STREPTOCOCCAL L-FORMS IV. : Comparison of the Metabolic Rates of a Streptococcus and Derived L-Form.

Panos, Charles (University of Illinois College of Medicine, Chicago, and Albert Einstein Medical Center, Philadelphia, Pa.). Streptococcal L-forms. IV. Comparison of the metabolic rates of a Streptococcus and derived L-form. J. Bacteriol. 84:921-928. 1962.-Glycolytic rates of hexoses, amino sugars, pentoses, two-carbon compounds, and certain intermediates of glycolysis and the adaptive response to glucose of a group A Streptococcus and its derived L-form were compared. It was found that removal of the streptococcal cell wall did not result in the loss of the homolactic characteristic of the parent coccus or in a marked increase in the metabolism of certain glycolytic intermediates by the L-form. It was shown that (i) a major difference exists between the coccus and its L-form in the metabolism of glucosamine and N-acetylglucosamine; (ii) apparently, a loss of selectivity and internal control occurred in the transformation to the L-form; and (iii) this form, unlike the parent coccus, displayed an adaptive response to glucose. These data were not the result of an internal loss of essential cofactors or enzymes by diffusion from within the L-form. Nor could they be accounted for by dry-weight differences due to loss of the streptococcal cell wall. Finally, it was observed that the sonically disintegrated L-form in 0.5 m NaCl was capable of a glycolytic activity of 46% of that of the total intact culture. These data suggest that the conversion of a streptococcus to the L-form is accompanied by an alteration in carbohydrate metabolism as well as the loss of the cell wall. Previously reported data are in agreement with these findings and support the conclusion that the resulting form is not merely a bacterial cell without a rigid cell wall.     

Asymmetrical intraguild predation between natural enemies of the citrus mealybug

The ability of a predator to discriminate against parasitized prey determines the extent of asymmetrical intraguild predation, which is often crucial for the outcome of biological control. Anagyrus nr. pseudococci (Girault) (Hymenoptera: Encyrtidae), a parasitoid of the citrus mealybug, Planococcus citri (Risso) (Hemiptera: Pseudococcidae), suffers from intraguild predation by coccinellids occurring in the same habitat. The level of intraguild predation on A. nr. pseudococci by Nephus includens (Kirsch) (Coleoptera: Coccinellidae) at different immature stages has been investigated with and without simultaneous offer of extraguild prey. Larvae of A. nr. pseudococci appeared to face increased intraguild predation at early developmental stages, whereas mummification provided adequate protection against the predatory coccinellid. Different predation levels on unparasitized vs. parasitized hosts at various developmental stages in choice assays indicated that N. includens preferences might be determined not solely by palatability of the prey but also by its ability to protect itself.     

Modulation of macrophage infiltration and inflammatory activity by the phosphatase SHP-1 in virus-induced demyelinating disease

The protein tyrosine phosphatase SHP-1 is a crucial negative regulator of cytokine signaling and inflammatory gene expression, both in the immune system and in the central nervous system (CNS). Mice genetically lacking SHP-1 (me/me) display severe inflammatory demyelinating disease following inoculation with the Theiler's murine encephalomyelitis virus (TMEV) compared to infected wild-type mice. Therefore, it became essential to investigate the mechanisms of TMEV-induced inflammation in the CNS of SHP-1-deficient mice. Herein, we show that the expression of several genes relevant to inflammatory demyelination in the CNS of infected me/me mice is elevated compared to that in wild-type mice. Furthermore, SHP-1 deficiency led to an abundant and exclusive increase in the infiltration of high-level-CD45-expressing (CD45^hi) CD11b⁺ Ly-6C^hi macrophages into the CNS of me/me mice, in concert with the development of paralysis. Histological analyses of spinal cords revealed the localization of these macrophages to extensive inflammatory demyelinating lesions in infected SHP-1-deficient mice. Sorted populations of CNS-infiltrating macrophages from infected me/me mice showed increased amounts of viral RNA and an enhanced inflammatory profile compared to wild-type macrophages. Importantly, the application of clodronate liposomes effectively depleted splenic and CNS-infiltrating macrophages and significantly delayed the onset of TMEV-induced paralysis. Furthermore, macrophage depletion resulted in lower viral loads and lower levels of inflammatory gene expression and demyelination in the spinal cords of me/me mice. Finally, me/me macrophages were more responsive than wild-type macrophages to chemoattractive stimuli secreted by me/me glial cells, indicating a mechanism for the increased numbers of infiltrating macrophages seen in the CNS of me/me mice. Taken together, these findings demonstrate that infiltrating macrophages in SHP-1-deficient mice play a crucial role in promoting viral replication by providing abundant viral targets and contribute to increased proinflammatory gene expression relevant to the effector mechanisms of macrophage-mediated demyelination.     

