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The Drosophila larva has a simple peripheral nervous system with a comparably small number of sensory neurons located externally at the head or internally along the pharynx to assess its chemical environment. It is assumed that larval taste coding occurs mainly via external organs (the dorsal, terminal, and ventral organ). However, the contribution of the internal pharyngeal sensory organs has not been explored. Here we find that larvae require a single pharyngeal gustatory receptor neuron pair called D1, which is located in the dorsal pharyngeal sensilla, in order to avoid caffeine and to associate an odor with caffeine punishment. In contrast, caffeine-driven reduction in feeding in non-choice situations does not require D1. Hence, this work provides data on taste coding via different receptor neurons, depending on the behavioral context. Furthermore, we show that the larval pharyngeal system is involved in bitter tasting. Using ectopic expressions, we show that the caffeine receptor in neuron D1 requires the function of at least four receptor genes: the putative co-receptors Gr33a, Gr66a, the putative caffeine-specific receptor Gr93a, and yet unknown additional molecular component(s). This suggests that larval taste perception is more complex than previously assumed already at the sensory level. Taste information from different sensory organs located outside at the head or inside along the pharynx of the larva is assembled to trigger taste guided behaviors.

Animals can form associations between temporally separated stimuli. To do so, the nervous system has to retain a neural representation of the first stimulus until the second stimulus appears. The neural substrate of such sensory stimulus memories is unknown. Here, we search for a sensory odor memory in the insect olfactory system and characterize odorant-evoked Ca activity at three consecutive layers of the olfactory system in : in olfactory receptor neurons (ORNs) and projection neurons (PNs) in the antennal lobe, and in Kenyon cells (KCs) in the mushroom body. We show that the post-stimulus responses in ORN axons, PN dendrites, PN somata, and KC dendrites are odor-specific, but they are not predictive of the chemical identity of past olfactory stimuli. However, the post-stimulus responses in KC somata carry information about the identity of previous olfactory stimuli. These findings show that the Ca dynamics in KC somata could encode a sensory memory of odorant identity and thus might serve as a basis for associations between temporally separated stimuli.

[This corrects the article on p. 128 in vol. 12, PMID: 29867361.].

Cancer cells and non-cancer cells differ in their metabolism and they emit distinct volatile compound profiles, allowing to recognise cancer cells by their scent. Insect odorant receptors are excellent chemosensors with high sensitivity and a broad receptive range unmatched by current gas sensors. We thus investigated the potential of utilising the fruit fly's olfactory system to detect cancer cells. Using in vivo calcium imaging, we recorded an array of olfactory receptor neurons on the fruit fly's antenna. We performed multidimensional analysis of antenna responses, finding that cell volatiles from different cell types lead to characteristic response vectors. The distances between these response vectors are conserved across flies and can be used to discriminate healthy mammary epithelial cells from different types of breast cancer cells. This may expand the repertoire of clinical diagnostics and it is the first step towards electronic noses equipped with biological sensors, integrating artificial and biological olfaction.

Neural activity can be mapped across individuals using brain atlases, but when spatial relationships are not equal, these techniques collapse. We map activity across individuals using functional registration, based on physiological responses to predetermined reference stimuli. Data from several individuals are integrated into a common multidimensional stimulus space, where dimensionality and axes are defined by these reference stimuli. We used this technique to discriminate volatile compounds with a cohort of Drosophila flies, by recording odor responses in receptor neurons on the flies’ antennae. We propose this technique for the development of reliable biological sensors when activity raw data cannot be calibrated. In particular, this technique will be useful for evaluating physiological measurements in natural chemosensory systems, and therefore will allow to exploit the sensitivity and selectivity of olfactory receptors present in the animal kingdom for analytical purposes.

Corynebacterium glutamicum is a Gram-positive soil bacterium belonging phylogenetically to the group of mycolic acid-containing actinomycetes. It has achieved outstanding biotechnological importance as an L-glutamate producing bacterium and is also used in various fermentation processes for the production of other amino acids like L-lysin, as well as nucleotides and vitamins. The cellular metabolism and especially the biosynthesis of amino acids strictly depend on the availability of nitrogen sources. To avoid a waste of energy and resources during the adaptation to varying nitrogen supply the organism features regulatory mechanisms that control nitrogen uptake and assimilation on the levels of gene expression, enzyme activity and proteolysis. This regulation is termed “nitrogen control”. The PII signal transduction protein GlnK plays a key role in the cell’s response to limiting nitrogen supply. GlnK is not present in cells that grow in ammonium-rich medium, but it is synthesised and adenylylated in response to ammonium limitation. By interacting with the repressor AmtR it causes a derepression of nitrogen regulated genes. An improvement of the nitrogen status leads to a deadenylylation of GlnK and its sequestration to the membrane. The localisation of GlnK at the membrane depends on the ammonium transporter AmtB and is the condition for the following GlnK degradation. The proteolysis of GlnK is influenced by the AAA+ proteases FtsH, ClpXP and ClpCP.In this study the global effects of the AAA+ proteases on proteome level and their influence on nitrogen metabolism were investigated. In contrast to other bacteria, the proteases in C. glutamicum were more involved in the regulation of energy and carbon metabolism, rather than in stress response. Another topic was the investigation of GlnK proteolysis on molecular level, whether all three proteases work together in GlnK degradation, or if only one protease is responsible and the impaired degradation in the other mutants is a jamming effect. Furthermore a probable degradation recognition signal of GlnK was analysed. Hints were obtained that the aminoterminal region of GlnK is involved into substrate recognition.