Black spot gill syndrome in the northern shrimp, Pandalus borealis, caused by the parasitic ciliate Synophrya sp.

Black spot gill syndrome in the northern shrimp, Pandalus borealis, is caused by an apostome ciliate, Synophrya sp., found within the gill lamellae. Whole mount staining, thin section histology, electron microscopy, and molecular studies were carried out on infected gills. The Synophrya 18S rRNA from Pandalus borealis (Genbank accession no. KX906568) and from two portunid crab species, Achelous spinimanus (Genbank accession no. MH395150) and Achelous gibbesii (Genbank accession no. MH395151) was sequenced. Phylogenetic analyses confirmed the identity of these ciliates as apostomes. The 18S rRNA sequence recovered from P. borealis shared 95% nucleotide similarity with the sequences recovered from the portunid crab species suggesting that it is a different species of Synophrya. The invasive hypertrophont stages, with a distinctive macronuclear reticulum, ranged in size from 300 to 400 µm with as many as 5 large forms/mm2 of gill tissue. Histotrophic hypertrophont stages and hypertomont stages were observed in these studies. The presence of the parasite was linked to the formation of melanized nodules (up to 9 nodules/mm2 of gill tissue) by the host and in some cases to extensive necrosis. Other studies have reported Synophrya sp. infections in P. borealis from Greenland, Labrador and Newfoundland, but further studies are necessary to determine the prevalence of this parasite in the dense schools of northern shrimp in the North Atlantic. Questions remain as to the possibility of epizootics of this pathogen and its impact on northern shrimp populations.

Long-Term Field Evaluation Reveals Huanglongbing Resistance in Citrus Relatives.

Citrus huanglongbing (HLB) is a destructive disease with no known cure. To identify sources of HLB resistance in the subfamily Aurantioideae to which citrus belongs, we conducted a six-year field trial under natural disease challenge conditions in an HLB endemic region. The study included 65 Citrus accessions and 33 accessions belonging to 20 other closely related genera. For each accession, eight seedling trees were evaluated. Based on quantitative polymerase chain reaction analysis of the pathogen titers and disease symptoms, eight disease-response categories were identified. We report two immune, six resistant, and 14 tolerant accessions. Resistance and tolerance observed in different accessions may be attributed to a multitude of factors, including psyllid colonization ability, absence of pathogen multiplication, transient replication of the bacterium, lack of pathogen establishment in the plant, delayed infection, or recovery from infection. Most citrus cultivars were considered susceptible: 15 citrons, lemons, and limes retained leaves in spite of the disease status. Resistance and high levels of field tolerance were observed in many noncitrus genera. Disease resistance/tolerance was observed in Australian citrus relative genera Eremocitrus and Microcitrus, which are sexually compatible with citrus and may be useful in future breeding trials to impart HLB resistance to cultivated citrus.

Huanglongbing: An overview of a complex pathosystem ravaging the world's citrus.

Citrus huanglongbing (HLB) has become a major disease and limiting factor of production in citrus areas that have become infected. The destruction to the affected citrus industries has resulted in a tremendous increase to support research that in return has resulted in significant information on both applied and basic knowledge concerning this important disease to the global citrus industry. Recent research indicates the relationship between citrus and the causal agent of HLB is shaped by multiple elements, in which host defense responses may also play an important role. This review is intended to provide an overview of the importance of HLB to a wider audience of plant biologists. Recent advances on host-pathogen interactions, population genetics and vectoring of the causal agent are discussed.

Detection of citrus huanglongbing-associated 'Candidatus Liberibacter asiaticus' in citrus and Diaphorina citri in Pakistan, seasonal variability, and implications for disease management.

