Structures of the P. aeruginosa FleQ-FleN master regulators reveal large-scale conformational switching in motility and biofilm control

Pseudomonas aeruginosa can cause a wide array of chronic and acute infections associated with its ability to rapidly switch between planktonic, biofilm, and dispersed lifestyles, each with a specific arsenal for bacterial survival and virulence. At the cellular level, many of the physiological transitions are orchestrated by the intracellular second messenger c-di-GMP and its receptor-effector FleQ. A bacterial enhancer binding protein, FleQ acts as a master regulator of both flagellar motility and adherence factor secretion and uses remarkably different transcription activation mechanisms depending on its dinucleotide loading state, adenosine triphosphatase (ATPase) activity, interactions with polymerase sigma (σ) factors, and complexation with a second ATPase, FleN. How the FleQ-FleN tandem can exert diverse effects through recognition of a conserved FleQ binding consensus has remained enigmatic. Here, we provide cryogenic electron microscopy (cryo-EM) structures of both c-di-GMP-bound and c-di-GMP-free FleQ-FleN complexes which deepen our understanding of the proteins' (di)nucleotide-dependent conformational switching and fine-tuned roles in gene expression regulation.

Bacterial crystalline cellulose secretion via a supramolecular BcsHD scaffold

Cellulose, the most abundant biopolymer on Earth, is not only the predominant constituent of plants but also a key extracellular polysaccharide in the biofilms of many bacterial species. Depending on the producers, chemical modifications, and three-dimensional assemblies, bacterial cellulose (BC) can present diverse degrees of crystallinity. Highly ordered, or crystalline, cellulose presents great economical relevance due to its ever-growing number of biotechnological applications. Even if some acetic acid bacteria have long been identified as BC superproducers, the molecular mechanisms determining the secretion of crystalline versus amorphous cellulose remain largely unknown. Here, we present structural and mechanistic insights into the role of the accessory subunits BcsH (CcpAx) and BcsD (CesD) that determine crystalline BC secretion in the Gluconacetobacter lineage. We show that oligomeric BcsH drives the assembly of BcsD into a supramolecular cytoskeletal scaffold that likely stabilizes the cellulose-extruding synthase nanoarrays through an unexpected inside-out mechanism for secretion system assembly.

Weaving of bacterial cellulose by the Bcs secretion systems

Cellulose is the most abundant biological compound on Earth and while it is the predominant building constituent of plants, it is also a key extracellular matrix component in many diverse bacterial species. While bacterial cellulose was first described in the 19th century, it was not until this last decade that a string of structural works provided insights into how the cellulose synthase BcsA, assisted by its inner-membrane partner BcsB, senses c-di-GMP to simultaneously polymerize its substrate and extrude the nascent polysaccharide across the inner bacterial membrane. It is now established that bacterial cellulose can be produced by several distinct types of cellulose secretion systems and that in addition to BcsAB, they can feature multiple accessory subunits, often indispensable for polysaccharide production. Importantly, the last years mark significant progress in our understanding not only of cellulose polymerization per se but also of the bigger picture of bacterial signaling, secretion system assembly, biofilm formation and host tissue colonization, as well as of structural and functional parallels of this dominant biosynthetic process between the bacterial and eukaryotic domains of life. Here, we review current mechanistic knowledge on bacterial cellulose secretion with focus on the structure, assembly and cooperativity of Bcs secretion system components.

Multifunctional SEVA shuttle vectors for actinomycetes and Gram-negative bacteria

Actinomycetales, such as the genus Streptomyces, are well‐known cell factories employed to produce a wide variety of secondary metabolites for industrial use. However, not only is the genetic engineering of Streptomyces more complicated and tedious than other model laboratory species, such as Escherichia coli, there is also a considerable lack of genetic tools, hindering its adoption as a common chassis for synthetic biology. In this work, 23 novel shuttle vectors are presented that follow the canonical SEVA (Standard European Vector Architecture) common architecture with the goal of increasing the genetic toolbox repertoire for Streptomyces and other actinomycetes. The ORI module of these plasmids is composed of the combination of two origins of replication, one for Gram‐negative bacteria and the other for Streptomyces, a Gram‐positive bacteria. Origins of replication have been included in the collection for integrative, low‐copy number, and medium‐to‐high‐copy number vectors for Streptomyces. Also, a new selection marker has been developed that confers resistance to apramycin. The functionality of these plasmids was tested via the heterologous expression of GFP and the heterologous production of the plant flavonoid apigenin in Streptomyces albus J1074, with successful results in both cases, therefore expanding the current repertoire of genetic manipulation tools in Streptomyces species.

