Increased heterologous production of the antitumoral polyketide mithramycin A by engineered Streptomyces lividans TK24 strains

Mithramycin A is an antitumor compound used for treatment of several types of cancer including chronic and acute myeloid leukemia, testicular carcinoma, hypercalcemia and Paget’s disease. Selective modifications of this molecule by combinatorial biosynthesis and biocatalysis opened the possibility to produce mithramycin analogues with improved properties that are currently under preclinical development. The mithramycin A biosynthetic gene cluster from Streptomyces argillaceus ATCC12956 was cloned by transformation assisted recombination in Saccharomyces cerevisiae and heterologous expression in Streptomyces lividans TK24 was evaluated. Mithramycin A was efficiently produced by S. lividans TK24 under standard fermentation conditions. To improve the yield of heterologously produced mithramycin A, a collection of derivative strains of S. lividans TK24 were constructed by sequential deletion of known potentially interfering secondary metabolite gene clusters using a protocol based on the positive selection of double crossover events with blue pigment indigoidine-producing gene. Mithramycin A production was evaluated in these S. lividans strains and substantially improved mithramycin A production was observed depending on the deleted gene clusters. A collection of S. lividans strains suitable for heterologous expression of actinomycetes secondary metabolites were generated and efficient production of mithramycin A with yields close to 3 g/L, under the tested fermentation conditions was achieved using these optimized collection of strains.

     

Lifetime inbreeding depression in a leaf beetle

Ongoing habitat loss and fragmentation result in rapid population size reductions, which can increase the levels of inbreeding. Consequently, many species are threatened by inbreeding depression, a loss of individual fitness following the mating of close relatives. Here, we investigated inbreeding effects on fitness‐related traits throughout the lifetime of the mustard leaf beetle (Phaedon cochleariae) and mechanisms for the avoidance of inbreeding. Previously, we found that these beetles have family‐specific cuticular hydrocarbon profiles, which are likely not used as recognition cue for precopulatory inbreeding avoidance. Thus, we examined whether adult beetles show postcopulatory inbreeding avoidance instead. For this purpose, we determined the larval hatching rate of eggs laid by females mated sequentially with two nonsiblings, two siblings, a nonsibling, and a sibling or vice versa. The beetles suffered from inbreeding depression throughout their entire ontogeny, as evinced by a prolonged larval development, a decreased larval and adult survival and a decreased reproductive output of inbred compared to outbred individuals. The highest larval hatching rates were detected when females were mated with two nonsiblings or first with a sibling and second with a nonsibling. Significantly lower hatching rates were measured in the treatments with a sibling as second male. Thus, the results do not support the existence of postcopulatory inbreeding avoidance in P. cochleariae, but revealed evidence for second male sperm precedence. Consequently, an alternative strategy to avoid inbreeding costs might exist in this beetle, such as a polyandrous mating system, potentially coupled with a specific dispersal behavior.     

Oxidation of HRas cysteine thiols by metabolic stress prevents palmitoylation in vivo and contributes to endothelial cell apoptosis

Here we demonstrate a new paradigm in redox signaling, whereby oxidants resulting from metabolic stress directly alter protein palmitoylation by oxidizing reactive cysteine thiolates. In mice fed a high-fat, high-sucrose diet and in cultured endothelial cells (ECs) treated with high palmitate and high glucose (HPHG), there was decreased HRas palmitoylation on Cys181/184 (61±24% decrease for cardiac tissue and 38±7.0% in ECs). This was due to oxidation of Cys181/184, detected using matrix-assisted laser desorption/ionization time of flight (MALDI TOF)-TOF. Decrease in HRas palmitoylation affected its compartmentalization and Ras binding domain binding activity, with a shift from plasma membrane tethering to Golgi localization. Loss of plasma membrane-bound HRas decreased growth factor-stimulated ERK phosphorylation (84±8.6% decrease) and increased apoptotic signaling (24±6.5-fold increase) after HPHG treatment that was prevented by overexpressing wild-type but not C181/184S HRas. The essential role of HRas in metabolic stress was made evident by the similar effects of expressing an inactive dominant negative N17-HRas or a MEK inhibitor. Furthermore, the relevance of thiol oxidation was demonstrated by overexpressing manganese superoxide dismutase, which improved HRas palmitoylation and ERK phosphorylation, while lessening apoptosis in HPHG treated ECs.     

Characterization of terminal deoxynucleotidyl transferase and polymerase μ in zebrafish

Terminal deoxynucleotidyl transferase (TdT) contributes to the junctional diversity of immunoglobulin and T-cell receptors by incorporating nucleotides in a template-independent manner. A closely related enzyme, polymerase μ (polμ), a template-directed polymerase, plays a role in general end-joining double-strand break repair. We cloned zebrafish TdT and polμ and found them to be 43% identical in amino acid sequence. Comparisons with sequences of other species revealed conserved residues typical for TdT in the zebrafish sequence that support the template independence of this enzyme. Some but not all of these features were identified in zebrafish polμ. In adult fish, TdT expression was most prominent in thymus, pro- and mesonephros, the primary lymphoid organs in teleost fish and in spleen, intestine, and the tissue around the intestine. Polμ expression was detected not only in pro- and mesonephros, the major sites for B-lymphocyte development, but also in ovary and testis and in all tissue preparations to a low extent. TdT expression starts at 4 dpf and increases thereafter. Polμ is expressed at all times to a similar extent. In situ studies showed a strong expression of TdT and polμ in the thymic cortex of 8-week-old fish. The characterization of zebrafish TdT and polμ provide new insights in fish lymphopoiesis and addresses the importance and evolution of TdT and polμ themselves.     