We report the detection of the huanglongbing (HLB)-associated bacterium 'Candidatus Liberibacter asiaticus' from both plants and insects in Pakistan and the seasonal variability in the numbers of 'Ca. L. asiaticus'-positive psyllid vector, Diaphorina citri. Our studies showed that 'Ca. L. asiaticus' was detectable from trees in areas with maximum temperatures reaching nearly 50°C (average maximum of 42°C). However, the bacterium was present at very low levels in psyllids both in summer (June to August) and autumn (September to November) in contrast to reports from Florida, where the bacterium was detectable at very high levels during October to November. We hypothesize that hot summer temperatures in Pakistan may interfere with acquisition and replication of 'Ca. L. asiaticus' in psyllids and may lead to dead or non transmissible 'Ca. L. asiaticus' in plants. Psyllid counts were very low in both summer and winter, showed a population peak ('Ca. L. asiaticus'-positive vectors) in spring, and showed a larger peak ('Ca. L. asiaticus'-free psyllids) in autumn. Natural thermotherapy during hot summers and a low vector population during environmental extremes may have played a major role in long-term survival of the citrus industry in Pakistan. These results may be useful in developing management strategies for U.S. citrus industries in Texas and California.

Methylation of mercury and tin by estuarine microbial mats.

After tin and mercury salts were added to estuarine microbial mats increasing amounts of methyltin and methylmercury, respectively, were formed over a 30 to 100 hour time period. Inhibition of the methylation by molybdate, a metabolic inhibitor of sulfate reduction, stimulation by pyruvate addition and lack of methylation by sterilized mats, were evidence that sulfate reducing bacteria within the mats were responsible for the tin and mercury methylation. Methyl mercury was formed from mercuric chloride and mercuric cysteine, but not from mercuric sulfide. We suggest that mercury bound to organic complexes in anoxic sediments is likely methylated by microbial mats. Since estuarine meiofauna and macrofauna fed on microbial mats, the methylmercury and methyltin formed by microbial mats could be an important avenue for the entrance of these compounds into the marine food web.

Effects of insecticides on behavior of adult Bactericera cockerelli (Hemiptera: Triozidae) and transmission of Candidatus Liberibacter psyllaurous.

The potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), is a serious pest of potatoes (Solanum tuberosum L.) that can cause yield loss by direct feeding on crop plants and by vectoring a bacterial pathogen, Candidatus Liberibacer psyllaurous. Current pest management practices rely on the use of insecticides to control the potato psyllid to lower disease incidences and increase yields. Although many studies have focused on the mortality that insecticides can cause on potato psyllid populations, little is known regarding the behavioral responses of the potato psyllid to insecticides or whether insecticides can decrease pathogen transmission. Thus, the objectives of this study were to determine the effects of insecticides on adult potato psyllid behaviors, the residual effects of insecticides on potato psyllid behaviors over time, and effects of these insecticides on Ca. L. psyllaurous transmission. Insecticides tested included imidacloprid, kaolin particle film, horticultural spray oil, abamectin, and pymetrozine. All insecticides significantly reduced probing durations and increased the amount of time adult psyllids spent off the leaflets, suggesting that these chemicals may be deterrents to feeding as well as repellents. Nonfeeding behaviors such as tasting, resting, and cleaning showed variable relationships with the different insecticide treatments over time. The insecticides imidacloprid and abamectin significantly lowered transmission of Ca. L. psyllaurous compared with untreated controls. The implications of our results for the selection of insecticides useful for an integrated pest management program for potato psyllid control are discussed.

An Improved Reference Gene for Detection of "Candidatus Liberibacter asiaticus" Associated with Citrus Huanglongbing by qPCR and Digital Droplet PCR Assays.

Citrus huanglongbing (HLB) disease associated with the 'Candidatus Liberibacter asiaticus' (CLas) bacterium has caused significant financial damage to many citrus industries. Large-scale pathogen surveys are routinely conducted in California to detect CLas early in the disease cycle by lab-based qPCR assays. We have developed an improved reference gene for the sensitive detection of CLas from plants in diagnostic duplex qPCR and analytical digital droplet PCR (ddPCR) assays. The mitochondrial cytochrome oxidase gene (COX), widely used as a reference, is not ideal because its high copy number can inhibit amplification of small quantities of target genes. In ddPCRs, oversaturation of droplets complicates data normalization and quantification. The variable copy numbers of COX gene in metabolically active young tissue, greenhouse plants, and citrus relatives suggest the need for a non-variable, nuclear, low copy, universal reference gene for analysis of HLB hosts. The single-copy nuclear gene, malate dehydrogenase (MDH), developed here as a reference gene, is amenable to data normalization, suitable for duplex qPCR and ddPCR assays. The sequence of MDH fragment selected is conserved in most HLB hosts in the taxonomic group Aurantioideae. This study emphasizes the need to develop standard guidelines for reference genes in DNA-based PCR assays.

