Membrane targeting of RecA during genetic transformation

Recombination in prokaryotes and eukaryotes is mediated by the RecA family of proteins. Although the interactions between RecA and DNA are well studied, the cellular location of these interactions is not known. Using genetic transformation of Streptococcus pneumoniae as a model system, there was increased expression of a protein, colligrin, and RecA, products of the rec locus during genetic transfer. These proteins formed a complex and were found associated with the membranes of genetically competent cells. With immunoelectron microscopy and subcellular fractionation, we showed that the induction of competence led to the translocation of RecA and colligrin to the membrane and to the formation of clusters of RecA in a colligrin-dependent step. Based on the behaviour of colligrin and RecA during genetic exchange and the numerous proteins in prokaryotes and eukaryotes with domains similar to colligrin, we suggest that there may exist a family of proteins, which gathers macromolecules at specific sites in biological membranes.     

Protistan microbial observatory in the Cariaco Basin,Caribbean. I. Pyrosequencing vs Sanger insights into species richness

Microbial diversity and distribution are topics of intensive research. In two companion papers in this issue, we describe the results of the Cariaco Microbial Observatory (Caribbean Sea, Venezuela). The Basin contains the largest body of marine anoxic water, and presents an opportunity to study protistan communities across biogeochemical gradients. In the first paper, we survey 18S ribosomal RNA (rRNA) gene sequence diversity using both Sanger- and pyrosequencing-based approaches, employing multiple PCR primers, and state-of-the-art statistical analyses to estimate microbial richness missed by the survey. Sampling the Basin at three stations, in two seasons, and at four depths with distinct biogeochemical regimes, we obtained the largest, and arguably the least biased collection of over 6000 nearly full-length protistan rRNA gene sequences from a given oceanographic regime to date, and over 80 000 pyrosequencing tags. These represent all major and many minor protistan taxa, at frequencies globally similar between the two sequence collections. This large data set provided, via the recently developed parametric modeling, the first statistically sound prediction of the total size of protistan richness in a large and varied environment, such as the Cariaco Basin: over 36 000 species, defined as almost full-length 18S rRNA gene sequence clusters sharing over 99% sequence homology. This richness is a small fraction of the grand total of known protists (over 100 000–500 000 species), suggesting a degree of protistan endemism.     

Effect of Cuticle Treatments on Infection of Phaseolus vulgaris by Rhizoctonia solani

Rhizoctonia solani, the causal agent of stem canker of beans, does not commonly infect beans more than two weeks old. Treatment of the cuticular layer by abrasion or chloroform rinsing results in decreased cuticular autofluorescence and the ability of stains to penetrate the hypocotyl surface. Infection cushions preferentially formed near these treated areas on both young and old plants. The morphology of infection cushions on older plants is simpler than those found on young, susceptible plants, but they are fully competent to form lesions.     

Optional tool use: The case of wild bearded capuchins (Sapajus libidinosus) cracking cashew nuts by biting or by using percussors

Tool use in humans can be optional, that is, the same person can use different tools or no tool to achieve a given goal. Strategies to reach the same goal may differ across individuals and cultures and at the intra‐individual level. This is the first experimental study at the intra‐individual level on the optional use of a tool in wild nonhuman primates. We investigated optional tool use by wild bearded capuchins (Sapajus libidinosus) of Fazenda Boa Vista (FBV; Piauí, Brazil). These monkeys habitually succeed in cracking open the mesocarp of dry cashew nuts (Anacardium spp.) by pounding them with stones and/or by biting. We assessed whether availability of a stone and resistance of the nut affected capuchins' choice to pound or to bite the nuts and their rates of success. Sixteen capuchins (1–16 years) received small and large dry cashew nuts by an anvil together with a stone (Stone condition) or without a stone (No‐Stone condition). In the Stone conditions, subjects used it to crack the nut in 89.1% (large nuts) and 90.1% (small nut) of the trials. Nut size significantly affected the number of strikes used to open it. Availability of the stone significantly increased the average percent of success. In the No‐Stone conditions, monkeys searched for and used other percussors to crack the nuts in 54% of trials. In all conditions, age affects percentage of success and number of strikes to reach success. We argue that exclusive use of stones in other sites may be due to the higher abundance of stones at these sites compared with FBV. Since capuchins opened cashews with a tool 1–2 years earlier than they succeed at cracking more resistant palm nuts, we suggest that success at opening cashew nuts with percussors may support the monkeys' persistent efforts to crack palm nuts.     

