Laminin-1 and epidermal growth factor family members co-stimulate fetal pancreas cell proliferation and colony formation

The epidermal growth factor (EGF) family is implicated in the development and function of multiple cells and organs, including the pancreas. We used a serum-free, low-cell density culture system to investigate the effect of EGFs on fetal pancreas cells. By RT-PCR, the EGF receptors ErbB 1-3 were detected in the developing mouse pancreas between embryonic day (E) 13.5 and E17.5, whereas ErbB4 was not detected until E17.5. The presence but not absence of the basement membrane glycoprotein laminin-1, betacellulin, and to a lesser extent EGF, transforming growth factor alpha, heparin binding EGF, and epiregulin induced E15.5 pancreatic cells to proliferate and form cystoid and solid colonies. These results demonstrate that laminin-1 and EGF signaling pathways interact to promote pancreas development.     

Amino acids control ammonia pulses in yeast colonies

Individual yeast colonies produce pulses of volatile ammonia separated by phases of medium acidification. Colonies of Saccharomyces cerevisiae mutant defective in the general amino acid permease, Gap1p, exhibit decreased ammonia production. Mutations in the S. cerevisiae amino acid sensor SPS completely abolish the colony ammonia pulses. In contrast, the ammonia pulse production is independent of external concentrations of ammonium and of its uptake by the ammonium permeases Mep1p, Mep2p, and Mep3p. It is concluded that in S. cerevisiae colonies, the extracellular amino acids, but not the extracellular ammonium, serve as a source for volatile ammonia production. These phenomena are not restricted to S. cerevisiae, since we observe that extracellular levels of 8 out of the 20 tested amino acids are necessary for ammonia pulses produced by Candida mogii colonies.     

Replicable and recombinogenic RNAs

This paper summarizes results of the 40-year studies on replication and recombination of RNA molecules in the cell-free amplification system of bacteriophage Q. Special attention is paid to the molecular colony technique that has provided for the discovery of the nature of "spontaneous" RNA synthesis by Q replicase and of the ability of RNA molecules to spontaneously rearrange their sequences under physiological conditions. Also discussed is the impact of these data on the concept of RNA World and on the development of new in vitro cloning and diagnostic tools.     

The ypdI gene codes for a putative lipoprotein involved in the synthesis of colanic acid in Escherichia coli

In Escherichia coli, the synthesis of colanic acid, an extracellular polysaccharide imminent in biofilm development, is a complicated process involving numerous genes and not yet wholly elucidated. Using a plasmid-borne E. coli K-12 gene library, we have identified a clone whose presence conferred mucoid colony phenotype onto E. coli CM2555 strain. Our results indicate that overexpression of a gene previously catalogued as ypdI, which encodes a putative lipoprotein, is responsible for this phenotype. We show that the mucoidy of ypdI -overexpressing bacteria is due to increased production of colanic acid. This phenotype depends on the function of the rcsA gene, but not on that of rcsF. These results suggest that the ypdI gene product might be an additional factor playing a role in colanic acid synthesis, indicating that this process can be even more complicated than supposed to date. However, no obvious phenotype was observed in the DeltaypdI::kan mutant cultivated under standard laboratory conditions.     

Evaluation of MALDI-TOF mass spectroscopy methods for determination of Escherichia coli pathotypes

It is rapidly becoming apparent that many E. coli pathotypes cause a considerable burden of human disease. Surveillance of these organisms is difficult because there are few or no simple, rapid methods for detecting and differentiating the different pathotypes. MALDI-TOF mass spectroscopy has recently been rapidly and enthusiastically adopted by many clinical laboratories as a diagnostic method because of its high throughput, relatively low cost, and adaptability to the laboratory workflow. To determine whether the method could be adapted for E. coli pathotype differentiation the Bruker Biotyper methodology and a second methodology adapted from the scientific literature were tested on isolates representing eight distinct pathotypes and two other groups of E. coli. A total of 136 isolates was used for this study. Results confirmed that the Bruker Biotyper methodology that included extraction of proteins from bacterial cells was capable of identifying E. coli isolates from all pathotypes to the species level and, furthermore, that the Bruker extraction and MALDI-TOF MS with the evaluation criteria developed in this work was effective for differentiating most pathotypes.     

Ecophysiology of gelatinous Nostoc colonies: unprecedented slow growth and survival in resource-poor and harsh environments

Background

The cyanobacterial genus Nostoc includes several species forming centimetre-large gelatinous colonies in nutrient-poor freshwaters and harsh semi-terrestrial environments with extended drought or freezing. These Nostoc species have filaments with normal photosynthetic cells and N₂-fixing heterocysts embedded in an extensive gelatinous matrix of polysaccharides and many other organic substances providing biological and environmental protection. Large colony size imposes constraints on the use of external resources and the gelatinous matrix represents extra costs and reduced growth rates.

Scope

The objective of this review is to evaluate the mechanisms behind the low rates of growth and mortality, protection against environmental hazards and the persistence and longevity of gelatinous Nostoc colonies, and their ability to economize with highly limiting resources.

