Regulation by cyclic di-GMP in Myxococcus xanthus

The nucleotide-based second messenger bis-(3’-5’)-cyclic dimeric GMP (c-di-GMP) is involved in regulating a plethora of processes in bacteria that are typically associated with lifestyle changes. Myxococcus xanthus undergoes major lifestyle changes in response to nutrient availability with the formation of spreading colonies in the presence of nutrients and spore-filled fruiting bodies in the absence of nutrients. Here, we investigated the function of c-di-GMP in M. xanthus. We show that this bacterium synthesizes c-di-GMP. Manipulation of the cellular c-di-GMP level by expression of either an active, heterologous diguanylate cyclase or an active, heterologous phosphodiesterase in vegetative cells caused defects in type IV pili (T4P)-dependent motility whereas gliding motility was unaffected. An increased level of c-di-GMP caused reduced transcription of the pilA gene that encodes the major pilin of T4P, reduced assembly of T4P and altered cell agglutination whereas a decreased level of c-di-GMP caused altered cell agglutination. The systematic inactivation of the 24 genes in M. xanthus encoding proteins containing GGDEF, EAL or HD-GYP domains, which are associated with c-di-GMP synthesis, degradation or binding, identified three genes encoding proteins important for T4P-dependent motility. These three proteins named DmxA, TmoK and SgmT all contain a GGDEF domain. Purified DmxA had diguanylate cyclase activity whereas the TmoK and SgmT (both hybrid histidine protein kinases) did not have diguanylate cyclase activity. During starvation, the c-di-GMP level in M. xanthus increases significantly. Manipulation of this level revealed that a low c-di-GMP level negatively affects the developmental program while an increased level does not interfere with development. Moreover, among the 24 genes encoding proteins containing GGDEF, EAL or HD-GYP domains, we identified two which are specifically involved in development: pmxA and dmxB. pmxA codes for an enzymatically active phosphodiesterase with an HD-GYP domain. dmxB codes for a developmentally induced, enzymatically active diguanylate cyclase. DmxB is essential for the increased c-di-GMP level and regulates exopolysaccharide accumulation during starvation. Our results show that c-di-GMP acts as an important signaling molecule during M. xanthus development, and suggest a model in which a minimal threshold level of c-di-GMP is essential for the successful progression and completion of the developmental program. Additionally, candidates for c-di-GMP effectors in M. xanthus were identified using a capture compound mass spectrometry approach. Some of the candidates were confirmed to bind c-di-GMP in vitro and deletion mutants for genes encoding those proteins were characterized in terms of T4P-dependent motility and development

A Minimal Threshold of c-di-GMP Is Essential for Fruiting Body Formation and Sporulation in Myxococcus xanthus

Generally, the second messenger bis-(3’-5’)-cyclic dimeric GMP (c-di-GMP) regulates the switch between motile and sessile lifestyles in bacteria. Here, we show that c-di-GMP is an essential regulator of multicellular development in the social bacterium Myxococcus xanthus. In response to starvation, M. xanthus initiates a developmental program that culminates in formation of spore-filled fruiting bodies. We show that c-di-GMP accumulates at elevated levels during development and that this increase is essential for completion of development whereas excess c-di-GMP does not interfere with development. MXAN3735 (renamed DmxB) is identified as a diguanylate cyclase that only functions during development and is responsible for this increased c-di-GMP accumulation. DmxB synthesis is induced in response to starvation, thereby restricting DmxB activity to development. DmxB is essential for development and functions downstream of the Dif chemosensory system to stimulate exopolysaccharide accumulation by inducing transcription of a subset of the genes encoding proteins involved in exopolysaccharide synthesis. The developmental defects in the dmxB mutant are non-cell autonomous and rescued by co-development with a strain proficient in exopolysaccharide synthesis, suggesting reduced exopolysaccharide accumulation as the causative defect in this mutant. The NtrC-like transcriptional regulator EpsI/Nla24, which is required for exopolysaccharide accumulation, is identified as a c-diGMP receptor, and thus a putative target for DmxB generated c-di-GMP. Because DmxB can be—at least partially—functionally replaced by a heterologous diguanylate cyclase, these results altogether suggest a model in which a minimum threshold level of c-di-GMP is essential for the successful completion of multicellular development in M. xanthus