Hyalophysa lynni n. sp. (Ciliophora, Apostomatida), a new pathogenic ciliate and causative agent of shrimp black gill in penaeid shrimp.

The parasitic ciliate causing shrimp black gill (sBG) infections in penaeid shrimp has been identified. The sBG ciliate has a unique life cycle that includes an encysted divisional stage on the host's gills. The ciliature of the encysted trophont stage has been determined and is quite similar to that of the closely related apostomes Hyalophysa bradburyae and H. chattoni. Hyalophysa bradburyae is a commensal ciliate associated with freshwater caridean shrimp and crayfish, while H. chattoni is a common commensal found on North American marine decapods. Based on 18S rRNA gene sequence comparisons, the sBG ciliate is more closely related to the marine species H. chattoni than to the freshwater species H. bradburyae. The unique life cycle, morphology, 18S rRNA gene sequence, hosts, location, and pathology of the sBG ciliate distinguish this organism as a new species, Hyalophysa lynni n. sp.

Transmission of the parasitic dinoflagellate Hematodinium sp. infection in blue crabs Callinectes sapidus by cannibalism.

Infection with the parasitic dinoflagellate Hematodinium sp. can be devastating to blue crab Callinectes sapidus populations. Morbidity and mortality appear to depend on the burden of parasitic organisms. Heavily infected crabs become lethargic and, if not preyed upon, succumb to overwhelming infection. We report on the transmission of Hematodinium sp. into blue crabs that were fed pieces of infected tissues and examined for evidence of infection at time periods from 1 to 48 h and for the general state of their health after 4 d. During the first 16 h after feeding, Hematodinium sp. was found in the gut, followed by large increases in hemolymph hemocytes and the appearance of hemocytic nodules in tissues. By 16 h, the hemocytic nodules appeared poorly circumscribed and disorganized. No nodules were seen in a heavily infected crab after 24 h. By the end of the 48 h after feeding, 73% (11 of 15) of the crabs had shown evidence of infection with Hematodinium sp. Those crabs with infection intensities (Hematodinium sp. as percent of cells in hemolymph) higher than 20% were dead within 4 d.

Codon Usage Bias Analysis of Citrus tristeza Virus: Higher Codon Adaptation to Citrus reticulata Host.

Citrus tristeza virus (CTV), a member of the aphid-transmitted closterovirus group, is the causal agent of the notorious tristeza disease in several citrus species worldwide. The codon usage patterns of viruses reflect the evolutionary changes for optimization of their survival and adaptation in their fitness to the external environment and the hosts. The codon usage adaptation of CTV to specific citrus hosts remains to be studied; thus, its role in CTV evolution is not clearly comprehended. Therefore, to better explain the host⁻virus interaction and evolutionary history of CTV, the codon usage patterns of the coat protein (CP) genes of 122 CTV isolates originating from three economically important citrus hosts (55 isolate from Citrus sinensis, 38 from C. reticulata, and 29 from C. aurantifolia) were studied using several codon usage indices and multivariate statistical methods. The present study shows that CTV displays low codon usage bias (CUB) and higher genomic stability. Neutrality plot and relative synonymous codon usage analyses revealed that the overall influence of natural selection was more profound than that of mutation pressure in shaping the CUB of CTV. The contribution of high-frequency codon analysis and codon adaptation index value show that CTV has host-specific codon usage patterns, resulting in higheradaptability of CTV isolates originating from C. reticulata (Cr-CTV), and low adaptability in the isolates originating from C. aurantifolia (Ca-CTV) and C. sinensis (Cs-CTV). The combination of codon analysis of CTV with citrus genealogy suggests that CTV evolved in C. reticulata or other Citrus progenitors. The outcome of the study enhances the understanding of the factors involved in viral adaptation, evolution, and fitness toward their hosts. This information will definitely help devise better management strategies of CTV.

Detection and discovery of crustacean parasites in blue crabs (Callinectes sapidus) by using 18S rRNA gene-targeted denaturing high-performance liquid chromatography.

