Allelopathic Potential of Invasive Plantago virginica on Four Lawn Species

Plantago virginica L. has invaded many lawn ecosystems in the Eastern part of China. The invasion has incurred an economic cost to remove them. In order to prevent the invasion, it is critical to understand the invasive mechanisms of this species. However, few studies have been conducted on the allelopathic mechanisms of its invasion. In this study, we examined allelopathic effects of P. virginica on germination of seeds and growth of seedlings of four widely used lawn species. We found extensive allelopathic potential of P. virginica on other lawn species, which varied with species and developmental stage. While most effects of the extracts of P. virginica were inhibitory, some variables in some species were promoted by the addition of the extracts. The extracts of P. virginica significantly inhibited seed germination of Agrostis matsumurae. While the overall differences in seed germination rate of Poa annua were significant among treatments, difference between control and any of the treatments was not significant. The height of seedlings of A. matsumurae and Cynodon dactylon was significantly lower under the treatments of adding extracts of P. virginica. In contrast, growth of seedlings of Festuca elata and P. annua did not show significant differences among treatments. The root length of A. matsumurae, C. dactylon and P. annua was suppressed by the extracts of P. virginica whereas root length of F. elata was not affected. Aboveground biomass of A. matsumurae and F. elata was significantly higher than control, except for F. elata at the concentration of 50mg/mL, whereas aboveground biomass of C. dactylon and P. annua was reduced at higher concentrations of the extracts. Except for A. matsumurae, root biomass of the other three lawn species declined under the treatments with the extracts of P. virginica. Our results revealed that P. virginica had allelopathic potential on four lawn species and supported the theory of “novel weapons hypothesis”. Invasion by P. virginica in lawn can be moderated by selecting those species that are not affected or promotionally affected by it.     

Chemotactic attraction between hemocytes of the oyster,Crassostrea virginica,and bacteria

Experiments were conducted to ascertain whether there is chemotactic attraction by Bacillus megaterium and Micrococcus varians, both Gram-positive species, and Escherichia coli and Vibrio parahaemolyticus, both Gram-negative species, for hemocytes of the American oyster, Crassostrea virginica. It was ascertained quantitatively that oyster hemocytes are attracted to live E. coli, B. megaterium, and M. varians but not to heat-killed bacteria. Furthermore, oyster cells are not attracted to either live or heat-killed V. parahaemolyticus. It is concluded that the chemoattractant is some molecule emitted by living vegetative cells of certain Gram-positive as well as Gramnegative bacteria.     

Effects of Physicochemical Factors and Bacterial Colony Morphotype on Association of Vibrio vulnificus with Hemocytes of Crassostrea virginica

Vibrio vulnificus is a naturally occurring marine bacterium that causes invasive disease of immunocompromised humans following the consumption of raw oysters. It is a component of the natural microbiota of Gulf Coast estuaries and has been found to inhabit tissues of oysters, Crassostrea virginica (Gmelin 1791). The interaction of V. vulnificus with oyster host defenses has not been reported in detail. We examined the interaction of V. vulnificus with phagocytic oyster hemocytes as a function of time, temperature, bacterial concentration, pretreatment with hemolymph, and V. vulnificus translucent and opaque colony morphotypes. Within these experimental parameters, the results showed that the association of V. vulnificus with hemocytes increased with time, temperature, and initial V. vulnificus/hemocyte ratio. Pretreatment of V. vulnificus with serum or an increased serum concentration did not enhance V. vulnificus-hemocyte associations, a result suggesting the absence of opsonic activity. More than 50% of hemocytes bound the translucent, avirulent morphotype, whereas 10 to 20% were associated with the opaque, virulent form, a result indicating that the degree of encapsulation was related to resistance to phagocytosis, as previously described for mammalian phagocytes. Understanding these cellular interactions may, in part, explain the persistence of V. vulnificus in oyster tissues and the ecology of V. vulnificus in estuarine environments.     

