Methylotrophic methanogenesis induced by ammonia nitrogen in an anaerobic digestion system.

OBJECTIVES: This lab-scale study aimed to investigate the effect of total ammonia nitrogen (TAN) stress on the methanogenic activity and the taxonomic and functional profiles of the microbial community of anaerobic sludge (AS) from a full-scale bioreactor. METHODS: The AS was subjected to a stepwise increase in TAN every 14 days at concentrations of 1, 2, 2.5, 3, 3.5, and 4 g-TAN/L (Acclimated-AS or AAS). This acclimation stage was followed by an ammonia stress stage (4 g/L). A blank-AS (BAS) was maintained without TAN during the acclimation stage. In the second stress stage (ST), the BAS was divided into two new treatments: a control (BAS') and one that received a shock load of TAN of 4 g/L (SBAS'). Methane production was measured, and a metagenomic analysis was conducted to describe the microbial community. RESULTS: A decrease in the relative abundance of Methanothrix soehngenii of 16% was related to a decrease of 23% in the methanogenic capacity of AAS when comparing with the final stage of BAS. However, recovery was observed at 3.5 g TAN/L, and a shift to methylotrophic metabolism occurred, indicated by a 4-fold increase in abundance of Methanosarcina mazei. The functional analysis of sludge metagenomes indicated that no statistical differences (p > 0.05, RM ANOVA) were found in the relative abundance of methanogenic genes that initiate acetoclastic and hydrogenotrophic pathways (acetyl-CoA synthetase, ACSS; acetate kinase, ackA; phosphate acetyltransferase, pta; and formylmethanofuran dehydrogenase subunit A, fwdA) into the BAS and AAS during the acclimation phase. The same was observed between groups of genes associated with methanogenesis from methylated compounds. In contrast, statistical differences (p < 0.05, one-way ANOVA) in the relative abundance of these genes were recorded during ST. The functional profiles of the genes involved in acetoclastic, hydrogenotrophic, and methylotrophic methanogenic pathways were brought to light for acclimatation and stress experimental stages. CONCLUSIONS: TAN inhibited methanogenic activity and acetoclastic metabolism. The gradual acclimatization to TAN leads to metabolic and taxonomic changes that allow for the subsequent recovery of methanogenic functionality. The study highlights the importance of adequate management of anaerobic bioprocesses with high nitrogen loads to maintain the methanogenic functionality of the microbial community.

Assessing metal(loid)s concentrations and biomarkers in tilapia (Oreochromis niloticus) and largemouth bass (Micropterus salmoides) of three ecosystems of the Yaqui River Basin, Mexico.

Aquatic ecosystems have been suffering deleterious effects due to the development of different economic activities. Metal(loid)s are one of the most persistent chemicals in environmental reservoirs, and may produce adverse effects on different organisms. Since fishes have been largely used in studies of metal(loid)s exposure, tilapia and largemouth bass were collected in three ecosystems from the Yaqui River Basin to measure the concentrations of metal(loid)s (chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), zinc (Zn) arsenic (As), mercury (Hg), and selenium (Se)) and some biomarkers (somatic indices, metallothionein expression and histopathological analysis) in tissues of both species. Metal(loid) concentrations varied seasonally among ecosystems in tissues of both species. The elements varied seasonally and spatially in tissues of both species, with a general distribution of liver > gills > gonads. Also, biomarkers showed variations indicative that the fish species were exposed to different environmental stressor conditions. The highest values of some biomarkers were in largemouth bass, possibly due to differences in their biological characteristics, mainly feeding habits. The multivariate analysis showed positive associations between metal(loid)s and biomarkers, which are usually associated to the use of these elements in metabolic and/or regulatory physiological processes. Both fish species presented histological damage at different levels, from SI types (changes that are reversible for organ structure) to SII types (changes that are more severe but may be repairable). Taken together, the results from this study suggest that the Yaqui River Basin is moderately impacted by metals and metalloids.

Ecotoxicological perspectives of microplastic pollution in amphibians.

