The biosynthetic pathway of ubiquinone contributes to pathogenicity of Francisella

Francisella tularensis is the causative agent of tularemia. Because of its extreme infectivity and high mortality rate, this pathogen was classified as a biothreat agent. Francisella spp are strict aerobe and ubiquinone (UQ) has been previously identified in these bacteria. While the UQ biosynthetic pathways were extensively studied in Escherichia coli allowing the identification of fifteen Ubi-proteins to date, little is known about Francisella spp. In this study, and using Francisella novicida as a surrogate organism, we first identified UQ8 as the major quinone found in the membranes of this bacterium. Then, we characterized the UQ biosynthetic pathway in F. novicida using a combination of bioinformatics, genetics and biochemical approaches. Our analysis disclosed the presence in Francisella of ten putative Ubi-proteins and we confirmed eight of them by heterologous complementation in E. coli. The UQ biosynthetic pathways from F. novicida and E. coli share a similar pattern. However, differences were highlighted: the decarboxylase remains unidentified in Francisella spp and homologs of the Ubi-proteins involved in the O2-independent UQ pathway are not present. This is in agreement with the strictly aerobic niche of this bacterium. Then, via two approaches, i.e. the use of an inhibitor (3-amino-4-hydroxybenzoic acid) and a transposon mutant, which both strongly impair the synthesis of UQ, we demonstrated that UQ is essential for the growth of F. novicida in a respiratory medium and contributes to its pathogenicity in Galleria mellonella used as an alternative animal model.

Respiratory medium and circulatory anatomy constrain size evolution in marine macrofauna

The typical marine animal has increased in biovolume by more than two orders of magnitude since the beginning of the Cambrian, but the causes of this trend remain unknown. We test the hypothesis that the efficiency of intra-organism oxygen delivery is a major constraint on body-size evolution in marine animals. To test this hypothesis, we compiled a dataset comprising 13,723 marine animal genera spanning the Phanerozoic. We coded each genus according to its respiratory medium, circulatory anatomy, and feeding mode. In extant genera, we find that respiratory medium and circulatory anatomy explain more of the difference in size than feeding modes. Likewise, we find that most of the Phanerozoic increase in mean biovolume is accounted for by size increase in taxa that accomplish oxygen delivery through closed circulatory systems. During the Cambrian, water-breathing animals with closed circulatory systems were smaller, on average, than contemporaries with open circulatory systems. However, genera with closed circulatory systems superseded in size genera with open circulatory systems by the Middle Ordovician, as part of their Phanerozoic-long trend of increasing size. In a regression analysis, respiratory and circulatory anatomy explain far more size variation in the living fauna than do feeding modes, even after accounting for taxonomic affinity at the class level. These findings suggest that ecological and environmental drivers of the Phanerozoic increase in the mean size of marine animals operated within strong, anatomically determined constraints.

The influence of feeding on aerial and aquatic oxygen consumption, nitrogenous waste excretion, and metabolic fuel usage in the African lungfish, Protopterus annectens

We studied the utilization of air versus water as a respiratory medium for O2 consumption (Mo2) in the bimodally breathing African lungfish, Protopterus annectens (Owen, 1839), (151.2 ± 3.7 g) at 26–28 °C. We also investigated the impact of a single meal on this respiratory allocation and nitrogenous waste excretion in lungfish entrained to a 48 h feeding cycle. Correction for the “microbial blank” was found to be critically important in assessing the aquatic component of Mo2. After correction, total Mo2 was low (~1000 μmol·kg–1·h–1), and lungfish took about 40% of Mo2 from water and 60% from air. Following a meal of chironomid larvae (3.3% of body mass), Mo2 values from both air and water increased in proportion over the first 3 h and continued to increase to a peak at 5–8 h postfeeding, at which point total Mo2 (still 40% from water) was approximately 2.5-fold greater than the prefeeding level. When the same fish, entrained to the same 48 h feeding regime, were fasted, Mo2 declined then later increased prior to the next anticipated feeding. In fed fish, the elevation in Mo2 relative to fasted values was approximately 3-fold at 0–3 h and 9-fold at 5–8 h. This specific dynamic action (SDA) effect lasted until 23–26 h and amounted to only 9.5% of the oxycalorific content of the ingested meal. N-waste efflux was only slightly elevated after feeding, where there was a tendency for greater urea–N excretion (significant at 42–48 h); however, the lungfish remained ammoniotelic overall during the 48 h postfeeding period.

