Diabetic cardiomyopathy is accompanied by metabolic and ultrastructural alterations, but the impact of the structural changes on metabolism itself is yet to be determined. Morphometric analysis of mitochondrial shape and spatial organization within transverse sections of cardiomyocytes from control and streptozotocin-induced type I diabetic Sprague-Dawley rats revealed that mitochondria are 20% smaller in size while their spatial density increases by 53% in diabetic cells relative to control myocytes. Diabetic cells formed larger clusters of mitochondria (60% more mitochondria per cluster) and the effective surface-to-volume ratio of these clusters increased by 22.5%. Using a biophysical computational model we found that this increase can have a moderate compensatory effect by increasing the availability of ATP in the cytosol when ATP synthesis within the mitochondrial matrix is compromised.

No abstract

Summary — Using Serratia marcescens as an indicator bacterium and the worker brood of the honey bee, experiments have shown that Varroa jacobsoni transmits bacterial infections to a recipient bee host. Integument and haemolymph of brood artificially contaminated with S marcescens, preferably individuals with Serratia septicaemia, were the source of bacterial contamination of the mites. The infected parasites during feeding carry S marcescens to about 20% of the healthy brood.

Based on the ability of bacterial associates of entomopathogenic nematodes to produce antibiotic compounds on artificial media, it has been commonly accepted that Xenorhabdus sp. and Photorhabdus sp. inhibit a wide range of invading microorganisms in insects infected with Steinernema spp. or Heterorhabditis spp. Therefore, the question of whether antibiotic compounds produced by the primary form of bacterial symbionts associated mutualistically with S. carpocapsae and H. bacteriophora explain why insect carcasses do not putrefy but provide nutritional requirements for insect parasitic rhabditoid nematodes to complete their life-cycle was examined. Laboratory bioassays of anti-bacterial activity on nutrient agar and during parasitism in larvae of Galleria mellonella have confirmed earlier observations that in virto colonies of the primary form of X. nematophilus and P. luminescens produced agar-diffusible antibiotic compounds of a broad spectrum of anti-bacterial activity; their role in parasitism seems doubtful, however. This hypothesis is supported by a low antibiotic potency of a limited spectrum of anti-bacterial activity throughout the life-cycle of the parasites, principally in Galleria infected with S. carpocapsae. Since the lack of putrefaction cannot be explained simply by antibiotic inhibition of contaminating bacterial microflora, other competition mechanisms must be operating in parasitized insects. I postulated that a rapid and massive colonization of the insect body by nematophilic bacteria creates unfavorable conditions for the growth and multiplication of bacterial (proteolytic) contaminators making the insect carcass decay-resistant. In the case of H. bacteriophora, low antibiotic activity at an early stage of parasitism could support the colonization by P. luminescens of the host.

A specific extracellular proteinase, degrading selectively the cecropin-based defence system of insects, is secreted into the larval body during parasitism of the greater wax moth by the Heterorhabditis bacteriophora/Photorhabdus luminescens complex and by phase 1 of P. luminescens. The proteolytic digestion of insect inducible cecropin-like immune molecules was demonstrated by the disappearance of the Galleria mellonella cecropins and purified Hyalophora cecropin B peptide PAGE bands upon exposure to infected extracts, and a similar abrogation of antibacterial activity using an agar diffusion assay. Proteolytic activity of infected extracts produced by nematode/bacterial complex and phase 1 variant of P. luminescens was shown to be correlated with cecropin-inhibitory activity, suggesting that this anti-cecropin agent may be responsible for the ability of bacteria to establish infection and the insecticidal nature of H. bacteriophora. Antibacterial activity of Galleria lysozyme and that of chicken egg-white lysozyme to which P. luminescens is insensitive, was unaffected by H. bacteriophora proteinase.