Profiles of Alexandrium catenella cysts in Puget Sound sediments and the relationship to paralytic shellfish poisoning events

The magnitude of paralytic shellfish poisoning (PSP) toxins in shellfish and the geographical scope of shellfish closures in Puget Sound have increased in recent decades. PSP, monitored by the Washington Department of Health, has spread from Sequim Bay in the 1950s into central Puget Sound in the 1970s and throughout Puget Sound by the 1990s. Alexandrium catenella, the species responsible for PSP toxins, produces a benthic resting cyst that, upon germinating, can seed blooms. This study examined whether there is a relationship between profiles of cysts in the sediment and temporal variation in PSP in shellfish and if the history of the toxin's southward expansion through Puget Sound can be seen in the cyst record. To address this question, sediment cores were collected from three Puget Sound basins, Sequim Bay, Penn Cove, and Carr Inlet, and cyst profiles were determined. Activities of ²¹⁰Pb were fitted to a depth-dependent diagenetic model to date the sediment cores and determine mixing and sediment-accumulation rates. In order to compare historical variation in PSP with cyst profiles that have been altered by bioturbation, a depth and time-dependent diagenetic model was then used to predict vertical profiles of cysts that would occur under the assumption that cyst deposition rates are proportional to PSP concentration in shellfish measured over several decades at each site. The cyst profiles predicted by the model were compared to measured cyst profiles. These comparisons suggested that Alexandrium blooms and resulting PSP concentration in shellfish are more closely linked to cyst germination and deposition at some stations than at others. Sequim Bay had relatively large numbers of cysts and it is likely that the persistent toxicity here is the result of recurrent seeding from the cyst bed. Penn Cove and Carr Inlet had few cysts despite occasional blooms, suggesting that blooms are transported into those areas, perhaps from other sites of cyst germination. Sequim Bay and Penn Cove had cysts from top to bottom of the cores so it was not possible to determine the date when cysts were first introduced into these bays, but it is likely that A. catenella has been in Penn Cove since at least 1955 or for about two decades before the WDOH PSP toxicity data would indicate. The cyst profile in Carr Inlet suggested a first appearance date of 1985 that is consistent with the first appearance of PSP in shellfish in 1988.     

Synchronized sexuality of an algal symbiont and its dinoflagellate host, Peridinium balticum (Levander) Lemmermann

We report synchronized sexual reproduction between the chlorophyll c-containing algal endosymbiont and its dinoflagellate host in Peridinium balticum (Pyrrhophyta). This organism's importance lies in that it may represent an intermediate between primitive non-photosynthetic and advanced photosynthetic dinoflagellates. Fusion of the endosymbionts and their nuclei occurred concomitantly with syngamy of the host gametes. Significant morphological changes, including condensation of chromatin and crystalline rod formation, occurred in the symbiont nucleus during zygote development. These observations provide evidence that the endosymbiotic nucleus is not passive in sexual processes, as opposed to its reported passive state during mitosis. P. balticum may not only represent an intermediate in the evolution of chloroplast acquisition by dinoflagellates, but also, an intermediate in the evolution of the peridinian dinoflagellate sexual life history.     

RecFOR and RecOR as distinct RecA loading pathways

The molecular role of the RecF protein in loading RecA protein onto single-stranded DNA (ssDNA)-binding protein-coated ssDNA has been obscured by the facility with which the RecO and RecR proteins alone perform this function. We now show that RecFOR and RecOR define distinct RecA loading functions that operate optimally in different contexts. RecFOR, but not RecOR, is most effective when RecF(R) is bound near an ssDNA/double-stranded (dsDNA) junction. However, RecF(R) has no enhanced binding affinity for such a junction. RecO and RecR proteins are both required under all conditions in which the RecFOR pathway operates. The RecOR pathway is uniquely distinguished by a required interaction between RecO protein and the ssDNA binding protein C terminus. The RecOR pathway is more efficient for RecA loading onto ssDNA when no proximal dsDNA is available. A merger of new and published results leads to a new model for RecFOR function.     

