Complete genomes and comparative analyses of Streptomyces phages that influence secondary metabolism and sporulation

Bacteria in the genus Streptomyces are found ubiquitously in nature and are known for the number and diversity of specialized metabolites they produce, as well as their complex developmental lifecycle. Studies of the viruses that prey on Streptomyces, known as phages, have aided the development of tools for genetic manipulation of these bacteria, as well as contributing to a deeper understanding of Streptomyces and their behaviours in the environment. Here, we present the genomic and biological characterization of twelve Streptomyces phages. Genome analyses reveal that these phages are closely related genetically, while experimental approaches show that they have broad overlapping host ranges, infect early in the Streptomyces lifecycle, and induce secondary metabolite production and sporulation in some Streptomyces species. This work expands the group of characterized Streptomyces phages and improves our understanding of Streptomyces phage-host dynamics.

A chemical defence against phage infection

The arms race between bacteria and the phages that infect them drives the continual evolution of diverse anti-phage defences. Previously described anti-phage systems have highly varied defence mechanisms^1-11; however, all mechanisms rely on protein components to mediate defence. Here we report a chemical anti-phage defence system that is widespread in Streptomyces. We show that three naturally produced molecules that insert into DNA are able to block phage replication, whereas molecules that target DNA by other mechanisms do not. Because double-stranded DNA phages are the most numerous group in the biosphere and the production of secondary metabolites by bacteria is ubiquitous¹², this mechanism of anti-phage defence probably has a major evolutionary role in shaping bacterial communities.

Identification of regions in interleukin-1 alpha important for activity

Saturation mutagenesis of the mature human interleukin-1 alpha (IL-1 alpha) gene has been performed. Following expression in Escherichia coli, the biological and receptor binding activities of the mutant proteins were examined. Most of the molecule could be altered with little effect on either function. More than 3,500 mutants were examined, and only 23 unique amino acid sequences were identified which resulted in an altered ratio of biological to binding activity when compared with wild-type IL-1 alpha. These proteins possessed mutations at 38 of the 159 amino acid residues in IL-1 alpha. Random mutagenesis at several of these positions identified further substitutions that affected activity. Examination of a model for IL-1 alpha localized most of the residues which altered activity along one face of the molecule. This region appears to be distinct from areas of IL-1 which have been postulated to make contact with IL-1 receptor.

Regulation of tumor necrosis factor/cachectin and IL-1 secretion in human mononuclear phagocytes

To determine whether the production and secretion of TNF and IL-1 by human mononuclear phagocytes could be independently modulated, we examined secretion of TNF and IL-1 by fresh monocytes and monocytes pretreated with IFN-gamma or granulocyte macrophage CSF before LPS stimulation. TNF and IL-1 secretion were in part differentially modulated. Fresh monocytes secreted large amounts of TNF and IL-1 after LPS stimulation and less than 6% as much without LPS. The capacity to secrete TNF in response to LPS decreased slightly in cultured monocytes but was markedly augmented by IFN-gamma (approximately five-fold more than fresh monocytes). In contrast, cultured monocytes secreted less than 5% as much IL-1 as fresh monocytes and, although augmented by IFN-gamma, IL-1 secretion remained much less than by fresh monocytes. These differences in modulation were reflected by differences in the molecular mechanisms regulating TNF and IL-1 secretion. TNF secretion was regulated primarily by changes in the duration of increased transcription and by an apparent increase in translation or protein stability in response to LPS; greater than 95% TNF produced was secreted under all conditions. In contrast, the changes in IL-1 secretion reflected primarily post-transcriptional regulation of IL1-alpha mRNA, transcriptional and post-transcriptional regulation of IL-1 beta mRNA and a decrease in the fraction of IL-1 secreted by cultured compared with fresh monocytes (10 and 60%, respectively). Changes in translational efficiency or protein processing or stability appeared not to be important mechanisms regulating IL-1 secretion. Additional evidence that TNF and IL-1 can be differentially modulated was the selective decrease in TNF secretion and the failure of IFN-gamma to enhance TNF secretion by cultured monocytes from neonates, whereas results for IL-1 were similar with adult and neonatal monocytes. Results with tissue macrophages were similar to those with cultured monocytes. These results indicate that TNF and IL-1 production and secretion by mononuclear phagocytes can be differentially modulated, reflecting in part different mechanisms of regulation; this may allow them to play partially independent roles in the host immune response.

