Acyl-homoserine lactone-mediated quorum sensing (QS) regulates diverse activities in many species of Proteobacteria. QS-controlled genes commonly code for production of secreted or excreted public goods. The acyl-homoserine lactones are synthesized by members of the LuxI signal synthase family and are detected by cognate members of the LuxR family of transcriptional regulators. QS affords a means of population density-dependent gene regulation. Control of public goods via QS provides a fitness benefit. Another potential role for QS is to anticipate overcrowding. As population density increases and stationary phase approaches, QS might induce functions important for existence in stationary phase. Here we provide evidence that in three related species of the genus Burkholderia QS allows individuals to anticipate and survive stationary-phase stress. Survival requires QS-dependent activation of cellular enzymes required for production of excreted oxalate, which serves to counteract ammonia-mediated alkaline toxicity during stationary phase. Our findings provide an example of QS serving as a means to anticipate stationary phase or life at the carrying capacity of a population by activating the expression of cytoplasmic enzymes, altering cellular metabolism, and producing a shared resource or public good, oxalate.Burkholderia carrying capacity | glumae | pseudomallei | thailandensis | cell death A cyl-homoserine lactone (AHL)-mediated quorum sensing (QS) regulates diverse activities, including bioluminescence, biofilm formation, motility, and virulence factor formation, in many Proteobacteria (1-3). AHLs are synthesized most typically by members of the LuxI family signal synthases and detected by members of the LuxR family of transcriptional regulators (1-3). A large body of work has characterized the molecular mechanisms of bacterial QS; demonstrating the population-wide benefits that drive QS-mediated cooperative behavior has proven difficult, however. Cooperative activities benefit individuals within a group (4, 5).QS-controlled genes commonly code for the production of extracellular public goods that can be shared by all members of the group regardless of which members produce them. These extracellular products are often important for nutrient acquisition, interspecies competition, or virulence (6-8). In Pseudomonas aeruginosa, QS control of secreted proteases provides fitness benefits, because the proteases are produced only when they can be used efficiently (9). Other potential roles of QS in bacteria have been proposed, including the hypothesis that QS enables bacteria to anticipate population carrying capacity in a given environment. Anticipation of stationary phase might allow individuals to modify their physiology in preparation for survival at population carrying capacity.Here we address the question of whether QS is involved in anticipation of stationary-phase stress in three closely related bacteria: the rice pathogen Burkholderia glumae, the opportunistic human pathogen Burkholderia pseudomallei, and the...

To measure the activity of neurons using whole-brain activity imaging, precise detection of each neuron or its nucleus is required. In the head region of the nematode C. elegans, the neuronal cell bodies are distributed densely in three-dimensional (3D) space. However, no existing computational methods of image analysis can separate them with sufficient accuracy. Here we propose a highly accurate segmentation method based on the curvatures of the iso-intensity surfaces. To obtain accurate positions of nuclei, we also developed a new procedure for least squares fitting with a Gaussian mixture model. Combining these methods enables accurate detection of densely distributed cell nuclei in a 3D space. The proposed method was implemented as a graphical user interface program that allows visualization and correction of the results of automatic detection. Additionally, the proposed method was applied to time-lapse 3D calcium imaging data, and most of the nuclei in the images were successfully tracked and measured.

We purified to homogeneity an enzyme from Citrobacter sp. strain KCTC 18061P capable of decolorizing triphenylmethane dyes. The native form of the enzyme was identified as a homodimer with a subunit molecular mass of about 31 kDa. It catalyzes the NADH-dependent reduction of triphenylmethane dyes, with remarkable substrate specificity related to dye structure. Maximal enzyme activity occurred at pH 9.0 and 60°C. The enzymatic reaction product of the triphenylmethane dye crystal violet was identified as its leuco form by UV-visible spectral changes and thin-layer chromatography. A gene encoding this enzyme was isolated based on its N-terminal and internal amino acid sequences. The nucleotide sequence of the gene has a single open reading frame encoding 287 amino acids with a predicted molecular mass of 30,954 Da. Although the deduced amino acid sequence displays 99% identity to the hypothetical protein from Listeria monocytogenes strain 4b H7858, it shows no overall functional similarity to any known protein in the public databases. At the N terminus, the amino acid sequence has high homology to sequences of NAD(P)H-dependent enzymes containing the dinucleotide-binding motif GXXGXXG. The enzyme was heterologously expressed in Escherichia coli, and the purified recombinant enzyme showed characteristics similar to those of the native enzyme. This is the first report of a triphenylmethane reductase characterized from any organism.Triphenylmethane dyes are aromatic xenobiotic compounds that are used extensively in many industrial processes, such as textile dyeing, paper printing, and food and cosmetic manufacture (11). Studies of the biodegradation of triphenylmethane dyes have focused primarily on the decolorization of dyes via reduction reactions. Several triphenylmethane dye-decolorizing microorganisms have been reported and their characteristics reviewed (2). The biochemical mechanism underlying the decolorization of triphenylmethane dyes has been elucidated in fungi (2,7,20,23) but not in bacteria. Triphenylmethane dyes are decolorized by lignin peroxidase of Phanerochaete chrysosporium (7). Laccase from the extracellular fluid of Cyathus bulleri (23) and peroxidase from Pleurotus ostreatus (20) also decolorize triphenylmethane dyes. The structural genes encoding lignin peroxidase and laccase have been cloned and characterized (8, 10). Although several triphenylmethane dye-decolorizing bacteria have been isolated (2), there are no reports of specific enzymes that decolorize these dyes. The decolorization of malachite green and crystal violet by intestinal microflora and several anaerobic bacteria proceeds through enzymatic reduction to their respective leuco derivatives (12, 16). However, the enzymes involved in this reduction have not yet been isolated or characterized in their purified forms. Their amino acid sequences and other biophysical parameters remain unknown.We recently isolated a new bacterium, Citrobacter sp. strain KCTC 18061P, that has a higher decolorization capability than any microorganism repor...

Purine catabolic pathway in Bacillus subtilis is consisted of more than 14 genes. Among these genes, pucL and pucM are required for uricase activity. While PucL is known to encode the uricase itself, the function of PucM is still unclear although this protein is also indispensable for uric acid decomposition. Here, we provide evidence that PucM, a transthyretin-related protein, functions to facilitate the hydrolysis of 5-hydroxyisourate, the end product of the uricase reaction. Based on these results, we propose that transthyretin-related proteins present in diverse organisms are not functionally related to transthyretin but actually function as a hydroxyisourate hydrolase.