The influences of spatial-temporal variability and ecological drivers on microplastic in marine fish in Hong Kong

This study examined microplastic (MP) occurrence and abundance in marine fish collected from the western and eastern waters of Hong Kong during the wet and dry seasons. Over half (57.1%) of the fish had MP in their gastrointestinal (GI) tracts, with overall MP abundance ranging from not detected to 44.0 items per individual. Statistical analysis revealed significant spatial and temporal differences in MP occurrence, with fish from more polluted areas having a higher likelihood of MP ingestion. Additionally, fish collected in the west during the wet season had significantly higher MP abundance, likely due to influence from the Pearl River Estuary. Omnivorous fish had significantly higher MP counts than carnivorous fish, regardless of collection location or time. Body length and weight were not significant predictors of MP occurrence or abundance. Our study identified several ecological drivers that affect MP ingestion by fish, including spatial-temporal variation, feeding mode, and feeding range. These findings provide a foundation for future research to investigate the relative importance of these factors in governing MP ingestion by fish in different ecosystems and species.

Microplastics pollution in the rivers of a metropolitan city and its estimated dependency on surrounding developed land

The spatial distribution and abundance of suspected microplastics (SMPs) in the surface water of a metropolitan city, as represented by four Hong Kong rivers, was studied during the dry season. Shing Mun River (SM), Lam Tsuen River (LT), and Tuen Mun River (TM) are located in urbanized areas, and SM and TM are tidal rivers. The fourth river, Silver River (SR) is situated in a rural area. TM had a significantly higher SMP abundance (53.80 ± 20.67 n/L) than the other rivers. The SMP abundance increased from upstream to downstream in non-tidal rivers (LT and SR), but not in tidal rivers (TM and SM), probably due to the tidal influence and a more homogeneous urban development along the tidal rivers. Inter-site differences in the SMP abundance were strongly correlated with the built area ratio (defined as the percentage of surrounding developed land area), human activities, and the nature of the river. About half (48.72 %) of the SMPs were <250 μm. Fibers and fragments were most abundant (>98 %), with most of them being transparent (58.54 %), black (14.68 %), or blue (12.12 %). Polyethylene terephthalate (26.96 %) and polyethylene (20.70 %) were the most common polymers. However, the MP abundance could be overestimated due to the presence of natural fibers. By contrast, an underestimation of the MP abundance could result from a smaller volume of water samples collected, due to a low filtration efficiency caused by high organic content and particle concentrations in the water. A more effective solid waste management strategy and upgrading of the sewage treatment facilities for removing microplastics are recommended to ameliorate the microplastic pollution in local rivers.

A short review on the recent method development for extraction and identification of microplastics in mussels and fish, two major groups of seafood

The prevalence of microplastics in the marine environment poses potential health risks to humans through seafood consumption. Relevant data are available but the diverse analytical approaches adopted to characterise microplastics have hampered data comparison among studies. Here, the techniques for extraction and identification of microplastics are summarised among studies of marine mussels and fish, two major groups of seafood. Among the reviewed papers published in 2018-2021, the most common practice to extract microplastics was through tissue digestion in alkaline chemicals (46 % for mussels, 56 % for fish) and oxidative chemicals (28 % for mussels, 12 % for fish). High-density solutions such as sodium chloride could be used to isolate microplastics from other undigested residues by flotation. Polymer analysis of microplastics was mainly carried out with Fourier-transform infrared (FTIR) spectroscopy (58 % for both mussels and fish) and Raman spectroscopy (14 % for mussels, 8 % for fish). Among these methods, we recommend alkaline digestion for microplastic extraction, and the automated mapping approach of FTIR or Raman spectroscopy for microplastic identification. Overall, this study highlights the need for a standard protocol for characterising microplastics in seafood samples.

Macroalgal morphology mediates microplastic accumulation on thallus and in sediments

The accumulation process of microplastics (MPs) is a key to understanding their fate in the environment. However, there is limited information about the short-term accumulation of MPs on macrophytes. The ability of macrophyte to attenuate wave and reduce current velocity is potentially facilitating MPs deposition. We hypothesize that the macroalgae retain MPs with their morphologies (filamentous and non-filamentous) being one of the factors to govern retention. Our hypothesis was tested by field observation during the dry season in Hong Kong when the macroalgae communities were the most diverse. MPs per biomass, surface area, or interstitial volume were used to represent the abundances on macroalgae. We found that filamentous algae retained a 2.35 times higher number of MPs when compared with non-filamentous algae if unit per biomass was considered. Other units, however, showed insignificant differences in MPs abundances between algal morphologies. Fibre was the most dominant shape of MPs with no significant difference in their abundances between filamentous and non-filamentous algae, suggesting fibres were retained regardless of the algal morphologies. To further evaluate the potential accumulation in the environment, sediment samples were also collected under the algal mat and immediate vicinity (~50 cm) of the algal mat. We found that sediment collected under the vegetated area contained significantly higher MPs. This was 3.39 times higher than the unvegetated area. Sediment collected under/near filamentous algae retained much higher abundances of MPs than those of non-filamentous algae. Provided that the observed retention of MPs on macroalgae, we speculate macrophyte system is one of the short-term MPs accumulation hotspots where the temporal increase of MPs depends on the seasonality of macrophyte in a given region.

