Browsing by Author "Stewart, A."

Now showing 1 - 2 of 2
  • Thumbnail Image
    A Burkholderia pseudomallei Colony Variant Necessary for Gastric Colonization
    Austin, C. R.; Goodyear, A. W.; Bartek, I. L.; Stewart, A.; Sutherland, M. D.; Silva, E. B.; Zweifel, A.; Vitko, N. P.; Tuanyok, A.; Highnam, G.; Mittelman, D.; Keim, P.; Schweizer, H. P.; Vazquez-Torres, A.; Dow, S. W. C.; Voskuil, M. I. (American Society for Microbiology, 2015-01)
    Diverse colony morphologies are a hallmark of Burkholderia pseudomallei recovered from infected patients. We observed that stresses that inhibit aerobic respiration shifted populations of B. pseudomallei from the canonical white colony morphotype toward two distinct, reversible, yet relatively stable yellow colony variants (YA and YB). As accumulating evidence supports the importance of B. pseudomallei enteric infection and gastric colonization, we tested the response of yellow variants to hypoxia, acidity, and stomach colonization. Yellow variants exhibited a competitive advantage under hypoxic and acidic conditions and alkalized culture media. The YB variant, although highly attenuated in acute virulence, was the only form capable of colonization and persistence in the murine stomach. The accumulation of extracellular DNA (eDNA) was a characteristic of YB as observed by 4',6-diamidino-2-phenylindole (DAPI) staining of gastric tissues, as well as in an in vitro stomach model where large amounts of eDNA were produced without cell lysis. Transposon mutagenesis identified a transcriptional regulator (BPSL1887, designated YelR) that when overexpressed produced the yellow phenotype. Deletion of yelR blocked a shift from white to the yellow forms. These data demonstrate that YB is a unique B. pseudomallei pathovariant controlled by YelR that is specifically adapted to the harsh gastric environment and necessary for persistent stomach colonization. IMPORTANCE Seemingly uniform populations of bacteria often contain subpopulations that are genetically identical but display unique characteristics which offer advantages when the population is faced with infrequent but predictable stresses. The pathogen Burkholderia pseudomallei is capable of forming several reversible colony types, and it interconverted between one white type and two yellow types under certain environmental stresses. The two yellow forms exhibited distinct advantages in low-oxygen and acidic environments. One yellow colony variant was the only form capable of chronic stomach colonization. Areas of gastric infection were marked by bacteria encased in a DNA matrix, and the yellow forms were able to produce large amounts of extracellular DNA in vitro. We also identified the regulator in control of yellow colony variant formation. These findings demonstrate a role in infection for colony variation and provide a mechanism for chronic stomach colonization-a frequently overlooked niche in melioidosis.
  • Conservation agriculture and sustainable crop intensification in Karatu District,Tanzania
    Owenya, M.; Mariki, W.; Stewart, A.; Friedrich, Theodor; Kienzle, Josef; Kassam, Amir H.; Shetto, R.; Mkomwa, S. (Rome, Italy: Plant Production and Protection Division: Food and Agriculture Organization of the United Nations, 2012)
    The report/case study discusses the importance of agriculture in the Karatu district, the loss of agricultural productivity from soil and land degradation, how climate change jeopardizes small farmers in the district, and how conservation agriculture (CA) could significantly address problems of agricultural productivity. The study/intervention was focused on five villages in the Karatu district and was intended to strengthen the livelihood and food security of small farmers through protection of ecosystem services that would allow for sustainable crop production intensification. These CA practices and services were implemented through outreach, education and training with small Tanzanian farmers. Involved stakeholders were farmers, government actors, intentional institutions, and non-governmental organizations. As conservation agriculture practices were adopted, scientists examined fluctuations in how farmers generating income and the various concerns that ensued. Critical factors that enable successful intervention were outlined as the following: strong interaction between all stakeholders, problem analysis by local farmers, involvement of facilitators skilled in CA practices, and initial provision of resources needed to implement CA. Factors that discouraged implementation of CA practices were lack of needed resources; lack of CA experts, training, and policy; and lack of involvement of stakeholders. Authors of the report suggested that the district should have an explicit, national policy approach to conservation agriculture; collaboration should be strengthened to align goals and implementation efforts; various approaches to CA should be utilized to maximize participation in CA; resources needed to implement CA s should be reasonably priced and accessible to local farmers. The report concludes that CA efforts should be expanded through stronger linkages with extension officers and national governmental agencies. Also, food processing strategies could be utilized to add value to the increased production gains from CA.