When microbial strains compete for the same limiting nutrient in continuous culture, resource-based competition theory predicts that only one strain will survive and all others will die out. The surviving strain expected from theory will be the one with the smallest subsistence or "break-even" concentration of the limiting resource, a concentration defined by the J parameter. This prediction has been confirmed in the case of auxotrophic bacterial strains competing for limiting tryptophan. Because the value of J can be measured on the strains grown alone, the theory can predict the qualitative outcomes of mixed-growth competition in advance of actual competition.

Epithelial tissues provide both a physical barrier and an antimicrobial barrier. Antimicrobial peptides of the human β-defensin (hBD) family are part of the innate immune responses that play a role in mucosal defense. hBDs are made in epithelia including oral epithelium where the bacterial load is particularly great. hBD-2 and hBD-3 are up-regulated in response to bacterial stimuli. Previous studies show that hBD-2 expression in human gingival epithelial cells (GEC) is stimulated by both nonpathogenic and pathogenic bacteria, including Porphyromonas gingivalis, a Gram-negative pathogen associated with periodontitis. Present evidence suggests that hBD-2 expression in GEC uses several signaling pathways, including an NF-κB-mediated pathway but without apparent LPS-TLR4 signaling. Protease-activated receptors (PAR) are G-protein-coupled receptors that mediate cellular responses to extracellular proteinases. P. gingivalis secretes multiple proteases that contribute to its virulence mechanisms. To determine whether PAR signaling is used in hBD-2 induction, GEC were stimulated with wild-type P. gingivalis or mutants lacking one or more proteases. hBD-2 mRNA expression was reduced in GEC stimulated with single protease mutants (11–67% compared with wild type), strongly reduced in double mutants (0.1–16%), and restored to wild-type levels (93%) in mutant with restored protease activity. Stimulation by wild type was partially blocked by inhibitors of phospholipase C, a main signaling pathway for PARs. Expression of hBD-3 was unaffected. Peptide agonist of PAR-2, but not PAR-1 activator, also induced hBD-2 in GEC. Thus, P. gingivalis proteases are directly involved in regulation of hBD-2 in cultured GEC, and this induction partially uses the PAR-2 receptor and signaling pathway.

In an Upper Sonoran Grassland Community, three species of Pogonomyrmex ants coexist. Due to the similarity in their diets and the apparent limitation of food, coexistence is aided by the differential utilization of the available food, according to size and type. Interspecific differences in morphology, physiology and microhabitat nesting sites facilitate this division. Differences in morphology enable the foragers to handle and collect seeds of different size and, consequently, type. Differences in desiccation resistance enable the foragers to be active at different times and, consequently, incorporate different amounts of insect material into their diets. Differences in microhabitat nest sites offers the foragers different proportions of the desired food resource.

We assessed the ability of a standard set of freshwater single-species toxicity tests to predict accurately effects of the insecticide diflubenzuron (1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea) on complex laboratory stream communities. The single-species tests complied with requirements prescribed for establishing freshwater quality criteria and included nine freshwater animal acute tests, five freshwater animal chronic tests, and one freshwater algal test. The stream communities were stocked from a natural source, equilibrated for 3 mo and then treated with diflubenzuron for 5 mo. Effects on these stream communities were assessed at the functional group level using biomass and diversity for the analysis. The single-species tests adequately predicted the concentrations of diflubenzuron which affected these stream communities; the most-sensitive test species, insects and crustaceans, were up to an order of magnitude more sensitive than the observed community effects. The single-species tests were less successful in predicting the exact nature of the community level effects. Those effects resulting from direct lethality to component species were clearly predicted; indirect effects due to altered interspecies interactions could only be predicted with an a priori knowledge of the system's trophic dynamics.Key words: toxicity, diflubenzuron, streams, community effects, toxicity testing

Effects were assessed on the total biological community in complex laboratory streams caused by continuous exposure to diflubenzuron (1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl) urea). The insect fauna suffered direct toxic effects at concentrations of 1.0 microgram/L and greater. The algal and fungal floras were mildly affected at the same concentrations; apparently indirect effects in response to the reduced herbivore and shredder components of the insect fauna. No effects were observed on the bacteria, oligochaetes or gastropods, at any of the test concentrations. Within the insect fauna, differences in sensitivities were observed: mayflies and stoneflies were affected at 1.0 microgram/L, dipterans were affected at 10.0 microgram/L, and coleopterans were apparently unaffected at any of the test concentrations. Effects on caddisflies could not be determined due to their failure to become established in the stream systems. These differences between insect orders in sensitivity, coupled with differences in generation time, may reduce the overall benefits of the insecticide. For example, if diflubenzuron is used for chironomid control, the result may be more severe and longer lasting effects on nontarget mayfly and stonefly populations.