Fate and Effects of Macro- and Microplastics in Coastal Wetlands

Coastal wetlands trap plastics from terrestrial and marine sources, but the stocks of plastics and their impacts on coastal wetlands are poorly known. We evaluated the stocks, fate, and biological and biogeochemical effects of plastics in coastal wetlands with plastic abundance data from 112 studies. The representative abundance of plastics that occurs in coastal wetland sediments and is ingested by marine animals reaches 156.7 and 98.3 items kg^-1, respectively, 200 times higher than that (0.43 items kg^-1) in the water column. Plastics are more abundant in mangrove forests and tidal marshes than in tidal flats and seagrass meadows. The variation in plastic abundance is related to climatic and geographic zones, seasons, and population density or plastic waste management. The abundance of plastics ingested by pelagic and demersal fish increases with fish length and dry weight. The dominant characteristics of plastics ingested by marine animals are correlated with those found in coastal wetland sediments. Microplastics exert negative effects on biota abundance and mangrove survival but positive effects on sediment nutrients, leaf drop, and carbon emission. We highlight that plastic pollution is widespread in coastal wetlands and actions are urged to include microplastics in ecosystem health and degradation assessment.

Bisphenol A and its analogues in sedimentary microplastics of Hong Kong

The occurrence and spatial distribution of bisphenol A (BPA) and analogues bisphenol B (BPB), bisphenol F (BPF) and bisphenol S (BPS) were investigated in microplastic on 11 beaches in Hong Kong. At 10 sites, BPA was the only detected chemical with concentrations ranged from 82.4-989 ng g^-1 microplastic. BPA, BPB and BPS co-occurred at only one site, where it is located close proximity to the outfall of a sewage treatment plant. There was no significant spatial difference of BPA concentrations in microplastic when all the sites were considered, indicating that some remote and presumably cleaner beaches have been contaminated. PE, PP and PS (represented >90% of total polymers) were the most dominated polymers, but there was no correlation between polymer types and BPA concentrations. No evidence was found that the BPA and its analogues accumulate on microplastic since the concentrations were comparable to those found in the sediment.

Effects of rubble zones from oyster cultivation on habitat utilization and foraging behaviour of the endangered tri-spine horseshoe crab: An implication for intertidal oyster cultivation practices

Estuarine structured habitats, including benthic cultivation structure, are widely cited as substantial nursery and feeding grounds for fish and macroinvertebrates. Activities such as locomotion and foraging behaviour of sediment-dwelling species, however, may be hindered in the presence of the obstacles. In this study, collected field evidence demonstrated that habitat utilization of the juvenile tri-spine horseshoe crab Tachypleus tridentatus, an iconic and endangered macroinvertebrate, was adversely affected by high-density intertidal oyster rubble zones. Despite the fact that the utilization area of individual juvenile horseshoe crabs was independent of the presence of these obstacles, the abundance and number of positional fixes of tagged juveniles in these areas were lower. The effects of these obstacles and their associated topographic changes on the movement of the juvenile horseshoe crabs was investigated in a simulated laboratory experiment. Both the simulated oyster cultches and hummocks formed between the cultches reduced the total distance and displacement of the feeding trail, and less juveniles preferred to forage on elevated, dry hummocks (dry at low tide) formed between the cultches. Our findings suggested that oyster cultches and rubbles reduced the habitat quality for juvenile horseshoe crabs. On-bottom oyster cultivation activities seeking to conserve horseshoe cabs by avoiding nursery habitats should instead consider off-bottom or offshore cultivation methods.

Microplastic ingestion reduces energy intake in the clam Atactodea striata

The effects of microplastic concentrations (10itemsl^-1 and 1000itemsl^-1) on the physiological responses of Atactodea striata (clearance rate, absorption efficiency, respiration rate) were investigated. The fates of ingested microplastics and the efficiency of depuration in removing ingested microplastics were also studied. A. striata ingested microplastics and the clearance rate was reduced at high concentration of microplastics. Since the respiration rate and absorption efficiency remained unchanged in exposed A. striata, reduction in the clearance rate would reduce the energy intake. Ingestion and retention of microplastics in the body were further limited by the production of pseudofaeces and faeces, and depuration in clean water, resulting in a very small amount of microplastics stored in the body of the clam.