Susceptibility of Hyphantria cunea to a granulosis virus isolated from Diacrisia virginica

The dosage-mortality response of Hyphantria cunea larvae to a granulosis virus isolated from Diacrisia virginica was studied. Serial decimal dilutions of the D. virginica granulosis virus were fed to early second-instar H. cunea larvae. the LD₅₀ for this virus (7.9 × 10⁵ capsules/larva) was significantly greater than the LD₅₀ calculated for the H. cunea granulosis virus (7.06 × 10⁴ capsules/larva) against the same instar of H. cunea. Time mortality studies demonstrated that the LT₅₀ values for the D. virginica granulosis were four to six times greater than for comparable dosages of H. cunea granulosis virus. Based on the mortality response of assayed H. cunea, it is possible to distinguish between the D. virginica granulosis virus and the H. cunea granulosis virus.     

Beta-glucuronidase in the serum and hemolymph cells of Mercenaria mercenaria and Crassostrea virginica (Mollusca: Pelecypoda).

The optimal pH of β-glucuronidase in the serum and cells of the hemolymph of the quahaug clam, Mercenaria mercenaria, and the American oyster, Crassostrea virginica, has been determined to be 4.5 by employing 0.2 M phosphate, 0.2 M glycylglycine, and 0.2 M acetate as the buffers.By comparing the optimal pH of lysozyme from C. virginica (which is either 5.0 or 5.5, depending on the buffer employed) with that of β-glucuronidase, it is concluded that if both of these lysosomal hydrolytic enzymes are to be concurrently operative at maximal efficiency, the hemolymph pH should be maintained between 4.5 and 5.5.The exact physiologic role of β-glucuronidase in M. mercenaria and C. virginica is undetermined; however, since this enzyme can hydrolyze acid mucopolysaccharides, which are constituents of bacterial walls, it may play a role in internal defense by acting on susceptible invading bacteria. Furthermore, the β-glucuronidase in cells may be correlated with cell proliferation.     

Effects of hemolymph of the American oyster, Crassostrea virginica, on marine cercariae

The interactions of cellular and humoral factors of hemolymph of the American oyster, Crassostrea virginica, and several species of marine cercariae were studied. Attraction of hemocytes to dead but not to living cercariae was observed. Dead cercariae were encapsulated in vitro by oyster hemocytes. The plasma of C. virginica was apparently not toxic to the species of cercariae tested.     

Integration of Vibrio vulnificus into Marine Aggregates and Its Subsequent Uptake by Crassostrea virginica Oysters

Marine aggregates are naturally forming conglomerations of larvacean houses, phytoplankton, microbes, and inorganics adhered together by exocellular polymers. In this study, we show in vitro that the bacterial pathogen Vibrio vulnificus can be concentrated into laboratory-generated aggregates from surrounding water. We further show that environmental (E-genotype) strains exhibit significantly more integration into these aggregates than clinical (C-genotype) strains. Experiments where marine aggregates with attached V. vulnificus cells were fed to oysters (Crassostrea virginica) resulted in greater uptake of both C and E types than nonaggregated controls. When C- and E-genotype strains were cocultured in competitive experiments, the aggregated E-genotype strains exhibited significantly greater uptake by oyster than the C-genotype strains.     

Invasive Lespedeza cuneata and native Lespedeza virginica experience asymmetrical benefits from rhizobial symbionts

Background and Aims

Lespedeza cuneata (Dum. Cours.) G. Don is an invasive legume that displaces populations of native N. American congeners. Our aims are to determine the growth benefits of different rhizobacterial strains for L. cuneata and native Lespedeza virginica (L.) Britton, and to determine if these strains influence competition between these plants.

Methods

Plants were grown under nitrogen-limiting conditions in sterilized soil in pairs consisting of two L. cuneata, two L. virginica, or one of each species, and then plants were inoculated with one of seven rhizobial isolates, or with a no-strain control. After 3 months, plants were harvested for determination of biomass and nodulation rate.