Regulation of tumor necrosis factor/cachectin and IL-1 secretion in human mononuclear phagocytes

To determine whether the production and secretion of TNF and IL-1 by human mononuclear phagocytes could be independently modulated, we examined secretion of TNF and IL-1 by fresh monocytes and monocytes pretreated with IFN-gamma or granulocyte macrophage CSF before LPS stimulation. TNF and IL-1 secretion were in part differentially modulated. Fresh monocytes secreted large amounts of TNF and IL-1 after LPS stimulation and less than 6% as much without LPS. The capacity to secrete TNF in response to LPS decreased slightly in cultured monocytes but was markedly augmented by IFN-gamma (approximately five-fold more than fresh monocytes). In contrast, cultured monocytes secreted less than 5% as much IL-1 as fresh monocytes and, although augmented by IFN-gamma, IL-1 secretion remained much less than by fresh monocytes. These differences in modulation were reflected by differences in the molecular mechanisms regulating TNF and IL-1 secretion. TNF secretion was regulated primarily by changes in the duration of increased transcription and by an apparent increase in translation or protein stability in response to LPS; greater than 95% TNF produced was secreted under all conditions. In contrast, the changes in IL-1 secretion reflected primarily post-transcriptional regulation of IL1-alpha mRNA, transcriptional and post-transcriptional regulation of IL-1 beta mRNA and a decrease in the fraction of IL-1 secreted by cultured compared with fresh monocytes (10 and 60%, respectively). Changes in translational efficiency or protein processing or stability appeared not to be important mechanisms regulating IL-1 secretion. Additional evidence that TNF and IL-1 can be differentially modulated was the selective decrease in TNF secretion and the failure of IFN-gamma to enhance TNF secretion by cultured monocytes from neonates, whereas results for IL-1 were similar with adult and neonatal monocytes. Results with tissue macrophages were similar to those with cultured monocytes. These results indicate that TNF and IL-1 production and secretion by mononuclear phagocytes can be differentially modulated, reflecting in part different mechanisms of regulation; this may allow them to play partially independent roles in the host immune response.

The nervous control of rat somatostatin, glucagon and insulin secretions

Somatostatin-like-immunoreactivity (SLI), immunoreactive insulin (IRI), glucagon (IRG) and catecholamine concentrations were measured in rat portal plasma during electrical stimulation of the vagus and splanchnic nerves, and during experimentally-induced hypovolaemia and hypoxaemia. Blood pressure, arterial gases and pH were monitored and hepatic blood flow was estimated (EHBF). Stimulation of the vagus nerves induced an increase in IRG and IRI concentrations, but had different influences on SLI level according to the concomitant experimental conditions. Stimulation of the left splanchnic nerve induced a sharp rise in SLI, IRG and catecholamine concentrations, whereas IRI level decreased hypovolaemia and hypoxaemia. Phentolamine treatment augmented the basal IRI, IRG and SLI concentrations. It did not suppress the hypovolaemia-induced rise of IRG and SLI concentrations, but unmasked a strong IRI release. By contrast, propranolol and atropine reduced significantly the A and D cell responses to acute hypovolaemia. These results are consistent with a profound influence of pancreatic nerves on A, B and D cell functions, which should be taken into account for interpretation of results during in vivo experiments.

A radioimmunoassay for neurotensin

A specific radioimmunoassay for neurotensin has been developed with a sensitivity of 40 pg/ml. Neurotensin-like immunoreactivity in human plasma shows characteristics similar to synthetic neurotensin on Sephadex G-25 (f) gel chromatography.

Substance P release from rat hypothalamus and spinal cord

A specific and sensitive radioimmunoassay for substance P has been developed to study the release of immunoreactive substance P from incubated rat hypothalamus and rat spinal cord in vitro. Release was significantly increased in the presence of two depolarizing stimuli (56 mM KCl and 75 microM veratrine) and was calcium-dependent. The released immunoreactive material diluted in parallel with synthetic substance P and showed close identity on Sephadex chromatography. A neuromodulator role for the peptide in the central nervous system is suggested.

Immunoreactive somatostatin release from rat spinal cord in vitro

A calcium-dependent release of immunoreactive somatostatin from rat spinal cord in vitro in response to two depolarising stimuli (60 mM KCl and 75 micrometer veratrine) has been demonstrated. Released somatostatin immunoreactivity comprised 0.53% of total tissue content, showed parallelism when serial dilutions were compared to the immunoassay dose-response curve and eluted similarly to synthetic somatostatin on Sephadex G-25 (f) chromatography. These results provide further evidence for a neurotransmitter or neuromodulator role for somatostatin in mammalian spinal cord.

