Metal Resistance Research Articles

Normal levels of Cu and Zn contamination present in swine manure increase the antibiotic resistance gene abundances in composting products

Cu and Zn are abundant heavy metals in swine manure. Heavy metals are not readily biodegradable and can continuously drive the co-selection of antibiotic resistance. Thus, to simulate the effects of different concentrations of heavy metals detected in swine manure on antibiotic resistance genes (ARGs), normal (L) and high (H) concentrations of Cu and Zn were added during composting. Compared with the control (CK), the total relative abundances (RAs) of ARGs in the composting products increased by 0.26–0.28 logs under CuL and ZnL. The total RAs of ARGs decreased by 0.84 logs under ZnH, and the RAs of sul1, tetX, and sul2 were 0.51–1.87 logs lower than those under CK (P < 0.05). Network analysis indicated that intI1 and ISCR1 were associated with the co-occurrence of ARGs and metal resistance genes. After composting, the abundances of intI1 were significantly higher under CuL and ZnL than CK (4.2–8.4 times), and normal concentrations of Cu and Zn promoted the horizontal transfer of ARGs. Moreover, the responses of the potential hosts to Cu and Zn affected the abundances of ARGs during composting. Overall, normal concentrations of heavy metals (CuL and ZnL) increased the ecological risk of ARGs in composting products.

Exploring the mechanisms of cadmium tolerance and bioaccumulation in a soil amoeba.

Cadmium (Cd) pollution is a global concern. Protists represent a prevalent yet understudied group in soil ecosystems, but our understanding of how protists interact with Cd remains limited. This study investigates the interaction between Cd and the soil amoeba Dictyostelium discoideum, focusing on its resistance, accumulation, and molecular mechanisms. We found that D. discoideum amoebae exhibit strong Cd resistance with an EC50 (half maximal effective concentration) of 899.2mg/kg and demonstrates significant Cd enrichment capabilities, achieving concentrations up to 1094.70±310.95mg/kg in stalks and a bioconcentration factor (BCF) of 7.30. Transcriptomic analysis revealed enriched pathways related to DNA replication and identified key genes involved in metal transport, detoxification, and stress response, including abc4, abc16, mms19, gcsA, ucpB, and sodA. Notably, microRNA (miRNA) regulation was found to play a critical role in modulating the expression of these genes. Our findings provide novel insights into the Cd enrichment potential of D. discoideum amoebae and elucidate its mechanisms of heavy metal resistance, highlighting the regulatory role of miRNAs. This study not only advances our understanding of protist-Cd interactions but also opens new avenues for the bioremediation of heavy metal-contaminated soils, where soil amoebae could serve as an effective agent due to their high bioaccumulation factor and rapid growth cycle.

Source-oriented risks of heavy metals and their effects on resistance genes in natural biofilms

Heavy metal (HM) introduction from various land-use patterns can be a major source of metal resistance genes (MRGs) entering river environments. This influx can trigger the occurrence of other resistomes, such as antibiotic resistance genes (ARGs), by improving co-resistant conjugative transfer. Biofilms, which form at water–solid interfaces, could serve as potential hotspots for HMs and resistance genes. However, the enrichment of HMs from various sources within biofilms and their effect on resistomes remain undocumented. This study aims to investigate the physicochemical properties of biofilm samples collected from the Heihui River, a tributary of the Lancang River, and to analyze the concentrations of nine HMs (As, Cd, Co, Cr, Cu, Ni, Pb, V, and Zn) within these biofilms. The 16S rRNA gene and metagenomic high-throughput sequencing techniques were integrated to uncover the association between HM accumulation levels in biofilms and ecological and health risks, considering the presence of two resistance genes. Natural sources (Co, Cr), industrial (As, Cu, V), agricultural (Cd, Ni), and transportation activities (Pb, Zn) markedly contributed to HM presence within biofilms, with industrial activities posing higher noncarcinogenic and carcinogenic risks than other sources. The network–correlation analyses revealed higher levels of ARG–MRG coexistence in biofilms, with the ecological and health risk index of HMs in biofilms closely associated with the abundance of both resistance genes. Furthermore, the biofilm As concentration markedly affected the abundance and expression of ARGs and MRGs, with elevated As levels within biofilms significantly and positively influencing all four functional categories of MRGs. Water pH also indirectly impacted these functional types by modulating the ionic form of HMs within the biofilm matrix. Our findings underscore the significance of integrating biofilms into environmental management practices and standards for assessing environmental quality.

