non-treated plant (respectively: 0.02, 0.2 and 0.001%) and Ni-, Au- and Ag-treatments (respectively: <0.4%, <0.2% and up to 0.2%). The exception was Au-treatment displaying the abundance 1.86% of Bacteroidetes. In addition, possible metal tolerant genera, namely: Acinetobacter, Asticcacaulis, Anabaena, Bacillus, Brevundimonas, Burkholderia, Dyella, Methyloversatilis, Rhizobium and Staphylococcus, which form the core microbiome, were recognized by combining their abundance in all samples with literature data. Additionally, the presence of known metal tolerant genera was confirmed: Mucilaginibacter, Pseudomonas, Mycobacterium, Corynebacterium, Stenotrophomonas, Clostridium, Micrococcus, Achromobacter, Geobacter, Flavobacterium, Arthrobacter and Delftia. We have evidenced that A. filiculoides possess a microbiome whose representatives belong to metal-resistant species which makes the fern the source of biotechnologically useful microorganisms for remediation processes.