Prenatal exposure to metals modified DNA methylation and the expression of antioxidant- and DNA defense-related genes in newborns in an urban area

The developmental period in utero is a critical window for environmental exposure. Epigenetic fetal programming via DNA methylation is a pathway through which metal exposure influences the risk of developing diseases later in life. Genetic damage repair can be modified by alterations in DNA methylation, which, in turn, may modulate gene expression due to metal exposure. We investigated the impact of prenatal metal exposure on global and gene-specific DNA methylation and mRNA expression in 181 umbilical cord blood samples from newborns in Mexico City. Global (LINE1) and promoter methylation of DNA-repair (OGG1 and PARP1) and antioxidant (Nrf2) genes was evaluated by pyrosequencing. Prenatal metal exposure (As, Cu, Hg, Mn, Mo, Pb, Se, and Zn) was determined by ICP-MS analysis of maternal urine samples. Multiple regression analyses revealed that DNA methylation of LINE1, Nrf2, OGG1, and PARP1 was associated with potentially toxic (As, Hg, Mn, Mo, and Pb) and essential (Cu, Se, and Zn) elements, and with their interactions. We also evaluated the association between gene expression (mRNA levels quantified by p-PCR) and DNA methylation. An increase in OGG1 methylation at all sites and at CpG2, CpG3, and CpG4 sites was associated with reduced mRNA levels; likewise, methylation at the CpG5, CpG8, and CpG11 sites of PARP1 was associated with reduced mRNA expression. In contrast, methylation at the PARP1 CpG7 site was positively associated with its mRNA levels. No associations between Nrf2 expression and CpG site methylation were observed. Our data suggest that DNA methylation can be influenced by prenatal metal exposure, which may contribute to alterations in the expression of repair genes, and therefore, result in a lower capacity for DNA damage repair in newborns.

Dietary and genetic determinants of homocysteine levels among Mexican women of reproductive age

OBJECTIVE

To evaluate the independent and joint effects of dietary folate, vitamin B(12) consumption and methylenetetrahydrofolate reductase (MTHFR) polymorphisms (677C>T and 1298A>C) on the circulating folate and homocysteine (Hcy) levels among Mexican women of reproductive age.

DESIGN

A cross-sectional, population-based study.

SUBJECTS

The first 130 healthy non-pregnant women (aged 16-34 years) who agreed to participate in a reproductive cohort in Morelos, Mexico.

MAIN OUTCOME MEASUREMENTS

Dietary intakes of vitamin B(12) and folate were estimated using a semiquantitative food frequency questionnaire. MTHFR 677C>T and 1298A>C polymorphisms were ascertained using the PCR-based method. Serum levels of Hcy and folate were determined using high-performance liquid chromatography and radioimmunoassay, respectively.

RESULTS

Genotype frequencies for the MTHFR 677C>T polymorphism were 21.5% (CC), 52.3% (CT) and 26.2% (TT) among Mexican women. Of the population, 22% had the MTHFR 1298AC genotype, while no individual carried the 1298CC genotype. We observed an increased level of Hcy among carriers of the 677TT genotype, compared to carriers of the 677CC genotype. The highest level of Hcy was observed among MTHFR 677TT carriers with low B(12) intake (<2.0 microg/day), which resulted with a significant interaction (P=0.01).

CONCLUSION

Vitamin B(12) is an important determinant of Hcy levels in Mexico. Supplementation of folic acid with vitamin B(12) may be preferable when the MTHFR 677T variant allele is prevalent.

Serum levels of beta-hexachlorocyclohexane, hexachlorobenzene and polychlorinated biphenyls and breast cancer in Mexican women

Information on the association between exposure to beta-hexachlorocyclohexane (beta-HCH), hexachlorobenzene (HCB) or polychlorinated biphenyls (PCBs) and the incidence of breast cancer is inconclusive. However, exposure to such compounds is a public health concern in Mexico and is subject to recent regulation. Serum levels of beta-HCH, HCB and PCBs were analysed in 95 histologically confirmed breast cancer cases and 95 hospital controls, 20-79 years of age, from Mexico City, enrolled between March 1994 and April 1996. After adjusting for established risk factors, there was no evidence of a relationship between beta-HCH, HCB and PCBs and breast cancer risk (OR for beta-HCH tertile 3 versus tertile 1: 1.05 95% CI 0.46-2.40; OR for HCB tertile 3 versus tertile 1: 0.46 95% CI 0.20-1.07; OR for PCBs 1.31 95% CI 0.33-5.21 for the high category of exposure). This study lends no support to the case for a role for beta-HCH, HCB or PCBs in breast cancer aetiology.