Microplastics (MPs) are contaminants widely distributed in the environment and biota. Previously, most studies focused on identifying and characterizing microplastics in the marine environment, while their impact on freshwater ecosystems remains to be determined. This review summarizes recent findings regarding MPs physiological, immunological, and genetic effects on amphibians based upon the biological relevance of this species as indicators of freshwater pollution. Data demonstrated that MPs contamination may potentially alter various physiological processes in aquatic animals, mainly in the embryonic stages. It is worthwhile noting that adverse effects might be enhanced in synergy with other pollutants. However, amphibians might counteract the effect of MPs and other pollutants through microbiota present both in the intestine and on the skin. In addition, amphibian microbial composition might also be altered by MPs themselves in a manner that leads to unpredicted health consequences in amphibians.

Risk and Benefit Analysis of Fish Consumption in NW Mexico: Mercury, Selenium, and Fatty Acids.

To balance the risks and benefits of fish consumption, selenium, fatty acids (DHA + EPA), and mercury in fishery products were determined. Analyzed products were canned tuna, frozen tuna (Thunnus albacares), smoked striped marlin (Tetrapturus audax), fresh Pacific sierra (Scomberomorus sierra), fresh dolphinfish (Coryphaena hippurus), fresh tilapia (Gerres cinereus), and fresh bullseye puffer (Sphoeroides annulatus). Mercury (µg g-1 wet weight) ranged from 0.01 (dolphinfish) to 0.23 (bullseye puffer); Se ranged from 0.12 to 0.25. EPA + DHA ranged from 1.16 to 10.72 mg g-1. Intake of EPA + DHA was comparable or above the recommended daily intake; Hg intake was below the reference dose but Se intake was below than recommended values for the different population groups. Considering the HBVSe, fishery products had positive values; i.e., they are healthy food items. According to the interaction of Hg and Se and the rate of fishery product consumption, the risk for consumers is below one percent.

Transcriptomic signaling in zebrafish (Danio rerio) embryos exposed to environmental concentrations of glyphosate.

Glyphosate [N-(phosphonomethyl)glycine] is one of the most popular herbicides worldwide. Globally, the use of glyphosate is increasing, and its residues have been found in drinking water and food products. The data regarding the possible toxic effects of this herbicide are controversial. Therefore, the aim of this study was to evaluate the effects of glyphosate at environmental concentrations in zebrafish (Danio rerio) embryos. Embryos were exposed to 0, 1, 100, and 1,000 µg/L glyphosate for 96 h, and mortality, heart rate, and hatching rate were evaluated. After the experiment, RNA was extracted from the embryos for transcriptional analysis. No mortality was recorded, and exposure to 100 µg/L and 1,000 µg/L of glyphosate resulted in lower heart rates at 48 h. In addition, RNA-seq analysis revealed that glyphosate exposure induced subtle changes in gene transcription profiles. We found 30 differentially expressed genes; however, the highest glyphosate concentration (1,000 µg/L) induced the greatest number of differentially expressed genes involved in oocyte maturation, metabolic processes, histone deacetylation, and nervous system development.

A metagenomic assessment of microbial communities in anaerobic bioreactors and sediments: Taxonomic and functional relationships.

The present study used metagenomic sequencing, metagenome assembly and physical-chemical analysis to describe taxonomically and functionally 3 anaerobic bioreactors treating manure (LI), brewery (BR) and cornmeal (CO) wastes, and an anaerobic estuarine sediment (ES). Proteobacteria, Firmicutes, Euryarchaeota and Bacteroidetes were the most abundant Phyla in all metagenomes. A bacteria/archaea ratio of 3.4 was found in the industrial full-scale anaerobic bioreactors BR and CO, while ratios greater than 10 were found for LI and ES. Canonical correspondence analysis showed that environmental variables such as chemical oxygen demand, lipid content, and ammonium nitrogen influenced the ordination of taxonomic groups. Mesotoga prima was linked to high-temperature conditions, particularly in the BR bioreactor, along with the presence of heat shock proteins genes. Likewise, the hydrogenotrophic methanogen, Methanoregula formicica, was associated with high ammonium concentration in LI bioreactor. The interactions of microbes with specific methanogenic pathways were identified using Clusters of Orthologous Groups (COG) functions, while metagenome-assembled genomes (MAGs) further confirmed relationships between taxa and functions. Our results provide valuable information to understand microbial processes in anaerobic environments.