Ultracentrifugation evidence for a somatostatin-binding protein in serum

Using a technique of high speed centrifugation of serum and a well validated immunoassay for the measurement of serum somatostatin-like immunoreactivity, we have demonstrated that somatostatin, unlike other peptide hormones, appears to sediment with large molecular weight proteins. When synthetic somatostatin of increasing concentration was incubated with serum prior to ultracentrifugation, a linear plot of concentration of somatostatin added against concentration sedimenting (or apparently bound to protein) revealed an association curve. These data provide further evidence for the existence of a serum-binding protein for somatostatin.

Tissue distribution of immunoreactive somatostatin in the South African clawed toad (Xenopus laevis)

Immunoreactive somatostatin is present in the brain, gut and pancreas of the South African clawed toad, but is absent from the skin, a rich source of many other brain-gut peptides.

Tissue and serum somatostatin-like immunoreactivity in fed, 15-h-fasted, and 72-h-fasted rats

Somatostatin-like immunoreactivity (SLI) was measured in extracts of gastric antrum, colon, pancreas, and central nervous system, as well as in unextracted portal and inferior vena caval serum from fed, 15-h-fasted, and 72-h-fasted rats. No differences were found in SLI in the central nervous system of the three groups. However, striking variations were found in the gastrointestinal tract and pancreas; the antrum, colon, and pancreas of 15-h-fasted rats contained the least SLI, the content being significantly elevated in these three areas after feeding and after a 72-h fast. Portal serum levels were highest after feeding but lowest in 72-h-fasted rats, in spite of high intestinal and pancreatic SLI content in both. These tissue and serum differences suggest a physiologic role for SLI in nutrient homeostasis not only at tissue level, but also putatively as a hormone in the portal system.

Growth hormone release inhibitory hormone-like immunoreactivity in pancreas and gut in streptozotocin diabetes in the rat and response to insulin administration

In streptozotocin diabetes in the rat, growth hormone release-inhibitory hormone-like immunoreactivity (GHRIH-LI) content of pancreas, gastric antrum and colon was increased. Insulin therapy significantly lowered the increased pancreatic GHRIH-LI content but did not affect that of the gastric antrum and colon at the dosage used. The relevance of these findings in relation to pancreatic and gastrointestinal function in diabetes awaits clarification.

Metabolic clearance and plasma half-disappearance time of exogenous somatostatin in man

The MCR and half-disappearance time of exogenously administered somatostatin have been measured during and after cessation of a constant infusion. Studies were performed on normal volunteers and patients with chronic liver disease and failure. Immunoreactive somatostatin was measured by a sensitive and specific RIA using an antiserum directed against the core of the molecule. Normal subjects had a mean MCR of 1949 +/- 250 ml/min (28.4 +/- 4.2 ml/min . kg BW) (mean +/- SEM), similar to values found in five patients with chronic liver disease. However, patients with chronic renal failure showed a highly significant (P less than 0.001) lowering of the MCR (501 +/- 32.7 ml/min or 7.8 +/- 0.6 ml/min . kg). The rate of disappearance of somatostatin after infusion was linear for 7-10 min, after which a much slower component was observed. In normal subjects, the t 1/2 of the first component varied from 1.1-3.0 min, in patients with liver disease it varied from 1.2-4.8 min, and in patients with chronic renal failure it varied from 2.6-4.9 min. Exogenously administered somatostatin is rapidly cleared in normal subjects and patients with chronic liver disease, but the MCR in end stage chronic renal failure is markedly lowered. The kidney may have a role in the metabolic clearance of exogenously administered somatostatin, or uremia may impair catabolism nonspecifically.

Stimulation by growth hormone of somatostatin release from the rat hypothalamus in vitro

Growth hormone (GH) has been shown to cause a dose-dependent increase in the release of immunoreactive somatostatin from the rat hypothalamus in vitro, thus providing further evidence that GH may be involved in a "short loop" feedback, controlling its own secretion via hypothalamic somatostatin release.

