Multiple genes affect sensitivity of Caenorhabditis elegans to the bacterial pathogen Microbacterium nematophilum

Interactions with bacteria play a major role in immune responses, ecology, and evolution of all animals, but they have been neglected until recently in the case of C. elegans. We report a genetic investigation of the interaction of C. elegans with the nematode-specific pathogen Microbacterium nematophilum, which colonizes the rectum and causes distinctive tail swelling in its host. A total of 121 mutants with altered response to infection were isolated from selections or screens for a bacterially unswollen (Bus) phenotype, using both chemical and transposon mutagenesis. Some of these correspond to known genes, affecting either bacterial adhesion or colonization (srf-2, srf-3, srf-5) or host swelling response (sur-2, egl-5). Most mutants define 15 new genes (bus-1-bus-6, bus-8, bus-10, bus-12-bus-18). The majority of these mutants exhibit little or no rectal infection when challenged with the pathogen and are probably altered in surface properties such that the bacteria can no longer infect worms. A number have corresponding alterations in lectin staining and cuticle fragility. Most of the uninfectable mutants grow better than wild type in the presence of the pathogen, but the sur-2 mutant is hypersensitive, indicating that the tail-swelling response is associated with a specific defense mechanism against this pathogen.     

Maternal nutrient restriction reduces concentrations of amino acids and polyamines in ovine maternal and fetal plasma and fetal fluids

Amino acids and polyamines are essential for placental and fetal growth, but little is known about their availability in the conceptus in response to maternal undernutrition. We hypothesized that maternal nutrient restriction reduces concentrations of amino acids and polyamines in the ovine conceptus. This hypothesis was tested in nutrient-restricted ewes between Days 28 and 78 (experiment 1) and between Days 28 and 135 (experiment 2) of gestation. In both experiments, ewes were assigned randomly on Day 28 of gestation to a control group fed 100% of National Research Council (NRC) nutrient requirements and to an nutrient-restricted group fed 50% of NRC requirements. Every 7 days beginning on Day 28 of gestation, ewes were weighed and rations adjusted for changes in body weight. On Day 78 of gestation, blood samples were obtained from the uterine artery and umbilical vein for analysis. In experiment 2, nutrient-restricted ewes on Day 78 of gestation either continued to be fed 50% of NRC requirements or were realimented to 100% of NRC requirements until Day 135. Fetal weight was reduced in nutrient-restricted ewes at both Day 78 (32%) and Day 135 (15%) compared with controls. Nutritional restriction markedly reduced (P < 0.05) concentrations of total alpha-amino acids (particularly serine, arginine-family amino acids, and branched-chain amino acids) and polyamines in maternal and fetal plasma and in fetal allantoic and amniotic fluids at both mid and late gestation. Realimentation of nutrient-restricted ewes increased (P < 0.05) concentrations of total alpha-amino acids and polyamines in all the measured compartments and prevented intrauterine growth retardation. These novel findings demonstrate that 50% global nutrient restriction decreases concentrations of amino acids and polyamines in the ovine conceptus that could adversely impact key fetal functions. The results have important implications for understanding the mechanisms responsible for both intrauterine growth retardation and developmental origins of adult disease.     

Central leptin stimulates ingestive behavior and urine flow in the near term ovine fetus.

