Growth factor superfamilies and mammalian embryogenesis

With the availability of amino acid and nucleotide sequence information has come the realization that growth factors can be clustered in to superfamilies. Several of these superfamilies contain molecules that were not initially identified because of growth-promoting activities; rather they were discovered through their ability to regulate other processes. Certain members of these superfamilies are present during early mammalian embryogenesis. However, until recently, it has been difficult to manipulate the developing mammalian embryo to observe directly the effects of inappropriate, excessive, or reduced expression of these molecules. Despite this limitation, at least some of these molecules have been implicated in the control of differentiation and morphogenesis, two actions unpredicted from the cell biology of most of the growth factors. Moreover, these actions are reflected in nonmammalian species where homologues of the mammalian growth factors control crucial steps in the choice of developmental fate. This review describes five growth factor superfamilies and the role these molecules may have in controlling proliferation, differentiation, and morphogenesis during mammalian development.     

Estimation of Campylobacter spp. in broth culture by bioluminescence assay of ATP.

The luciferin-luciferase bioluminescence reaction was used to estimate cell numbers of Campylobacter jejuni and Campylobacter coli in broth cultures based on a linear relationship between cell numbers (in excess of 10(4) to 10(5] and ATP levels. The sensitivity was lower than that obtained with Escherichia coli. The calculated amount of intracellular ATP per cell of C. jejuni and C. coli ranged from 1.7 to 2.1 fg.     

Colicin V can be produced by lactic acid bacteria

Colicin V is a small, proteinaceous bacterial toxin, produced by many strains of Escherichia coli and other members of the Enterobacteriaceae, that fits the definition of class II bacteriocins of Gram-positive bacteria. Export of colicin V is dependent on specific ABC (ATP-binding cassette) secretion proteins which recognize a double-glycine-type leader peptide on the immature colicin V bacteriocin. Replacement of the colicin V leader peptide by a signal peptide from the signal sequence-dependent bacteriocin divergicin A allowed expression of colicin V in lactic acid bacteria. This system may serve as a model for the heterologous expression of other small bacteriocins active against Gram-negative bacteria and other antibacterial peptides from lactic acid bacteria.     

Light and dissolved nutrients mediate recalcitrant organic matter decomposition via microbial priming in experimental streams

1. Environmental factors such as nutrient and light availability may play important roles in determining the magnitude and direction of microbial priming and detrital decomposition and, therefore, the relative importance of microbial priming in carbon (C) dynamics in freshwater ecosystems.
2. We integrated light availability with an existing conceptual model predicting the magnitude of the priming effect (PE) along a dissolved nutrient gradient (i.e. nutrient PE model). Our modified light-nutrient PE model hypothesises how light may mediate priming at any given nutrient concentration and provides a calculation method for quantitative PE values (i.e. light effect size at a given nutrient concentration).
3. We used recirculating stream mesocosms with Quercus stellata (post oak) leaf litter as an organic matter (OM) substrate in a 150-day experiment to test our model predictions. We manipulated light levels [ambient (full light), shaded (c. 19% of ambient)] and phosphorus (P) concentration (10, 100, 500 µg PO₄-P/L) in a fully factorial design. We also supplied all mesocosms with 500 µg/L dissolved inorganic nitrogen. Microbial biomass, water column dissolved organic C, and leaf litter dry mass and recalcitrant OM [i.e. the fibre (cellulose + lignin) component of post oak substrate] were measured. Recalcitrant OM (ROM) k-rates (day⁻¹) were used to calculate the light effect size within P treatments as a log response ratio (ln[ambient k-rate/shade k-rate]) to ascertain PE magnitude and direction (positive or negative).
4. Light was an important driver of dissolved organic C, a potential source of additional labile organic matter essential for priming heterotrophic microbes. There were weak PEs in total leaf litter dry mass remaining, but PEs were more pronounced in leaf litter ROM remaining. The strongest positive PEs (specific to litter ROM pools) occur in the highest P treatment, presumably due to a change in which nutrient, nitrogen versus P, was a limiting factor for microbes based on nutrient ratios rather than P concentration alone. These results illustrate the importance of considering light levels, nutrient ratios (rather than individual nutrients), and detrital ROM components in further PE model development.