Malpighamoeba infection compromises fluid secretion and P-glycoprotein detoxification in Malpighian tubules.

Malpighian tubules, analogous to vertebrate nephrons, play a key role in insect osmoregulation and detoxification. Tubules can become infected with a protozoan, Malpighamoeba, which damages their epithelial cells, potentially compromising their function. Here we used a modified Ramsay assay to quantify the impact of Malpighamoeba infection on fluid secretion and P-glycoprotein-dependent detoxification by desert locust Malpighian tubules. Infected tubules have a greater surface area and a higher fluid secretion rate than uninfected tubules. Infection also impairs P-glycoprotein-dependent detoxification by reducing the net rhodamine extrusion per surface area. However, due to the increased surface area and fluid secretion rate, infected tubules have similar total net extrusion per tubule to uninfected tubules. Increased fluid secretion rate of infected tubules likely exposes locusts to greater water stress and increased energy costs. Coupled with reduced efficiency of P-glycoprotein detoxification per surface area, Malpighamoeba infection is likely to reduce insect survival in natural environments.

Busting biofilms: free-living amoebae disrupt preformed methicillin-resistant Staphylococcus aureus (MRSA) and Mycobacterium bovis biofilms.

Biofilm-associated infections are difficult to eradicate because of their ability to tolerate antibiotics and evade host immune responses. Amoebae and/or their secreted products may provide alternative strategies to inhibit and disperse biofilms on biotic and abiotic surfaces. We evaluated the potential of five predatory amoebae - Acanthamoeba castellanii, Acanthamoeba lenticulata, Acanthamoeba polyphaga, Vermamoeba vermiformis and Dictyostelium discoideum - and their cell-free secretions to disrupt biofilms formed by methicillin-resistant Staphylococcus aureus (MRSA) and Mycobacterium bovis. The biofilm biomass produced by MRSA and M. bovis was significantly reduced when co-incubated with A. castellanii, A. lenticulata and A. polyphaga, and their corresponding cell-free supernatants (CFS). Acanthamoeba spp. generally produced CFS that mediated biofilm dispersal rather than directly killing the bacteria; however, A. polyphaga CFS demonstrated active killing of MRSA planktonic cells when the bacteria were present at low concentrations. The active component(s) of the A. polyphaga CFS is resistant to freezing, but can be inactivated to differing degrees by mechanical disruption and exposure to heat. D. discoideum and its CFS also reduced preformed M. bovis biofilms, whereas V. vermiformis only decreased M. bovis biofilm biomass when amoebae were added. These results highlight the potential of using select amoebae species or their CFS to disrupt preformed bacterial biofilms.

Arcellacea (testate lobose amoebae) as pH indicators in a pyrite mine-acidified lake, Northeastern Ontario, Canada.

Arcellacea (testate lobose amoebae) were examined in 24 sediment-water interface samples collected over two late August field seasons in 2010 and 2011, from James and Granite lakes, Temagami Region, Northeastern Ontario. The work was carried out to quantitatively test species-environment relationships in a lake system known to be characterized by a significant pH gradient, partially the result of contamination from the early twentieth century Northland Pyrite Mine Co., located on the shoreline in the southern basin of James Lake. Redundancy analysis confirmed that arcellacean assemblage structure was most strongly controlled by pH, explaining 14.06 % (p < 0.002) of the total variance. Q- and R-mode cluster analysis supported by detrended correspondence analysis yielded two major faunal assemblages. The Oligotrophic Assemblage (1) had a Shannon Diversity Index (SDI) ranging up to 2.45, typical of healthy boreal lakes. This assemblage characterized samples collected from higher pH stations within James and Granite lakes away from the immediate area of the mine site, while the Low pH Assemblage 2010 (2a) and Low pH Assemblage 2011 (2b) groupings were from the very low pH environments of James Lake adjacent to the former mine site. Both low diversity assemblages (SDI ranging from 0.62 to 1.22) were characterized by Arcella vulgaris, a species known to thrive in hostile lacustrine environments. Differing depositional conditions during August 2010, a probable result of different prevailing wind patterns that summer, led to allochthonous specimens of the seasonally planktic Cucurbitella tricuspis dominating the Low pH Assemblage 2010 (2a) fauna.