Adaptive modification of antiviral defense systems in microbial community under Cr-induced stress

BackgroundThe prokaryotic antiviral defense systems are crucial for mediating prokaryote-virus interactions that influence microbiome functioning and evolutionary dynamics. Despite the prevalence and significance of prokaryotic antiviral defense systems, their responses to abiotic stress and ecological consequences remain poorly understood in soil ecosystems. We established microcosm systems with varying concentrations of hexavalent chromium (Cr(VI)) to investigate the adaptive modifications of prokaryotic antiviral defense systems under abiotic stress.ResultsUtilizing hybrid metagenomic assembly with long-read and short-read sequencing, we discovered that antiviral defense systems were more diverse and prevalent in heavily polluted soils, which was corroborated by meta-analyses of public datasets from various heavy metal-contaminated sites. As the Cr(VI) concentration increased, prokaryotes with defense systems favoring prokaryote-virus mutualism gradually supplanted those with defense systems incurring high adaptive costs. Additionally, as Cr(VI) concentrations increased, enriched antiviral defense systems exhibited synchronization with microbial heavy metal resistance genes. Furthermore, the proportion of antiviral defense systems carried by mobile genetic elements (MGEs), including plasmids and viruses, increased by approximately 43% and 39%, respectively, with rising Cr concentrations. This trend is conducive to strengthening the dissemination and sharing of defense resources within microbial communities.ConclusionsOverall, our study reveals the adaptive modification of prokaryotic antiviral defense systems in soil ecosystems under abiotic stress, as well as their positive contributions to establishing prokaryote-virus mutualism and the evolution of microbial heavy metal resistance. These findings advance our understanding of microbial adaptation in stressful environments and may inspire novel approaches for microbiome manipulation and bioremediation.2TMZqA39L8WnC4j2fhC46gVideo

P-310. Evolutionary dynamics of the Chilean-Cordobes MRSA clone allowed the emergence of new MRSA clones in Chile