Results

Five of the assayed stains improved L. cuneata biomass over uninoculated controls, but none of the strains benefited L. virginica. L. cuneata plants had more biomass and root nodules when grown in competition with L. virginica than with a conspecific.

Conclusions

Asymmetrical benefits from these symbionts accrued to invasive L. cuneata but not to native L. virginica, and this may provide the invader with a growth advantage in the field. Changes in the availability of effective symbionts in the soils of invaded sites can shape performance of native and invasive plants.     

An assessment of Pseudo-nitzschia population dynamics and domoic acid production in coastal Louisiana

Over 1200 samples were collected from Louisiana estuarine and coastal shelf waters between 1989 and 2002, and analyzed to examine the population dynamics of Pseudo-nitzschia and to assess the potential threat posed by domoic acid (DA), a potent neurotoxin produced by some members within this toxigenic diatom genus. Results demonstrated that three species in this region (Pseudo-nitzschia multiseries, P. pseudodelicatissima complex, P. delicatissima) produce DA, and that particulate toxin levels were highest (up to 3.05 μg L⁻¹) during the spring bloom, while cellular concentrations were highest in the winter/early spring when P. multiseries was most abundant (up to 30 pg cell⁻¹). These particulate toxin levels are comparable to those seen in other regions (e.g., United States west coast) where DA poisoning events have occurred in the past. Pseudo-nitzschia were most abundant under dissolved inorganic nitrogen-replete conditions coupled with lower silicate and/or phosphate concentrations, and in the early spring months when temperatures were cooler. Pseudo-nitzschia were occasionally well-represented in the phytoplankton assemblage (≥10⁶ cells L⁻¹ in 14% of samples, over 50% of total phytoplankton in 5% of samples), indicating that planktivores (e.g., Gulf menhaden, Brevoortia patronus) may have little choice but to consume Pseudo-nitzschia cells, thereby providing potential vectors for DA transfer to higher trophic levels. By comparison, eastern oysters (Crassostrea virginica) present in estuarine waters may be more exposed to this toxin when Pseudo-nitzschia cells are part of a mixed assemblage, reducing selective grazing by these bivalves. C. virginica may thus represent the most effective vector for DA exposure in humans.     

铝胁迫下北美车前和车前生长及叶绿素荧光特性的比较研究

采用系列浓度AlCl₃溶液（100、500、800、2 000 mg·L^-1）进行处理,在处理后不同时间（0,10、20、30 d）,测定北美车前（Plantago viriginica）和车前(P.asiatica)的生长及叶绿素荧光特征指数,旨在比较外来入侵种北美车前和同属本地种车前的生长及叶绿素荧光对铝胁迫响应的差异。结果表明,车前和北美车前的根冠比在轻度铝（Al³⁺=100 mg·L^-1）处理下略有上升,在中度（Al³⁺=500 mg·L^-1）以上铝浓度处理下开始显著下降;叶绿素a、b含量在轻度铝处理下变化不明显,随着铝浓度的增加和处理时间的延长呈现明显下降趋势;叶绿素荧光参数F_v/F_m、Φ_PSⅡ及F_v/F_o值在低浓度铝的短时间处理下略有上升,随着铝浓度的升高和处理时间的延长则明显下降。结果表明铝胁迫对上述两种植物的生长和叶绿素荧光参数均有一定影响,但北美车前各参数的下降幅度小于车前,表现出比车前更为耐铝的生理特性。     

Mortalities of Eastern and Pacific Oyster Larvae Caused by the Pathogens Vibrio coralliilyticus and Vibrio tubiashii