Interaction between polyketide synthase and transporter suggests coupled synthesis and export of virulence lipid in M. tuberculosis

Virulent mycobacteria utilize surface-exposed polyketides to interact with host cells, but the mechanism by which these hydrophobic molecules are transported across the cell envelope to the surface of the bacteria is poorly understood. Phthiocerol dimycocerosate (PDIM), a surface-exposed polyketide lipid necessary for Mycobacterium tuberculosis virulence, is the product of several polyketide synthases including PpsE. Transport of PDIM requires MmpL7, a member of the MmpL family of RND permeases. Here we show that a domain of MmpL7 biochemically interacts with PpsE, the first report of an interaction between a biosynthetic enzyme and its cognate transporter. Overexpression of the interaction domain of MmpL7 acts as a dominant negative to PDIM synthesis by poisoning the interaction between synthase and transporter. This suggests that MmpL7 acts in complex with the synthesis machinery to efficiently transport PDIM across the cell membrane. Coordination of synthesis and transport may not only be a feature of MmpL-mediated transport in M. tuberculosis, but may also represent a general mechanism of polyketide export in many different microorganisms.     

Aggregated LDL and lipid dispersions induce lysosomal cholesteryl ester accumulation in macrophage foam cells

Macrophage foam cells in atherosclerotic lesions accumulate substantial cholesterol stores within large, swollen lysosomes. Previous studies with mildly oxidized low density lipoprotein (OxLDL)-treated THP-1 macrophages suggest an initial buildup of free cholesterol (FC), followed by an inhibition of lysosomal cholesteryl ester (CE) hydrolysis and a subsequent lysosomal accumulation of unhydrolyzed lipoprotein CE. We examined whether other potential sources of cholesterol found within atherosclerotic lesions could also induce similar lysosomal accumulation. Biochemical analysis combined with microscopic analysis showed that treatment of THP-1 macrophages with aggregated low density lipoprotein (AggLDL) or CE-rich lipid dispersions (DISP) produced a similar lysosomal accumulation of both FC and CE. Co-treatment with an ACAT inhibitor, CP113,818, confirmed that the CE accumulation was primarily the result of the inhibition of lysosomal CE hydrolysis. The rate of unhydrolyzed CE buildup was more rapid with DISP than with AggLDL. However, with both treatments, FC appeared to accumulate in lysosomes before the inhibition in hydrolysis and CE accumulation, a sequence shared with mildly OxLDL. Thus, lysosomal accumulation of FC and CE can be attributable to more general mechanisms than just the inhibition of hydrolysis by oxidized lipids.     

Effects of excess selenomethionine on selenium status indicators in pregnant long-tailed macaques (Macaca fascicularis)

Forty pregnant long-tailed macaques were treated daily for 30 d with 0, 25, 150 or 300 μg selenium as L-selenomethionine/kg body weight. Erythrocyte and plasma selenium and glutathione peroxidase specific activities, hair and fecal selenium, and urinary selenium excretion were increased by and were linearly related to L-selenomethionine dose. Hair selenium was most sensitive to L-selenomethionine dose, with an 84-fold increase in the 300 μg selenium/(kg-d) group relative to controls (r=0.917). Daily urinary selenium excretion (80-fold,r=0.958), plasma selenium (22-fold,r=0.885), erythrocyte selenium (24-fold,r=0.920), and fecal selenium (18-fold,r=0.911) also responded strongly to L-selenomethionine. Erythrocyte and plasma glutathione peroxidase specific activities increased 154% and 69% over controls, respectively. Toxicity was associated with erythrocyte selenium >2.3 μg/mL, plasma selenium >2.8 μg/mL, and hair selenium >27 μg/g. Plasma, erythrocyte, and hair selenium concentrations may be useful for monitoring and preventing the toxicity of L-selenomethionine administered to humans in cancer chemoprevention trials.