Recently, we described a novel denaturing high-performance liquid chromatography (DHPLC) approach useful for initial detection and identification of crustacean parasites. Because this approach utilizes general primers targeted to conserved regions of the 18S rRNA gene, a priori genetic sequence information on eukaryotic parasites is not required. This distinction provides a significant advantage over specifically targeted PCR assays that do not allow for the detection of unknown or unsuspected parasites. However, initial field evaluations of the DHPLC assay suggested that because of PCR-biased amplification of dominant host genes it was not possible to detect relatively rare parasite genes in infected crab tissue. Here, we describe the use of a peptide nucleic acid (PNA) PCR hybridization blocking probe in association with DHPLC (PNA-PCR DHPLC) to overcome inherent PCR bias associated with amplification of rare target genes by use of generic primers. This approach was utilized to detect infection of blue crabs (Callinectes sapidus) by the parasitic dinoflagellate Hematodinium sp. Evaluation of 76 crabs caught in Wassaw Sound, GA, indicated a 97% correspondence between detection of the parasite by use of a specific PCR diagnostic assay and that by use of PNA-PCR DHPLC. During these studies, we discovered one crab with an association with a previously undescribed protist symbiont. Phylogenetic analysis of the amplified symbiont 18S rRNA gene indicated that it is most closely related to the free-living kinetoplastid parasite Procryptobia sorokini. To our knowledge, this is the first report of this parasite group in a decapod crab and of this organism exhibiting a presumably parasitic life history.

Development of a denaturing high-performance liquid chromatography method for detection of protist parasites of metazoans.

Increasingly, diseases of marine organisms are recognized as significant biotic factors affecting ecosystem health. However, the responsible disease agents are often unknown and the discovery and description of novel parasites most often rely on morphological descriptions made by highly trained specialists. Here, we describe a new approach for parasite discovery, utilizing denaturing high-performance liquid chromatography (DHPLC) reverse-phase ion-pairing technology. Systematic investigations of major DHPLC variables, including temperature, gradient conditions, and target amplicon characteristics were conducted to develop a mechanistic understanding of DNA fragment separation by DHPLC. As a model system, 18S rRNA genes from the blue crab (Callinectes sapidus) and a parasitic dinoflagellate Hematodinium sp. were used. Binding of 18S rRNA gene PCR amplicons to the DNA separation column in the presence of triethylammonium acetate (TEAA) was inversely correlated with temperature and could be predicted based on the estimated DNA helicity of the PCR amplicon. Amplicons of up to 498 bp were resolved as single chromatographic peaks if they had high (>95%) DNA helicity. Amplicons that differed by as few as 2 bp could be resolved. Separation of 18S rRNA gene PCR amplicons was optimized by simultaneous manipulation of both temperature and solvent gradients. The optimal conditions included targeting regions of high DNA helicity (>95%), temperatures in the range of 57 to 63 degrees C, and a linear acetonitrile gradient from 13.75 to 17.5% acetonitrile in 0.1 M TEAA (55 to 70% buffer B) over a 9-min period. Under these conditions, amplicons from a variety of parasites and their hosts can be separated and detected by DHPLC.

DNA strand breaks in grass shrimp embryos exposed to highway runoff sediments and sediments with coal fly ash.

Embryo production was reduced in female grass shrimp exposed to sediments with added coal fly ash and to sediments collected from an estuarine station containing high PAH concentrations due to its proximity to a highway storm drain. Grass shrimp embryos exposed to pore water from the high PAH and high metal sediments showed both reduced hatching and increases in DNA strand breaks (comet assay). Sediments with added coal fly ash had high concentrations of vanadium and selenium which may have contributed to effects similar to those observed with sediments with high PAH. The embryo pore water bioassay (hatching/DNA strand breaks) gave results comparable to those observed for reproduction effects (reduced embryo production/embryo hatching) with female grass shrimp exposed to whole sediment.

The utilization of lipovitellin during blue crab (Callinectes sapidus) embryogenesis.