Abstract Background The global spread of methicillin-resistant Staphylococcus aureus (MRSA) is associated with distinct clones predominating in specific geographical regions. Available evidence suggests that the Chilean-Cordobes clone (ChC), an ST5-SCCmecI lineage, has predominated in Chilean hospitals ever since its first description in 1998. However, we recently reported a gradual decrease in this lineage over time, with frequencies dropping from 94% (2000) to 52% (2016). To understand this clonal replacement event, we aimed to reconstruct the genomic evolution of the ChC in Latin America. Characterization of clades and sub-lineages of the ChC clone.Figure 1.Characterization of clades and sub-lineages of the ChC clone. A) Maximum clade credibility molecular clock analysis of the 596 MRSA genomes. A Bayesian molecular clock analysis was performed with BEAST using the isolation date of each genome as calibrator. The vertical lines show the scale of years. The colored strip showed the country of origin. The dots show the presence of mecA genotypes, heavy metal resistance genes (HMRGs), and SNPs in Sau1. The branches are colored based on the sub-lineage identification: ChC-I (magenta), ChC-II (orange), and ChC-III (green). B) Characterization of the ChC clades. The presence of each genetic element considered to characterize the clades are marked by a + symbol. C) Relative frequency of the ChC sub-lineages in Chile over time. The colored bars represent the relative frequency of each sub-lineage: ChC-I (magenta), ChC-II (orange), ChC-III (green), and unclassified (gray). Methods A total of 596 ChC MRSA isolates obtained from 6 Latin American countries between 1999-2018 were whole-genome sequenced and characterized using a Bayesian molecular clock analysis (MCA). Sub-lineages (SLs) observed in major divergence events were further characterized. Additionally, the frequency of each SL observed in our 1999-2018 collection was assessed in an independent group of genomes from 274 Chilean clinical MRSA isolates collected in 2022. Results Our MCA of ChC MRSA revealed 3 clades strongly related with different genomic traits, including: i) mecA genotype, ii) heavy metal resistance genes (HMRGs), and iii) changes in the Sau1 restriction-modification system (Sau1) (Fig. 1A). Each clade was classified as sub-lineage: ChC-I, ChC-II, and ChC-III (Fig. 1B). All the genomes from Argentina, Colombia, and Venezuela – countries where ChC was largely replaced - belonged to the ChC-II SL and harbored a Sau1 mutation (Fig. 1A). On the other hand, genomes obtained from Chile distributed in different SLs and exhibited a dynamic interchange over time (Fig. 1C). While between 1999-2003 most of the genomes belonged to SLs ChC-I and ChC-II, both SLs virtually disappeared in 2013-2018, period were &amp;gt;90% ChC genomes corresponded to ChC-III (Fig. 1C). In 2022, a majority of ChC MRSA had genomic features compatible with the ChC-III SL (Fig. 1C). Finally, the MCA revealed an evolutionary event within ChC-III dated in 2005, which was accompanied by the loss of HMRGs (Fig. 1A) Conclusion We describe the time evolution of several ChC clades, giving rise to sub-lineages that seem to play a role in the loss of dominance of the ChC MRSA clone in Chile and a consequent change in its epidemiology in the country. Disclosures José M Munita, MD, MSD: Grant/Research Support|Pfizer: Grant/Research Support

Exploring Viral Interactions in Clavibacter Species: In Silico Analysis of Prophage Prevalence and Antiviral Defenses

Clavibacter is a phytopathogenic genus that causes severe diseases in economically important crops, yet the role of prophages in its evolution, pathogenicity, and adaptation remains poorly understood. In this study, we used PHASTER, Prophage Hunter, and VirSorter2 to identify prophage-like sequences in publicly available Clavibacter genomes. Prophage predictions were checked by hand to make them more accurate. We identified 353 prophages, predominantly in chromosomes, with some detected phage-plasmids. Most prophages exhibited traits of advanced domestication, such as an unimodal genome length distribution, reduced numbers of integrases, and minimal transposable elements, suggesting long-term interactions with their bacterial hosts. Comparative genomic analyses uncovered high genetic diversity, with distinct prophage clusters showing species-specific and interspecies conservation patterns. Functional annotation revealed prophage-encoded genes were involved in sugar metabolism, heavy metal resistance, virulence factors, and antibiotic resistance, highlighting their contribution to host fitness and environmental adaptation. Defense system analyses revealed that, despite lacking CRISPR-Cas, Clavibacter genomes harbor diverse antiviral systems, including PD-Lambda-1, AbiE, and MMB_gp29_gp30, some encoded within prophages. These findings underscore the pervasive presence of prophages in Clavibacter and their role in shaping bacterial adaptability and evolution.

Unraveling nitrogen metabolism, cold and stress adaptation in polar Bosea sp. PAMC26642 through comparative genome analysis