A comparison of pesticide residues in soils from two highly technified agricultural valleys in northwestern Mexico.

A pesticide characterization is presented for two highly technified valleys in northwest Mexico: Culiacan Valley (CV) in Sinaloa and Yaqui Valley (YV) in Sonora. Approximately 250,000 kg of active ingredients are used every year, half of which are considered highly hazardous pesticides. Legacy pesticides are still present in the soils of these valleys. The aim of the present study was to identify and quantify a wide variety of pesticides in soils and correlate their concentrations with historical and current use. Agricultural soils from both valleys were sampled and analyzed using accelerated solvent extraction and subsequent quantification by gas chromatography with selective detectors. The most frequently detected pesticides (mean, µg g-1) in CV were organochlorines (0.1967), organophosphates (0.0928), synthetic pyrethroids (0.2565), organonitrogen (0.0552), and miscellaneous pesticides (0.1851). In YV, the most frequently detected pesticides were organochlorines (0.8607), organophosphates (0.0001), synthetic pyrethroids (0.0124), and miscellaneous pesticides (0.0009). The pesticides were more diverse in CV compared to those of YV, which was based on the types of crops produced. Both locations presented highly hazardous pesticides, including concentrations above the action levels established by the Canadian Soil Quality Guide. A follow-up risk assessment is recommended to assess potential effects.

Bioaccumulation of organochlorine pesticides in the Western Sandpiper (Calidris mauri) during the wintering season in Sinaloa, Mexico.

The Western Sandpiper, Calidris mauri, is one of the most abundant migratory shorebirds in the Western Hemisphere. Both Bahia Santa Maria (SM) and Ensenada Pabellones (EP) in Sinaloa, Mexico, are critical wintering sites for this species. We described the presence and concentration of 16 organochlorine pesticides (OCPs) in Western Sandpiper muscle and liver tissues collected from SM and EP during the wintering (December-January) and premigration (March-April) periods of 2010 and 2011, respectively. The individual OCP concentrations varied from 0.003 to 0.127 µg/g dry weight (dw) and were lower than the established thresholds for either acute or chronic effects. Western Sandpipers in SM-Premigration had the highest frequency of OCPs (39.3%), followed by EP-Winter (32.1%) and SM-Winter (28.5%). The frequency of occurrence of all OCPs in the liver presented differences between sites during the wintering period as well as between the wintering and premigration periods in SM. As the primary organ responsible for pollutant detoxification, the liver may bioaccumulate these compounds. No clear trends were observed in muscle tissues or among age-sex groups. Our results showed evidence of OCP bioaccumulation in the Western Sandpiper during the wintering period, which may be related to hyperphagia during the premigration period and to the differential intake of OCP types and quantities between sites due to differences in their availability. However, these conclusions are based on relatively low sample sizes for some groups and require further study with non-pooled samples.

Multiple biomarker approach in the fiddler crab to assess anthropogenic pollution in tropical coastal environments.

CONTEXT: Fiddler crabs are important to the ecology of estuarine systems around the world, however, few studies have incorporated them as bioindicators. Urias estuary represents one of the most urbanized lagoons in the Gulf of California region and received discharges from different sources: shrimp farm, thermoelectric plant, fish processing plants, and untreated domestic and sewage wastes. OBJECTIVE: Assess the effects on anthropogenic contamination on female fiddler crabs reproduction, survival and genetic stability. METHODS: Exposition of wild crabs from a less impacted (reference) site to naturally contaminated sediments on under controlled laboratory conditions. Reproductive parameters, levels of DNA damage and mortality rates were measured, together with chemical analyses of sediments. RESULTS: The most contaminated sediments corresponded to the site where fish processing plants were located and the integrated biomarker response analysis revealed that the most adverse effects were produced by exposure to sediments from this site; these crabs showed higher mortality (67%) and poorer ovarian development than those crabs exposed to sediments from other sites. CONCLUSIONS: Female crabs under pollution stress are able to trade-off reproduction for survival, and surviving animals were able to restore genetic stability possibly by activating DNA repair mechanisms. Multiple biomarker approach discriminates different coastal contamination scenarios.