Embryos of the blue crab Callinectes sapidus develop in egg sacs carried on the abdomen of the female. They develop over a period of 10-13 days at 28 degrees C and are nutritionally dependent on yolk until they emerge from the egg sacs as free-swimming zoeae. The principal component of blue crab yolk is lipovitellin (LpII), a water-soluble lipoprotein composed of approximately equal amounts of lipid and protein. We followed changes in the concentration of apoproteins of LpII during embryogenesis by ELISA and Western blots, using monoclonal antibodies against two LpII apoprotein associated peptides identified as Protein A (107 kDa) and Protein B (75 kDa). During embryogenesis there was a decrease in Protein B but an increase in two smaller peptides (52 and 35 kDa) that reacted with the Protein B antibody. Utilization of LpII during embryogenesis was also followed morphologically by immunohistochemistry. Utilization of LpII was slow in early embryonic stages, followed by rapid utilization in late embryonic stages, such that only traces of LpII were present at the end of embryogenesis. The cells of the developing hepatopancreas appear to play an important role in the utilization of LpII.

Characterization of lipovitellin in eggs of the polychaete Neanthes arenaceodentata.

The ooplasm of mature oocytes of the polychaete Neanthes arenaceodentata is characteristically filled with yolk platelets. A major component of these structures is lipovitellin, which provides energy and materials required by newly hatched larvae. The lipovitellin isolated and purified from the fertilized eggs of this polychaete was a high-density lipoprotein composed of protein (57%), lipid (42%) and carbohydrate (1%). The lipid component included phospholipids (92% of lipid), triacylglycerol (3% of lipid) and cholesterol (3% of lipid), while sodium dodecyl sulfate-gel electrophoresis showed the major protein component was a 120-kDa peptide. Microscopically, mature oocytes were present in the coelom along with phagocytic eleocytes. The presence of muscle fragments and oil droplets in eleocytes suggests that eleocytes play an important role in providing the protein and lipid needed for the assembly of lipovitellin in the oocytes.

Significance of cytochrome P450 system responses and levels of bile fluorescent aromatic compounds in marine wildlife following oil spills.

The relationships among cytochrome P450 induction in marine wildlife species, levels of fluorescent aromatic compounds (FAC) in their bile, the chemical composition of the inducing compounds, the significance of the exposure pathway, and any resulting injury, as a consequence of exposure to crude oil following a spill, are reviewed. Fish collected after oil spills often show increases in cytochrome P450 system activity, cytochrome P4501A (CYP1A) and bile fluorescent aromatic compounds (FAC), that are correlated with exposure to polycyclic aromatic hydrocarbons (PAH) in the oil. There is also some evidence for increases in bile FAC and induction of cytochrome P450 in marine birds and mammals after oil spills. However, when observed, increases in these exposure indicators are transitory and generally decrease to background levels within one year after the exposure. Laboratory studies have shown induction of cytochrome P450 systems occurs after exposure of fish to crude oil in water, sediment or food. Most of the PAH found in crude oil (dominantly 2- and 3-ring PAH) are not strong inducers of cytochrome P450. Exposure to the 4-ring chrysenes or the photooxidized products of the PAH may account for the cytochrome P450 responses in fish collected from oil-spill sites. The contribution of non-spill background PAH, particularly combustion-derived (pyrogenic) PAH, to bile FAC and cytochrome P450 system responses can be confounding and needs to be considered when evaluating oil spill effects. The ubiquity of pyrogenic PAH makes it important to fully characterize all sources of PAH, including PAH from natural resources, e.g. retene, in oil spill studies. In addition, such parameters as species, sex, age, ambient temperature and season need to be taken into account. While increases in fish bile FAC and cytochrome P450 system responses, can together, be sensitive general indicators of PAH exposure after an oil spill, there is little unequivocal evidence to suggest a linkage to higher order biological effects, e.g. toxicity, lesions, reproductive failure.

Control of virus diseases of citrus.

