RESUMEN
The biology of placental and fetal development suggests that alcohol may play a significant role in increasing the risk of feto-infant morbidity and mortality, but study results are inconsistent and the mechanism remains poorly defined. Previous studies have not examined the risk of placenta-associated syndromes (PASs: defined as the occurrence of either placental abruption, placenta previa, preeclampsia, small for gestational age, preterm, or stillbirth) as a unique entity. Therefore, we sought to examine the relationship between prenatal alcohol use and the risk of PAS among singleton births in the Missouri maternally linked data files covering the period 1989-2005. Logistic regression with adjustment for intracluster correlation was used to generate adjusted odds ratios (ORs) and 95% confidence intervals (CIs). Compared with nondrinkers, drinkers were more likely to be smokers, 35 years of age or older, black, and multiparous. Drinkers had an increased risk of PAS (OR=1.26, 95% CI=1.22,1.31) when compared with their nondrinking counterparts. The risk of PAS was progressively amplified with increasing prenatal alcohol consumption (P for trend <.01). Women who reported consuming five or more alcoholic drinks per week had more than twofold increased risk of PASs, whereas women in the lowest drinking category (one to two drinks per week) had only a slight increased risk of PAS (OR=1.09, 95% CI=1.05, 1.14). Enhanced understanding of the mechanism by which prenatal alcohol consumption leads to PAS may aid in the development of more targeted interventions designed to prevent adverse pregnancy outcomes. Screening women for alcohol use may assist providers in protecting developing fetuses from the potential dangers of prenatal alcohol use.
Asunto(s)
Etanol/efectos adversos , Enfermedades Placentarias/epidemiología , Desprendimiento Prematuro de la Placenta/epidemiología , Adulto , Población Negra , Relación Dosis-Respuesta a Droga , Etanol/administración & dosificación , Femenino , Humanos , Recién Nacido , Recién Nacido Pequeño para la Edad Gestacional , Modelos Logísticos , Edad Materna , Enfermedades Placentarias/inducido químicamente , Enfermedades Placentarias/prevención & control , Placenta Previa/epidemiología , Preeclampsia/epidemiología , Embarazo , Nacimiento Prematuro/epidemiología , Factores de Riesgo , Mortinato , Población BlancaRESUMEN
We sought to assess the contribution of paternal involvement to racial disparities in infant mortality. Using vital records data from singleton births in Florida between 1998 and 2005, we generated odds ratios (OR), 95% confidence intervals (CI), and preventative fractions to assess the association between paternal involvement and infant mortality. Paternal involvement status was based on presence/absence of paternal first and/or last name on the birth certificate. Disparities in infant mortality were observed between and within racial/ethnic subpopulations. When compared to Hispanic (NH)-white women with involved fathers, NH-black women with involved fathers had a two-fold increased risk of infant mortality whereas infants born to black women with absent fathers had a seven-fold increased risk of infant mortality. Elevated risks of infant mortality were also observed for Hispanic infants with absent fathers (OR = 3.33. 95%CI = 2.66-4.17). About 65-75% of excess mortality could be prevented with increased paternal involvement. Paternal absence widens the black-white gap in infant mortality almost four-fold. Intervention programs to improve perinatal paternal involvement may decrease the burden of absent father-associated infant mortality.