Disentangling the link between leaf photosynthesis and turgor in fruit growth

Despite the importance of understanding plant growth, the mechanisms underlying how plant and fruit growth declines during drought remain poorly understood. Specifically, it remains unresolved whether carbon or water factors are responsible for limiting growth as drought progresses. We examine questions regarding the relative importance of water and carbon to fruit growth depending on the water deficit level and the fruit growth stage by measuring fruit diameter, leaf photosynthesis, and a proxy of cell turgor in olive (Olea europaea). Flow cytometry was also applied to determine the fruit cell division stage. We found that photosynthesis and turgor were related to fruit growth; specifically, the relative importance of photosynthesis was higher during periods of more intense cell division, while turgor had higher relative importance in periods where cell division comes close to ceasing and fruit growth is dependent mainly on cell expansion. This pattern was found regardless of the water deficit level, although turgor and growth ceased at more similar values of leaf water potential than photosynthesis. Cell division occurred even when fruit growth seemed to stop under water deficit conditions, which likely helped fruits to grow disproportionately when trees were hydrated again, compensating for periods with low turgor. As a result, the final fruit size was not severely penalized. We conclude that carbon and water processes are able to explain fruit growth, with importance placed on the combination of cell division and expansion. However, the major limitation to growth is turgor, which adds evidence to the sink limitation hypothesis.     

Emerging Patterns of HIV Infection and Control in the Philippines

A total of 50 carriers of the human immunodeficiency virus (HIV), 46 of them female prostitutes, have been detected through seroprevalence surveys by the Department of Health, Manila. Infection rates are highest in two small cities near foreign military bases and in the tourist district of MetroManila. Nine patients with the acquired immunodeficiency syndrome (AIDS) who contracted the disease outside the country have been reported, with opportunistic infections being the major clinical feature. Public information measures heavily utilize the mass media, and there is anecdotal evidence that awareness of the disease among the urban population is increasing. The National AIDS Committee foresees that a large proportion of the cases seen in the Philippines over the next few years will be returning nationals who were infected abroad.     

Impaired responsiveness of homosexual men with HIV antibodies to plasma derived hepatitis B vaccine.

Thirty five homosexual men (17 positive for antibody to the human immunodeficiency virus (HIV) and 18 consistently negative) were vaccinated against hepatitis B virus infection. Eight of the 17 seropositive patients failed to develop detectable hepatitis B surface antibody within three months of the third injection compared with only one of the 18 seronegative patients (p less than 0.01). HIV infection is prevalent in the developed world in groups at risk for hepatitis B infection and in certain Third World countries where widespread vaccination programmes exist. This study shows the impact that coincident HIV infection may have on an otherwise efficacious vaccine. The efficacy of this and other vaccines in patients infected with HIV needs to be studied urgently.     

Comparisons of redox kinetics of methemerythrin and mu-sulfidomethemerythrin. Implications for interactions with cytochrome b5

We have examined the effects on redox kinetics of changing the reduction potential of the mu-oxo-bridged binuclear iron center in octameric hemerythrin (Hr) from Phascolopsis gouldii. The opportunity to examine such effects is provided by the availability of mu-sulfidomethemerythrin (mu-S2-metHr), whose [Fe(III),Fe(III)]met----[Fe(II),Fe(III)]semi-met reduction potential is approximately 200 mV higher than that of methemerythrin (metHr). We have used, as redox partners to Hr, a set of metal complexes and the heme proteins deoxymyoglobin (Mb) and cytochrome b5. The latter protein from P. gouldii is a presumed physiological redox partner of Hr. Similar kinetics at pH 8 in the presence or absence of the allosteric effector perchlorate suggest reduction of the iron atom closer to the outer surface of each subunit in the Hr octamer during the met----semi-met transformation. For all reducing agents, the experimentally determined ratio of second-order rate constants for reductions of mu-S2-metHr and metHr, k12(mu-S2-met)/k12(met), is close to the value of 40 predicted by the simple Marcus relation for "outer-sphere" electron transfer. For oxidations of (semi-met)RHr and mu-S2-semi-metHr, the predicted value of 40 for k12[(semi-met)R]/k12(mu-S2-semi-met) is closely approximated when Fe(CN)6(3-) is used as oxidant. The ionic strength dependence of the second-order rate constant suggests electrostatic interactions of opposite charges during reduction of metHr by P. gouldii cytochrome b5.(ABSTRACT TRUNCATED AT 250 WORDS)