Citrus is thought to have originated in Southeast Asia and horticulturally desirable clonal selections have been clonally cultivated for hundreds of years. While some citrus species have nucellar embryony, most cultivation of citrus has been by clonal propagation to ensure that propagated plants have the same traits as the parent selection. Clonal propagation also avoids juvenility, and the propagated plants produce fruit sooner. Because of the clonal propagation of citrus, citrus has accumulated a large number of viruses; many of these viruses are asymptomatic until a susceptible rootstock and/or scion is encountered. The viruses reported to occur in citrus will be summarized in this review. Methods of therapy to clean selected clones from viruses will be reviewed; the use of quarantine, clean stock, and certification programs for control of citrus viruses and other strategies to control insect spread citrus viruses, such as mild strain cross-protection and the use of pest management areas will be discussed.

The amount and accumulation rate of plastic debris on marshes and beaches on the Georgia coast.

The amount and accumulation rate of plastic debris at 20 sites along the Georgia coast were prepared using data reported by a number of volunteer organizations. The amount of plastic debris at highly visited barrier island beaches and estuarine marshes ranged from 300 to >1000 kg. Relatively large amount of plastics (180-500 kg) were found on less visited barrier island beaches, i.e. Blackbeard, Ossabaw and Cumberland Islands. A follow up monthly or quarterly collection study was carried out on two of the sites, a barrier beach and estuarine marsh, to determine accumulation rate in 8000 m(2) areas. Accumulation rates ranged from 0.18 to 1.28 kg/30 days-8000 m(2) on the barrier island beach and from 0.6 to 1.61 kg/30 days-8000 m(2) at the estuarine marsh site. The major type of plastics, e.g. bottles, food wrappers, plastic fragments, was highly variable at different seasons and sites. The authors recommend consideration of a standardization in reporting plastic debris, with respect to quantitation of debris and sample area.

Use of the single cell gel electrophoresis/comet assay for detecting DNA damage in aquatic (marine and freshwater) animals.

The comet assay is a rapid, sensitive and inexpensive method for measuring DNA strand breaks. The comet assay has advantages over other DNA damage methods, such as sister chromatid exchange, alkali elution and micronucleus assay, because of its high sensitivity and that DNA strand breaks are determined in individual cells. This review describes a number of studies that used the comet assay to determine DNA strand breaks in aquatic animals exposed to genotoxicants both in vitro and in vivo, including assessment of DNA damage in aquatic animals collected from contaminated sites. One difficulty of using the comet assay in environmental work is that of comparing results from studies that used different methods, such as empirical scoring or comet tail lengths. There seems to be a consensus in more recent studies to use both the intensity of the tail and the length of the tail, i.e. DNA tail moment, percentage of DNA in the tail. The comet assay has been used to assess DNA repair and apoptosis in aquatic animals and modifications of the comet assay have allowed the detection of specific DNA lesions. There have been some recent studies to link DNA strand breaks in aquatic animals to effects on the immune system, reproduction, growth, and population dynamics. Further work is required before the comet assay can be used as a standard bio-indicator in aquatic environments, including standardization of methods (such as ASTM method E2186-02a) and measurements.

Genotoxicant induced DNA damage and repair in early and late developmental stages of the grass shrimp Paleomonetes pugio embryo as measured by the comet assay.

In this study, data are presented which link frequency of DNA strand breaks and repair capability to developmental stage. Stages 4 and 7 embryos of the grass shrimp (Palaemonetes pugio) were exposed to various concentrations of benzo[alpha]pyrene (BalphaP), Cr(VI) and hydrogen peroxide. Following exposure, responses were measured as changes in hatching rates and DNA strand breaks (using the comet assay). The comet assay was modified by treatment of isolated nuclei with endonucleases which cleave DNA at oxidative lesions in DNA prior to electrophoresis. DNA repair was followed by transfer of toxicant exposed embryos to clean water and periodic determination of strand breaks. DNA strand breaks were higher in stage 7 embryos than in stage 4 embryos after exposure to the same concentration of different genotoxicants. However, when samples were treated with endonucleases to measure oxidative lesions, the total amount of DNA damage between stages 4 and 7 were similar. After toxicant exposure and transfer to clean water, DNA strand breaks in stage 7 embryos returned to background levels more rapidly than in stage 4 embryos. Similarly, samples treated with endonucleases during DNA repair studies showed that oxidative lesions were repaired more rapidly in stage 7 than in stage 4. These findings suggest that because of rapid DNA repair in late embryo stages that early embryo stages are more likely to have developmental effects after genotoxicant exposure.