This article describes the development and preliminary validation of a brief questionnaire that assesses exposure to a broad range of potentially traumatic events. Items were generated from multiple sources of information. Events were described in behaviorally descriptive terms. consistent with Diagnostic ami Statistical Manual of Mental Disorders IV posttraumatic stress disorder stressor criterion A I. When events were endorsed, respondents were asked if they experienced intense fear, helplessness, or horror (stressor criterion A2). In separate studies with college students. Vietnam veterans. battered women. and residents of a substance abuse program. most items possessed adequate to excellent temporal stability. In a study comparing questionnaire and structured-interview inquiries of trauma history. the 2 formats yielded similar rates of disclosure. Preliminary data on positive predictive power are also presented. Traumatic events, such as exposure to warfare, disasters, serious accidents. sudden deaths of loved ones, and physical and sexual abuse, are commonplace. Epidemiological research suggests that at least two-thirds of American adults have experienced at least one traumatic event in the course of their lives (Norris, 1992;

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Pure cultures of the marine ammonium-oxidizing bacterium Nitrosomonas sp. were grown in the laboratory at oxygen partial pressures between 0.005 and 0.2 atm (0.18 to 7 mg/liter). Low oxygen conditions induced a marked decrease in the rate for production of N02 , from 3.6 x 1010 to 0.5 x 10`0 mmol of N02 per cell per day. In contrast, evolution of N20 increased from 1 x 10-12 to 4.3 x 10-12 mmol of N per cell per day. The yield of N20 relative to N02increased from 0.3% to nearly 10% (moles of N in N20 per mole of N02-) as the oxygen level was reduced, although bacterial growth rates changed by less than 30%. Nitrifying bacteria from the genera Nitrosomonas, Nitrosolobus, Nitrosospira, and Nitrosococcus exhibited similar yields of N20 at atmospheric oxygen levels. Nitriteoxidizing bacteria (Nitrobacter sp.) and the dinoflagellate Exuviaella sp. did not produce detectable quantities of N20 during growth. The results support the view that nitrification is an important source of N20 in the environment.

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Lipopolysaccharide (LPS), or endotoxin, is the major mediator of septic shock, a serious complication of Gram‐negative bacterial infections in humans. Molecules that bind LPS and neutralize its biological effects or enhance its clearance could have important clinical applications. Limulus anti‐LPS factor (LALF) binds LPS tightly, and, in animal models, reduces mortality when administered before or after LPS challenge or bacterial infection. Here we present the high resolution structure of a recombinant LALF. It has a single domain consisting of three alpha‐helices packed against a four‐stranded beta‐sheet. The wedge‐shaped molecule has a striking charge distribution and amphipathicity that suggest how it can insert into membranes. The binding site for LPS probably involves an extended amphipathic loop, and we propose that two mammalian LPS‐binding proteins will have a similar loop. The amphipathic loop structure may be used in the design of molecules with therapeutic properties against septic shock.

Three techniques for the measurement of bacterial numbers and biomass in the marine environment are described. Two are direct methods for counting bacteria. The first employs an epifluorescence microscope to view bacteria that have been concentrated on membrane filters and stained with acridine orange. The second uses a transmission electron microscope for observing replicas of bacteria that are concentrated on membrane filters. The other technique uses Limulus amebocyte lysate, an aqueous extract from the amebocytes of the horseshoe crab, Limulus polyphemus, to quantitate lipopolysaccharide (LPS) in seawater samples. The biomass of gram-negative (LPS containing) bacteria was shown to be related to the LPS content of the samples. A factor of 6.35 was determined for converting LPS to bacterial carbon.