Leptin inhibits ingestive behavior and induces diuresis and natriuresis. To examine whether leptin influences fetal physiologic functions, we investigated the effect of central leptin on ovine fetal swallowing activity and urine flow. Six pregnant ewes with singleton fetuses (130 +/- 2 d gestation) were prepared with maternal and fetal arterial and venous catheters, fetal lateral intra-ventricle cannula, fetal bladder and amniotic fluid catheters. Electromyogram wires were placed in the fetal thyrohyoid muscle and upper and lower nuchal esophagus and electrodes were implanted on the parietal dura. Five days after surgery, recombinant human leptin was infused into the lateral ventricle and the fetus monitored for 8 h. Central leptin increased fetal swallowing activity during low-voltage electrocortical activity from basal values (0.96 +/- 0.08 swallows/min) at 2 h (1.41 +/- 0.24 swallows/min), 4 h (2.81 +/- 0.57 swallows/min), 6 h (2.53 +/- 0.59 swallows/min) and 8 h (2.08 +/- 0.39 swallows/min, p < 0.05). In comparison to basal values, low voltage electrocortical activity decreased (57 +/- 5% to 42 +/- 4%) and high voltage electrocortical increased (43 +/- 5% to 61 +/- 4%). In response to leptin, fetal urine flow initially decreased from basal values at 2 h (0.12 +/- 0.03 to 0.08 +/- 0.02 ml/kg/min, p < 0.05) then subsequently increased at 4 h and 6 h (0.20 +/- 0.04; 0.21 +/- 0.04 ml/kg/min, respectively, p < 0.05). Central leptin significantly increases near term ovine fetal swallowing activity and urine output, suggesting that leptin contributes to in utero development of ingestive behavior.     

Bacterial olfaction

Sensing their environment is a crucial ability of all life forms. In higher eukaryotes the sensing of airborne volatile compounds, or olfaction, is well developed. In plants, slime moulds and yeast there is also compelling evidence that these organisms can smell their environment and respond accordingly. Here we show that bacteria are also capable of olfaction. Bacillus licheniformis was able to sense airborne volatile metabolites produced by neighbouring bacterial cultures and cells could respond to this chemical information in a coordinated way. When Bacillus licheniformis was grown in a microtitre plate adjacent to a bacterial culture of the same or a different species, growing in complex medium, biofilm formation and pigment production were elicited by volatile molecules. A weaker response occurred in increasingly distant wells. The emitted volatile molecule was identified as ammonia. These data demonstrate that B. licheniformis has evolved the ability collect information about its environment from the surrounding air and physiologically respond to it in a manner similar to olfaction. This is the first time that a behavioural response triggered by odorant molecules received through the gas phase is described in bacteria.     

Dispersal of biofilms by secreted, matrix degrading, bacterial DNase

Microbial biofilms are composed of a hydrated matrix of biopolymers including polypeptides, polysaccharides and nucleic acids and act as a protective barrier and microenvironment for the inhabiting microbes. While studying marine biofilms, we observed that supernatant produced by a marine isolate of Bacillus licheniformis was capable of dispersing bacterial biofilms. We investigated the source of this activity and identified the active compound as an extracellular DNase (NucB). We have shown that this enzyme rapidly breaks up the biofilms of both Gram-positive and Gram-negative bacteria. We demonstrate that bacteria can use secreted nucleases as an elegant strategy to disperse established biofilms and to prevent de novo formation of biofilms of competitors. DNA therefore plays an important dynamic role as a reversible structural adhesin within the biofilm.     

Carbon and Water Footprints and Energy Use of Greenhouse Tomato Production in Northern Italy

This study reports on the carbon, water, and energy footprints of tomatoes grown in a greenhouse in Northern Italy and two possible future variations of heating and carbon dioxide (CO₂) fertilization on the current setup. The heat supply in place, consisting of natural gas (NG) and canola oil combustion, is compared to cogeneration and incineration of municipal solid waste for heating and CO₂ from industrial exhaust for fertilization. As a benchmark, the current system is also compared to a conventional system, in which heat is delivered solely based on NG. Each kilogram (kg) of fresh tomatoes (“Cuore di Bue” variety) produced in the current greenhouse emits 2.28 kg CO₂ equivalents (eq) and uses 95.5 megajoules (MJ) eq energy and 122 liters (L) of water. Relative to the system in place, the carbon footprint (CF) is 57.5% and 18% higher with conventional NG heating and cogeneration and is 40% lower with waste valorization. Further, 33%, 55%, and 63% less energy and 9%, 96%, and 14% less water are used in the conventional, cogeneration, and waste valorization scenarios, respectively. This confirms that there are multiple strategies to reduce the impact of the tomato production under consideration.