Vibrio tubiashii is reported to be a bacterial pathogen of larval Eastern oysters (Crassostrea virginica) and Pacific oysters (Crassostrea gigas) and has been associated with major hatchery crashes, causing shortages in seed oysters for commercial shellfish producers. Another bacterium, Vibrio coralliilyticus, a well-known coral pathogen, has recently been shown to elicit mortality in fish and shellfish. Several strains of V. coralliilyticus, such as ATCC 19105 and Pacific isolates RE22 and RE98, were misidentified as V. tubiashii until recently. We compared the mortalities caused by two V. tubiashii and four V. coralliilyticus strains in Eastern and Pacific oyster larvae. The 50% lethal dose (LD₅₀) of V. coralliilyticus in Eastern oysters (defined here as the dose required to kill 50% of the population in 6 days) ranged from 1.1 × 10⁴ to 3.0 × 10⁴ CFU/ml seawater; strains RE98 and RE22 were the most virulent. This study shows that V. coralliilyticus causes mortality in Eastern oyster larvae. Results for Pacific oysters were similar, with LD₅₀s between 1.2 × 10⁴ and 4.0 × 10⁴ CFU/ml. Vibrio tubiashii ATCC 19106 and ATCC 19109 were highly infectious toward Eastern oyster larvae but were essentially nonpathogenic toward healthy Pacific oyster larvae at dosages of ≥1.1 × 10⁴ CFU/ml. These data, coupled with the fact that several isolates originally thought to be V. tubiashii are actually V. coralliilyticus, suggest that V. coralliilyticus has been a more significant pathogen for larval bivalve shellfish than V. tubiashii, particularly on the U.S. West Coast, contributing to substantial hatchery-associated morbidity and mortality in recent years.     

First record of the non-indigenous jellyfish <Emphasis Type="Italic">Blackfordia virginica</Emphasis> (Mayer, 1910) in the Baltic Sea

Marine invasions are of increasing concern for biodiversity conservation worldwide. Gelatinous macrozooplankton contain members, which have become globally invasive, for example the ctenophore Mnemiopsis leidyi or the hydromedusae Blackfordia virginica. B. virginica is characterised by a large salinity tolerance, with a brackish-water habitat preference, and by a metagenic life history strategy with an alternation between sexually reproducing planktonic medusae and asexually reproducing benthic polyps to complete the life cycle. In this study we analysed 8 years of ichthyoplankton survey data (2010–2017) from the Kiel Canal and 14 ichthyoplankton summer surveys in the central Baltic Sea (2008–2017). We report the first presence of B. virginica in northern Europe, namely from the southwestern Baltic Sea and the Kiel Canal. In the Kiel Canal, B. virginica was first sporadically sighted in 2014 and 2015 and has developed persistent populations since summer 2016. Changes in size-frequency distributions during summer 2016 indicate active recruitment in the Kiel Canal at salinities between 7 and 13 and temperatures?>?14 °C. Close vicinity to and direct connection with the southwestern Baltic Sea, where B. virginica was observed during 2017, indicate that the Baltic Sea and other brackish-water habitats of Northern Europe are at risk for colonisation of this non-indigenous species. Our results highlight that monitoring activities should consider gelatinous macrozooplankton for standard assessments to allow for the detection of non-indigenous species at an early stage of their colonisation.     

Effects of nonnative invertebrates on two life stages of the native eastern oyster <Emphasis Type="Italic">Crassostrea virginica</Emphasis>