Asunto(s)
Población Negra/estadística & datos numéricos , Relaciones Padre-Hijo/etnología , Disparidades en el Estado de Salud , Hispánicos o Latinos/estadística & datos numéricos , Mortalidad Infantil/etnología , Privación Paterna/etnología , Población Blanca/estadística & datos numéricos , Adulto , Certificado de Nacimiento , Certificado de Defunción , Femenino , Florida/epidemiología , Humanos , Lactante , Mortalidad Infantil/tendencias , Masculino , Medición de RiesgoRESUMEN
OBJECTIVE: To assess the impact of obesity on preterm birth among nulliparous women. METHODS: Retrospective cohort study of nulliparous mothers delivering infants in Florida between 2004 and 2007. Women were classified as non-obese (pre-pregnancy body mass index (BMI) <30) or obese (BMI ≥ 30). The main outcomes assessed were preterm birth, very preterm birth and extremely preterm birth. Risk estimates were obtained using logistic regression. Multiparous non-obese mothers were the referent group for all analyses. RESULTS: As compared to multiparous women, nulliparous mothers had an increased risk of very preterm and extremely preterm birth with the highest risk observed for extremely preterm birth (odds ratios (OR) = 1.37, 95% CI = 1.28, 1.47) (p for trend <0.01). Obese nulliparous mothers had an elevated risk of preterm, very preterm and extremely preterm birth, with the risk of extremely preterm birth being the most pronounced (OR=1.97, 95% CI=1.75-2.22) [p for trend <0.05]. The heightened risk associated with obesity among nulliparous women was observed across all racial/ethnic sub-populations, with black nulliparous obese mothers being at greatest risk of all preterm birth-subtypes. CONCLUSIONS: Obesity is a risk marker for preterm, very preterm and extremely preterm birth among first-time mothers and particularly among blacks and Hispanics.
Asunto(s)
Obesidad/complicaciones , Paridad , Complicaciones del Embarazo , Nacimiento Prematuro/epidemiología , Adulto , Peso al Nacer , Población Negra , Índice de Masa Corporal , Estudios de Cohortes , Etnicidad , Femenino , Edad Gestacional , Hispánicos o Latinos , Humanos , Modelos Logísticos , Oportunidad Relativa , Embarazo , Complicaciones del Embarazo/epidemiología , Estudios Retrospectivos , Factores de RiesgoRESUMEN
Lack of paternal involvement during pregnancy and infancy may account for a significant burden of the adverse pregnancy outcomes among black women and could therefore, represent an important avenue providing the opportunity to improve feto-infant health and survival. This study aimed to review the literature on paternal involvement during the perinatal period and its influence on feto-infant health and survival. Literature for this review was identified by searching the PubMed database from the National Center for Biotechnology Information at the US National Library of Medicine as well as the ISI Web of Knowledge Databases, OVID, and CINAHL. A total of seven papers were identified and included in this review. There is paucity of data in this domain. Overall findings suggest that paternal involvement during pregnancy may have important implications for maternal prenatal health behaviors and feto-infant health. Although results are limited, results suggest that paternal involvement has a positive influence on prenatal care usage, abstinence from alcohol and smoking, and a reduction in low birth weight and small for gestational age infants. None of the papers examined the relationship between stillbirth and paternal involvement. Additional studies with enhanced measures of paternal involvement are needed to better assess the role of fathers in enhancing prenatal health behaviors and pregnancy outcomes. Efforts should be made to include fathers in future studies and reduce reliance on maternal report and to investigate paternal roles across different racial groups so that appropriate interventions can be developed.
Asunto(s)
Padre , Mortalidad Fetal , Mortalidad Infantil , Resultado del Embarazo , Femenino , Edad Gestacional , Conductas Relacionadas con la Salud , Humanos , Lactante , Recién Nacido de Bajo Peso , Recién Nacido , Masculino , Bienestar Materno , Morbilidad , Paternidad , Embarazo , Atención PrenatalRESUMEN
Few studies have examined paternal involvement in relation to feto-infant health; therefore we aim to assess the impact of absence of the father on birth outcomes among racial-ethnic subgroups. Florida vital statistics records for singleton births occurring between 1998 and 2005 were used for this study. Births to women less than 20 years of age and births outside the gestational age range of 20-44 weeks were excluded. Adjusted and unadjusted odds ratios and 95% confidence intervals were generated to examine the impact of paternal involvement, as defined by presence of paternal information on the birth certificate, on feto-infant morbidity across racial-ethnic sub-populations. There were higher rates of low birth weight, very low birth weight, preterm birth, very preterm birth, and small for gestational age (SGA) among father-absent births. Within each racial-ethnic subgroup, women with absent fathers had higher risks of poor birth outcomes than their counterparts with involved fathers. Black women with absent fathers had the highest risk of low birth weight, very low birth weight, preterm birth, very preterm birth, and SGA. Promoting paternal involvement during the perinatal period may provide a means to decrease the proportion of infants born of very low birth weight or very preterm, thus potentially reducing the black-white disparity in infant mortality.
