The cellular ecology of progressive neoplastic transformation: A clonal analysis

A comparison was made of the competence for neoplastic transformation in three different sublines of NIH 3T3 cells and multiple clonal derivatives of each. Over 90% of the neoplastic foci produced by an uncloned transformed (t-SA′) subline on a confluent background of nontransformed cells were of the dense, multilayered type, but about half of the t-SA′ clones produced only light foci in assays without background. This asymmetry apparently arose from the failure of the light focus formers to register on a background of nontransformed cells. Comparison was made of the capacity for confluence-mediated transformation between uncloned parental cultures and their clonal derivatives by using two nontransformed sublines, one of which was highly sensitive and the other relatively refractory to confluence-mediated transformation. Transformation was more frequent in the clones than in the uncloned parental cultures for both sublines. This was dramatically so in the refractory subline, where the uncloned culture showed no overt sign of transformation in serially repeated assays but increasing numbers of its clones exhibited progressive transformation. The reason for the greater susceptibility of the pure clones is apparently the suppression of transformation among the diverse membership that makes up the uncloned parental culture. Progressive selection toward increasing degrees of transformation in confluent cultures plays a major role in the development of dense focus formers, but direct induction by the constraint of confluence may contribute by heritably damaging cells. In view of our finding of increased susceptibility to transformation in clonal versus uncloned populations, expansion of some clones at the expense of others during the aging process would contribute to the marked increase of cancer with age.

16S rRNA genes reveal stratified open ocean bacterioplankton populations related to the Green Non-Sulfur bacteria.

Microorganisms play an important role in the biogeochemistry of the ocean surface layer, but spatial and temporal structures in the distributions of specific bacterioplankton species are largely unexplored, with the exceptions of those organisms that can be detected by either autofluorescence or culture methods. The use of rRNA genes as genetic markers provides a tool by which patterns in the growth, distribution, and activity of abundant bacterioplankton species can be studied regardless of the ease with which they can be cultured. Here we report an unusual cluster of related 16S rRNA genes (SAR202, SAR263, SAR279, SAR287, SAR293, SAR307) cloned from seawater collected at 250 m in the Sargasso Sea in August 1991, when the water column was highly stratified and the deep chlorophyll maximum was located at a depth of 120 m. Phylogenetic analysis and an unusual 15-bp deletion confirmed that the genes were related to the Green Non-Sulfur phylum of the domain Bacteria. This is the first evidence that representatives of this phylum occur in the open ocean. Oligonucleotide probes were used to examine the distribution of the SAR202 gene cluster in vertical profiles (0-250 m) from the Atlantic and Pacific Oceans, and in discrete (monthly) time series (O and 200 m) (over 30 consecutive months in the Western Sargasso Sea. The data provide robust statistical support for the conclusion that the SAR202 gene cluster is proportionately most abundant at the lower boundary of the deep chlorophyll maximum (P = 2.33 x 10(-5)). These results suggest that previously unsuspected stratification of microbial populations may be a significant factor in the ecology of the ocean surface layer.

Parasite abundance and diversity in mammals: correlates with host ecology.

Fecally dispersed parasites of 12 wild mammal species in Mudumalai Sanctuary, southern India, were studied. Fecal propagule densities and parasite diversity measures were correlated with host ecological variables. Host species with higher predatory pressure had lower parasite loads and parasite diversity. Host body weight, home range, population density, gregariousness, and diet did not show predicted effects on parasite loads. Measures of alpha diversity were positively correlated with parasite abundance and were negatively correlated with beta diversity. Based on these data, hypotheses regarding determinants of parasite community are discussed.