Long-term changes in temperate marine fish assemblages are driven by a small subset of species

The species composition of plant and animal assemblages across the globe has changed substantially over the past century. How do the dynamics of individual species cause this change? We classified species into seven unique categories of temporal dynamics based on the ordered sequence of presences and absences that each species contributes to an assemblage time series. We applied this framework to 14,434 species trajectories comprising 280 assemblages of temperate marine fishes surveyed annually for 20 or more years. Although 90% of the assemblages diverged in species composition from the baseline year, this compositional change was largely driven by only 8% of the species' trajectories. Quantifying the reorganization of assemblages based on species shared temporal dynamics should facilitate the task of monitoring and restoring biodiversity. We suggest ways in which our framework could provide informative measures of compositional change, as well as leverage future research on pattern and process in ecological systems.     

Cleaner fish become hosts: a novel form of parasite transmission

Adult bucephalid trematodes (Digenea) generally only occur in piscivorous fish. Within labrid fishes they are very rare, however, we have found them in labrid cleaner fish that feed on the ectoparasites of fish. We surveyed 969 labrid fishes from the tropical Pacific and found bucephalids only in cleaners (Labroides dimidiatus, L. bicolor, and Bodianus axillaris) and none in piscivores. The prevalences of bucephalids in L. dimidiatus at Lizard Island, Heron Island, Orpheus Island (all on the Great Barrier Reef), New Caledonia, and Moorea (French Polynesia) were 51, 47, 67, 56, and 67%, respectively. All of the L. bicolor examined from Moorea were infected. Bucephalids were highly prevalent in all size classes of L. dimidiatus from Lizard Island. Bucephalids were found in a 1.6-cm long juvenile L. dimidiatus, in which, piscivory is highly unlikely. We examined the literature on the worldwide bucephalid fauna in labrids and all hosts were found to be cleaners (Symphodus tinca, S. mediterraneus, L. dimidiatus, L. bicolor, and Bodianus axillaris) except Notolabrus parilus, whose ecology is unknown. We suggest that cleaners eat bucephalid metacercariae directly from the exterior surface of client fish during cleaning interactions. This is the first evidence of digeneans in the diet of L. dimidiatus, and the first study to show this novel form of parasite transmission where infective stages are eaten as a result of cleaning behaviour. Cleaning-mediated parasite transmission may result in behavioural modification of second intermediate hosts because clients and parasites both benefit from transmission. If the infection is costly to cleaners and acquired during cheating behaviour, then this parasite might regulate mutualism. Alternatively, if infective stages are targeted, infection by these bucephalids may be a negative consequence of an honest foraging strategy.Communicated by: P. F. Sale     

Identification of a new segment involved in cagA 3' region variation of Helicobacter pylori

The cagA 3' region shows marked variation among Helicobacter pylori strains. Two segments of 102 bp and 57 bp are reportedly responsible for this variation. We analysed the cagA 3' region in 70 H. pylori strains using polymerase chain reaction and sequencing. We found that another segment, namely beta segment, was also involved in the variation of this region. The beta segment was 105 bp long and located between the aforementioned two segments. Six genotypes were identified based on the structure of the cagA 3' region. No relationship was found between these genotypes and the clinical outcomes or vacA genotypes. The numbers of tyrosine phosphorylation sites within the cagA 3' region varied among strains, but this was not related to the cagA genotypes. Our data suggest that the cagA 3' region is significantly variable. It appears that the variation of the cagA 3' region might contribute to the modification of virulence.     

Aza-peptide epoxides: potent and selective inhibitors of Schistosoma mansoni and pig kidney legumains (asparaginyl endopeptidases)

Aza-peptide epoxides are a new class of irreversible cysteine protease inhibitors. Derivatives containing a P1 aza-asparagine residue are specific for Schistosoma mansoni and pig kidney legumains, which are clan CD cysteine proteases. The inhibitors have second-order rate constants of up to 10(4) M(-1) s(-1) with pig kidney legumain and IC50 values as low as 45 nM with S. mansoni legumain. The most potent epoxides contain an ester moiety with S,S stereochemistry attached to the epoxide. Interestingly, amide and amino acid derivatives of the epoxysuccinate moiety were not inhibitors of legumain, while disubstituted amide derivatives are quite potent. The inhibitors have little or no inhibitory activity with other proteases such as caspases, chymotrypsin, papain, cathepsin B, granzyme B, and various aspartyl proteases.     