Asunto(s)
Población Negra/estadística & datos numéricos , Hispánicos o Latinos/estadística & datos numéricos , Mortalidad Infantil , Paternidad , Población Blanca/estadística & datos numéricos , Certificado de Nacimiento , Padre , Femenino , Florida/epidemiología , Edad Gestacional , Humanos , Lactante , Recién Nacido de Bajo Peso , Recién Nacido , Morbilidad , Embarazo , Resultado del Embarazo , Nacimiento PrematuroRESUMEN
BACKGROUND: The prevalence of gastroschisis is increasing in many parts of the world, although the etiology is largely unexplained. Young maternal age has been the only consistently identified, strong risk factor. The objective of this study was to examine the role of maternal nativity in relation to other suspected risk factors for gastroschisis in Florida. METHODS: We conducted a retrospective cohort study of singleton infants born in Florida from 1998-2003. Gastroschisis cases were identified from the Florida Birth Defects Registry. Demographic and perinatal data were obtained from birth records. Multivariable Poisson regression was used to estimate adjusted prevalence ratios (PRs) and 95% confidence intervals (CIs) for each factor of interest. RESULTS: The 6-year birth prevalence of gastroschisis was 3.26 per 10,000 live births, and the annual rate increased 41% during the study period. In addition to maternal age and marital status, maternal race/ethnicity and nativity were significantly associated with the risk of delivering an infant with gastroschisis. Compared with non-Hispanic white women, non-Hispanic black women had the lowest risk of delivering an infant with gastroschisis (PR, 0.19; 95% CI, 0.13-0.26), followed by Hispanic women (PR, 0.60; 95% CI, 0.43-0.83). Women born outside the United States were significantly less likely than U.S.-born women to deliver an infant with gastroschisis (PR, 0.59; 95% CI, 0.41-0.86). CONCLUSIONS: Although young maternal age remains a strong significant risk factor for gastroschisis in Florida, other factors such as maternal race/ethnicity and nativity could be important in explaining the increasing prevalence of gastroschisis.
Asunto(s)
Gastrosquisis/epidemiología , Vigilancia de la Población , Adulto , Femenino , Humanos , Embarazo , Prevalencia , Estudios Retrospectivos , Factores de Riesgo , Estados Unidos/epidemiologíaRESUMEN
OBJECTIVE: The association between underweight and stillbirth remains poorly defined, especially across racial/ethnic sub-populations. We investigate the association of pre-pregnancy underweight on the risk for early and late stillbirth among black and white mothers. METHODS: We conducted analysis on the Missouri maternally linked data files covering the period 1989-1997 inclusive. Using body mass index (BMI), we categorized mothers as underweight (BMI <18.5) and normal weight (BMI = 18.5-24.9). By applying logistic regression modeling with adjustment for intracluster correlation, we estimated the risk for total, early (-28 weeks of gestation), and late stillbirth (>28 weeks of gestation) among black and white mothers. RESULTS: A total of 1808 cases of stillbirth were registered. The rate of stillbirth among white mothers was 3.7 per 1000, while the rate among blacks was 7.1 per 1000. Underweight black mothers had comparable risk for total (OR, 0.9; 95% CI, 0.7-1.2), early (OR, 1.1; 95% CI, 0.8-1.5), and late stillbirth (OR, 0.8; 95% CI, 0.5-1.2) as compared to their normal-weight counterparts. By contrast, underweight white gravidas had a 30% reduced likelihood (OR, 0.7; 95% CI, 0.6-0.9) for late stillbirth as compared to normal-weight white mothers. However, the risks for total and early stillbirth among underweight white mothers were similar to those of normal-weight white mothers. CONCLUSION: Low prepregnancy BMI has similar effects on fetal survival in both blacks and whites except for late stillbirth. The underweight white survival advantage over blacks in late pregnancy could probably be due to greater access for identified white at-risk groups to effective obstetrical interventions as previously reported.