Since their recent introductions into Florida waters, three sessile invertebrates [Perna viridis (Asian green mussel), Mytella charruana (charru mussel) and Megabalanus coccopoma (pink titan acorn barnacle)] have expanded their range along the Atlantic coast in estuarine waters. Little research has been done to understand how these nonnative species interact with the ecologically and economically important eastern oyster Crassostrea virginica. To assess the potential effects of P. viridis, M. charruana and M. coccopoma on C. virginica, the following questions were addressed in manipulative experiments. (1) Does the presence of nonnative species decrease oyster larval settlement? (2) Do oyster larvae avoid settling on nonnative species? (3) Do nonnative species decrease survival of juvenile oysters (spat)? (4) Do nonnative species hinder spat growth? We included two controls: absence of nonnative species and presence of the native mussel Geukensia demissa. The nonnative species influenced settlement, growth and survival of C. virginica in different ways. M. coccopoma and P. viridis negatively influenced larval settlement, whereas M. charruana had no influence on the total number of settled larvae. Oyster larvae avoided settling on all three nonnative species and the native G. demissa. Both nonnative mussels negatively affected survival of juvenile oysters but only M. charruana also reduced spat growth. The native mussel, G. demissa, had no negative impacts on total settlement, survival and growth of C. virginica; in fact, it increased larval settlement in some trials. These three nonnative species should be classified as invasive because all had negative effects on native C. virginica.     

Predatory Bacteria as Natural Modulators of Vibrio parahaemolyticus and Vibrio vulnificus in Seawater and Oysters

This study shows that naturally occurring Vibrio predatory bacteria (VPB) exert a major role in controlling pathogenic vibrios in seawater and shellfish. The growth and persistence of Vibrio parahaemolyticus and Vibrio vulnificus were assessed in natural seawater and in the Eastern oyster, Crassostrea virginica. The pathogens examined were V. vulnificus strain VV1003, V. parahaemolyticus O1:KUT (KUT stands for K untypeable), and V. parahaemolyticus O3:K6 and corresponding O3:K6 mutants deficient in the toxRS virulence regulatory gene or the rpoS alternative stress response sigma factor gene. Vibrios were selected for streptomycin resistance, which facilitated their enumeration. In natural seawater, oysters bioconcentrated each Vibrio strain for 24 h at 22°C; however, counts rapidly declined to near negligible levels by 72 h. In natural seawater with or without oysters, vibrios decreased more than 3 log units to near negligible levels within 72 h. Neither toxRS nor rpoS had a significant effect on Vibrio levels. In autoclaved seawater, V. parahaemolyticus O3:K6 counts increased 1,000-fold over 72 h. Failure of the vibrios to persist in natural seawater and oysters led to screening of the water samples for VPB on lawns of V. parahaemolyticus O3:K6 host cells. Many VPB, including Bdellovibrio and like organisms (BALOs; Bdellovibrio bacteriovorus and Bacteriovorax stolpii) and Micavibrio aeruginosavorus-like predators, were detected by plaque assay and electron microscopic analysis of plaque-purified isolates from Atlantic, Gulf Coast, and Hawaiian seawater. When V. parahaemolyticus O3:K6 was added to natural seawater containing trace amounts of VPB, Vibrio counts diminished 3 log units to nondetectable levels, while VPB increased 3 log units within 48 h. We propose a new paradigm that VPB are important modulators of pathogenic vibrios in seawater and oysters.     

The effect of a toxic dinoflagellate (Alexandrium tamarense) on the oxygen uptake of juvenile filter-feeding bivalve molluscs

• 1.1. Oxygen uptake and grazing rates of juvenile bivalve molluscs Mytilus edulis, Mya arenaria, Geukensia demissa, Placopecten magellanicus and Crassostrea virginica were measured following 1 hr exposure to bloom concentrations (10⁶ cells/1) of the toxic dinoflagellate Alexandrium tamarense (GT429) using a non-toxic clone of the same species (PLY 173) as control.
• 2.2. For all bivalves, prefeeding estimates of V̇O₂ were similar to postfeeding values and values recorded 24 hr after exposure to bloom conditions.
• 3.3. V̇O₂ was similar for bivalves fed on both the toxic and non-toxic strains of A. tamarense suggesting that there were no adverse effects on V̇O₂ following 1 hr exposure to toxic GT429.
• 4.4. Bivalves differed in their rates of grazing between toxic GT429 and non-toxic PLY 173. Similar grazing rates were recorded for M. edulis and G. demissa. For P. magellanicus and M. arenaria reduced rates of clearance were recorded in GT429 compared with the non-toxic strain.