Functional properties of cartilaginous tissues engineered from infrapatellar fat pad-derived mesenchymal stem cells

Articular cartilage has a poor intrinsic capacity for self-repair. The advent of autologous chondrocyte implantation has provided a feasible method to treat cartilage defects. However, the associated drawbacks with the isolation and expansion of chondrocytes from autologous tissue has prompted research into alternative cell sources such as mesenchymal stem cells (MSCs) which have been found to exist in the bone marrow as well as other joint tissues such as the infrapatellar fat pad (IFP), synovium and within the synovial fluid itself. In this work we assessed the chondrogenic potential of IFP-derived porcine cells over a 6 week period in agarose hydrogel culture in terms of mechanical properties, biochemical content and histology. It was found that IFP cells underwent robust chondrogenesis as assessed by glycosaminoglycan (1.47±0.22% w/w) and collagen (1.44±0.22% w/w) accumulation after 42 days of culture. The 1 Hz dynamic modulus of the engineered tissue at this time point was 272.8 kPa (±46.8). The removal of TGF-β3 from culture after 21 days was shown to have a significant effect on both the mechanical properties and biochemical content of IFP constructs after 42 days, with minimal increases occurring from day 21 to day 42 without continued supplementation of TGF-β3. These findings further strengthen the case that the IFP may be a promising cell source for putative cartilage repair strategies.     

Cerebral Hemodynamic Changes of Mild Traumatic Brain Injury at the Acute Stage

Mild traumatic brain injury (mTBI) is a significant public health care burden in the United States. However, we lack a detailed understanding of the pathophysiology following mTBI and its relation to symptoms and recovery. With advanced magnetic resonance imaging (MRI), we can investigate brain perfusion and oxygenation in regions known to be implicated in symptoms, including cortical gray matter and subcortical structures. In this study, we assessed 14 mTBI patients and 18 controls with susceptibility weighted imaging and mapping (SWIM) for blood oxygenation quantification. In addition to SWIM, 7 patients and 12 controls had cerebral perfusion measured with arterial spin labeling (ASL). We found increases in regional cerebral blood flow (CBF) in the left striatum, and in frontal and occipital lobes in patients as compared to controls (p = 0.01, 0.03, 0.03 respectively). We also found decreases in venous susceptibility, indicating increases in venous oxygenation, in the left thalamostriate vein and right basal vein of Rosenthal (p = 0.04 in both). mTBI patients had significantly lower delayed recall scores on the standardized assessment of concussion, but neither susceptibility nor CBF measures were found to correlate with symptoms as assessed by neuropsychological testing. The increased CBF combined with increased venous oxygenation suggests an increase in cerebral blood flow that exceeds the oxygen demand of the tissue, in contrast to the regional hypoxia seen in more severe TBI. This may represent a neuroprotective response following mTBI, which warrants further investigation.     

Intracellular Accumulation of High Levels of γ-Aminobutyrate by Listeria monocytogenes 10403S in Response to Low pH: Uncoupling of γ-Aminobutyrate Synthesis from Efflux in a Chemically Defined Medium

