Bacteriocins and the assembly of natural Pseudomonas fluorescens populations.

When competing for space and resources, bacteria produce toxins known as bacteriocins to gain an advantage over competitors. Recent studies in the laboratory have confirmed theoretical predictions that bacteriocin production can determine coexistence, by eradicating sensitive competitors or driving the emergence of resistant genotypes. However, there is currently limited evidence that bacteriocin-mediated competition influences the coexistence and distribution of genotypes in natural environments, and what factors drive interactions towards inhibition remain unclear. Using natural soil populations of Pseudomonas fluorescens, we assessed the ability of the isolates to inhibit one another with respect to spatial proximity in the field, genetic similarity and niche overlap. The majority of isolates were found to produce bacteriocins; however, widespread resistance between coexisting isolates meant relatively few interactions resulted in inhibition. When inhibition did occur, it occurred more frequently between ecologically similar isolates. However, in contrast with results from other natural populations, we found no relationship between the frequency of inhibition and the genetic similarity of competitors. Our results suggest that bacteriocin production plays an important role in mediating competition over resources in natural settings and, by selecting for isolates resistant to local bacteriocin production, can influence the assembly of natural populations of P. fluorescens.

Pyoverdin cheats fail to invade bacterial populations in stationary phase.

Microbes engage in cooperative behaviours by producing and secreting public goods, the benefits of which are shared among cells, and are therefore susceptible to exploitation by nonproducing cheats. In nature, bacteria are not typically colonizing sterile, rich environments in contrast to laboratory experiments, which involve inoculating sterile culture with few bacterial cells that then race to fill the available niche. Here, we study the potential implications of this difference, using the production of pyoverdin, an iron-scavenging siderophore that acts as a public good in the bacteria Pseudomonas aeruginosa. We show that (1) nonproducers are able to invade cultures of producers when added at the start of growth or during early exponential growth phase, but not during late exponential or stationary phase; (2) the producer strain does not produce pyoverdin in the late exponential and stationary phases and so is not paying the cost of cooperating during those phases. These results suggest that whether a nonproducing mutant can invade will depend upon when the mutation arises, as well as the population structure, and raise a potential difficulty with the use of antimicrobial treatment strategies that propose to exploit the invasive abilities of cheats.

Implantable, multifunctional, bioresorbable optics.

Advances in personalized medicine are symbiotic with the development of novel technologies for biomedical devices. We present an approach that combines enhanced imaging of malignancies, therapeutics, and feedback about therapeutics in a single implantable, biocompatible, and resorbable device. This confluence of form and function is accomplished by capitalizing on the unique properties of silk proteins as a mechanically robust, biocompatible, optically clear biomaterial matrix that can house, stabilize, and retain the function of therapeutic components. By developing a form of high-quality microstructured optical elements, improved imaging of malignancies and of treatment monitoring can be achieved. The results demonstrate a unique family of devices for in vitro and in vivo use that provide functional biomaterials with built-in optical signal and contrast enhancement, demonstrated here with simultaneous drug delivery and feedback about drug delivery with no adverse biological effects, all while slowly degrading to regenerate native tissue.

Sustained volume retention in vivo with adipocyte and lipoaspirate seeded silk scaffolds.

Current approaches to soft tissue regeneration include the use of fat grafts, natural or synthetic biomaterials as filler materials. Fat grafts and natural biomaterials resorb too quickly to maintain tissue regeneration, while synthetic materials do not degrade or regenerate tissue. Here, we present a simple approach to volume stable filling of soft tissue defects. In this study, we combined lipoaspirate with a silk protein matrix in a subcutaneous rat model. Silk biomaterials can be tailored to fit a variety of needs, and here were processed silk biomaterials into a porous sponge format to allow for tissue ingrowth while remaining mechanically robust. Over an 18 month period, the lipoaspirate seeded silk protein matrix regenerated subcutaneous adipose tissue while maintaining the original implanted volume. A silk protein matrix alone was not sufficient to regenerate adipose tissue, but yielded a fibrous tissue, although implanted volume was maintained. This work presents a significant improvement to the standard approaches to filling soft tissue defects by matching biomaterial degradation and tissue regeneration profiles.

Insulin and myoelectric activity of the small intestine of the pig.

The effect of insulin on the myoelectric activity of the small intestine was determined in conscious pigs. Animals were implanted with electrodes along the small intestine, a strain gage on the stomach and catheters in both saphenous arteries. Feeding modified the migrating myoelectric complex (MMC), a cyclic pattern of action potential activity of the small intestine characteristic of fasting. The first period of regular spiking activity (RSA) on the duodenum after feeding was delayed and was not followed by quiescence. Plasma insulin and glucose concentrations during the first three MMC after feeding were highest just before periods of duodenal RSA. Injection or infusion of insulin into fasted pigs with production of hypoglycemia caused disruption of stomach motility and duodenal electrical activity. The duodenal MMC was not altered when glucose to prevent hypoglycemia was infused together with insulin or when glucose was infused alone. These studies suggest that insulin is not directly responsible for the postprandial modification of MMC activity as insulin infusions only modify the MMC when hypoglycemia occurs.

The protein-sparing effect of carbohydrate. 2. The role of insulin.

1. In five experiments with growing female pigs of 38-63 kg, insulin (2 mU/kg) per min) and glucose (9-17 mg/kg per min) were infused continuously for 3-7 d. In three further experiments, glucose (9 mg/kg per min) was infused alone for 5 d. 2. In response to the combined infusion, plasma insulin increased 2-7-fold, plasma glucose decreased, on average, by 50% and plasma urea concentration was reduced by 40%. Urinary excretion of urea and nitrogen decreased after the first day of infusion to values averaging 70% of control levels. 3. The infusion of glucose alone provoked only a small increase in plasma insulin. The reduction of urinary urea and of N excretion were approximately 25% of those observed with the combined infusions.