Identification of F. o. cucumerinum and F. o. luffae by RAPD-generated DNA probes

AIMS

To create a fast, sensitive and specific method for identifying Fusarium oxysporum f. sp. cucumerinum and F. o. luffae.

METHODS AND RESULTS

Specific DNA bands were selected as probes from RAPD profiles of 13 formae speciales of F. oxysporum. The forma specialis-specific probe OPC18300c and OPC18520f could be used to identify F. o. cucumerinum and F. o. luffae by RAPD-PCR followed dot blot hybridization, respectively.

CONCLUSIONS

A specific method for identifying F. o. cucumerinum and F. o. luffae was achieved.

SIGNIFICANCE AND IMPACT OF THE STUDY

F. oxysporum formae speciales identification with a DNA probe can be relatively rapid and provides a method to identify the pathogen without host inoculation tests.

Genetic polymorphism and Parkinson's disease in Taiwan: study of debrisoquine 4-hydroxylase (CYP2D6)

Debrisoquine 4-hydroxylase (CYP2D6) is one of the cytochrome P450 enzyme families that catalyze the breakdown of a variety of exogenous and endogenous compounds. Previous reports have suggested that genetic polymorphisms of debrisoquine 4-hydroxylase are associated with susceptibility to Parkinson's disease (PD) in Caucasians. To determine if CYP2D6 also confers susceptibility to PD in Chinese patients, we carried out a study of genetic association using three polymorphic markers of the CYP2D6 gene, 188C/T, 1934G/A (mutant B), and 4268G/C. No differences of allele or genotype frequencies of these three polymorphisms were detected upon comparison of primary PD patients (n=53) with normal controls (n=94). The 1934A allele (mutant B), which accounts for the majority of poor metabolizers in Caucasians, is extremely rare in Chinese. Our data do not support the suggestion that the CYP2D6 gene is related to PD susceptibility in Chinese.

Associations among PH and SH3 domain-containing proteins and Rho-type GTPases in Yeast

The src homology region 3 (SH3) domain-bearing protein Bem1p and the Rho-type GTPase Cdc42p are important for bud emergence in Saccharomyces cervisiae. Here, we present evidence that through its second SH3 domain, Bem1p binds to the structurally and functionally similar proteins Boi1p and Boi2p, each of which contain an SH3 and pleckstrin homology (PH) domain. Deletion of BOI1 and BO12 together leads to impaired morphogenesis and poor ability. A PH domain-bearing segment of Boi1p that lacks the Bem1p-binding site is necessary and sufficient for function. This segment of Boi1p displays a two-hybrid interaction with Cdc42p, suggesting that Boi1p either binds directly to or is part of a larger complex that contains Cdc42p. Consistent with these possibilities, overexpression of Boi1p inhibits bud emergence, but this inhibition is counteracted by cooverexpression of Cdc42p. Increased expression of the Rho-type GTPase Rho3p, which is implicated in bud growth defects of boil boi2 mutants, suggesting that Boi1p and Boi2p may also play roles in the activation or function of Rho3p. These findings provide an example of a tight coupling in function between PH domain-bearing proteins and both Rho-type GTPases and SH3 domain-containing proteins, and they raise the possibility that Boi1p and Boi2 play a role in linking the actions of Cdc42p and Rho3p.

Pentatrichomonas hominis: purine salvage pathway

1. Pentatrichomonas hominis was found incapable of de novo synthesis of purines. 2. Pentatrichomonas hominis can salvage adenine, guanine, hypoxanthine, adenosine, guanosine and inosine, but not xanthine for the synthesis of nucleotides. 3. HPLC tracing of radiolabelled purines or purine nucleosides revealed that adenine, adenosine and hypoxanthine are incorporated into adenine nucleotides and IMP through a similar channel while guanine and guanosine are salvaged into guanine nucleotides via another route. There appears to be no direct interconversion between adenine and guanine nucleotides. Interconversion between AMP and IMP was observed. 4. Assays of purine salvage enzymes revealed that P. hominis possess adenosine kinase; adenosine, guanosine and inosine phosphotransferases; adenosine, guanosine and inosine phosphorylases and AMP deaminase.