Tissue growth hormone release inhibiting hormone-like immunoreactivity in experimental hypothyroidism and hypopituitarism

Hypothyroidism in rats was associated with an increase in immuno-reactive GH-RIH in brain, pancreas and gut, although release from the latter may be diminished as portal GH-RIH-like immunoreactivity was lower than control values. Hypophysectomy resulted in a depletion of immunoreactive GH-RIH in the septum and preoptic area of the brain and gastric antrum, but an increase in pancreas; portal venous GH-RIH-like immunoreactivity was not different from control concentrations, possibly reflecting both elevated and lowered immunol-reactive GH-RIH in different regions of tissue subserved by the portal vein. Inferior vena caval GH-RIH-like immunoreactivity was always lower than in the portal vein and was not influenced by tissue pertubations in hypothyroidism and hypopituitarism which made regional blood sampling of great important in evaluating tissue changes.

The characterization of somatostatin-like immunoreactivity in human serum

We describe the characterization of somatostatin-like immunoreactivity (SRIF-LI) found by radioimmunoassay (RIA) to be present in normal human serum. Degradation by serum of 125I-Tyr1 SRIF in the assay, as assessed by chromatoelectrophoresis and immunoprecipitation, was overcome by using EDTA in the assay buffer and Trasylol in the blood samples. Serum samples thus obtained from 48 normal subjects revealed a bimodal distribution of SRIF-LI; 92 per cent (group 1) had a mean level of 0.274 +/- 0.009 ng. per milliliter. What was measured in these sera showed identity to synthetic SRIF on serial dilutions, Sephadex G-25 chromatography, and thin-layer chromatography, and it was shown to be immunoreactive by an antibody-Sepharose affinity system. Higher levels (1.0 +/- 0.041 ng. per milliliter) were found in 8 per cent of the sera; 50 per cent of this material behaved identically as serum SRIF-LI from group 1. The remainder proved to be heterogeneous, consisting of two peaks of large molecular weight, both of which shared immunologic identity with synthetic SRIF as shown by binding to the antibody-Sepharose affinity system. Their further nature is unknown.

Somatostatin-like immunoreactivity in rat blood. Characterization, regional differences, and responses to oral and intravenous glucose

Somatostatin-like immunoreactivity (SLI) has been demonstrated by radioimmunoassay (RIA) in rat serum using an antiserum specific for somatostatin and cross-reacting maximally with the biologically important area on the peptide. The RIA has a sensitivity of 35 pg/ml. SLI dilutes in parallel with synthetic somatostatin standard in the RIA and shows characteristics similar to synthetic somatostatin on Sephadex G-25 (f) gel chromatography eluting largely as a single peak with 1 M acetic acid. Significant regional differences in serum SLI are present. A positive gradient was found in paired samples from aorta (mean+/-SEM, 0.304+/-0.024 ng/ml) and portal vein (0.495+/-0.047 ng/ml) consistent with the known presence of somatostatin in gut and pancreas, and a negative gradient was noted between paired samples from portal vein (0.523+/-0.076 ng/ml) and hepatic vein (0.290+/-0.048 ng/ml) indicating hepatic clearance. No significant differences were demonstrated between aorta and confluence of cerebral venous sinuses or between aorta and inferior vena cava (IVC). After intragastric glucose, a significant and marked elevation of portal SLI was observed, maximal at 5 min (0.416+/-0.137 vs. 1.55+/-0.30 ng/ml at 5 min). A significant biphasic elevation of portal SLI also occurred after intravenous glucose. After both routes of glucose administration, the patterns of portal SLI followed closely those of portal glucose and insulin. By contrast, IVC SLI failed to reflect these changes.Thus, SLI in the rat shows chromatographic similarity with synthetic somatostatin. Regional differences in serum levels are marked; the highest concentrations being found in the portal venous effluent of pancreas and gut. Furthermore, glucose causes elevation of portal SLI in a pattern similar to portal insulin and glucose and without concomitant elevation in IVC. This differential elevation of SLI after glucose is consistent with a hormonal action within the portal system as a direct effect of somatostatin on the liver has previously been demonstrated. In addition, the liver is important in the clearance of portal SLI, possibly to prevent extraportal effects in response to gut and pancreatic stimulation. Finally, it is clear that regional sampling of serum for SLI measurement may be critical in the investigation of the putative physiological roles for somatostatin.

