A histidine-kinase cheA gene of Pseudomonas pseudoalcaligens KF707 not only has a key role in chemotaxis but also affects biofilm formation and cell metabolism

A histidine-kinase cheA gene in Pseudomonas pseudoalcaligenes KF707 plays a central role in the regulation of metabolic responses as well as in chemotaxis. Non-chemotactic mutants harboring insertions into the cheA gene were screened for their ability to form biofilms in the Calgary biofilm device. Notably, ≥95% decrease in the number of cells attached to the polystyrene surface was observed in cheA mutants compared to the KF707 wild-type biofilm phenotype. The ability to form mature biofilms was restored to wild-type levels, providing functional copies of the KF707 cheA gene to the mutants. In addition, phenotype micro-arrays and proteomic analyses revealed that several basic metabolic activities and a few periplasmic binding proteins of cheA mutant cells differed compared to those of wild-type cells. These results are interpreted as evidence of a strong integration between chemotactic and metabolic pathways in the process of biofilm development by P. pseudoalcaligenes KF707.     

A summer-winter comparison of zooplankton in the oceanic area Around South Georgia

Summary Zooplankton was sampled with RMT (1+8) gear on a synoptic grid of stations centred on South Georgia during the austral summer (November/December 1981) and winter (July/August 1983). This initial paper compares zooplankton biomass, vertical distribution and species composition from RMT 1 catches in the oceanic portion of the grid (water depth greater than 2000 m) during the two surveys. In the winter survey, mean zooplankton biomass within the top 1000 m of the water column was 68% of its summer level. This drop was largely due to a decrease in abundance of krill (Euphausia superba), although biomass of copepods and remaining zooplankton also decreased. Copepods averaged 48% of total biomass in summer and winter, but outnumbered all other taxa put together by a factor of 10. Antarctic epipelagic species predominated around the island in the summer survey but tended to be replaced by sub-Antarctic or cosmopolitan species during the winter survey. The majority of zooplankton also showed a downwards seasonal migration out of the top 250 m layer in winter. However, several epipelagic species, including E. superba, did not migrate, and these tended to have the largest summer-winter differences in overall abundance. These trends were attributed to variation in the position of the Polar Front, which lay north of the island during the summer survey but lay across the survey area in winter, resulting in a greater influence of sub-Antarctic water and the displacement of Antarctic species.     

Enzymatic activity and filament assembly of Acanthamoeba myosin II are regulated by adjacent domains at the end of the tail

Polyclonal antibodies raised against a synthetic peptide consisting of the last 19 amino acids at the end of the coiled-coil region of the heavy chains inhibited the actin-activated Mg2+-ATPase activity of myosin II and its ability to form filaments. Antibodies against a synthetic peptide corresponding to the 21 adjacent amino acids at the beginning of the non-helical tailpiece, which include the three regulatory phosphorylatable serines, had no effect on either activity.     

Characterisation of the first enzymes committed to lysine biosynthesis in Arabidopsis thaliana

In plants, the lysine biosynthetic pathway is an attractive target for both the development of herbicides and increasing the nutritional value of crops given that lysine is a limiting amino acid in cereals. Dihydrodipicolinate synthase (DHDPS) and dihydrodipicolinate reductase (DHDPR) catalyse the first two committed steps of lysine biosynthesis. Here, we carry out for the first time a comprehensive characterisation of the structure and activity of both DHDPS and DHDPR from Arabidopsis thaliana. The A. thaliana DHDPS enzyme (At-DHDPS2) has similar activity to the bacterial form of the enzyme, but is more strongly allosterically inhibited by (S)-lysine. Structural studies of At-DHDPS2 show (S)-lysine bound at a cleft between two monomers, highlighting the allosteric site; however, unlike previous studies, binding is not accompanied by conformational changes, suggesting that binding may cause changes in protein dynamics rather than large conformation changes. DHDPR from A. thaliana (At-DHDPR2) has similar specificity for both NADH and NADPH during catalysis, and has tighter binding of substrate than has previously been reported. While all known bacterial DHDPR enzymes have a tetrameric structure, analytical ultracentrifugation, and scattering data unequivocally show that At-DHDPR2 exists as a dimer in solution. The exact arrangement of the dimeric protein is as yet unknown, but ab initio modelling of x-ray scattering data is consistent with an elongated structure in solution, which does not correspond to any of the possible dimeric pairings observed in the X-ray crystal structure of DHDPR from other organisms. This increased knowledge of the structure and function of plant lysine biosynthetic enzymes will aid future work aimed at improving primary production.     