     

Phages Infecting Vibrio vulnificus Are Abundant and Diverse in Oysters (Crassostrea virginica) Collected from the Gulf of Mexico

Phages infecting Vibrio vulnificus were abundant (>10⁴ phages g of oyster tissue⁻¹) throughout the year in oysters (Crassostrea virginica) collected from estuaries adjacent to the Gulf of Mexico (Apalachicola Bay, Fla.; Mobile Bay, Ala.; and Black Bay, La.). Estimates of abundance ranged from 10¹ to 10⁵ phages g of oyster tissue⁻¹ and were dependent on the bacterial strain used to assay the sample. V. vulnificus was near or below detection limits (<0.3 cell g⁻¹) from January through March and was most abundant (10³ to 10⁴ cells g⁻¹) during the summer and fall, when phage abundances also tended to be greatest. The phages isolated were specific to strains of V. vulnificus, except for one isolate that caused lysis in a few strains of V. parahaemolyticus. Based on morphological evidence obtained by transmission electron microscopy, the isolates belonged to the Podoviridae, Styloviridae, and Myoviridae, three families of double-stranded DNA phages. One newly described morphotype belonging to the Podoviridae appears to be ubiquitous in Gulf Coast oysters. Isolates of this morphotype have an elongated capsid (mean, 258 nm; standard deviation, 4 nm; n = 35), with some isolates having a relatively broad host range among strains of V. vulnificus. Results from this study indicate that a morphologically diverse group of phages which infect V. vulnificus is abundant and widely distributed in oysters from estuaries bordering the northeastern Gulf of Mexico.     

Role of Type IV Pilins in Persistence of Vibrio vulnificus in Crassostrea virginica Oysters

Vibrio vulnificus is part of the natural estuarine microflora and accumulates in shellfish through filter feeding. It is responsible for the majority of seafood-associated fatalities in the United States mainly through consumption of raw oysters. Previously we have shown that a V. vulnificus mutant unable to express PilD, the type IV prepilin peptidase, does not express pili on the surface of the bacterium and is defective in adherence to human epithelial cells (R. N. Paranjpye, J. C. Lara, J. C. Pepe, C. M. Pepe, and M. S. Strom, Infect. Immun. 66:5659-5668, 1998). A mutant unable to express one of the type IV pilins, PilA, is also defective in adherence to epithelial cells as well as biofilm formation on abiotic surfaces (R. N. Paranjpye and M. S. Strom, Infect. Immun. 73:1411-1422, 2005). In this study we report that the loss of PilD or PilA significantly reduces the ability of V. vulnificus to persist in Crassostrea virginica over a 66-h interval, strongly suggesting that pili expressed by this bacterium play a role in colonization or persistence in oysters.     

Kinetic properties of lysozyme from the hemolymph of Crassostrea virginica

Lysozyme activity has been demonstrated in both the supernatant and pellet fractions of whole hemolymph of the American oyster, Crassostrea virginica, subjected to centrifugation at 4000 and 10,000 × g. In each case the enzyme activity is greater in the supernatant than in the pellet.The lytic activity of the molluscan lysozyme on Micrococcus lysodeikticus, like that of egg-white lysozyme, is salt dependent, is relatively heat stable, and is very sensitive to changes in ionic concentration. The optimal pH of the molluscan enzyme, however, ranges from 5.0 to 5.5, depending on the buffer employed.When tested against a number of bacteria, the oyster lysozyme has been found to be active against not only M. lysodeikticus but also Bacillus subtilis, B. megaterium, Escherichia coli, Gaffkya tetragena, Salmonella pullorum, and Shigella sonnei, although it is less active against the last four mentioned. It is not active against Staphylococcus aureus.It is postulated that the lysozyme in the serum of C. virginica has its origin in cytoplasmic phagosomes of granulocytes and is released when these organelles become ruptured.