The efficiency of conjugal transfer of plasmids from Escherichia coli to the cyanobacterium Anabaena sp. strain PCC 7120 was quantitated as a function of the number of restriction sites for the restriction enzymes carried by the recipient. In addition to the previously recognized isoschizomers of AvaI and AvaII, PCC 7120 was found to possess an isoschizomer of AvaIII. Plasmids modified in E. coli with methylases that protect in vitro against restriction by the three enzymes were transferred with high efficiency, nearly independent of the number of restriction sites on the plasmid. Plasmids left unprotected against one of the three restriction enzymes were transferred with lower efficiencies. For low numbers of sites, the efficiency of conjugal transfer decreased as an exponential function of the number of unprotected sites. The methods presented may be used to increase the efficiency of conjugal transfer into restriction-competent bacteria.Since first recognized, restriction in vivo has been most closely identified with the reduction of plating efficiency of bacteriophage (7, 10). Although conjugal transfer of unmodified DNA also was shown to be sensitive to restriction in Escherichia coli (10), the inability of certain restriction enzymes to act on single-stranded DNA (49, 56) has led to the view that conjugally transferred single-stranded DNA (37) should be immune from restriction (5, 69). Accordingly, there are many examples in which conjugal transfer is unaffected by restriction barriers that prevent the infection of unmodified phage or the transformation of unmodified DNA (5,20,36,41,55,66). However, there are also reports of restriction in nonenteric bacteria indeed limiting conjugal efficiency (18,44,64,79).Regardless of the biological importance of restriction, the resulting inefficiency of DNA transfer is a frequently encountered barrier against introducing DNA into bacteria of experimental interest. While restriction may reduce the frequency of DNA transfer below levels of detectability (40,42,79), it is also possible that some introduced DNA with unmodified restriction sites may escape destruction. With this in mind, it is often of practical importance to know quantitatively the degree to which each restriction site impairs DNA transfer into restriction-competent recipients.The effect of restriction sites on the efficiency of DNA transfer has been quantitated in several studies using plasmids or phage with a known number of sites. Such studies have measured the effect of restriction on phage infection (47, 48, 54), phage transfection (35), transformation (17,51,71), and electroporation (8,34,43). Reduction of conjugal transfer efficiency by restriction has not been systematically studied, although there have been some quantitative reports (30,70 (14,18,42). We report here the construction of plasmids carrying methylases that protect against one or more restriction activities of Anabaena sp. strain PCC 7120, including a third restriction activity reported here for the first time. Using these plasmids, ...
The recent discovery of a diverse phylogenetic assemblage of picoeukaryotes from environments such as oceans, salt marshes and acidic habitats, has expanded the debates about the extent and origin of microbial eukaryotes. However, the diversity of these eukaryote microorganisms, that overlap bacteria in size, and their environmental and biogeographical ubiquity remains poorly understood. Here we survey picoeukaryotes (microbial eukaryotes of 0.2-5 microm in size) from an oligotrophic (nutrient deficient) freshwater habitat using ribosomal RNA gene sequences. Three taxonomic groups the Heterokonta, Cryptomonads and the Alveolata dominated the detected diversity. Most sequences represented previously unsampled species, with several being unassignable to known taxonomic groups and plausibly represent new or unsampled phyla. Many freshwater phylogenetic groups identified in this study appeared unrelated to picoeukaryotic sequences identified in marine ecosystems, suggesting that aspects of eukaryote microbial diversity are specific to certain aquatic environments. Conversely, at least five phylogenetic clusters comprised sequences from freshwater and globally dispersed and often contrasting environments, supporting the concept that a number of picoeukaryotic lineages are widely distributed.
Cyanobacterin LU-1, produced by Nostoc linckia CALU 892, inhibits the growth of many cyanobacteria and eukaryotic algae. The minimum effective dose of a crude preparation to Synechococcus sp. R-2 is ca 1 g ml-1. The antibiotic hinders cell division and light-dependent oxygen evolution in Synechococcus sp. R-2 (PCC 7942) cells. It is not active against heterotrophic bacteria and fungi, and is non-toxic to mice.Purified cyanobacterin LU-1 contains a nitrous heterocycle with sugar and phenolic substituents. Cyanobacterin LU-1 accumulates in the medium during the course of growth, although not in direct proportion to cell density. Productivity of the culture depends on temperature.
Cyclotrichiids are of ecological and evolutionary interest by virtue of their importance in red tide formation, their highly divergent small subunit (SSU) ribosomal RNA (rRNA) genes, kleptoplastidy, and utility as indicators of eutrophication. However, only seven strains have had their SSU rRNA genes sequenced and their environmental diversity and distribution are largely unknown. We probed 67 globally dispersed freshwater column/sediment and soil DNA samples (eDNAs) and constructed 24 environmental gene libraries using polymerase chain reaction primers specific to an uncharacterised cyclotrichiid subgroup. We reveal a novel, globally ubiquitous freshwater clade comprising 25 genetically distinct SSU ribosomal DNA (rDNA) sequences (SSU-types). Some identical SSU-types were detected at globally widely distributed sites. The SSU-types form four distinct phylogenetic clusters according to marine or non-marine provenance, suggesting at least one major marine-freshwater evolutionary transition within the cyclotrichiids. We used the same primers to sample intensively 18 sampling points in 13 closely situated lakes, each characterised by 14 environmental variables, and showed that molecular detection or non-detection of cyclotrichiids was most significantly influenced by levels of total phosphorus, dissolved organic carbon, and chlorophyll a. Within the subset of lakes in which cyclotrichiids were detected, closely related SSU-types differed in their ecological preferences to pH, total phosphorus, and sample depth.
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