Nitrogen metabolism, related genes, and other stress-resistance genes are poorly understood in Bosea strain. To date, most of the research work in Bosea strains has been focused on thiosulfate oxidation and arsenic reduction. This work aimed to better understand and identify genomic features that enable thiosulfate-oxidizing lichen-associated Bosea sp. PAMC26642 from the Arctic region of Svalbard, Norway, to withstand harsh environments. Comparative genomic analysis was performed using various bioinformatics tools to compare Bosea sp. PAMC26642 with other strains of the same genus, emphasizing nitrogen metabolism and stress adaptability. During genomic analysis of Bosea sp. PAMC26642, assimilatory nitrogen metabolic pathway and its associated enzymes such as nitrate reductase, NAD(P)H-nitrite reductase, ferredoxin-nitrite reductase, glutamine synthetase, glutamine synthase, and glutamate dehydrogenase were identified. In addition, carbonic anhydrase, cyanate lyase, and nitronate monooxygenase were also identified. Furthermore, the strain demonstrated nitrate reduction at two different temperatures (15°C and 25°C). Enzymes associated with various stress adaptation pathways, including oxidative stress (superoxide dismutase, catalase, and thiol peroxidase), osmotic stress (OmpR), temperature stress (Csp and Hsp), and heavy metal resistance, were also identified. The average Nucleotide Identity (ANI) value is found to be below the threshold of 94-95%, indicating this bacterium might be a potential new species. This study is very helpful in determining the diversity of thiosulfate-oxidizing nitrate-reducing bacteria, as well as their ability to adapt to extreme environments. These bacteria can be used in the future for environmental, biotechnological, and agricultural purposes, particularly in processes involving sulfur and nitrogen transformation.

Ecogenomic insights into the resilience of keystone Blastococcus Species in extreme environments: a comprehensive analysis

BackgroundThe stone-dwelling genus Blastococcus plays a key role in ecosystems facing extreme conditions such as drought, salinity, alkalinity, and heavy metal contamination. Despite its ecological significance, little is known about the genomic factors underpinning its adaptability and resilience in such harsh environments. This study investigates the genomic basis of Blastococcus's adaptability within its specific microniches, offering insights into its potential for biotechnological applications.ResultsComprehensive pangenome analysis revealed that Blastococcus possesses a highly dynamic genetic composition, characterized by a small core genome and a large accessory genome, indicating significant genomic plasticity. Ecogenomic assessments highlighted the genus's capabilities in substrate degradation, nutrient transport, and stress tolerance, particularly on stone surfaces and archaeological sites. The strains also exhibited plant growth-promoting traits, enhanced heavy metal resistance, and the ability to degrade environmental pollutants, positioning Blastococcus as a candidate for sustainable agriculture and bioremediation. Interestingly, no correlation was found between the ecological or plant growth-promoting traits (PGPR) of the strains and their isolation source, suggesting that these traits are not linked to their specific environments.ConclusionsThis research highlights the ecological and biotechnological potential of Blastococcus species in ecosystem health, soil fertility improvement, and stress mitigation strategies. It calls for further studies on the adaptation mechanisms of the genus, emphasizing the need to validate these findings through wet lab experiments. This study enhances our understanding of microbial ecology in extreme environments and supports the use of Blastococcus in environmental management, particularly in soil remediation and sustainable agricultural practices.

Residual heavy metals and antibiotic pollution in abandoned breeding areas along the northeast coast of Hainan Island, China.

To assess the environmental status of an abandoned aquaculture and breeding area in the northeast coast of the Hainan Island, surface and well water, sediment and surface soils were sampled and analyzed for conventional physicochemical properties, heavy metals and antibiotics. Metagenome tests were also conducted to determine the composition and diversity of the microbial community in typical habitats. Affected by the discharge of wastewater from higher-place pond aquaculture, coastal freshwater rivers have undergone significant salinization, Cl- and Na+ were as high as 4.51×103 and 1.42×103mg/L. The 3 hand-pumped wells surveyed were also suffered from varying degrees of salinization and heavy metal pollution, especially the threat of arsenic pollution. Compared with the local background values, significantly higher valves of Cu, Zn, As and Cd were observed in the surface soil and sediment, and the average concentrations for Cu, Zn, As and Cd are 5.71, 17.6, 15.4 and 0.09mg/kg respectively. For As，the Nemerow index ranges from 7 to 16 and the geoaccumulation index is between 2 and 4, indicating moderate to severe pollution levels in surface soil. 14 antibiotics were detected in the soil and sediment samples, and the highest total amount was 73μg/kg, with tetracycline being the dominant antibiotic. Sediment and forest soil showed different microbial community and the genetic diversity index of sediment was lower than that of the forest soils. For typical vegetation soil, the genetic diversity followed the order as P. elliottii × P. caribaea>Eucalyptus > C. equisetifolia. Among the soil and sediment samples, the highest abundances of antibiotic resistance genes (ARGs) were associated with elfamycin, peptide, rifamycin, and the most common antibiotic resistance mechanisms were antibiotic target alteration (54.5%), antibiotic efflux (27.6%) and antibiotic target replacement (12.1%). The metal resistance genes (MRGs) for Cu, Fe, and Zn resistance were the main MRGs in the samples. This study identified the potential ecological environment risk factors in the abandoned coastal breeding areas, and suggested continuous monitoring and assessment of the residual pollutant abatement processes in the future.