Breast-feeding and serum p,p'DDT levels among Mexican women of childbearing age: a pilot study

For almost 50 years, millions of Mexicans have been directly and/or indirectly exposed to (1,1,1-trichloro-2,2-bis[p-chlorophenyl]ethane) (p,p'DDT). The potential related health outcomes of this exposure are of international concern. The objective of the study was to determine the effect of breast-feeding on serum levels of 1,1-dichloro-2; 2'-bis(p-chlorophenyl)ethylene (p,p'DDE) and p,p'DDT in women of childbearing age who were residents of the state of Morelos, Mexico. In March 1999, we examined a sample of 24 women, ages 21 to 36 years, who came with their children to the outpatient facility of a county Health Center in the state of Morelos. The geometric mean for p,p'DDE was 21.8 ng/ml+/-2.58 (GSD) and 2.9 ng/ml+/-2.84 for p,p'DDT. For each month of breast-feeding we observed similar significant decreases for both p,p'DDE (beta=-0.0403 per log concentration unit, P=0.001) and p,p'DDT (beta=-0.0309, P=0.03) serum levels, adjusted by mothers' age and number of children. The adjusted half-life estimate for p,p'DDE serum levels was 17 months. It was concluded that breast-feeding leads to rapid removal of p,p'DDT from the body (<2 year half-life) compared to nonlactational elimination rates (<5 year half-life). In this population, serum p,p'DDE levels were similar to those found 20 years ago in the United States.

Food sources of phytoestrogens and breast cancer risk in Mexican women

We analyzed the intake of selected foods that contain phytoestrogens in relation to breast cancer (BC) risk using data from a hospital-based case-control study performed in Mexico City from 1994 to 1995. A total of 198 women with BC, aged 21-79 years, were individually age matched to an identical number of women with no breast disease. By a direct interview, information on socioeconomic characteristics and diet was obtained. A semiquantitative questionnaire was used to estimate the frequency of consumption of 95 foods. The effect of selected foods that contain phytoestrogens on BC risk was estimated using logistic regression models. The adjusted odds ratio for the consumption of more than one slice of onion per day and BC was 0.27 (95% confidence interval = 0.16-0.47), with a statistically significant trend (p < 0.001). This protective effect remained after adjustment for known risk factors of BC. Among premenopausal women, there was also a protective and significant effect due to the intake of lettuce and spinach and nonsignificant protective effects for the consumption of apples and herbal tea. Additional studies aimed at evaluating the potential protective effect of particular phytoestrogens on BC risk are needed.

[Identification of malignant breast lesions in Mexico]

OBJECTIVE

To evaluate the modes of detection of breast malignancies in Mexico City and to estimate the number of patients diagnosed in advanced stages.

MATERIAL AND METHODS

This cross-sectional study was conducted between 1994 and 1996, among 256 women with a histological diagnosis of breast cancer, at three tertiary level public hospitals in Mexico City. Personal interviews were conducted to collect data on reproductive characteristics, clinical history, and breast cancer modes of detection. Data analysis consisted of percentages, odds ratios, and 95% confidence intervals.

RESULTS

Ninety percent of women sought medical care after identifying a breast lump by themselves. Only 10% of patients had a stage-I tumor; all 27 cases first identified by a physician were in stage II-B and higher.

CONCLUSIONS

An increasing trend of breast cancer mortality in Mexico City will persist, unless a greater proportion of tumors in situ is detected; this would require enhancing breast cancer screening programs and conducting an intense educational intervention among women at risk.

[Lead elimination by traditional curing]

OBJECTIVE

To evaluate traditional acidic curing as a preventive method for reducing lead content of glazed ceramic ware.

MATERIAL AND METHODS

In 27 ceramic ware pieces from four states in Mexico, the level of residual lead was determined through atomic absorption spectrophotometry after four washings with acetic acid 3%.

RESULTS

The lead content of the vinegar washing diminished proportionally with the number of washings, although it remained highly above the permissible levels of this metal (2.5-7.0 p.p.m.).

CONCLUSIONS

Traditional acidic curing of glazed ceramic ware is not a useful preventive measure for reducing lead exposure.

