Interactions Among Fuel Management,Species Composition,Bark Beetles,and Climate Change and the Potential Effects on Forests of the Lake Tahoe Basin

Climate-driven increases in wildfires, drought conditions, and insect outbreaks are critical threats to forest carbon stores. In particular, bark beetles are important disturbance agents although their long-term interactions with future climate change are poorly understood. Droughts and the associated moisture deficit contribute to the onset of bark beetle outbreaks although outbreak extent and severity is dependent upon the density of host trees, wildfire, and forest management. Our objective was to estimate the effects of climate change and bark beetle outbreaks on ecosystem carbon dynamics over the next century in a western US forest. Specifically, we hypothesized that (a) bark beetle outbreaks under climate change would reduce net ecosystem carbon balance (NECB) and increase uncertainty and (b) these effects could be ameliorated by fuels management. We also examined the specific tree species dynamics—competition and release—that determined NECB response to bark beetle outbreaks. Our study area was the Lake Tahoe Basin (LTB), CA and NV, USA, an area of diverse forest types encompassing steep elevation and climatic gradients and representative of mixed-conifer forests throughout the western United States. We simulated climate change, bark beetles, wildfire, and fuels management using a landscape-scale stochastic model of disturbance and succession. We simulated the period 2010–2100 using downscaled climate projections. Recurring droughts generated conditions conducive to large-scale outbreaks; the resulting large and sustained outbreaks significantly increased the probability of LTB forests becoming C sources over decadal time scales, with slower-than-anticipated landscape-scale recovery. Tree species composition was substantially altered with a reduction in functional redundancy and productivity. Results indicate heightened uncertainty due to the synergistic influences of climate change and interacting disturbances. Our results further indicate that current fuel management practices will not be effective at reducing landscape-scale outbreak mortality. Our results provide critical insights into the interaction of drivers (bark beetles, wildfire, fuel management) that increase the risk of C loss and shifting community composition if bark beetle outbreaks become more frequent.     

An Escherichia coli mutant unable to support site-specific recombination of bacteriophage lambda

We report the isolation of mutations in, and the characterization of, an Escherichia coli gene, hip, that is required for site-specific recombination of phage lambda. hip mutants are recessive and are located near minute 20 on the linkage map. The gene product is not vital to bacterial growth, since deletion mutants are viable. The absence of hip product reduces lambda integration to barely detectable levels and also reduces prophage excision, but less drastically. Certain mutations in the lambda int gene partially restore integration and excision in hip- hosts. Homologous recombination promoted by recA does not require hip function. In addition to their defect in site-specific recombination, hip mutants are unable to support lytic growth of phage Mu or of certain lambda mutants. Their pleiotropic phenotype closely resembles that of himA mutants, but complementation, mapping and DNA sequencing show that hip and himA are different genes.     

Regulation of cardiac contractile proteins by phosphorylation

Several of the contractile proteins of the heart can be phosphorylated, but in studies with isolated proteins only phosphorylation of the inhibitory subunit of troponin (TnI) produces a major change in the properties of the contractile system. As TnI is phosphorylated, the concentration of calcium required for activation of contraction is increased. Phosphorylation of the tropomyosin-binding subunit of troponin (TnT) or of the light chain of myosin fails to change ATPase activity of the isolated protein system. Phosphorylation of TnI is stimulated by the beta-adrenergic system and inhibited by the cholinergic system. Maximum calcium-activated force produced by the contractile system can be increased in hyperpermeable cardiac cells by cyclic AmP (cAMP) or agents that stimulate cAMP synthesis. This change in the contractile system, which appears to be part of the physiological response to beta-adrenergic stimulation, is mediated by phosphorylation of an intermediate that then modifies the contractile system. Phosphorylation of the contractile proteins is not involved.     

Ultrastructure ofAspergillus nidulans conidia and conidial lomasomes

Summary Lomasomes in the conidia ofAspergillus nidulans can be divided into at least two distinct structures. The first is a twice double membrane bound core of cytoplasmic origin. The outermost membrane of the lomasome becomes incorporated into the plasmalemma as it migrates to rest next to the cell wall. The second lomasome structure appears to be a triangle shaped series of tubules arranged in a parallel fashion. The wide end next to the cell wall connected to the plasmalemma and the opposite end to an element of the endoplasmic reticulum. The term membranosome has been coined to designate this lomasome structure with its function of plasmalemma extension. Various structures of the conidium such as wall, endoplasmic reticulum and the cytoplasmic matrix undergo changes from the conidial chain stage to the free or resting conidial stage. This suggests that after conidiation and before the resting stage, the conidium continues to mature.     