Distinct response of nitrogen metabolism to exogenous cadmium (Cd) in river sediments with and without Cd contamination history.

The role of metal resistance on nitrogen metabolism function and community resilience against Cd is important for elucidating the evolutionary dynamics of key ecological functions in river ecosystems. In this study, the response of nitrogen transforming function to Cd exposure in river sediments from the Yangtze River Basin with varying levels of heavy metal contamination history (Cd-contaminated and Cd-free sediments) was compared to understand how Cd influenced nitrogen metabolism under varying metal resistance conditions. The results showed that chronic and persistent Cd pollution of sediments caused an elevation of transport efflux metal resistance genes (MRGs) and a reduction in the uptake MRGs, leading to a stronger tolerance to Cd for Cd-contaminated sediment than Cd-free ones. Specifically, denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA) respectively responded to Cd through different mechanisms. Exogenous Cd (5-100 mg kg-1) influenced denitrification rates (-70 %-100 % deviation to control group) by regulating key genera (Thiobacillus, Magnetospirillum, Sideroxydans etc.) and gene clusters for denitrification. Both adaptive nature of anammox bacteria and co-regulation of key genera (Candidatus_Scalindua, Candidatus_Jettenia, Planctomyces etc.) and gene hzsA were drivers of differential responses in sediments from various contamination history. Environmental factors rather than contamination history, key genera or genes were probably critical ones determining Cd-resistance in DNRA, being more tolerant to Cd in sediments with higher TOC and NH4+. Stimulation of N2O reduction process (genera Gemmatimonas and Gemmatirosa and genes nosZ) in Cd-contaminated sediments by exogenous Cd lowered N2O emission risk, whereas the reverse was true for Cd-free sediments. These results enrich our understanding about the linkages among MRGs and nitrogen reduction functions in river.

Investigation of multiple resistance frequencies (antibiotic and heavy metal) of bacteria isolated from Gökçeada Island coastal marine sediment

Marine sediments are important reservoirs for antibiotics and heavy metals. Bacteria play a key role in polluted sedimentary habitats. This study aimed to identify heavy metal and antibiotic resistance in marine sediment bacteria isolated from Gökçeada Island in Turkiye. The samples were collected seasonally from 10 different sampling stations in 2015. Ninety isolates determined by VITEK 2 were tested against seven antibiotics using the disk diffusion method. The minimum inhibitory concentration values were measured against four heavy metal salts. The antibiotic resistance frequency rates were ordered as sulphonamides compound (93.3%), cefotaxime (78.9), ampicillin (77.8%), oxacillin (67.8%), rifampicin (57.8%), imipenem (1.1%), and oxytetracycline (0%). The heavy metal resistance ratios against ZnCl2, CuSO4, Pb(CH3COO)2, and HgCl2 were measured as 100%, 100%, 96.7%, and 73.3% respectively. The multiple heavy metal resistance index values were ranged from 0.75 (22.2%) to 1.0 (77.8%). The results show significant heavy metal and antibiotic contamination in the sediments of the Gökçeada Island. It is recommended that measures be taken against antibiotics and heavy metal pollution, as well as identifying and monitoring critical control points.

Manure application increases soil doxycycline and zinc levels and resistance gene abundance.