Suspended material availability and filtration–biodeposition processes performed by a native and invasive bivalve species in streams

Unionid mussels are among the most threatened group of freshwater organisms globally. They are known for their ability to filter food particles from flowing and standing waters. However, invasive bivalve species, such as the Asian clam (Corbicula fluminea) in North America, have the potential to overlap in feeding and potentially out-compete the native species. Yet, the feeding preferences of unionid mussels and C. fluminea are incompletely understood. We hypothesized that Elliptio crassidens (native) and C. fluminea (invasive) would select for specific organic components present within seston. We examined changes in seston (dry mass and ash-free dry mass) resulting from bivalve feeding activity for three size classes of material that were isolated using gravimetric filtration. The treatments were also sub-sampled for flow cytometry (FC) which separated the suspended materials in the stream water into five categories: detritus, heterotrophic bacteria, picoautotrophs, nanoautotrophs, and heterotrophic nanoeukaryotes. Our results indicated that both species of bivalve showed preferences for organic and living materials. E. crassidens preferentially filtered nanoeukaryotes, whose decreases were associated with an increase in bacteria. In contrast, C. fluminea preferred smaller materials through selective filtration of picoautotrophs. In addition, both species increased the concentration of large materials toward the end of the experiment because of the suspension of their pseudofeces biodeposits. To our knowledge, this study is the first to examine grazing by bivalve species on natural stream particulate matter using FC. Our results suggest that native and non-native mussels have different functional roles, which has important implications for organic matter processing and food webs in streams.     

Transient Activation of Plasmalemma K Efflux and H Influx in Tobacco by a Pectate Lyase Isozyme from Erwinia chrysanthemi

A purified pectate lyase isozyme derived from Erwinia chrysanthemi induced rapid net K⁺ efflux and H⁺ influx in suspension-cultured tobacco cells. Comparable fluxes of other ions (Na⁺, Cl⁻) were not observed. The K⁺ efflux/H⁺ influx response began within 15 minutes after addition of enzyme to cell suspensions and continued for approximately 1 hour after which cells resumed the net H⁺ efflux exhibited prior to enzyme treatment. The response was not prolonged by a second enzyme dose 1 hour after the first. The K⁺/H⁺ response was characterized by saturation at low enzymic activity (2 × 10⁻³ units per milliliter), and inhibition by the protonophore, carbonyl cyanide m-chlorophenylhydrazone, and was not associated with membrane leakiness caused by structural cell wall damage. The total K⁺ loss and H⁺ uptake induced by enzyme was one-fourth to one-third that induced by Pseudomonas syringae pv. pisi and did not reduce cell viability. These results indicate that pectate lyase induces a K⁺ efflux/H⁺ influx response in tobacco similar to but of shorter duration than that induced by P. syringae pv. pisi during the hypersensitive response. Pectate lyase or other cell wall degrading enzymes may therefore influence the induction of hypersensitivity.     

ENDOLITHIC MICROFLORA ARE MAJOR PRIMARY PRODUCERS IN DEAD CARBONATE SUBSTRATES OF HAWAIIAN CORAL REEFS1

To quantify the contribution of endolithic phototrophs to primary production of dead carbonate substrates, experimental blocks of cleaned Porites lobata Dana skeleton were placed at three different sites in Kaneohe Bay, Hawaii: inshore, lagoonal, and oceanic. After 6 months of exposure, experimental blocks were colonized by communities characteristic of their estuarine (inshore, lagoonal) and oceanic (ocean) environments. Blocks were sub-sampled; net photosynthesis (NP) and chl a concentrations of the whole blocks (epi- and endoliths) and scrapped blocks (only endoliths) were quantified. Green turf algae colonized predominantly inshore and lagoonal blocks, while encrusting corallines were the dominant epiliths colonizing oceanic blocks. Four main species of endolithic phototrophs were identified in all blocks: Mastigocoleus testarum Lagerheim, Plectonema terebrans Bornet and Flahault (cyanobacteria), Phaeophila dendroides Crouan and Crouan, and Ostreobium quekettii Bornet and Flahault (Chlorophytes). While epiliths were very different between sites, NP rates and chl a concentration of endoliths did not vary significantly and were positively correlated (191±25 mmol C·m⁻²·day⁻¹ and 590±150 mg chl a·m⁻² of reef, respectively). Assimilation numbers for whole communities, including both epilithic and endolithic communities, were similar to those measured for endolithic communities alone (average of 0.3 g C·g chl a·h⁻¹). Under experimental conditions, the contribution of endolithic phototrophs to community NP rates of blocks ranged from 56% to 81%, and under natural conditions, we estimated that this contribution ranged between 32% and 46%. Thus, we showed that the endolithic phototrophs are one of the major primary producers in dead coral substrates in a wide range of coral reef environments.     

Satisfaction (not) guaranteed: re-evaluating the use of animal models of type 1 diabetes

Without a doubt, rodent models have been instrumental in describing pathways that lead to pancreatic beta-cell destruction, evaluating potential causes of type 1 diabetes and providing proof-of-principle for the potential of immune-based interventions. However, despite more than two decades of productive research, we are still yet to define an initiating autoantigen for the human disease, to determine the precise mechanisms of beta-cell destruction in humans and to design interventions that prevent or cure type 1 diabetes. In this Perspective article, we propose that a major philosophical change would benefit this field, a proposition that is based on evaluation of situations in which rodent models have provided useful guidance and in which they have led to disappointments.