It is well established that the glutamate decarboxylase (GAD) system is central to the survival of Listeria monocytogenes at low pH, both in acidic foods and within the mammalian stomach. The accepted model proposes that under acidic conditions extracellular glutamate is transported into the cell in exchange for an intracellular γ-aminobutyrate (GABA_i). The glutamate is then decarboxylated to GABA_i, a reaction that consumes a proton, thereby helping to prevent acidification of the cytoplasm. In this study, we show that glutamate supplementation had no influence on either growth rate at pH 5.0 or survival at pH 2.5 when L. monocytogenes 10403S was grown in a chemically defined medium (DM). In response to acidification, cells grown in DM failed to efflux GABA, even when glutamate was added to the medium. In contrast, in brain heart infusion (BHI), the same strain produced significant extracellular GABA (GABA_e) in response to acidification. In addition, high levels of GABA_i (>80 mM) were found in the cytoplasm in response to low pH in both growth media. Medium-swap and medium-mixing experiments revealed that the GABA efflux apparatus was nonfunctional in DM, even when glutamate was present. It was also found that the GadT2D2 antiporter/decarboxylase system was transcribed poorly in DM-grown cultures while overexpression of gadD1T1 and gadD3 occurred in response to pH 3.5. Interestingly, BHI-grown cells did not respond with upregulation of any of the GAD system genes when challenged at pH 3.5. The accumulation of GABA_i in cells grown in DM in the absence of extracellular glutamate indicates that intracellular glutamate is the source of the GABA_i. These results demonstrate that GABA production can be uncoupled from GABA efflux, a finding that alters the way we should view the operation of bacterial GAD systems.The capacity to produce γ-aminobutyric acid (GABA) through glutamate decarboxylation is commonly found in both Gram-negative and Gram-positive bacterial genera (10, 12). In several cases, this reaction has been shown to be critical for bacteria to survive potentially lethal acidic environments (15, 18, 20). It is generally held that the hydrogen ion consumed during the decarboxylation reaction helps to prevent excessive acidification of the cytoplasm, thereby protecting the cells against acidic environments. The GABA produced in the reaction is removed from the cell through the activity of an antiporter that exchanges a GABA molecule for an extracellular glutamate (Glu) molecule (6, 12).In Listeria monocytogenes, the Gram-positive food-borne pathogen that was the focus of the present study, the glutamate decarboxylase (GAD) system has been shown to play an essential role in acid tolerance (8, 9). Mutants compromised in their ability to catalyze this decarboxylation reaction survive poorly both in acidic foods (8) and gastric juice (9). The GAD system in most L. monocytogenes strains is encoded by a total of five genes. There are three genes, designated gadD1, gadD2, and gadD3, that encode distinct glutamate decarboxylase enzymes and two genes, designated gadT1 and gadT2, that encode two Glu-GABA antiporters. These genes are organized at three separate genetic loci: gadD1T1, gadT2D2, and gadD3 (11). The decarboxylase/antiporter system encoded by gadT2D2 plays a central role in allowing survival under extreme acidic conditions; mutants lacking either the GadT2 antiporter or the GadD2 decarboxylase are highly sensitive to low pH (9, 11). In contrast, the GadD1/GadT1 decarboxylase/antiporter system appears to be more important for growth under moderately acidic conditions (11). The genes encoding this system are absent from most serotype 4 strains, and this generally correlates with a reduced ability of these strains to grow well at low pH (11). The role of GadD3 is less clear since it has not been possible to generate a deletion mutant lacking the corresponding gene (9).Although the activity of the decarboxylase is generally thought to be coupled directly to the antiporter activity (i.e., the efflux of GABA is coupled to the supply of Glu) there is little direct evidence for this, even in bacteria where the system has been very well characterized. Most studies of the bacterial GAD system have used complex growth media when studying acid tolerance and GABA production (7, 8, 15). In the present study, we sought to determine whether extracellular Glu is a requirement for the production of GABA in L. monocytogenes. To do this, we have used a chemically defined growth medium (DM) that supports the growth of L. monocytogenes but does not include Glu. The results indicate that cells cultured in this medium do not produce extracellular GABA (GABA_e) in response to low pH but are capable of accumulating substantial pools of intracellular GABA (GABA_i). We establish that some component of complex medium is indispensable for efficient efflux of GABA. Surprisingly, supplementation of the DM with Glu failed to stimulate the extracellular release of GABA. We show that the GadD2/GadT2 decarboxylase/antiporter system is not transcribed when cells are grown in DM and suggest that this accounts for much of the difference in GABA production between cells cultured in DM and complex growth medium.