Patch residence decisions made by Aphidius colemani in the presence of a facultative predator

One of the key questions in ecology is how animals optimally allocate their time in an environment with patchily distributed resources and competing organisms. Here we investigate the effects that an aphid predator, Macrolophus caliginosus (Wagner) (Hemiptera: Miridae), has on the searching behavior and the patch residence decisions of an aphid parasitoid, Aphidius colemani (Viereck) (Hymenoptera: Aphidiidae). A computer programme was designed that allowed the recording and saving of direct observations. The time allocated to different activities by a female parasitoid wasp in the presence or absence of the predator M. caliginosus was investigated. The experiments were conducted under controlled environment conditions using leaves of sweet pepper, Capsicum annuum L. (Solanaceae) and Myzus persicae (Sulzer) (Hemiptera: Aphididae) as the host plant–prey species system. The parasitoid spent significantly less time on ‘secondary’ activities, such as preening and resting, when the predator was present. Survival analysis showed that the parasitoid had a higher patch-leaving tendency when the predator was present.     

Presenilin-based genetic screens in Drosophila melanogaster identify novel notch pathway modifiers

Presenilin is the enzymatic component of gamma-secretase, a multisubunit intramembrane protease that processes several transmembrane receptors, such as the amyloid precursor protein (APP). Mutations in human Presenilins lead to altered APP cleavage and early-onset Alzheimer's disease. Presenilins also play an essential role in Notch receptor cleavage and signaling. The Notch pathway is a highly conserved signaling pathway that functions during the development of multicellular organisms, including vertebrates, Drosophila, and C. elegans. Recent studies have shown that Notch signaling is sensitive to perturbations in subcellular trafficking, although the specific mechanisms are largely unknown. To identify genes that regulate Notch pathway function, we have performed two genetic screens in Drosophila for modifiers of Presenilin-dependent Notch phenotypes. We describe here the cloning and identification of 19 modifiers, including nicastrin and several genes with previously undescribed involvement in Notch biology. The predicted functions of these newly identified genes are consistent with extracellular matrix and vesicular trafficking mechanisms in Presenilin and Notch pathway regulation and suggest a novel role for gamma-tubulin in the pathway.     

Helicase binding to DnaI exposes a cryptic DNA-binding site during helicase loading in Bacillus subtilis

The Bacillus subtilis DnaI, DnaB and DnaD proteins load the replicative ring helicase DnaC onto DNA during priming of DNA replication. Here we show that DnaI consists of a C-terminal domain (Cd) with ATPase and DNA-binding activities and an N-terminal domain (Nd) that interacts with the replicative ring helicase. A Zn²⁺-binding module mediates the interaction with the helicase and C67, C70 and H84 are involved in the coordination of the Zn²⁺. DnaI binds ATP and exhibits ATPase activity that is not stimulated by ssDNA, because the DNA-binding site on Cd is masked by Nd. The ATPase activity resides on the Cd domain and when detached from the Nd domain, it becomes sensitive to stimulation by ssDNA because its cryptic DNA-binding site is exposed. Therefore, Nd acts as a molecular ‘switch’ regulating access to the ssDNA binding site on Cd, in response to binding of the helicase. DnaI is sufficient to load the replicative helicase from a complex with six DnaI molecules, so there is no requirement for a dual helicase loader system.