The characterization of growth hormone release inhibiting hormone-like immunoreactivity in normal urine

Using a previously described radioimmunoassay for growth hormone release inhibiting hormone (GH-RIH), the presence of GH-RIH-like immunoreactivity in urine has been characterized by demonstrating mobility identical to synthetic GH-RIH standard on two sephadex gel chromatographic systems, and parallelism of dilutions of the sephadex fractions with synthetic GH-RIH. Furthermore, 74% of the sephadex fraction cross-reacting in the immunoassay bound to antibody conjugated to sepharose and could be eluted by 1 M acetic acid. This immunospecific eluate showed identity with synthetic GH-RIH on both ion exchange and thin layer chromatography. Thus GH-RIH-like immunoreactivity is present in normal urine; this may have potential relevance in the search for a physiological role for this peptide.

The presence of immunoreactive growth hormone release-inhibiting hormone in normal cerebrospinal fluid

Immunoreactive GHRIH is present in normal CSF at a level of 55 +/- 28 pg/ml. Immunoreactivity shows mobility identical to synthetic GHRIH standard on sephadex and thin layer chromatography, and can be removed by antibody conjugated to sepharose.

An investigation into gonadal dysfunction in patients with idiopathic haemochromatosis

Endocrine studies were performed on twelve patients with proven idiopathic haemochromatosis. Basal gonadotrophin levels and/or their responses to LH releasing hormone (LHRH) were low in nine patients, all of whom showed low plasma testosterone levels and clinical evidence of hypogonadism. Those patients with normal gonadotrophin responses had higher testosterone values, suggesting that the poor testosterone secretion was primarily due to inadequate trophic stimulation. No patient showed hypothyroidism of hypothalamic-pituitary origin, while the cortisol response to hypoglycaemia was normal in all six patients studied. GH responses were more variable and difficult to interpret, since the number of the patients studied was small and the degree of hypoglycaemia after insulin was unpredictable.

A radioimmunoassay for growth hormone release-inhibiting hormone: method and quantitative tissue distribution

A specific antiserum has been produced to haemocyanin conjugaed synthetic growth hormone release inhibiting hormone (GHRIH). This has allowed the development of a radioimmunoassay for GHRIH sensitive to 5 pg/tube. GHRIH content in 2 m acetic acid extracts of rat tissues have been measured and show the majority to be CNS-especially hypothalamus and septum and preoptic areas with substantial amounts in spinal cord and thalamus. Extra neurological localization in pancreas, gastric antrum, colon and thyroid have been demonstrated.

Somatostatin, 1976

Somatostatin, a growth hormone release-inhibiting factor, isolated originally from the hypothalamus, has been shown to have widespread effects on brain and endocrine and exocrine pancreatic and gut function. Furthermore, it has a widespread distribution in the CNS, gut and C cells of the thyroid -- cells which probably migrated originally from the neural crest during development. While the pharmacological effects of somatostatin are diffuse, its physiological role is at present unknown, but in view of its concentration in synaptosomal fractions of neural tissue, it may have a neurotransmitter or a synaptic modulator function.

The effect of alanine infusions on growth hormone, insulin, and glucose in protein-calorie malnutrition

In view of the previously reported inverse correlation between the elevated serum growth hormone (HGH) and low alanine in children with protein-calorie malnutrition (PCM), 30-min alanine infusions were performed in five children with PCM and 12-hr infusions in four children before and after therapy. These infusions did not lower basal HGH or improve its glucose suppressibility in untreated PCM, excluding a feedback relationship between HGH and alanine. There was no insulinotropic effect during 30-min infusions, but an improved insulin response to glucose after the 12-hr alanine infusion was found in three of four children before therapy. Plasma glucose rose slightly during alanine infusion in three of five children before treatment, but the magnitude of change was small and the relevance unclear.

Disappearance rates of plasma growth hormone after intravenous somatostatin in renal and liver disease

Plasma immunoreactive growth hormone (hGH) was measured before, during and after the administration of intravenous somatostatin to 3 patients with chronic renal failure and 4 with severe liver disease who had elevation of basal hGH. During somatostatin infusion, the hGH levels declined acutely in a linear fashion when log hGH was plotted against time. Rather surprisingly, the plasma hGH half disappearance time (t 1/2) was 27 min and 18 min in liver and renal disease respectively. These values do not differ from data obtained on normal subjects using exogenous hGH, labelled or unlabelled. Control data on normal subjects using this technique are not available as it was not possible to measure subnormal levels of plasma hGH with the required precision. It is possible that our findings of plasma hGH T 1/2 in liver and renal disease within the normal range reported using exogenous hGH might suggest that high levels of plasma hGH found in these two diseases are primarily caused by hypersecretion rather than impaired clearance.