Mercury Levels and Risk Implications Through Fish Consumption on the Sinaloa Coasts (Gulf of California, Northwest Mexico).

Fish consumption is the major source of mercury to humans. Fetuses and children are the most sensitive groups of populations to the effects of mercury. Consequently, fish consumption by pregnant women, children, and women of childbearing age is of concern because of the effects of mercury exposure on human health. To assess mercury exposure in a population in northwest Mexico, the allowed daily consumption of fish (which indicates the maximum daily amount of fish that can be consumed without causing adverse noncarcinogenic effects) was calculated for the general population (GP) and fishing-related population (FRP). The studied groups for both sectors of the population were children A (3-10 years old), children B (11-15 years old), women of childbearing age (16-40 years old), and the rest of the population (men ≥16 years old, and women ≥41 years old). Mercury content in canned and frozen tuna, smoked marlin, tilapia, Pacific sierra, dolphinfish, and bullseye puffer ranged from 0.01 to 0.23 µg/g wet weight; none of the values were above the limit set by Mexico. Regarding mercury concentrations and rates of fish consumption, the GP consumes 1.7-2.7 times the allowed daily consumption, and the FRP consumes 1.6-3.9 that limit. The risk analysis showed the children A and B groups from the GP and adults of FRP to be the highest percentage of the population at risk (approximately 35%). These results highlight the need for adequate strategies that consider mercury exposure as part of public health policies associated with fish consumption in Mexico.

Agrochemical loading in drains and rivers and its connection with pollution in coastal lagoons of the Mexican Pacific.

The state of Sinaloa in Mexico is an industrialized agricultural region with a documented pesticide usage of 700 t year-1; which at least 17 of the pesticides are classified as moderately to highly toxic. Pollutants in the water column of rivers and drains are of great concern because the water flows into coastal lagoons and nearshore waters and thereby affects aquatic organisms. This study was done in four municipalities in the state of Sinaloa that produce food intensively. To investigate the link between pollution in the lagoons and their proximity to agricultural sites, water was sampled in three coastal lagoons and in the rivers and drains that flow into them. Seawater from the Gulf of California, 10 km from the coast, was also analyzed. Concentrations of nutrients, organochlorines, and organophosphorus pesticides were determined. Nutrient determination showed an unhealthy environment with N/P ratios of <16, thus favoring nitrogen-fixing cyanobacteria. The organochlorine pesticides showed a clear accumulation in the coastal lagoons from the drains and rivers, with ΣHCH showing the highest concentrations. In the southern part of the region studied, pollution of the coastal lagoon of Pabellones could be traced mainly to the drains from the agricultural sites. Accumulation of OC pesticides was also observed in the Gulf of California. Tests for 22 organophosphates revealed only five (diazinon, disulfoton, methyl parathion, chlorpyrifos, and mevinphos); diazinon was detected at all the sites, although methyl parathion was present at some sites at concentrations one order of magnitude higher than diazinon.

Distribution of the deep-sea genus Bathypterois (Pisces: Ipnopidae) in the Eastern Central Pacific.