The adipose tissue to serum dichlorodiphenyldichloroethane (DDE) ratio: some methodological considerations

Dichlorodiphenyldichloroethane (DDE) adipose tissue level has been regarded as a preferred indicator of accumulated human exposure to DDT; however, blood sera are more feasible to obtain and analyze than adipose tissue samples. Inconsistent and scarce information exists in relation to the adipose tissue/serum DDE ratio. As a part of a hospital-based case-control study performed in Mexico City from 1994 to 1996, 198 paired serum and adipose tissue samples were obtained from 72 women with histologically confirmed breast cancer and 126 women with benign breast disease. Both adipose tissue and serum DDE levels were determined by gas-liquid chromatography and reported as ppb lipid weight (ng/g) as well as wet basis (ng/ml). Results showed that the adipose tissue/serum DDE ratio (ADSE) varies according to the type of information (lipid vs wet basis, arithmetic vs geometric means) used for its estimation. ADSE gets a value near 1 (1.1) only when the geometric DDE levels in lipid basis are used for its estimation. The correlation between DDE serum and adipose tissue levels was found (r=0.364, P<0.001). The ADSE did not vary by disease status, nor was it altered by parity, history of breast-feeding, and other reproductive characteristics. We endorse the use of venipuncture instead of biopsy as a way to estimate DDT body burden levels in further research.

Levels of dichloro-dyphenyl-trichloroethane (DDT) metabolites in maternal milk and their determinant factors

To document the levels and the determinants of dichloro-dyphenyl-trichloroethane (DDT) metabolites in maternal milk, we conducted a cohort study of 50 adult females who lived in Mexico City. We measured social and dietary characteristics via interview. Levels of DDT metabolites were determined by gas-liquid chromatography. The mean values (lipid milk basis) were 0.162 ppm p,p'-DDT; 0.138 ppm o,p'-DDT; and 0.594 ppm 2,2(bis)p-chlorophyenyl-1-1-dichloroethylene (DDE). The main determinants of DDT metabolites were maternal age, lifetime lactation, history of living in an agricultural area, and consumption of salted meat and fish. We estimated that 6.0% of the breast-fed babies had daily intakes of DDT above the level of 0.005 mg/kg d recommended by the World Health Organization/Food and Agriculture Organization of the United Nations (WHO/FAO). Health-outcomes research among children is needed, and investigators should design or adjust current surveillance programs.

Prevalence and determinants of lead intoxication in Mexican children of low socioeconomic status

This paper reports on the prevalence of lead poisoning in children between 1 and 5 years of age living in a marginal area to the north of Mexico City and also includes an evaluation of sources of exposure to this metal in the same area. The results show that 67.5% of the children studied have blood lead (PbB) levels > or = 10 micrograms/100 ml. Twenty-one percent of these children (1987) had PbB levels that required medical evaluation (> or = 20 micrograms/100 ml- < or = 40 micrograms/100 ml), and 112 children needed medical treatment (PbB > or = 40 micrograms/100 ml). In addition, the study found that the probability of higher blood lead levels (> or = 20 micrograms/dl) corresponds to children whose mothers use lead-glazed pottery dishes (OR = 2.80; CI 95%, 1.55-5.07) and to children who habitually bite colored pencils (OR = 2.05; CI 95%, 1.13-3.71) compared, respectively, with children whose mothers do not use that type of dishes and children who do not bite pencils. Our results provide baseline information for estimating the impact and costs of population-based interventions aimed at these populations and also confirm the need to strengthen health education programs to promote the reduction of lead exposure in the general population.

Is DDT use a public health problem in Mexico?

We review the potential impact of DDT on public health in Mexico. DDT production and consumption patterns in Mexico during the last 20 years are described and compared with those in the United States. In spite of the restrictions on DDT use in antimalaria campaigns in Mexico, use of DDT is still higher than in other Latin American countries. We analyzed information from published studies to determine accumulated levels of this insecticide in blood, adipose tissue, and breast milk samples from Mexican women. Current lipid-adjusted DDE levels from women living in Mexico City are 6.66 ppb in mammary adipose tissue and 0.594 ppm in total breast milk. Finally, the methodological limitations of existing epidemiological studies on DDT exposure and breast cancer are discussed. We conclude that DDT use in Mexico is a public health problem, and suggest two solutions: identification of alternatives for the control of malaria and educational intervention to reduce DDT exposure. We also recommend strengthening epidemiological studies to evaluate the association between accumulated DDT levels in adipose tissue and breast cancer incidence among Mexican women.