Human ribosomal genes (rDNA) are located in nucleolar organizer regions (NORs) on the short arms of acrocentric chromosomes. Metaphase NORs that were transcriptionally active in the previous cell cycle appear as prominent chromosomal features termed secondary constrictions that are achromatic in chromosome banding and positive in silver staining. The architectural RNA polymerase I (pol I) transcription factor UBF binds extensively across rDNA throughout the cell cycle. To determine if UBF binding underpins NOR structure, we integrated large arrays of heterologous UBF-binding sequences at ectopic sites on human chromosomes. These arrays efficiently recruit UBF even to sites outside the nucleolus and, during metaphase, form novel silver stainable secondary constrictions, termed pseudo-NORs, morphologically similar to NORs. We demonstrate for the first time that in addition to UBF the other components of the pol I machinery are found associated with sequences across the entire human rDNA repeat. Remarkably, a significant fraction of these same pol I factors are sequestered by pseudo-NORs independent of both transcription and nucleoli. Because of the heterologous nature of the sequence employed, we infer that sequestration is mediated primarily by protein-protein interactions with UBF. These results suggest that extensive binding of UBF is responsible for formation and maintenance of the secondary constriction at active NORs. Furthermore, we propose that UBF mediates recruitment of the pol I machinery to nucleoli independently of promoter elements.

Cyanobacterial samples were collected between April 1989 and May 1997 from six drainage divisions in coastal areas of Australia: the northeast coast, southeast coast, Tasmania, Murray-Darling Basin, South Australian coast and southwest coast. Saxitoxins were detected in approximately 70% of all field samples and 57% of cultured strains of Anabaena circinalis. Maximum saxitoxin concentrations were 4466 and 2553 mug g(-1) dry weight cells in field samples and strains, respectively. Toxin profiles were similar in the majority of field samples and strains. The toxins were predominantly C-toxins (C1 and C2) and gonyautoxins (GTX2 and GTX3), with saxitoxin sensu stricto (STX). GTX5 and decarbamoyl gonyautoxins (dcGTX2 and dcGTX3) being present in minor amounts, A unique toxin composition (exclusively STX and GTX5) was Found in a geographically isolated strain from the southwest coast of Australia. N1-hydroxy saxitoxins (neoSTX, GTX1 and GTX4) were not detected in any field sample or cultured strain. Anabaena circinalis may not be the only Anabaena species producing saxitoxins, as very low concentrations of GTX3 (14 mug g(-1) dry weight cells or less) were detected in two other Anabaena species: A. perturbata var. tumida and A. spiroides. One decarbamoyl gonyautoxin (dcGTX3) was also present in one A. perturbata var. tumida strain. Anatoxin-a was not detected in Australian strains of Anabaena. Trace amounts of 0.23 and 0.10 mug microcystin-LR equivalents g(-1) dry weight cells were found in two cultured strains of Anabaena cylindrica. An increase in toxin concentration from 0 to 4423 mug saxitoxins gl dry weight cells was observed over a 3-month period in a series of samples collected from a persistent bloom of A. circinalis at Wongulla Lagoon. South Australia. This temporal variation in saxitoxin concentrations is similar to that reported for microcystins in Microcystis aeruginosa (Chroococcales, Cyanophyta).

A low-cost activated carbon from the pan-tropical multipurpose tree Moringa oleifera removes the cyanobacterial hepatotoxin microcystin-LR in quantitative amounts from water in batch adsorption trials. The potential of M. oleifera seed husk carbon for cyanobacterial toxin removal in drinking water treatment in tropical countries is discussed.

The Patos Lagoon is the largest lagoonal system in South America. Its waters are formed by a huge drainage basin (201,600 km2) situated in the most industrialized areas of the Southern state of Rio Grande do Sul. On its margins more than 3 million inhabitants live in several cities and towns. The lagoon waters are used for leisure, drinking, industry, fisheries, agriculture and navigation. A monitoring and sampling program was developed from February 1994 to January 1996 with emphasis on the estuarine area, aiming to evaluate the occurrence of algal blooms. In the last 15 years, several cyanobacterial (blue-green algal) blooms of theMicrocystis aeruginosa have been registered in the lagoon estuary. HighM. aeruginosa biomass (50 to 9,000 μg chla l−1) was observed in the whole region in late summer and autumn 1994, and early summer 1995. The LD50 of toxic bloom samples tested in mice varied from 22 to 250 mg dry weight kg body weight−1 while levels of toxicity (LC50) in the brine shrimp varied from 0.47 to 2.44 mg ml−1. Toxicity varied in different blooms, in the distances along the scum and with time, within the same bloom. The hepatotoxin microcystin-LR was identified in almost all samples.

Two ubiquitous organic acid-producing soil fungi, Aspergillus niger and Penicillium simplicissimum, were screened for the ability to solubilize eight insoluble metal compounds: Al2O3, Al-x(PO4)(x), CaCO3, Ca-3(PO4)(2), Co-3(PO4)(2), Mn-x(PO4)(x), ZnO and Zn-3(PO4)(2). From these, three were selected as test metal compounds for the screening of species, strains and isolates for solubilization properties: ZnO, Zn-3(PO4)(2) and Co-3(PO4)(2). These compounds were used effectively to screen a further 56 strains of fungi, including soil isolates, for solubilizing activity (as revealed by the appearance of clear zones of solubilization around colonies) and metal tolerance (by comparison of colony growth rates). Ratios of the colony growth rate in the presence of a given metal compound (R(m)) to the control colony growth rate (R(c)), and the rate of extension of the clear zone of solubilization (R(s)) in relation to the growth rate of that colony (R(m)), were useful in characterizing these properties. Almost one-third of the natural isolates screened were able to solubilize at least one of ZnO, Zn-3(PO4)(2) and Co-3(PO4)(2), with five strains (out of 56) being capable of solubilizing all three. Cobalt phosphate was the most toxic of the three compounds; zinc phosphate was the least toxic, and was most resistant to solubilization. Zinc oxide was the most readily solubilized compound. In addition to screening for solubilizing abilities and metal tolerance, the method described can also be used for comparison of species and strains to obtain isolates with specific properties for possible biotechnological use and also to examine natural fungal populations. The incorporation of selected metal compounds in the test medium may also be used to assess responses to specific metals and their compounds as a preclude to physiological studies.