The genus Bathypterois (tripod fish) comprises 19 species of deep-sea fishes distributed worldwide. The biology and distribution of the species of this genus are relatively poorly known throughout the Eastern Central Pacific (ECP). This work aims to update the geographic and bathymetric distribution of species of Bathypterois throughout the ECP. To describe the influence of depth, temperature and dissolved oxygen concentrations (DO) on latitudinal and depth distribution of members of the genus throughout the Mexican Pacific, 51 specimens of B. atricolor (12 trawls) and 112 of B. ventralis (18 trawls), collected during TALUD project, were analyzed. Bathypterois atricolor had broader environmental niches (depth: 0.47, temperature: 0.46, DO: 0.39), and inhabits deeper and colder sites (Electivity positives: > 1 000 m, < 3.2 °C, 1.0-1.62 mL/L) than B. ventralis, which had narrow environmental niches (depth: 0.34, temperature: 0.32, DO: 0.28), with high affinity to warmer sites and lower DO concentrations (Electivity positives: 778-1 400 m, 3.3-5.8 °C, < 1.0 mL/L). Both species used different environmental strata (niche overlap; depth: 0.34, temperature: 0.32, DO: 0.28). The adaptation of B. atricolor to live in a broad range of DO concentrations explains its almost circumglobal distribution, while B. ventralis lives almost permanently in the Oxygen Minimum Zone (< 0.05 mL/L), so the DO could be a limiting factor, reducing its potential geographic and bathymetric distributions. None of these species had been previously recorded in the central Gulf of California, and B. ventralis had not been recorded along the West coast of Baja California. This study confirms that both species have a continuous distribution within the ECP, our new records extended the known northernmost range for B. atricolor by 886 km (from 22°46' N to 30°45' N) and for B. ventralis by 645 km (from 21°18' N to 27°07' N).

The white mullet (Mugil curema) as biological indicator to assess environmental stress in tropical coastal lagoons.

Several coastal lagoons and estuaries in Mexico receive untreated domestic and industrial discharges which contain complex mixtures of contaminants. In order to assess the effects of chemical contamination, we used the White mullet (Mugil curema) as biological indicator. We worked in two estuaries located in Northwest Mexico: Urias (highly polluted) and Teacapan (less polluted, therefore used as reference site). We measured several endpoints at different levels of biological organization: vitellogenin transcription in males as biomarker of estrogenic contamination, as well as reproductive, morphological (deformities), morphometric, and meristic parameters. Total RNA was isolated from the liver, and a partial sequence of the mullet vitellogenin gene was obtained; gene expression was analyzed by quantitative PCR. At the same time, gonad samples were analyzed by histologic techniques to determine sex ratios and the reproductive cycle stage. The reproductive season was detected from February to June in both sites, but the gonadosomatic index was consistently higher in Teacapan. Sex ratios were female-biased in both estuaries, and one intersex gonad and several malformations were found in fish from Urias. Vitellogenin gene transcription in males was detected in both sites, although gene expression was slightly higher in Urias. The results obtained in this study indicate that biological effects of contamination are evident in fish, environmental estrogens may be present in both estuaries, and the white mullet is useful as biological indicator to identify and characterize environmental stressors in tropical coastal ecosystems.

Field and experimental evidence of Vibrio parahaemolyticus as the causative agent of acute hepatopancreatic necrosis disease of cultured shrimp (Litopenaeus vannamei) in Northwestern Mexico.

Moribund shrimp affected by acute hepatopancreatic necrosis disease (AHPND) from farms in northwestern Mexico were sampled for bacteriological and histological analysis. Bacterial isolates were molecularly identified as Vibrio parahaemolyticus by the presence of the tlh gene. The tdh-negative, trh-negative, and tlh-positive V. parahaemolyticus strains were further characterized by repetitive extragenic palindromic element-PCR (rep-PCR), and primers AP1, AP2, AP3, and AP and an ems2 IQ2000 detection kit (GeneReach, Taiwan) were used in the diagnostic tests for AHPND. The V. parahaemolyticus strains were used in immersion challenges with shrimp, and farmed and challenged shrimp presented the same clinical and pathological symptoms: lethargy, empty gut, pale and aqueous hepatopancreas, and expanded chromatophores. Using histological analysis and bacterial density count, three stages of AHNPD (initial, acute, and terminal) were identified in the affected shrimp. The pathognomonic lesions indicating severe desquamation of tubular epithelial cells of the hepatopancreas were observed in both challenged and pond-infected shrimp. The results showed that different V. parahaemolyticus strains have different virulences; some of the less virulent strains do not induce 100% mortality, and mortality rates also rise more slowly than they do for the more virulent strains. The virulence of V. parahaemolyticus strains was dose dependent, where the threshold infective density was 10(4) CFU ml(-1); below that density, no mortality was observed. The AP3 primer set had the best sensitivity and specificity. Field and experimental results showed that the V. parahaemolyticus strain that causes AHPND acts as a primary pathogen for shrimp in Mexico compared with the V. parahaemolyticus strains reported to date.