Regulation by cyclic di-GMP in Myxococcus xanthus

The nucleotide-based second messenger bis-(3’-5’)-cyclic dimeric GMP (c-di-GMP) is involved in regulating a plethora of processes in bacteria that are typically associated with lifestyle changes. Myxococcus xanthus undergoes major lifestyle changes in response to nutrient availability with the formation of spreading colonies in the presence of nutrients and spore-filled fruiting bodies in the absence of nutrients. Here, we investigated the function of c-di-GMP in M. xanthus. We show that this bacterium synthesizes c-di-GMP. Manipulation of the cellular c-di-GMP level by expression of either an active, heterologous diguanylate cyclase or an active, heterologous phosphodiesterase in vegetative cells caused defects in type IV pili (T4P)-dependent motility whereas gliding motility was unaffected. An increased level of c-di-GMP caused reduced transcription of the pilA gene that encodes the major pilin of T4P, reduced assembly of T4P and altered cell agglutination whereas a decreased level of c-di-GMP caused altered cell agglutination. The systematic inactivation of the 24 genes in M. xanthus encoding proteins containing GGDEF, EAL or HD-GYP domains, which are associated with c-di-GMP synthesis, degradation or binding, identified three genes encoding proteins important for T4P-dependent motility. These three proteins named DmxA, TmoK and SgmT all contain a GGDEF domain. Purified DmxA had diguanylate cyclase activity whereas the TmoK and SgmT (both hybrid histidine protein kinases) did not have diguanylate cyclase activity. During starvation, the c-di-GMP level in M. xanthus increases significantly. Manipulation of this level revealed that a low c-di-GMP level negatively affects the developmental program while an increased level does not interfere with development. Moreover, among the 24 genes encoding proteins containing GGDEF, EAL or HD-GYP domains, we identified two which are specifically involved in development: pmxA and dmxB. pmxA codes for an enzymatically active phosphodiesterase with an HD-GYP domain. dmxB codes for a developmentally induced, enzymatically active diguanylate cyclase. DmxB is essential for the increased c-di-GMP level and regulates exopolysaccharide accumulation during starvation. Our results show that c-di-GMP acts as an important signaling molecule during M. xanthus development, and suggest a model in which a minimal threshold level of c-di-GMP is essential for the successful progression and completion of the developmental program. Additionally, candidates for c-di-GMP effectors in M. xanthus were identified using a capture compound mass spectrometry approach. Some of the candidates were confirmed to bind c-di-GMP in vitro and deletion mutants for genes encoding those proteins were characterized in terms of T4P-dependent motility and development

During heat stress in Myxococcus xanthus, the CdbS PilZ domain protein, in concert with two PilZ-DnaK chaperones, perturbs chromosome organization and accelerates cell death.

C-di-GMP is a bacterial second messenger that regulates diverse processes in response to environmental or cellular cues. The nucleoid-associated protein (NAP) CdbA in Myxococcus xanthus binds c-di-GMP and DNA in a mutually exclusive manner in vitro. CdbA is essential for viability, and CdbA depletion causes defects in chromosome organization, leading to a block in cell division and, ultimately, cell death. Most NAPs are not essential; therefore, to explore the paradoxical cdbA essentiality, we isolated suppressor mutations that restored cell viability without CdbA. Most mutations mapped to cdbS, which encodes a stand-alone c-di-GMP binding PilZ domain protein, and caused loss-of-function of cdbS. Cells lacking CdbA and CdbS or only CdbS were fully viable and had no defects in chromosome organization. CdbA depletion caused post-transcriptional upregulation of CdbS accumulation, and this CdbS over-accumulation was sufficient to disrupt chromosome organization and cause cell death. CdbA depletion also caused increased accumulation of CsdK1 and CsdK2, two unusual PilZ-DnaK chaperones. During CdbA depletion, CsdK1 and CsdK2, in turn, enabled the increased accumulation and toxicity of CdbS, likely by stabilizing CdbS. Moreover, we demonstrate that heat stress, possibly involving an increased cellular c-di-GMP concentration, induced the CdbA/CsdK1/CsdK2/CdbS system, causing a CsdK1- and CsdK2-dependent increase in CdbS accumulation. Thereby this system accelerates heat stress-induced chromosome mis-organization and cell death. Collectively, this work describes a unique system that contributes to regulated cell death in M. xanthus and suggests a link between c-di-GMP signaling and regulated cell death in bacteria