Doxycycline (DOX) and zinc (Zn), are frequently detected in livestock manure. Untreated excrement carries a sizable load of DOX and Zn into the soil, exacerbating agricultural nonpoint source pollution. However, research on the effects of DOX and Zn on soil microbial diversity and the prevalence of resistance genes is limited. Through an 8-year field experiment coupled with 16S rRNA sequence analysis, we explored the dynamics of DOX and Zn contamination and their influence on soil microbial diversity and resistance gene expression. Our findings revealed a pronounced positive correlation between pig manure application and residual DOX and Zn levels in the soil, with the high pig manure) treatment resulting in increases of 16.42- and 1.14-fold in soil DOX and Zn levels, respectively, compared to those of the control. Soil DOX levels increased with pig and chicken manure application, whereas soil Zn levels showed divergent trends, increasing with pig manure application but decreasing with chicken manure application. As soil depth increased, the contamination risks from DOX and Zn in the soil decreased. Notably, soil DOX and Zn levels exhibited a significant positive correlation with Bacteroidota, Firmicutes, and Proteobacteria. The application of livestock and poultry manures amplified the abundance of antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) in the soil, with higher ARG levels in pig manure-treated soil than in soil treated with chicken manure. Conversely, a greater abundance of MRGs was found in the soil treated with chicken manure than in the soil treated with pig manure. The results of this study on the DOX and Zn levels, microbial composition, and resistance genes with the continuous application of livestock and poultry manure in China will be highly valuable for the surveillance, maintenance, and biological removal of DOX and Zn composite pollution in manure.

Antibiotic resistance genes in the coastal atmosphere under varied weather conditions: Distribution, influencing factors, and transmission mechanisms.

Antibiotic resistance genes (ARGs) have escalated to levels of concern worldwide as emerging environmental pollutants. Increasing evidence suggests that non-antibiotic antimicrobial substances expedite the spread of ARGs. However, the drivers and mechanisms involved in the generation and spread of ARGs in the atmosphere remain inadequately elucidated. Co-occurrence networks, mantel test analysis, and partial least squares path modeling were used to analyze the symbiotic relationships of ARGs with meteorological conditions, atmospheric pollutants, water-soluble inorganic ions, bacteria, mobile genetic elements (MGEs), antibacterial biocide and metal resistance genes, and to identify the direct drivers of ARGs. The types and abundance of ARGs exhibited different seasonal distribution. Specifically, the types exhibited a strong alignment with the diversity of air masses terrestrial sources, while the abundance displayed a significant positive correlation with both biocide resistance genes (BRGs) and metal resistance genes (MRGs). The contribution of bacterial communities and MGEs to the generation and spread of ARGs was constrained by the low levels of antibiotics in the atmosphere and the existence of "viral intermediates". Conversely, antibacterial biocides and metals influenced mutation rates, cellular SOS responses, and oxidative stress of bacteria, consequently facilitating the generation and spread of ARGs. Moreover, the co-selection among their derivatives, resistance genes, ensured a stable presence of ARGs. The research highlighted the significant impact of residual antimicrobial substances on both the generation and spread of ARGs. Elucidating the sources of aerosols and the co-selection mechanism linking with ARGs, BRGs, and MRGs were crucial for preserving the stability of ARGs in the atmosphere.

Sn-modified VWTi catalysts for efficiently improving alkali metal resistance&amp;mdash;experimental and simulation investigation

Sn-modified VWTi catalysts for efficiently improving alkali metal resistance&amp;mdash;experimental and simulation investigation

Draft genome sequence of Modicisalibacter sp. strain Wilcox isolated from produced water.

The draft genome sequence of Modicisalibacter sp. strain Wilcox, isolated from produced water, is presented. The genome is 3.6 Mb in size with 3,283 protein-coding genes, including genes for hydrocarbon degradation, heavy metal resistance, and adaptation to high salinity. This genome provides insights into molecular mechanisms of hydrocarbon degradation under hypersaline conditions.

Digital insights into Pseudomonas aeruginosa PBH03: in-silico analysis for genomic toolbox and unraveling cues for heavy metal bioremediation.