Determination of carbon-reduction-cycle intermediates in leaves of Arbutus unedo L. suffering depressions in photosynthesis after application of abscisic acid or exposure to dry air

Gas exchange and contents of photosynthetic intermediates of leaves of Arbutus unedo L. were determined with the aim of recognizing the mechanisms of inhibition that were responsible for the midday depression of photosynthesis following exposure to dry air, and the decline in photosynthetic capacity following application of abscisic acid (ABA). Rapidly killed (<0.1 s) leaf samples were taken when gas analysis showed reduced CO₂ assimilation. Determination of the contents of 3-phosphoglyceric acid (PGA), ribulose 1,5-bisphosphate (RuBP), triose phosphates, fructose 1,6-bisphosphate and hexose phosphates in the samples showed that significant variation occurred only in the level of PGA. As a result, the ratio PGA/RuBP decreased with increasing inhibition of photosynthesis, particularly when application of ABA had been the cause. A comparison of metabolite patterns did not bring out qualitative differences that would have indicated that effects of ABA and of dry air had been caused by separate mechanisms. Depression of photosynthesis occurred in the presence of sufficient RuBP which indicated that the carboxylation reaction of the carbon-reduction-cycle was inhibited after application of ABA or exposure to dry air.Abbreviations and symbols ABA abscisic acid - C _a partial pressure of CO₂ in the ambient air - C _i partial pressure of CO₂ in the intercellular spaces - I quantum flux - PGA 3-phosphoglyceric acid - RuBP ribulose 1,5-bisphosphate - I _L leaf temperature - w water-vapor pressure difference between leaf and air     

Exogenous Isolation of Antibiotic Resistance Plasmids from Piggery Manure Slurries Reveals a High Prevalence and Diversity of IncQ-Like Plasmids

Antibiotic resistance plasmids were exogenously isolated in biparental matings with piggery manure bacteria as plasmid donors in Escherichia coli CV601 and Pseudomonas putida UWC1 recipients. Surprisingly, IncQ-like plasmids were detected by dot blot hybridization with an IncQ oriV probe in several P. putida UWC1 transconjugants. The capture of IncQ-like plasmids in biparental matings indicates not only their high prevalence in manure slurries but also the presence of efficiently mobilizing plasmids. In order to elucidate unusual hybridization data (weak or no hybridization with IncQ repB or IncQ oriT probes) four IncQ-like plasmids (pIE1107, pIE1115, pIE1120, and pIE1130), each representing a different EcoRV restriction pattern, were selected for a more thorough plasmid characterization after transfer into E. coli K-12 strain DH5α by transformation. The characterization of the IncQ-like plasmids revealed an astonishingly high diversity with regard to phenotypic and genotypic properties. Four different multiple antibiotic resistance patterns were found to be conferred by the IncQ-like plasmids. The plasmids could be mobilized by the RP4 derivative pTH10 into Acinetobacter sp., Ralstonia eutropha, Agrobacterium tumefaciens, and P. putida, but they showed diverse patterns of stability under nonselective growth conditions in different host backgrounds. Incompatibility testing and PCR analysis clearly revealed at least two different types of IncQ-like plasmids. PCR amplification of total DNA extracted directly from different manure samples and other environments indicated the prevalence of both types of IncQ plasmids in manure, sewage, and farm soil. These findings suggest that IncQ plasmids play an important role in disseminating antibiotic resistance genes.     

Better safe than sorry: The response to a simulated predator and unfamiliar scent by the European hare

Predator presence can create a “landscape of fear,” which is defined as the spatially explicit distribution of perceived predation risk as seen by prey. Prey species can alter their behavior and space use as a response to increased predation risk, which might be traded off with energetic requirements. Thus, whether or not an anti-predator behavior is performed might depend on the perceived risk. In this study, we investigated the behavioral and spatial response of the European hare (Lepus europaeus) toward the presence of a predator scent, using red fox (Vulpes vulpes) scat, an unfamiliar control scent (butyric acid), and a true control (no scent). We collected data on hare activity times and behavior using 50 camera trap locations and spatial data using GPS telemetry (30,481 GPS positions of 12 hares). Hares showed spatial anti-predator behaviors within their home range, for example, the local avoidance of areas treated with scent and remaining further from field edges, in response to sympatric predator scent and partly also in response to unfamiliar butyric acid. Conversely, more costly anti-predator behaviors, that is, increased vigilance at the expense of foraging, were only shown in response to the predator scent. Our results suggest that prey species respond flexibly toward scent cues, utilizing less costly anti-predator behaviors independent of the perceived threat, whereas costly anti-predator responses are only used in the presence of “real” threat. Further, our findings emphasize that a combination of camera trap and GPS data can provide detailed information on animal behavior and space use, and caution that interpretation of one data source alone might lead to incomplete conclusions.     

Co-oligopeptides of aromatic amino acids and glycine with variable distance between the aromatic residues. VII. Enzymatic synthesis of N-protected peptide amides

Several N-protected peptide amides, containing two aromatic residues spaced by one glycyl residue, have been enzymatically synthesized starting from P-Ar-OH and H-Gly-Ar-NH₂ (P is the protecting group and Ar is the aromatic residue) and using α-chymotrypsin as the catalyst for the coupling step. Reactions have been carried out in water solution, at room temperature, and afford yields ranging between 20 and 75% ca. This coupling reaction occurs in a much more restricted set of conditions than the hydrolysis reaction, e.g., only within a small pH range (ca. 6.5–7.5) and with particular buffering agents. The advantages and limitations of this type of reaction, compared with conventional coupling procedures, are discussed.