Transcriptional Regulation of Fatty Acid Biosynthesis in Lactococcus lactis

Here we study the influence of the putative fatty acid biosynthesis (FAB) regulator FabT (originally called RmaG [Llmg_1788]) on gene transcription in Lactococcus lactis MG1363. A strain with a knockout mutation of the putative regulator was constructed, and its transcriptome was compared to that of the wild-type strain. Almost all FAB genes were significantly upregulated in the knockout. Using electrophoretic mobility shift assays (EMSAs) and DNase I footprinting, the binding motif of the regulator and the binding locations in the genome were characterized. Fatty acid composition analysis revealed that a strain lacking FabT contained significantly more saturated acyl chains in its phospholipids. This observation demonstrates that the vital pathway of FAB in L. lactis is regulated by the repressor FabT.

Chemical Composition, Nutritional Value, and Acceptance of Nut Bars with the Addition of Edible Insect Powder

Six types of nut-based bars with the addition of edible insect flour were obtained. Flours made from three different insects (Tenebrio molitor L., Acheta domesticus L., Alphitobius diaperinus P.) were used at two different additive levels (15% and 30%) in relation to the weight of the nuts. The addition of insect flour significantly increased protein content and the insoluble fraction of dietary fiber. The largest amount of these compounds was found in bars with 30% cricket flour, 15.51 g/100 g and 6.04 g/100 g, respectively, in comparison to standard bars, 10.78 g/100 g and 3.14 g/100 g, respectively. The greatest consumer acceptance was found in relation to bars with buffalo worm flour. The overall acceptance of these bars was 6.26–6.28 points compared to 6.48 for standard bars. Bars and raw materials were characterized by the high biological value of the protein. Cis linoleic acid dominated among unsaturated fatty acids. The percentage of this compound was in the range of 69.56%, for bars with a 30% addition of buffalo worm flour, to 73.88%, for bars with 15% cricket flour. Instrumental analysis of taste and smell compounds showed the presence of compounds such as 3-methylbutanoic acid, hexanal, and 2,3-pentanedione

Bioactive Compounds and Antioxidant Composition of Nut Bars with Addition of Various Edible Insect Flours

Edible insects represent a new functional source of nutrients that can contribute to solving nutritional deficiency problems. The antioxidant potential and bioactive compounds of nut bars with the addition of three edible insects were evaluated. Acheta domesticus L., Alphitobius diaperinus P. and Tenebrio molitor L. flours were used. A 30% share of insect flour in the bars resulted in significantly greater antioxidant activity (TPC increased from 190.19 for standard bars to 309.45 mg catechin/100 g for bars with 30% addition of cricket flour). Insect flour contributed significantly to an increase in 2,5-dihydrobenzoic acid (from 0.12 for bars with a 15% share of buffalo worm flour to 0.44 mg/100 g in the case of bars with a 30% share of cricket flour) and chlorogenic acid in all bars (from 0.58 for bars with a 15% share of cricket flour to 3.28 mg/100 g for bars with a 30% addition of buffalo worm flour), compared to the standard. The highest content of tocopherols was found in bars with cricket flour, compared to standard bars (43.57 and 24.06 mg/100 g of fat, respectively). The dominant sterol in bars enriched with insect powder was cholesterol. The highest amount of it was found in cricket bars, and the lowest in mealworm bars (64.16 and 21.62 mg/100 g of fat, respectively). The enrichment of nut bars with insect flours raises the levels of valuable phytosterols in the final product. The addition of edible insect flours reduced the perception of most sensory attributes of the bars, compared to the standard bar