The role of amoeboid protists and the microbial community in moss-rich terrestrial ecosystems: biogeochemical implications for the carbon budget and carbon cycle, especially at higher latitudes.

Moss-rich terrestrial communities are widely distributed in low- and high-latitude environments, covering vast surface areas in the boreal forests and tundra. The microbial biota in these organic-rich communities may contribute substantially to the carbon budget of terrestrial communities and the carbon cycle on a global scale. Recent research is reported on the carbon content of microbial communities in some temperate and high-latitude moss communities. The total carbon content and potential respiratory carbon dioxide (CO(2)) efflux is reported for bacteria, microflagellates, naked amoebae, and testate amoebae within sampling sites at a northeastern forest and the tundra at Toolik, Alaska. Quantitative models of the predicted total CO(2) efflux from the microbes, based on microscopic observations and enumeration of the microbiota in samples from the research sites, are described and predictions are compared with published field-based data of CO(2) efflux. The significance of the predictions for climate change and global warming are discussed.

A seasonal study of the carbon content of planktonic naked amoebae in the Hudson Estuary and in a productive freshwater pond with comparative data for ciliates.

The total carbon contents of gymnamoebae and ciliates, dwelling in the water column of the Hudson Estuary and a highly productive freshwater pond, were monitored during a 7-month period from April through October 2006. The carbon contents of the gymnamoebae and the ciliates were greater in the pond compared with the estuary, and carbon contents of gymnamoebae were greater in the spring and autumn in both locations than those of ciliates. Given the global distribution of gymnamoebae, these results suggest that greater attention should be given to the potential role of gymnamoebae in microbial food webs.

Evolution of size and pattern in the social amoebas.

A fundamental goal of biology is to understand how novel phenotypes evolved through changes in existing genes. The Dictyostelia or social amoebas represent a simple form of multicellularity, where starving cells aggregate to build fruiting structures. This review summarizes efforts to provide a framework for investigating the genetic changes that generated novel morphologies in the Dictyostelia. The foundation is a recently constructed molecular phylogeny of the Dictyostelia, which was used to examine trends in the evolution of novel forms and in the divergence of genes that shape these forms. There is a major trend towards the formation of large unbranched fruiting bodies, which is correlated with the use of cyclic AMP (cAMP) as a secreted signal to coordinate cell aggregation. The role of cAMP in aggregation arose through co-option of a pathway that originally acted to coordinate fruiting body formation. The genotypic changes that caused this innovation and the role of dynamic cAMP signaling in defining fruiting body size and pattern throughout social amoeba evolution are discussed.

Fasting induces cyanide-resistant respiration and oxidative stress in the amoeba Chaos carolinensis: implications for the cubic structural transition in mitochondrial membranes.

Large free-living amoeba (Chaos carolinensis) can survive in spring water without food intake for several weeks. Starvation is associated with a dramatic change in mitochondrial cristae from random tubular to ordered (paracrystalline) cubic morphology. Whole-cell polarography was used to monitor changes in respiratory activity during fasting. Basal respiration per cell decreased progressively during starvation, while the cyanide-resistant fraction increased. Spectrofluorometric assay of H2O2 and reactive oxygen species (ROS) in cell lysates (using the dye 2',7'-dichlorofluorescein diacetate) indicates greater H2O2 and ROS generation in starved than in fed cells. Fluorescence microscopy of intact cells incubated with the same dye demonstrates that H2O2 and ROS tend to accumulate in vacuoles. A remarkable generation of O2 observed with starved cells after addition of KCN may be explained by release of H2O2 from these compartments into the cytosol, where it can react with catalase. Together, these observations suggest that fasting increases oxidative stress in the amoeba and that this organism has several protective mechanisms to deal with it, including activation of a plantlike alternative oxidase. The hypothesis is forwarded that the cubic structural transition of the mitochondrial inner membrane represents another protective mechanism, reducing oxidative damage by enhancing the efflux of H2O2 and ROS and by reducing the susceptibility of membrane lipids to the oxidants.