Mechanisms of ventilation in lower vertebrates: adaptations to respiratory and nonrespiratory constraints

The design of vertebrate respiratory systems has been subject to two major sets of constraints. The first is the need to satisfy the primary function of the respiratory surface as an organ of gas exchange. These constraints include the need to reduce the diffusion gradient between air and blood while providing adequate ventilation and perfusion of the exchange surface. The second set of constraints arises from the need to satisfy other physiological, environmental, and behavioral demands. The constraints imposed by the low oxygen content and high density of water as a respiratory medium, the rigid shell of turtles, and the long thin body of snakes, as well as the life-style and habitat of diving animals, are all used to illustrate the unique features of several experiments in the design and performance of respiratory pumps. It is shown, however, that despite the tremendous diversity that exists among species, all mechanisms allow ventilation to be powered by surprisingly similar changes in pulmonary pressure.

Biomodal Gas Exchange During Variation in Environmental Oxygen and Carbon Dioxide in the Air Breathing Fish Trichogaster Trichopterus

Gas exchange in the gourami, Trichogaster trichopterus, an obligate air breather, is achieved both by branchial exchange with water and aerial exchange via labyrinth organs lying within the suprabranchial chamber. Ventilation of the suprabranchial chamber, MOO2, MCOCO2, gas exchange ratios of both gills and labyrinth organs, and air convection requirements have been measured under conditions of hypoxia, hyperoxia or hypercapnia in either water or air. In undisturbed fish in control conditions (27 °C), air breathing frequency was 12 breaths/h, gas tidal volume 30 μl/g, total oxygen uptake 5.2 μ.M/g/h and total carbon dioxide excretion 4.1 μM/g/h, indicating a total gas exchange ratio of approximately 0.8. The aerial labyrinth organs accounted for 40% of oxygen uptake but only 15% of carbon dioxide elimination. Hypoxia, in either inspired water or air, stimulated air breathing. Total MOO2 was continuously maintained at or above control levels by an augmentation of oxygen uptake by the labyrinth during aquatic hypoxia or by the gills during aerial hypoxia. Hypoxia had no effect on MCOl partitioning between air and water. Hypercapnia in water greatly stimulated air breathing. About 60% of total MCOCO2 then occurred via aerial excretion, a situation unusual among air breathing fish, enabling the overall gas exchange to remain at control levels. Aerial hypercapnia had no effect on air breathing or O2 partitioning, but resulted in a net aerial CO2 uptake and a decrease in overall gas exchange ratio. Trichogaster is thus an air breathing fish which is able to maintain a respiratory homeostasis under varying environmental conditions by exploiting whichever respiratory medium at a particular time is the most effective for O2 uptake and CO2 elimination.

Studies on the Queensland Lungfish, Neoceratodus forsteri (Krefft).

The lung of Neoceratodus forsteri consists of a single elongated sac dorsal to the gut and attached firmly along the dorsal mid-line in the region of the vertebral column. It communicates with the gut through the pneumatic duct which opens ventrolaterally via the glottis, on the right side of the pharynx. The embryological origin of the lung as a ventral outgrowth from the gut is reflected in the marked similarity between their tissues, and in the unusual configuration of the duct and blood vessels. Internally, the lung is divided into compartments formed by septa resulting from infolding of the walls. These compartments are further subdivided to form a spongy alveolar region. In this region of increased surface area run blood capillaries in proximity to the respiratory medium, close enough to allow gaseous exchange with it. Filling the lung is accomplished by a buccal force-pump, as in Amphibia, consisting of the hyoid apparatus and the muscular walls of the buccal cavity. Exhalation of air is effected by contraction of the smooth muscle components of the lung, assisted by its natural elasticity provided by elastin fibres present in both connective tissue and smooth muscle. The structure of the lung, its spongy walls, vascular supply with capillaries close to the air space, open pneumatic duct, regular exchange of air at the surface of the water, and the ability of the fish to survive out of water if kept moist, all point to the function of the lung as a respiratory organ. This is borne out by lung-gas analyses which consistently show lower oxygen level compared with air.