Persistence of hepatitis B viral antigens in Culex quinquefasciatus

Culex quinquefasciatus mosquitoes were fed on or inoculated with blood or serum positive for hepatitis B viral antigens and pools of mosquitoes were tested by radioimmunoassay daily for 3 weeks after exposure to detect the viral antigens. Hepatitis B surface antigen (HBsAg) was detectable up to 3 weeks, while hepatitis B e antigen (HBeAg) persisted only for 3 days in mosquitoes after feeding on hepatitis B viral antigens-positive blood. Mosquitoes inoculated with serum were HBsAg-positive for 3 weeks and HBeAg positive for 4 days after inoculation. These results suggest that biological multiplication of hepatitis B virus did not occur in these mosquitoes. The possibility of mechanical transmission of hepatitis B antigens by mosquitoes is discussed.

Purine salvage in Entamoeba histolytica

Pulse-labeling of the nucleotide pool in Entamoeba histolytica with radioactive precursors, and subsequent high performance liquid chromatographic (HPLC) analysis of the radiolabeled nucleotides, indicate that E. histolytica is incapable of de novo synthesis of purine nucleotides. Hypoxanthine, inosine and xanthine could not be converted to nucleotides in E. histolytica, which suggests the absence of interconversion between adenine nucleotides and guanine nucleotides through formation of IMP. Adenosine was actively incorporated into nucleotides at an initial rate of 130 pmoles per minute per 10(6) trophozoites. Adenine, guanosine and guanine were also incorporated at much lower rates. The rate of adenine incorporation was enhanced by the presence of guanosine; the rate of guanine incorporation was significantly increased by adenosine. These stimulatory effects suggest that the ribose moiety of adenosine or guanosine can be transferred to another purine base to form a new nucleoside, and that the purine nucleosides are the immediate precursors of E. histolytica nucleotides. HPLC results showed that the radiolabel in adenine was exclusively incorporated into adenine nucleotides and that guanine was found only among guanine nucleotides, whereas the radioactivity associated with the ribose moiety of adenosine or guanosine was distributed among both adenine and guanine nucleotides.

Purification and properties of NADP-linked, alcohol dehydrogenase from Entamoeba histolytica

An NADP-linked, alcohol dehydrogenase from Entamoeba histolytica was purified to apparent homogeneity by Blue Sepharose affinity chromatography. Molecular weights of 130,000 and 30,000 were estimated by gel filtration and by sodium dodecyl sulfate polyacrylamide gel electrophoresis, respectively, suggesting that the enzyme is a tetramer. The enzyme exhibited more than 20-fold selectivity for NADP(H) over NAD(H). Although the purified enzyme acts on both primary and secondary alcohols, higher activity was found with secondary alcohols.

Glucose dissimilation in Entamoeba histolytica

The endproducts of glucose dissimilation in Entamoeba histolytica were found to be carbon dioxide, acetate and ethanol. This organism possesses the same Embden-Meyerhof intermediates as found in most investigated organisms. In its glucose-to-pyruvate pathway several unusual features were demonstrated. The pyruvate-to-acetate and pyruvate-to-ethanol pathways are also unique as compared with that of other organisms. The distinctive properties of the metabolic enzymes provide the basis for the development of new chemotherapeutic agents against this parasitic protozoa.

[Trichomonas hominis: isolation and axenic cultivation (author's transl)]

Recently we have isolated Trichomonas hominis from diarrheic stools of a patient and established it in an axenic culture medium. The procedures are as follows: Diarrheic stool containing numerous trophozoites was first inoculated into the TYM (Trypticase Yeast extract Maltose) medium of Diamond (1975) to establish a polyxenic culture. Antibiotics, containing penicillin (1000 U/ml), streptomycin (1000 micrograms/ml), and cephalosporin (20 micrograms/ml) were added to prevent overgrowth of bacteria and fungi. After several passages, a specially-designed culture-tube was employed to separate T. hominis from the contaminants. The isolated T. hominis was then introduced into the modified TYI-S-33 (Trypticase Yeast extract Iron-Serum-33) medium of Diamond (1978). The organism established itself readily to this axenic culture medium. Sterility tests employing fluid thioglycollate, nutrient broth, and blood agar plate gave negative results indicating the absence of contaminants. The axenic culture of T. hominis provides us with a source of pure flagellates for biological, biochemical, and immunological studies.

Serum gangliosides in cerebral astrocytoma

The serum concentration and composition of gangliosides were examined in 80 humans including 10 normal subjects. A significant increase was found in the total gangliosides of serum in 7 patients with cerebral astrocytomas. There was also an increased percentage of serum gangliosides with simpler structure, particularly GM3. The serum of patients with other intracranial tumors, including pituitary adenomas, ependymoma, teratoma, and metastases, did not show an increase in total ganglioside; however the pattern of simplification was found in these and in a few patients with extracranial tumors as well. The findings suggest that astrocytoma tumors shed sialoglycolipids into the circulation, and their assay may be useful in monitoring oncological therapy.