The genomes of publicly available electroactive Pseudomonas aeruginosa strains are currently limited to in-silico analyses. This study analyzed the electroactive Pseudomonas aeruginosa PBH03 genome using comparative in-silico studies for biotechnological applications. Comparative in-silico and experimental analyses were conducted to identify the novel traits of P. aeruginosa PBH03 by genome sequencing. The publicly available genomes of Pseudomonas aeruginosa strains (PA01, PA14, and KRP1) were used for a comparative in-silico study with PBH03. Genome assembly, annotation, phylogenetic analysis, metabolic reconstruction, and comparative functional genes analysis were conducted using bioinformatics tools. The experimental analyses were conducted to validate the heavy metal resistance (Hg and Cu), salinity tolerance levels of PBH03, and acetate assimilation under microaerobic conditions. Computational analysis showed that the PBH03 genome had a size of 6.8Mb base pairs with a GC content of 65.7%. Whole genome annotation identified the unique genes absent in the previously sequenced Pseudomonas aeruginosa genomes. These genes were associated with resistance to heavy metals, such as Cu, Hg, As, and a Co-Zn-Cd efflux system. In addition, clustered, regularly interspaced short palindromic repeats, transposable elements, and conjugative transfer proteins were observed in the clustering-based systems. The strain exhibited resistance to Hg (150mg/L) and Cu (500mg/L) and showed growth at salinity levels of 40g/L (typical sea/ocean levels). PBH03 could consume acetate up to 110mM. Integrating in-silico and experimental data highlights the intriguing adaptive genomic qualities of PBH03, making it a promising candidate for various biotechnological applications.

Genetic and biochemical determinants in potentially toxic metals resistance and plant growth promotion in Rhizobium sp LBMP-C04.

The association of bacteria resistant to potentially toxic metals (PTMs) with plants to remove, transfer, or stabilize these elements from the soil is an appropriate tool for phytoremediation processes in metal-contaminated environments. The objective of this study was to evaluate the potential ofRhizobiumsp. LBMP-C04 forphytoremediation processes and plant growth promotion in metal-contaminated soils. Functional annotation allowed us to predict a variety of genes related to PTMs resistance and plant growth promotion in the bacterial genome. Resistance genes are mainly associated with DNA repair, and the import or export of metals in bacterial cells to maintain cell homeostasis. Genes that promote plant growth are related to mechanisms of osmotic stress tolerance, phosphate solubilization, nitrogen metabolism, biological nitrogen fixation, biofilm formation, heat shock responses, indole-3-acetic acid (IAA) biosynthesis, tryptophan, and organic acids metabolism. Biochemical tests indicated thatRhizobiumsp. LBMP-C04 can solubilize calcium phosphate and produce siderophores and IAAin vitroin the presence of the PTMs Cd2+,Cu2+,Cr3+,Cr6+, Zn2+, and Ni2+. Results indicate the possibility of usingRhizobiumsp. LBMP-C04 as a potentially efficient bacterium in phytoremediation processesin environments contaminated by PTMs and simultaneously promote plant growth.

On the results of tribological studies of railway rails

Metal resistance to the formation of contact fatigue defects and wear development has a great influence on the consumer properties of rails. The most significant factors limiting the service life of rails in curved sections of the railway track are wear of rails of the outer threads and development of contact fatigue defects in the inner threads of the track. In this regard, methods of reliable laboratory assessment of the rail metal resistance become important in the development of new products. The paper describes the change in the nature of damage to rails of various hardness categories by contact fatigue defects, and evaluates their wear resistance. The study of defects and forecasting of the rail resource require an integrated approach. The paper provides a brief description of modeling the conditions of formation and accumulation of contact fatigue defects. The parameters under consideration have an effect on the wear resistance of rail metal of various chemical compositions. During the testing, the rails microstructure and the nature of crack growth change. The authors made a comparative analysis of the data obtained characterizing the wear resistance of rail steels of various hardness categories. The basis of the methodology for assessing the wear resistance of railway rails is the physical modeling of adhesion-deformation mechanism of friction of the samples on a roller friction machine (tribometer). During laboratory tests of the studied categories of rails, the friction machine automatically outputs and records a number of computational parameters shown in the work. The conducted research is promising from a practical point of view. The results obtained can be used to develop a theory to increase the service life of differentially hardened rails produced by JSC EVRAZ United West Siberian Metallurgical Plant.

