dictyNews Electronic Edition Volume 39, number 14 May 10, 2013 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu or by using the form at http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit. Back issues of dictyNews, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. Follow dictyBase on twitter: http://twitter.com/dictybase ========= Abstracts ========= Hydrolysis of aromatic b-glucosides by non-pathogenic bacteria confers a chemical weapon against predators Authors: Robert Sonowal1, Krithi Nandimath1, Sucheta S. Kulkarni2, Sandhya P. Koushika2,3, Vidyanand Nanjundiah1 and S. Mahadevan1 Affiliations: 1 Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore 560 012, India 2 National Centre for Biological Sciences, Bangalore 560065, India 3 Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India Proceedings of The Royal Society B, in press Bacteria present in natural environments such as soil have evolved multiple strategies to escape from predation.We report that natural isolates of Enterobacteriaceae that actively hydrolyze plant-derived aromatic beta-glucosides such as salicin, arbutin and esculin, are able to avoid predation by the bacteriovorous amoeba Dictyostelium discoideum and nematodes of multiple genera belonging to the family Rhabditidae. This advantage can be observed under laboratory culture conditions as well as in the soil environment. The aglycone moiety released by the hydrolysis of beta-glucosides is toxic to predators and acts via the dopaminergic receptor Dop-1 in the case of Caenorhabditis elegans. While soil isolates of nematodes belonging to the family Rhabditidae are repelled by the aglycone, laboratory strains and natural isolates of Caenorhabditis sp. are attracted to the compound, mediated by receptors that are independent of Dop-1, leading to their death. The beta-glucosides-positive (Bgl+) bacteria that are otherwise non-pathogenic can obtain additional nutrients from the dead predators, thereby switching their role from prey to predator. This study also offers an evolutionary explanation for the retention by bacteria of 'cryptic' or 'silent' genetic systems such as the bgl operon. Submitted by Robert Sonowal [robert_sonowal@mrdg.iisc.ernet.in] --------------------------------------------------------------------------- Bacterial discrimination by Dictyostelid amoebae reveals the complexity of ancient interspecies interactions Waleed Nasser1, Balaji Santhanam2,3, Edward Roshan Miranda2,4, Anup Parikh 2,3, Kavina Juneja5, Gregor Rot6, Chris Dinh1, Rui Chen2,3,4, Blaz Zupan2,6, Gad Shaulsky2,3,4 and Adam Kuspa1,2,4* 1 - Verna and Marrs McLean Department of Biochemistry and Molecular Biology, 2 - Department of Molecular and Human Genetics, 3 - Structural and Computational Biology and Molecular Biophysics Program, 4 - Developmental Biology Program, Baylor College of Medicine, Houston, TX 77030; 5 - Department of Biochemistry and Cell Biology, Rice University, Houston, TX 77005; 6 - Faculty of Computer and Information Science, University of Ljubljana, Slovenia. Current Biology, in press Background: Amoebae and bacteria interact within predator/prey and host/pathogen relationships, but the general response of amoeba to bacteria is not well understood. The amoeba Dictyostelium discoideum feeds on, and is colonized by diverse bacterial species including Gram- positive [Gram(+)] and Gram-negative [Gram(-)] bacteria, two major groups of bacteria that differ in structure and macromolecular composition. Results: Transcriptional profiling of D. discoideum revealed sets of genes whose expression is enriched in amoebae interacting with different species of bacteria, including sets that appear specific to amoebae interacting with Gram(+), or with Gram(-) bacteria. In a genetic screen utilizing the growth of mutant amoebae on a variety of bacteria as a phenotypic readout, we identified amoebal genes that are only required for growth on Gram(+) bacteria, including one that encodes the cell surface protein gp130, as well as several genes that are only required for growth on Gram(-) bacteria including one that encodes a putative lysozyme, AlyL. These genes are required for parts of the transcriptional response of wild-type amoebae, and this allowed their classification into potential response pathways. Conclusions: We have defined genes that are critical for amoebal survival during feeding on Gram(+), or Gram(-), bacteria which we propose form part of a regulatory network that allows D. discoideum to elicit specific cellular responses to different species of bacteria in order to optimize survival. Submitted by Adam Kuspa [akuspa@bcm.edu] --------------------------------------------------------------------------- Systematic analysis of gamma-aminobutyric acid (GABA) metabolism and function in the social amoeba Dictyostelium discoideum. Wu Y, Janetopoulos C. Department of Biological Sciences, Vanderbilt University, United States. Journal of Biological Chemistry, in press While GABA has been suggested to regulate spore encapsulation in the social amoeba Dictyostellium discoideum, the metabolic profile and other potential functions of GABA during development remain unclear. In this study, we investigated the homeostasis of GABA metabolism by disrupting genes related to GABA metabolism and signaling. Extracellular levels of GABA are tightly regulated during early development, and GABA is generated by the glutamate decarboxylase, GadB, during growth and in early development. However, overexpression of the prespore-specific homologue, GadA, in the presence of GadB reduces production of extracellular GABA. Perturbation of extracellular GABA levels delays the process of aggregation. Cytosolic GABA is degraded by the GABA transaminase, GabT, in the mitochondria. Disruption of a putative vesicular GABA transporter (vGAT) homologue DdvGAT reduces secreted GABA. We identified the GABAB receptor-like family member GrlB as the major GABA receptor during early development, and either disruption or overexpression of GrlB delays aggregation. This delay is likely the result of an abolished pre-starvation response and late expression of several early developmental genes. Distinct genes are employed for GABA generation during sporulation. During sporulation, GadA alone is required for generating GABA and DdvGAT is likely responsible for GABA secretion. GrlE but not GrlB is the GABA receptor during late development. Submitted by Chris Janetopoulos [c.janetopoulos@vanderbilt.edu] --------------------------------------------------------------------------- The G alpha subunit Galpha8 inhibits proliferation, promotes adhesion and regulates cell differentiation Wu Y, Janetopoulos C. Department of Biological Sciences, Vanderbilt University, United States. Developmental Biology, in press Heterotrimeric G protein-mediated signal transduction plays a pivotal role in both vegetative and developmental stages in the eukaryote Dictyostelium discoideum. Here we describe novel functions of the G protein alpha subunit Galpha8 during vegetative and development stages. Galpha8 is expressed at low levels during vegetative growth. Loss of Galpha8 promotes cell proliferation, whereas excess Galpha8 expression dramatically inhibits growth and induces aberrant cytokinesis on substrates in a Gbeta-dependent manner. Overexpression of Galpha8 also leads to increased cell-cell cohesion and cell-substrate adhesion. We demonstrate that the increased cell-cell cohesion is mainly caused by induced CadA expression, and the induced cell-substrate adhesion is responsible for the cytokinesis defects. However, the expression of several putative constitutively active mutants of Galpha8 does not augment the phenotypes caused by intact Galpha8. Galpha8 is strongly induced after starvation, and loss of Galpha8 results in decreased expression of certain adhesion molecules including CsA and tgrC1. Interestingly, Galpha8 is preferentially distributed in the upper and lower cup of the fruiting body. Lack of Galpha8 decreases the expression of the specific marker of the anterior-like cells, suggesting that Galpha8 is required for anterior-like cell differentiation. Submitted by Chris Janetopoulos [c.janetopoulos@vanderbilt.edu] ============================================================== [End dictyNews, volume 39, number 14]