Commuting between kingdoms: The biosynthesis of the only nonplant stilbene 1 from Photorhabdus bacteria has been solved by identification of all the genes involved in its biosynthesis and by feeding experiments. Stilbene 1 is derived from the condensation of two β‐ketoacyl thioesters and is required for the normal development of Heterorhabditis nematodes, the natural host of Photorhabdus.

Type II polyketide synthases are involved in the biosynthesis of numerous clinically relevant secondary metabolites with potent antibiotic or anticancer activity. Until recently the only known producers of type II PKSs were members of the Gram-positive actimomycetes, well-known producers of secondary metabolites in general. Here we present the second example of a type II PKS from Gram-negative bacteria. We have identified the biosynthesis gene cluster responsible for the production of anthraquinones (AQs) from the entomopathogenic bacterium Photorhabdus luminescens. This is the first example of AQ production in Gram-negative bacteria, and their heptaketide origin was confirmed by feeding experiments. Deletion of a cyclase/aromatase involved in AQ biosynthesis resulted in accumulation of mutactin and dehydromutactin, which have been described as shunt products of typical octaketide compounds from streptomycetes, and a pathway for AQ formation from octaketide intermediates is discussed.

Cellular homeostasis relies upon precise regulation of Ca2+ concentration. Stromal interaction molecule (STIM) proteins regulate store-operated calcium entry (SOCE) by sensing Ca2+ concentration in the ER and forming oligomers to trigger Ca2+ entry through plasma membrane-localized Orai1 channels. Here we characterize a STIM2 splice variant, STIM2.1, which retains an additional exon within the region encoding the channel-activating domain. Expression of STIM2.1 is ubiquitous but its abundance relative to the more common STIM2.2 variant is dependent upon cell type and highest in naive T cells. STIM2.1 knockdown increases SOCE in naive CD4+ T cells, whereas knockdown of STIM2.2 decreases SOCE. Conversely, overexpression of STIM2.1, but not STIM2.2, decreases SOCE, indicating its inhibitory role. STIM2.1 interaction with Orai1 is impaired and prevents Orai1 activation, but STIM2.1 shows increased affinity towards calmodulin. Our results imply STIM2.1 as an additional player tuning Orai1 activation in vivo.

Cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells are required to protect the human body against cancer. Ca is a key metabolic factor for lymphocyte function and cancer homeostasis. We analysed the Ca dependence of CTL and NK cell cytotoxicity against cancer cells and found that CTLs have a bell-shaped Ca dependence with an optimum for cancer cell elimination at rather low [Ca ] (23-625 μm) and [Ca ] (122-334 nm). This finding predicts that a partial inhibition of Orai1 should increase (rather than decrease) cytotoxicity of CTLs at [Ca ] higher than 625 μm. We tested this hypothesis in CTLs and indeed found that partial down-regulation of Orai1 by siRNA increases the efficiency of cancer cell killing. We found two mechanisms that may account for the Ca optimum of cancer cell killing: (1) migration velocity and persistence have a moderate optimum between 500 and 1000 μm [Ca ] in CTLs, and (2) lytic granule release at the immune synapse between CTLs and cancer cells is increased at 146 μm compared to 3 or 800 μm, compatible with the Ca optimum for cancer cell killing. It has been demonstrated in many cancer cell types that Orai1-dependent Ca signals enhance proliferation. We propose that a decrease of [Ca ] or partial inhibition of Orai1 activity by selective blockers in the tumour microenvironment could efficiently reduce cancer growth by simultaneously increasing CTL and NK cell cytotoxicity and decreasing cancer cell proliferation.

Myxobacteria are Gram-negative soil bacteria that can form fruiting bodies under starvation conditions (1). These fruiting bodies are visible to the naked eye and can reach a tree-like complexity in some species. During the developmental process, a certain amount of vegetative cells differentiates into heat-and desiccation-resistant myxospores enabling the survival of the colony. The model organism to study this highly complex process is Myxococcus xanthus from which different extracellular signals and regulators have already been described that can be combined in a model likely reflecting the essential parts of the underlying regulatory network (2, 3). However, the biochemical changes that are involved in this process or appear as a result of it have been barely identified. That biochemical changes occur is evident from change in cell shape from vegetative rods to round myxospores with thick spore coats (4, 5) and high amounts of trehalose (6), which is proposed to act as a compatible solute. Furthermore, the pioneering work of White and co-workers (7-9) showed that several enzymes involved in increase of carbohydrate biosynthesis are induced during sporulation.Ten years ago, Downard and coworkers identified a mutant that was disrupted in the branched-chain keto acid dehydrogenase (Bkd) 2 complex, which resulted in a developmental phenotype forming almost no aggregates or spores under starvation conditions (10). The Bkd complex is involved in the degradation of the branched-chain amino acids leucine, valine, and isoleucine, with all three being essential amino acids for M. xanthus (11). The degradation products of these amino acids are isovaleryl-CoA, isobutyryl-CoA, and 2-methylbutyryl-CoA, respectively (12), which are used as starting units for iso-and anteiso-fatty acids and also for several secondary metabolites from different bacteria (e.g. avermectin from Streptomyces avermitilis (13) or myxothiazol (14), myxalamides (15), and aurafuron * This work was supported by Deutsche Forschungsgemeinschaft Grants Bo1834/3-1 and Bo1834/4-1 (to H. B. B.) and Schu984/6-1 (to S. S.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. □ S The on-line version of this article (available at http://www.jbc.org) contains supplemental text and references. 1 To whom correspondence should be addressed. Tel.: 49-681-302-5494; Fax:49-681-302-5473; E-mail: h.bode@mx.uni-saarland.de.2 The abbreviations used are: Bkd, branched-chain keto acid dehydrogenase; FA, fatty acid; SCFA, straight-chain fatty acid; FAME, fatty acid methyl ester; IVA, isovalerate;