Cadmium-Induced Oxidative Damage and the Expression and Function of Mitochondrial Thioredoxin in Phascolosoma esculenta.

Phascolosoma esculenta is a unique aquatic invertebrate native to China, whose habitat is highly susceptible to environmental pollution, making it an ideal model for studying aquatic toxicology. Mitochondrial thioredoxin (Trx2), a key component of the Trx system, plays an essential role in scavenging reactive oxygen species (ROS), regulating mitochondrial membrane potential, and preventing ROS-induced oxidative stress and apoptosis. This study investigated the toxicity of cadmium (Cd) on P. esculenta and the role of P. esculenta Trx2 (PeTrx2) in Cd detoxification. The results showed that Cd stress altered the activities of T-SOD and CAT, as well as the contents of GSH and MDA in the intestine. After 96 h of exposure, histological damages such as vacuolization, cell necrosis, and mitophagy were observed. Suggesting that Cd stress caused oxidative damage in P. esculenta. Furthermore, with the prolongation of stress time, the expression level of intestinal PeTrx2 mRNA initially increased and then decreased. The recombinant PeTrx2 (rPeTrx2) protein displayed dose-dependent redox activity and antioxidant capacity and enhanced Cd tolerance of Escherichia coli. After RNA interference (RNAi) with PeTrx2, significant changes in the expression of apoptosis-related genes (Caspase-3, Bax, Bcl-2, and Bcl-XL) were observed. Proving that PeTrx2 rapidly responded to Cd stress and played a vital role in mitigating Cd-induced oxidative stress and apoptosis. Our study demonstrated that PeTrx2 is a key factor for P. esculenta to endure the toxicity of Cd, providing foundational data for further exploration of the molecular mechanisms underlying heavy metal resistance in P. esculenta.

Presence of metal-resistance and antibiotic-resistance genes in Salmonella spp. isolated from broiler chicken farms in Vinh Long province, Vietnam

Salmonella can carry multiple antibiotic-resistant and metalresistant genes and transmit these genes among strains worldwide. This study examined seventy-five Salmonella isolates from small-scale chicken farms (chicken feces, bedding, feed, wild animals) in Vinh Long province for the presence and relation of antibiotic and metal-resistance genes in these strains. The single PCR method was applied to detect seven antibiotic-resistance genes (blaampC, blaTEM, dfrA1, tetA, strA, sul2, mcr1) and four metal-resistance genes (pcoR, czcD, cnrA, silE). The results indicated that those Salmonella isolates harbored several patterns of antibiotic-resistance genes. Genes blaampC and tetA were the most prevalent (48.00%), while genes mcr1 and dfrA were the most minor (1.33%). Of those Salmonella isolates, 92.00% harbored one to five antibiotic-resistance genes, and the blaampC + strA pattern was frequently obtained (12.00%). Moreover, 30.67% of Salmonella isolates showed multidrug resistance to three or four antibiotic categories. Among metal-resistance genes, gene pcoR encoding for copper resistance was the most predominant (53.33%), and gene cnrA encoding for cobalt-nickel resistance was the lowest (5.33%). There were diverse patterns of metalresistance genes, and one Salmonella isolate carried four examined genes (1.33%). Furthermore, these Salmonella isolates had several combined patterns of metal-resistance and antibiotic-resistance genes. Among them, pcoR, czcD, and silE genes had a significant coefficient relation to the examined antibiotic-resistance genes. It indicated the correlation between metal resistance and antibiotic resistance genes and revealed the potential risk of increasing antibiotic resistance in Salmonella isolates in chicken farms in Vinh Long province.