The A34R glycoprotein gene is required for induction of specialized actin-containing microvilli and efficient cell-to-cell transmission of vaccinia virus.

The mechanisms allowing vaccinia virus to spread from cell to cell are incompletely understood. The A34R gene of vaccinia virus encodes a glycoprotein that is localized in the outer membranes of extracellular virions. The small-plaque phenotype of an A34R deletion mutant was similar to that of mutants with deletions in other envelope genes that fail to produce extracellular vaccinia virions. Transmission electron microscopy, however, revealed that the A34R mutant produced numerous extracellular particles that were labeled with antibodies to other outer-envelope proteins and with protein A-colloidal gold. Fluorescence and scanning electron microscopy indicated that expression of the A34R protein was necessary for detection of vaccinia virus-induced actin tails, which provide motility to the intracellular enveloped form of vaccinia virus, and of virus-tipped specialized microvilli that project from the cell. The ability of vaccinia virus-infected cells to form syncytia after a brief exposure to a pH below 6, known as fusion from within, failed to occur in the absence of expression of the A34R protein; nevertheless, purified A34R- virions were capable of mediating low-pH-induced fusion from without. The present study provides genetic and microscopic evidence for the involvement of a specific viral protein in the formation or stability of actin-containing microvilli and for a role of these structures in cell-to-cell spread rather than in formation of extracellular virions.     

On the role of the bacteriophage lambda int gene product in site specific recombination

Integrative recombination of phage λ DNA occurs in extracts made from cells synthesizing int protein. In this paper we show that extracts of cells containing temperature-sensitive int protein are inactivated more rapidly by incubation at 38 °C than are wild-type extracts. This indicates that the int protein is directly involved in the recombination reaction.     

Packaging of coliphage lambda DNA. I. The role of the cohesive end site and the gene A protein

The cohesive ends of the DNA of bacteriophage λ particles are normally formed by the action of a nuclease on the cohesive end sites (cos) of concatemeric λ DNA (reviewed by Hohn et al., 1977). The nuclease also cuts the cos site of an integrated prophage, and DNA located to the right is preferentially packaged into phage particles. This process occurs with approximately the same efficiency and rate in a single lysogen as in a tandem polylysogen. Thus, the rate of cos cutting does not increase when the number of cos sites per molecule increases, an hypothesis that has been proposed to explain why cohesive ends are not formed in circular monomers of λ DNA. We propose instead that the interaction of Ter with cos is influenced by the configuration of the DNA outside of cos during packaging, and that this configuration is different for circular monomers than for other forms of λ DNA. A model that gives rise to such a difference is described.We also found that missense mutations in the λ A gene changed the efficiency of packaging of phage relative to host DNA. This was not the case for missense mutations in several phage genes required for capsid formation. Thus, the product of gene A plays a role in determining packaging specificity, as expected if it is or is part of the nuclease that cuts λ DNA at cos.     

Ingestion,egestion, excretion,growth, and conversion efficiency for the mummichog, Fundulus heteroclitus (L.)

The food conversion efficiency of Fundulus heteroclitus (L.) was measured in terms of calories and nitrogen for three diets: Palaemonetes sp., Nereis sp., and Uca pugnax. Fish were allowed to feed ad libitum for 30–60 min each day. Growth, ingestion, egestion, and excretion were measured for fish fed each diet. The growth rates of Fundulus heteroclitus fed two of the single item diets of invertebrates were higher than growth rates previously estimated for mummichogs from the natural population in Canary Creek marsh. In comparison with other fish species, F. heteroclitus was found to have a higher than average assimilation efficiency ($\text{X}\text{?}\text{= 87\%}$ for all three diets) and a lower than average gross growth efficiency (≈12% for two of the diets). Metabolic costs accounted for an average of 69% of ingested energy. Excretion rates were also large, with excretion accounting for more energy than egestion in two of the three diets.