Riboflavin requirement for the cultivation of axenic Entamoeba histolytica

Riboflavin was found to be essential for the cultivation of axenic Entamoeba histolytica. This is the first demonstration of a flavin requirement by the organism. Panmede, the principal source of flavins in the axenic medium, was treated with activated carbon to remove flavins. Medium made with this flavin-deficient Panmede, and supplemented with ribonucleic acid failed to support the multiplication of amebae in serial subculture, but did so when riboflavin was added. The concentration of riboflavin required to achieve maximal growth was about 1.3 microgram per ml medium. Studies on riboflavin uptake revealed that amebae lack a high-affinity transport system for this vitamin. The rate of riboflavin uptake was equivalent to the rate of pinocytotic uptake of fluid as previously determined.

Pyruvate-to-ethanol pathway in Entamoeba histolytica

The pyruvate-to-ethanol pathway in Entamoeba histolytica is unusual when compared with most investigated organisms. Pyruvate decarboxylase (EC 4.1.1.1), a key enzyme for ethanol production, is not found. Pyruvate is converted into acetyl-CoA and CO2 by the enzyme pyruvate synthase (EC 1.2.7.1), which has been demonstrated previously in this parasitic amoeba. Acetyl-CoA is reduced to acetaldehyde and CoA by the enzyme aldehyde dehydrogenase (acylating) (EC 1.2.1.10) at an enzyme activity of 9 units per g of fresh cells with NADH as a reductant. Acetaldehyde is further reduced by either a previously identified NADP+-linked alcohol dehydrogenase or by a newly found NAD+-linked alcohol dehydrogenase at an enzyme activity of 136 units per g of fresh cells. Ethanol is identified as the product of soluble enzymes of amoeba acting on pyruvate or acetyl-CoA. This result is confirmed by radioactive isotopic, spectrophotometric and gas-chromatographic methods.

An energy-conserving pyruvate-to-acetate pathway in Entamoeba histolytica. Pyruvate synthase and a new acetate thiokinase

Under anaerobic conditions, cells of Entamoeba histolytica grown with bacteria produce H2 and acetate while cells grown axenically produce neither. Aerobically, acetate is produced and O2 is consumed by amebae from either type of cells. Centrifuged extracts, 2.4 x 106 x g x min, from both types of cells contain pyruvate synthase (EC 1.2.7.1) and an acetate thiokinase which, together, form a system capable of converting pyruvate to acetate. Pyruvate synthase catalyzes the reaction: pyruvate + CoA leads to CO2 + acetyl-CoA + 2E. Electron acceptors which function with this enzyme are FAD, FMN, riboflavin, ferredoxin, and methyl viologen, but not NAD or NADP. The amebal acetate thiokinase catalyzes the reaction acetyl-CoA + ADP + Pi leads to acetate + ATP + CoA. For this apparently new enzyme we suggest the trivial name acetyl-CoA-synthetase (ADP-forming). Extracts from axenic amebae do not contain hydrogenase, but extracts from cells grown with bacteria do. It is postulated that in bacteria-grown amebae electrons generated at the pyruvate synthase step are utilized anaerobically to produce H2 via the hydrogenase and that the acetyl-CoA is converted to acetate in an energy-conserving step catalyzed by amebal acetyl-CoA synthetase. Aerobically, cells grown under either regimen may utilize the energy-conserving pyruvate-to-acetate pathway since O2 then serves as the ultimate electron acceptor.

Identification of Chromobacterium violaceum: pigmented and non-pigmented strains

The classification and, therefore, identification of Chromobacterium violaceum has been based upon its ability to produce a violet pigment. Although the organism may yield non-pigmented variants when subcultured on artificial media, the isolation of non-pigmented strains from pathological tissues or from nature had not been reported. With a method established for the identification of C. violaceum regardless of violet pigmentation, non-pigmented strains were isolated from nature. The presence of non-pigmented strains of C. violaceum in nature is of significance to taxonomy and clinical bacteriology. Pigmentation cannot be held as an essential characteristic of the definition of the genus Chromobacterium and gives credence to the suspicion of Sneath (1960, 1966) that the genus is not a natural one. Non-pigmented strains may have been isolated from clinical material but wrongly identified as belonging to other genera of non-pigmented Gram-negative bacilli and regarded as not being pathogenic.