Asunto(s)
Negro o Afroamericano/estadística & datos numéricos , Complicaciones del Embarazo/epidemiología , Resultado del Embarazo/epidemiología , Mortinato/epidemiología , Delgadez/complicaciones , Población Blanca/estadística & datos numéricos , Factores de Edad , Índice de Masa Corporal , Intervalos de Confianza , Femenino , Edad Gestacional , Humanos , Modelos Logísticos , Bienestar Materno , Missouri/epidemiología , Oportunidad Relativa , Embarazo , Complicaciones del Embarazo/etnología , Nacimiento Prematuro , Factores de Riesgo , Mortinato/etnología , Delgadez/epidemiología , Factores de Tiempo , Estados Unidos/epidemiologíaRESUMEN
OBJECTIVE: To estimate the distribution and success of programmed fetal growth phenotypes among obese women. METHODS: This was a retrospective cohort study using the Missouri maternally linked cohort files (years 1978-1997). Maternal body mass index was classified as Normal (18.5-24.9) (referent group), Obese (class 1, 30.0-34.9; class 2, 35.0-39.9; and extreme or class 3, 40 or more). Fetal growth phenotypes were defined as large for gestational age (LGA), appropriate for gestational age (AGA), and small for gestational age (SGA). We used adjusted odds ratio with correction for intracluster correlation to estimate the risk of neonatal mortality for each fetal growth phenotype. RESULTS: As compared with normal weight mothers, obese gravidas tended to program LGA infants at a higher and increasing rate with ascending obesity severity. The opposite effect was observed with respect to AGA and SGA programming patterns. Neonatal mortality among LGA infants was similar for obese (6.2 in 1,000) and normal (4.9 in 1,000) weight mothers (OR 1.05, 95% confidence interval [CI] 0.75-1.48) and regardless of obesity subtype. By contrast, SGA and AGA infants programmed by obese mothers experienced greater neonatal mortality as compared with those born to normal weight mothers (AGA OR 1.45, 95% CI 1.32-1.59; SGA OR 1.72, 95% CI 1.49-1.98). CONCLUSION: Compared with normal weight mothers, obese women are least successful at programming SGA, less successful at programming AGA, and equally as successful at programming LGA infants. LEVEL OF EVIDENCE: II.
Asunto(s)
Desarrollo Fetal/fisiología , Obesidad/fisiopatología , Complicaciones del Embarazo/fisiopatología , Adulto , Índice de Masa Corporal , Estudios de Cohortes , Femenino , Edad Gestacional , Humanos , Mortalidad Infantil , Recién Nacido , Fenotipo , Embarazo , Estudios RetrospectivosRESUMEN
OBJECTIVE: We sought to estimate the association between severity of maternal pre-pregnancy underweight and feto-infant morbidity outcomes. METHODS: Missouri maternally linked cohort records from 1989 to 1997 inclusive were analysed. Using pre-pregnancy maternal body mass index (BMI), we classified study participants into: Normal (18.5-24.9) [referent group], mild thinness (17.0-18.5), moderate thinness (16.0-16.9) and severe thinness (<16.0). We estimated the association between pre-pregnancy underweight, underweight subtypes and feto-infant morbidity outcomes using adjusted odds ratios to approximate relative risks with correction for intra-cluster correlations. RESULTS: Fetal growth curve trajectories for the two groups became divergent as from 30 gestational weeks. Underweight mothers were at increased risk for low birthweight (OR = 1.82; 95% CI = 1.77-1.88), very low birthweight (OR = 1.41; 95% CI = 1.31-1.51), small for gestational age (OR = 1.80; 95% CI = 1.76-1.84), preterm (OR = 1.37; 95% CI = 1.33-1.40) and very preterm (OR = 1.42; 95% CI = 1.34-1.50). These risk estimates increased in a dose-effect fashion with increasing severity of underweight status except for very preterm (p for trend < 0.01). CONCLUSION: Pre-pregnancy underweight is a risk factor for a spectrum of feto-infant morbidity outcomes, with risk estimates being most pronounced among extremely underweight mothers.
