Browsing by Subject "Growth rate"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Restricted
    The Effect of CO2 Availability on the Growth, Iron Oxidation and CO2-Fixation Rates of Pure Cultures of Leptospirillum ferriphilum and Acidithiobacillus ferrooxidans
    (Wiley, 2012) Bryan, C G; Davis-Belmar, C S; van Wyk, N; Fraser, M K; Dew, D; Rautenbach, G F; Harrison, S T L
    Understanding how bioleaching systems respond to the availability of CO2 is essential to developing operating conditions that select for optimum microbial performance. Therefore, the effect of inlet gas and associated dissolved CO2 concentration on the growth, iron oxidation and CO2-fixation rates of pure cultures of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum was investigated in a batch stirred tank system. The minimum inlet CO2 concentrations required to promote the growth of At. ferrooxidans and L. ferriphilum were 25 and 70 ppm, respectively, and corresponded to dissolved CO2 concentrations of 0.71 and 1.57 mM (at 308C and 378C, respectively). An actively growing culture of L. ferriphilum was able to maintain growth at inlet CO2 concentrations less than 30 ppm (0.31–0.45 mM in solution). The highest total new cell production and maximum specific growth rates from the stationary phase inocula were observed with CO2 inlet concentrations less than that of air. In contrast, the amount of CO2 fixed per new cell produced increased with increasing inlet CO2 concentrations above 100 ppm. Where inlet gas CO2 concentrations were increased above that of air the additional CO2 was consumed by the organisms but did not lead to increased cell production or significantly increase performance in terms of iron oxidation. It is proposed that At. ferrooxidans has two CO2 uptake mechanisms, a high affinity system operating at low available CO2 concentrations, which is subject to substrate inhibition and a low affinity system operating at higher available CO2 concentrations. L. ferriphilum has a single uptake system characterised by a moderate CO2 affinity. At. ferrooxidans performed better than L. ferriphilum at lower CO2 availabilities, and was less affected by CO2 starvation. Finally, the results demonstrate the limitations of using CO2 uptake or ferrous iron oxidation data as indirect measures of cell growth and performance across varying physiological conditions. Biotechnol. Bioeng. 2012;109: 1693–1703
  • Thumbnail Image
    Item
    Restricted
    The effects of marine protected areas on the population dynamics of a South African limpet, Cymbula oculus, relative to the influence of wave action
    (2003) Branch, G M; Odendaal, F
    Populations of a protandric limpet, Cymbula oculus, were compared between two South African Marine Protected Areas (MPAs), Dwesa and Tsitsikamma, and four exploited sites, and between sites exposed to or sheltered from strong wave action. Harvesting is decimating populations of this limpet. Compared with harvested sites, limpets in MPAs were 30–50% larger, adult densities 75% greater and biomass 30–90% greater. The female:male ratio was 0.58:1 inside the MPAs, but 0.11:1 at harvested sites. Growth rate and age-at-maturity were unaffected by harvesting, but survivorship was 10-fold higher inside MPAs, and reproductive output a staggering 80-fold higher. Conversely, recruitment was three times higher in harvested than protected areas, and inversely correlated with adult density. Wave action had negative effects of similar magnitude to harvesting. Limpets at sheltered sites were 65% larger, biomass 80% greater, female proportions 40% higher, survivorship 25% greater and growth 33% greater. Recruitment was, however, 45% greater at wave-exposed sites. All these effects were detected only inside the MPAs, being masked by harvesting elsewhere. The impacts of harvesting and wave action could never have been detected without the existence of MPAs, emphasizing their importance for base-line studies as well as protection. Dwesa MPA is under threat from poaching and demands for access to resources, but a strong case exists for retaining at least a core fully protected area. Our results clearly illustrate the need for MPAs among the tools used for coastal management.