Multi-and transgenerational synergistic effects of glyphosate and chlorpyrifos at environmentally relevant concentrations in the estuarine rotifer Proales similis.

We evaluated the multi-and transgenerational effects of single and combined environmentally relevant concentrations of glyphosate (GLY) and chlorpyrifos (CPF) in the estuarine rotifer Proales similis. The acute and chronic toxicities of GLY and CPF were determined as individual compounds and as a mixture. Rotifers were exposed to environmental concentrations of GLY (1, 10, 100, and 1000 µg/L) and CPF (0.1, 1, 5, and 10 µg/L). The main findings were as follows: (i) the LC50 values were 33.91 mg/L (GLY) and 280 µg/L (CPF); (ii) the toxic unit (TU50) of the mixture was 0.30, corresponding to 10.17 mg/L GLY and 83 µg/L CPF; (iii) the multigenerational study indicated that the tested concentrations of GLY and CPF, both single and combined, significantly and consistently decreased the growth rates of P. similis from the F0 to F6 generations; (iv) in most cases, GLY and CPF mixtures induced a strong synergistic effect; and (v) transgenerational effects were detected in the F4 generation, especially GLY and CPF in higher equitoxic proportions. These effects seem to dissipate in F5. Across multigeneration, a slight recovery could indicate population resilience to pollution. Our findings suggest that a mixture of GLY and CPF at environmental concentrations is likely to occur under real field conditions, increasing the risk to marine and estuarine invertebrates such as rotifers.

Micronuclei in embryos of eight seabird species in northwestern Mexico: A biomarker of exposure to coastal pollution?

The micronucleus (MN) test may be used to evaluate genome instability in birds and the potential of different species to function as biomarkers of genotoxicity. However, little is known regarding genome instability in seabird embryos or the instability present among embryonic development stages. Therefore, the present study aimed to describe the frequencies of micronucleated erythrocytes (MNE) and micronucleated polychromatic erythrocytes (MNPCE) in blood samples collected from the embryos of eight seabird species nesting on the coast of Sinaloa, Mexico. An additional description of blood cell maturation along with embryo development during incubation was conducted based on the proportion of polychromatic erythrocytes (PCE), and the potential relationships between metals (Hg and Cd concentrations in egg content) and the MN frequencies in embryo blood were evaluated. The PCE proportion appears to decline as incubation advances (initial stage > intermediate stage > advanced stage), and the values varied between species (Suliformes/Pelecaniformes < Charadriiformes: Laridae), which may be related to differences among incubation periods and reproductive strategies. Interspecific variation in the MNPCE frequency was found in embryos showing advanced development, which could be related to both variations in life-history traits and ecological factors and not Hg or Cd exposure. The genomic instability values in this study are the first to be reported for embryos of seabird species nesting in a subtropical coastal region.

Distribution of pesticides and PCBs in sediments of agricultural drains in the Culiacan Valley, Sinaloa, Mexico.

Agriculture is one of the most important economic activities in Sinaloa, Mexico. The Culiacan Valley is an extensive agricultural region characterized by a variety of crops with high-yield productions. In this study, concentrations of organochlorine (OCPs) and organophosphorus (OPs) pesticides and polychlorobiphenyls (PCBs) were determined in sediments of the agricultural drainage system of Culiacan Valley. Overall, 32 compounds were detected, with concentrations widely ranging from 0.03 to 1 294 ng g(-1) dry weight. OCP concentrations (15) ranged from 0.1 to 20.19 ng g(-1) dw. OP concentrations (8) ranged from 0.03 to 1294 ng g(-1) dw, and diazinon was the compound with the highest concentration. PCB concentrations were also determined and varied from 0.05 to 3.29 ng g(-1) dw. Other compounds detected included permethrin, triadimefon, and fipronil. The central zone registered the higher concentrations and the greatest number of compounds, which could be related to the occurrence of horticultural fields in this zone. According to sediment quality guidelines, the compounds exceeding the probable effect level were γ-HCH, p,p'-DDT and p,p'-DDE, while the pesticides above the maximum permissible concentration were endosulfan, azinphos methyl, diazinon, dichlorvos, and permethrin. Although Sinaloa is an important agricultural crop producer in northwest Mexico, there are not many studies dealing with pesticide distribution in agricultural areas.