Asunto(s)
Enfermedades Fetales/epidemiología , Enfermedades del Recién Nacido/epidemiología , Madres , Complicaciones del Embarazo/epidemiología , Delgadez/complicaciones , Adulto , Índice de Masa Corporal , Estudios de Cohortes , Femenino , Enfermedades Fetales/etiología , Humanos , Recién Nacido , Enfermedades del Recién Nacido/etiología , Intercambio Materno-Fetal/fisiología , Morbilidad , Madres/estadística & datos numéricos , Complicaciones del Trabajo de Parto/epidemiología , Complicaciones del Trabajo de Parto/etiología , Población , Embarazo , Resultado del Embarazo , Prevalencia , Adulto JovenRESUMEN
BACKGROUND: Congenital malformations are the major cause of infant mortality in the United States, but their contribution to overall racial disparity--a major public health concern--is poorly understood. We sought to estimate the contribution of a congenitally acquired central nervous system lesion, Dandy-Walker Syndrome (DWS), to black-white disparity in infant mortality. METHODS: Data were obtained from the New York State Congenital Malformations Registry, an ongoing population-based validated surveillance system. We compared black to white infants with respect to infant, neonatal, and postneonatal mortality using Cox proportional hazards regression models. RESULTS: A total of 196 live-born neonates were diagnosed with DWS in the state from 1992 to 2005 inclusive. Of these, 53 were non-Hispanic black and 76 were non-Hispanic white. Neonatal mortality was similar for non-Hispanic blacks and non-Hispanic whites (adjusted hazards ratio [AHR], 1.42; 95% CI, 0.52-3.82), but non-Hispanic blacks had an 8-fold increased risk for postneonatal mortality (AHR, 8.26; 95% CI, 2.08-32.72). Adjustment for fetal growth and other maternal and infant characteristics resulted in a 10-fold increased risk of mortality for non-Hispanic black infants as compared to non-Hispanic whites. By contrast, adjustment for preterm birth attenuated the risk, but non-Hispanic black infants were still more than 6 times as likely to die during the postneonatal period than non-Hispanic whites (AHR, 6.36, 95% CI, 1.52-26.60). CONCLUSION: DWS has one of the largest black-white disparities in postneonatal survival. This underscores the importance of evaluating racial disparities in infant mortality by specific conditions in order to formulate targeted interventions to reduce disparities.
Asunto(s)
Negro o Afroamericano/estadística & datos numéricos , Síndrome de Dandy-Walker/etnología , Síndrome de Dandy-Walker/mortalidad , Disparidades en el Estado de Salud , Población Blanca/estadística & datos numéricos , Adulto , Intervalos de Confianza , Síndrome de Dandy-Walker/epidemiología , Femenino , Humanos , Lactante , Recién Nacido , Masculino , New York/epidemiología , Modelos de Riesgos Proporcionales , Sistema de Registros , RiesgoRESUMEN
OBJECTIVES: To assess infant mortality patterns associated with Dandy-Walker syndrome (DWS) and the impact of concomitant anomalies. METHODS: Data for this study were obtained from the New York State Congenital Malformations Registry, an ongoing population-based validated surveillance system. RESULTS: The 196 cases of DWS had a high infant mortality rate (250/1,000), and the elevated risk correlated positively with additional anomalies in a dose-effect pattern (p for trend <0.01). Infants with DWS and two or more affected organ systems were about 6 times as likely to die postneonatally than their counterparts with isolated DWS [adjusted hazards ratio (AHR) = 6.01; 95% CI = 1.52-24.21]. CONCLUSION: This study confirms the widely held notion that DWS is a heterogeneous rather than a homogeneous entity as shown by the dissimilar infant survival patterns found.
