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Oxygen toxicity is considered significant in the poor survival of probiotic bacteria such as Lactobacillus acidophilus and Bifidobacterium spp. in yoghurts. This study investigated methods to protect these bacteria from oxygen exposure. To confirm the accuracy of the reported survival estimates of L. acidophilus or Bifidobacterium spp. in yoghurts, the reliability of several enumeration media was evaluated with different commercial yoghurts. None of the media however, was found reliable thereby casting doubts on the reported cell numbers of probiotic bacteria in yoghurts. After much research,it was found that although oxygen can be detrimental to L. acidophilus and Bifidobacterium spp.in culture broths, it may not be significant for their poor survival in yoghurts. Nevertheless, techniques such as oxidative stress stress adaption, alternative packaging materials and microencapsulation as investigated in this study, can serve as general protective techniques to help yoghurt manufacturers in maintaining the recommended numbers of probiotic bacteria in their products. This would eventually assist in the efficient delivery of probiotic health benefits to yoghurt consumers. / Doctor of Philosphy (PhD)

Broad relationships among bacteria can be identified by ribosomal RNA analysis, but the resulting groups may not be easily definable by phenotypic characteristics. This is exemplified by the genus <i>Campylobacter</i>, which consists of at least three separate groups that cannot be differentiated readily by phenotypic characteristics. Examination of the type strains of all Campylobacter species (except <i>Campylobacter pylori), Wolinella recta, Wolinella curva, Bacteroides ureolyticus</i>, and <i>Bacteroides gracilis</i> revealed that sheathed flagella occur only in species of rRNA group II (except <i>W.succinogenes</i>). This is helpful in differentiating this group. Campylobacters are microaerophilic: they can respire with oxygen but cannot grow at the full level of oxygen found in an air atmosphere (21% O₂). Although <i>W. recta, W. curva, B. ureolyticus</i>, and <i>B. gracilis</i> are closely related to the campylobacters of rRNA group I, they were thought to be anaerobes, incapable of oxygen-dependent growth and of respiring with O₂. However, the present study revealed that they are in fact microaerophiles. They exhibited oxygen-dependent growth but failed to grow at 21% O₂ and grew only very slightly under anaerobic conditions unless provided with electron acceptors such as fumarate and nitrate. They exhibited 0₂ uptake with H₂ or formate as electron donors (<i>W. recta</i> showed only a low O₂ uptake with H₂). Oxygen uptake was inhibited by KCN and 2-heptyl-4-hydroxyquinoline N-oxide. The organisms possessed membrane bound cytochromes (cytochromes b560 and C551-553, and a CO-binding cytochrome c), as well as soluble cytochrome C552 and CO-binding cytochrome c. The cytochromes were reduced by H₂ and formate as electron donors. Proton efflux from cells in anaerobic suspensions containing H₂ or formate occurred upon addition of a pulse of oxygen. With formate as the electron donor, H+/O ratios of <i>W. curva, W. recta, B. ureolyticus</i>, and <i>B. gracilis</i> were 0.75, 1.66,2.06, and 2.04, respectively. With H₂ as the electron donor, H⁺/O ratios of <i>W.curva, B. ureoyticus, and B. gracilis</i> were 1.25, 1.97, and 2.36, respectively; technical difficulties prevented measurement of the ratio in <i>W. recta</i>. Proton translocation was inhibited by the protonophore carbonylcyanide <i>m</i>-chlorophenylhydrazone. The results confirm the relationship of these organisms to campylobacters. / Ph. D.

Indiana University-Purdue University Indianapolis (IUPUI) / Long term no-till (NT) farming can improve the CH4 oxidation capacity of agricultural lands through creation of a favorable soil environment for methanotrophs and diffusive gas transport. However, limited data is available to evaluate the merit of that contention. Although the potential for biological CH4 oxidation may exist in NT soils, restricted diffusion could limit expression of that potential in fine-textured soils. A study was conducted to assess the CH4 oxidation potential and gaseous diffusivity of soils under plow till (PT) and NT for > 50 years. Intact cores and composite soils samples (0-10 and 10-20 cm) were collected from NT and PT plots located at a well-drained site (Wooster silt loam) and at a poorly-drained (Crosby silt loam) site in Ohio. Adjacent deciduous forest soils were also sampled to determine maximum rate expected in undisturbed soils in the region. Regardless of study sites and soil depth, CH4 oxidation rate (measured at near ambient CH4) and oxidation potential (Vmax, measured at elevated CH4) were 3-4 and 1.5 times higher in NT than in PT soils, respectively. Activity in the NT soils approached (66-80 %) that in the forest soils. Half saturation constants (Km) and threshold for CH4 oxidation (Th) were lower in NT (Km: 100.5 µL CH4 L-1; Th: 0.5 µL CH4 L-1) than in PT soils (Km: 134 µL CH4 L-1; Th: 2.8 µL CH4 L-1) suggesting a greater affinity of long-term NT soils for CH4, and a possible shift in methanotrophic community composition. CH4 oxidation rates were lower in intact soil cores compared to sieved soils, suggesting that CH4 oxidation was limited by diffusion, a factor that could lead to lower field-measured CH4 uptake than suggested by biological oxidation capacity measured in the laboratory. Regardless of soil drainage characteristic, long-term NT resulted in significantly higher (2-3 times) CH4 diffusivity (mean: 2.5 x 10-3 cm2 s-1) than PT (1.5 x 10-3 cm2 s-1), probably due to improved soil aggregation and greater macro-pores volume in NT soils. Overall, these results confirm the positive impact of NT on the restoration of the biological (Vmax, Km and Th) and physical (diffusivity) soil attributes essential for CH4 uptake in croplands. Long-term implementation of NT farming can therefore contribute to the mitigation of CH4 emission from agriculture.