Epigenetic Transgenerational Modifications Induced by Xenobiotic Exposure in Zebrafish.

Zebrafish (Danio rerio) is a well-established vertebrate model in ecotoxicology research that responds to a wide range of xenobiotics such as pesticides, drugs, and endocrine-disrupting compounds. The epigenome can interact with the environment and transform internal and/or external signals into phenotypic responses through changes in gene transcription. Environmental exposures can also generate epigenetic variations in offspring even by indirect exposure. In this review, we address the advantages of using zebrafish as an experimental animal model to study transgenerational epigenetic processes upon exposure to xenobiotics. We focused mostly on DNA methylation, although studies on post-translational modifications of histones, and non-coding RNAs related to xenobiotic exposure in zebrafish are also discussed. A revision of the methods used to study epigenetic changes in zebrafish revealed the relevance and reproducibility for epigenetics-related research. PubMed and Google Scholar databases were consulted for original research articles published from 2013 to date, by using six keywords: zebrafish, epigenetics, exposure, parental, transgenerational, and F2. From 499 articles identified, 92 were considered, of which 14 were selected as included F2 and epigenetic mechanisms. Current knowledge regarding the effect of xenobiotics on DNA methylation, histone modifications, and changes in non-coding RNAs expressed in F2 is summarized, along with key experimental design considerations to characterize transgenerational effects.

Changes in microtubule stability in zebrafish (Danio rerio) embryos after glyphosate exposure.

Glyphosate, the most commonly used pesticide worldwide, blocks aromatic amino acid biosynthetic pathways and inhibits growth in plants. Although the specific mode of action of glyphosate in animals remains unclear, adverse effects during embryonic development have been reported, including epiboly delays, morphological alterations, and changes in central nervous system development and cardiogenesis. In this study, we suggest a possible toxicity mechanism for this herbicide related to changes in microtubule stability, which could alter the distribution and dynamics of cytoskeleton components. Using zebrafish embryos to evaluate in vivo effects of glyphosate exposure (5, 10, and 50 µg/ml), we found significant reductions in the levels of acetylated α-tubulin (50 µg/ml) and in the polymeric tubulin percentage in zebrafish embryos that had been exposed to 10 and 50 µg/ml glyphosate, without any changes in either the expression patterns of α-tubulin or the stability of actin filaments. These results indicate that high concentrations of glyphosate were associated with reduced levels of acetylated α-tubulin and altered microtubule stability, which may explain some of the neurotoxic and cardiotoxic effects that have been attributed to this herbicide.

Short exposure to glyphosate induces locomotor, craniofacial, and bone disorders in zebrafish (Danio rerio) embryos.

Glyphosate [N-(phosphonomethyl)glycine] is the active ingredient in widely used broad-spectrum herbicides. Even though the toxicity mechanism of this herbicide in vertebrates is poorly understood, evidence suggests that glyphosate is an endocrine disruptor capable of producing morphological anomalies as well as cardiotoxic and neurotoxic effects. We used the zebrafish model to assess the effects of early life glyphosate exposure on the development of cartilage and bone tissues and organismal responses. We found functional alterations, including a reduction in the cardiac rate, significant changes in the spontaneous tail movement pattern, and defects in craniofacial development. These effects were concomitant with alterations in the level of the estrogen receptor alpha osteopontin and bone sialoprotein. We also found that embryos exposed to glyphosate presented spine deformities as adults. These developmental alterations are likely induced by changes in protein levels related to bone and cartilage formation.