Asunto(s)
Anomalías Múltiples/mortalidad , Síndrome de Dandy-Walker/mortalidad , Anomalías Múltiples/patología , Adulto , Síndrome de Dandy-Walker/patología , Femenino , Humanos , Lactante , Mortalidad Infantil , Recién Nacido , Estimación de Kaplan-Meier , Masculino , New York/epidemiología , Vigilancia de la Población , Modelos de Riesgos Proporcionales , Sistema de Registros , Medición de Riesgo , Factores de TiempoRESUMEN
Congenital heart defects (CHDs) are the most common type of birth defect, making significant contributions to infant morbidity and mortality, but not all CHDs contribute equally to such outcomes. Although cyanotic CHDs constitute some of the most serious CHDs, its epidemiology is poorly understood. We present a comprehensive systematic review of the literature on the epidemiology of cyanotic CHD, with emphasis on the most current knowledge on identified risk/etiologic factors. Literature for this review was identified by searching the PubMed database from the National Center for Biotechnology Information at the US National Library of Medicine as well as bibliographies of identified papers. The 100 reports that contributed to this review describe risk factors such as infant sex, race, and ethnicity, environmental exposures, and maternal and paternal age. Several studies reported differences in prevalence rates by race and ethnicity and elevated sex ratios, and they identified some risk factors, including advanced maternal age. Investigators have made significant progress in the effort to describe the etiology of cyanotic CHDs, but discrepancies, such as the variation in prevalence rates by race and ethnicity and the impact of environmental exposures, still need to be addressed.
Asunto(s)
Cianosis , Cardiopatías Congénitas/epidemiología , Factores de Edad , Exposición a Riesgos Ambientales/estadística & datos numéricos , Femenino , Cardiopatías Congénitas/etnología , Humanos , Recién Nacido , Masculino , Edad Materna , Estado Nutricional , Embarazo , Complicaciones del Embarazo/epidemiología , Factores Sexuales , Trastornos Relacionados con Sustancias/epidemiologíaRESUMEN
We describe the reproductive health and practices of Hmong immigrants before and after migration to the United States. Data were gathered as part of an ongoing study on the impact of perinatal exposure to environmental chemicals on children's health in Hmong residents of Green Bay, Wisconsin between August 1999 and May 2002. Of the 742 pregnancies reported by 141 reproductive-aged couples, 669 were live births. The Hmong have an average of 5.2 children (range 0-14) and the sex ratio differed by country of birth. Prenatal care began in the first trimester for 60% of US-born infants, up from 12% prior to immigration. Breastfeeding decreased from 94% and 88% in Laos and Thailand to only 11% for Hmong born in the US. Contraceptive use was reported by 25.5% of women; few reported smoking and alcohol consumption. The results suggest that Hmong immigrants may benefit from public health support targeting prenatal care and breastfeeding practices.
Asunto(s)
Características Culturales , Emigrantes e Inmigrantes/estadística & datos numéricos , Historia Reproductiva , Adolescente , Adulto , Anticoncepción/estadística & datos numéricos , Composición Familiar/etnología , Femenino , Conductas Relacionadas con la Salud , Humanos , Laos/etnología , Masculino , Persona de Mediana Edad , Embarazo , Resultado del Embarazo/etnología , Atención Prenatal/estadística & datos numéricos , Factores Socioeconómicos , Tailandia/etnología , Estados Unidos/epidemiologíaRESUMEN
BACKGROUND: Birth defects and preterm birth (PTB) are leading causes of infant morbidity and mortality in the United States. Infants with birth defects are more likely to be born preterm (<37 weeks), yet the roles of maternal ethnicity and fetal growth in this relationship are unclear. This study aimed to assess the risk of PTB among non-Hispanic (NH) Black, NH-White, and Hispanic infants with congenital heart defects (CHD), adjusting for fetal growth. METHODS: Florida Birth Defects Registry data were used to conduct a retrospective cohort study on 14,319 live-born infants with CHDs born January 1, 1998 to December 31, 2002. ORs and 95% CIs were computed for each growth category (small-for-gestational age [SGA], appropriate-for-gestational-age [AGA], and large-for-gestational-age [LGA]) by ethnicity and adjusted for maternal and infant covariates using logistic regression. RESULTS: After adjusting for potential confounders, SGA and AGA NH-Black infants with CHDs had increased risk of PTB compared to NH-White infants with CHDs (OR 1.79; 95% CI: 1.40, 2.30 and OR 1.89; 95% CI: 1.68, 2.13, respectively). Hispanic SGA, AGA, and infants with CHDs had no increased risk of PTB compared to NH-White infants. CONCLUSIONS: The increased risk of PTB among SGA and AGA NH-Black infants with CHDs is not explained by the overall disparities in risk of PTB between NH-Blacks and NH-Whites. Additional studies are needed to determine the specific subtypes of CHD for which these relationships are present and if these findings are seen among infants with other birth defects.