Conclusions

Simple models predict the decline in uptake of dissolved inorganic carbon (DIC) and a decline in the growth rate of spherical freshwater colonies of N. pruniforme and N. zetterstedtii and sheet-like colonies of N. commune in response to a thicker diffusion boundary layer, lower external DIC concentration and higher organic carbon mass per surface area (CMA) of the colony. Measured growth rates of N. commune and N. pruniforme at high DIC availability comply with general empirical predictions of maximum growth rate (i.e. doubling time 10–14 d) as functions of CMA for marine macroalgae and as functions of tissue thickness for aquatic and terrestrial plants, while extremely low growth rates of N. zetterstedtii (i.e. doubling time 2–3 years) are 10-fold lower than model predictions, either because of very low ambient DIC and/or an extremely costly colony matrix. DIC uptake is limited by diffusion at low concentrations for all species, although they exhibit efficient HCO₃^– uptake, accumulation of respiratory DIC within the colonies and very low CO₂ compensation points. Long light paths and light attenuation by structural substances in large Nostoc colonies cause lower quantum efficiency and assimilation number and higher light compensation points than in unicells and other aquatic macrophytes. Extremely low growth and mortality rates of N. zetterstedtii reflect stress-selected adaptation to nutrient- and DIC-poor temperate lakes, while N. pruniforme exhibits a mixed ruderal- and stress-selected strategy with slow growth and year-long survival prevailing in sub-Arctic lakes and faster growth and shorter longevity in temperate lakes. Nostoc commune and its close relative N. flagelliforme have a mixed stress–disturbance strategy not found among higher plants, with stress selection to limiting water and nutrients and disturbance selection in quiescent dry or frozen stages. Despite profound ecological differences between species, active growth of temperate specimens is mostly restricted to the same temperature range (0–35 °C; maximum at 25 °C). Future studies should aim to unravel the processes behind the extreme persistence and low metabolism of Nostoc species under ambient resource supply on sediment and soil surfaces.     

Are workers of Atta leafcutter ants capable of reproduction?

Summary. Workers of most eusocial Hymenoptera can produce sons after queen loss, which (posthumously) benefits the queen and increases worker inclusive fitness. However, the evolutionary loss of worker ovaries has occurred in several lineages, while workers in other taxa may be infertile despite having ovaries. Workers of Atta leafcutter ants only lay trophic eggs in queenright colonies. Although Atta colonies are commonly kept at universities, museums, and zoos, no reports of worker sons in orphaned colonies exist, suggesting that Atta workers are infertile. To explicitly test this, we created eleven orphaned laboratory nests of Atta cephalotes, A. sexdens, and A. colombica, and maintained them for 3–6 months after queen loss. Eight colonies did not produce any brood, but three nests produced 1–4 worker-derived male larvae and pupae. Microsatellite genotyping indicated that these were worker sons. However, all males were tiny (3.5–9 mm long) compared to normal queen sons (16 mm long), and would almost certainly be unable to mate. We also found reproductive eggs, but most of these had no yolk and were thus inviable. We conclude that Atta workers are not completely infertile, but that worker fertility is low compared to the sister genus Acromyrmex, where workers routinely produce normally-size males after queen loss in the laboratory. We hypothesize that worker reproduction in orphaned Atta field colonies is almost never successful because the last workers die before their sons can be raised to adulthood, but that the importance of worker-laid trophic eggs for queen feeding has precluded the evolutionary loss of worker ovaries. Received 17 January 2005; revised 12 September 2005; accepted 3 October 2005.     

Nonlinearity in the Growth of Bacterial Colonies: Conditions and Causes

The universally recognized kinetic model of colony growth, introduced by Pirt, predicts a linear increase of colony size. The linearity follows from the assumption that the colony expands through the growth of only such cells that are located immediately behind the moving colony front, in the so-called peripheral zone of constant width and density. In this work, Pirt's model was tested on two bacteria—Alcaligenes sp. and Pseudomonas fluorescens—having markedly distinct cultural properties and grown on an agarized medium with pyruvate. The colony size dynamics was followed for different densities of the inoculum, ranging from a single cell to a microdroplet of bacterial suspension (10⁵–10⁶ cells), and for different depths of the agar layer, determining the amount of available substrate. A linear growth mode was observed only with P. fluorescens and only in the case of growth from a microdroplet. When originating from a single cell, colonies of both organisms displayed nonlinear growth with a distinct peak of K _r (the rate of colony radius increase) occurring after 2–3 days of growth. The growth of P. fluorescens colonies showed virtually no dependence on the depth of the agarized medium, whereas the rate of colony size increase of Alcaligenes sp. turned out to be directly related to the medium layer thickness. The departure from linearity is consistently explained by a new kinetic scheme stipulating a possible contribution to the colony growth not only of peripheral cells but also (much more distinct in Alcaligenes) of cells at the colony center. The colony growth dynamics is determined not only by the concentration of the limiting substrate but also by the amount of autoinhibitor, the synthesis of which is governed by the age of cells. The distinctions of growth from a single cell and microdroplet could also originate as a result of dissociation into the R- and S-forms and competition between the corresponding subpopulations for oxygen and the common substrate.     

单菌落PCR法直接快速鉴定重组克隆

利用单菌落PCR法直接筛选含有GFP、LTB-ST外源基因的重组克隆,阳性克隆可以扩增出目的条带,和质粒PCR扩增的结果一致。同时,单菌落PCR法也可应用于重组质粒转化后的农杆菌的筛选,单菌落PCR法的扩增结果和农杆菌液扩增的结果一致。结果表明,单菌落PCR法是一个有效简便的鉴定重组阳性克隆的方法。