Asunto(s)
Etnicidad , Cardiopatías Congénitas/epidemiología , Enfermedades del Prematuro/epidemiología , Adolescente , Adulto , Estudios de Cohortes , Femenino , Edad Gestacional , Disparidades en Atención de Salud , Humanos , Recién Nacido , Recien Nacido Prematuro , Recién Nacido Pequeño para la Edad Gestacional , Persona de Mediana Edad , Prevalencia , Sistema de Registros , Estudios Retrospectivos , Factores de RiesgoRESUMEN
The identity of the numerically dominant N(2)-fixing bacteria in biological soil crusts of the Colorado Plateau region and two outlying areas was determined using multiple approaches, to link the environmental diversity of nifH gene sequences to cultured bacterial isolates from the regions. Of the nifH sequence-types detected in soil crusts of the Colorado Plateau, 89% (421/473) were most closely related to nifH signature sequences from cyanobacteria of the order Nostocales. N(2)-fixing cyanobacterial strains were cultured from crusts and their morphotypes, 16S rRNA gene and nifH gene sequences were characterized. The numerically dominant diazotrophs in the Colorado Plateau crusts fell within three clades of heterocystous cyanobacteria. Two clades are well-represented by phylogenetically and morphologically coherent strains, corresponding to the descriptions of Nostoc commune and Scytonema hyalinum, which are widely recognized as important N(2)-fixing components of soil crusts. A third, previously-overlooked clade was represented by a phylogenetically coherent but morphologically diverse group of strains that encompass the morphogenera Tolypothrix and Spirirestis. Many of the strains in each of these groups contained at least two nifH copies that represent different clusters in the nifH environmental survey.
Asunto(s)
Cianobacterias/clasificación , Cianobacterias/genética , Ecosistema , Fijación del Nitrógeno , Microbiología del Suelo , Colorado , Cianobacterias/metabolismo , ADN Bacteriano/análisis , ADN Bacteriano/aislamiento & purificación , Genes de ARNr , Datos de Secuencia Molecular , Nostoc/clasificación , Nostoc/genética , Nostoc/metabolismo , Oxidorreductasas/genética , Filogenia , ARN Ribosómico 16S/genética , Análisis de Secuencia de ADNRESUMEN
The objective of this study was to characterize the community structure and activity of N2-fixing microorganisms in mature and poorly developed biological soil crusts from both the Colorado Plateau and Chihuahuan Desert. Nitrogenase activity was approximately 10 and 2.5 times higher in mature crusts than in poorly developed crusts at the Colorado Plateau site and Chihuahuan Desert site, respectively. Analysis of nifH sequences by clone sequencing and the terminal restriction fragment length polymorphism technique indicated that the crust diazotrophic community was 80 to 90% heterocystous cyanobacteria most closely related to Nostoc spp. and that the composition of N2-fixing species did not vary significantly between the poorly developed and mature crusts at either site. In contrast, the abundance of nifH sequences was approximately 7.5 times greater (per microgram of total DNA) in mature crusts than in poorly developed crusts at a given site as measured by quantitative PCR. 16S rRNA gene clone sequencing and microscopic analysis of the cyanobacterial community within both crust types demonstrated a transition from a Microcoleus vaginatus-dominated, poorly developed crust to mature crusts harboring a greater percentage of Nostoc and Scytonema spp. We hypothesize that ecological factors, such as soil instability and water stress, may constrain the growth of N2-fixing microorganisms at our study sites and that the transition to a mature, nitrogen-producing crust initially requires bioengineering of the surface microenvironment by Microcoleus vaginatus.