Microscopic visualisation of succinate producing biofilms of Actinobacillus succinogenes

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dc.contributor.advisor Nicol, Willie en
dc.contributor.postgraduate Mokwatlo, Sekgetho Charles en
dc.date.accessioned 2017-10-13T13:41:20Z
dc.date.available 2017-10-13T13:41:20Z
dc.date.created 2017-09-08 en
dc.date.issued 2017 en
dc.description Dissertation (MEng)--University of Pretoria, 2017. en
dc.description.abstract Biofilms of Actinobacillus succinogenes, grown in a biofilm reactor system, were investigated for structure and cell viability, through microscopic visualisation with a confocal scanning laser microscope (CSLM) and a scanning electron microscope (SEM). Biofilms were sampled and visualised at steady state conditions with the broth containing succinic acid titres between 15 and 21 g/L. All sampled biofilm was 6 days old. Six-day-old biofilms of A. succinogenes showed a heterogeneous biofilm architecture composed of cell micro-colony pillars which varied considerably in thickness, area and shape. Microcolony pillars consisted of a densely packed entanglement of sessile cells. Quantitative analysis revealed that the pillars were mostly large, with a mean pillar diameter of 170 m and a mean thickness of 92 m, although pillar diameter and thickness were variable as they ranged from 25 – 500 m and 30 – 300 m, respectively. In the regions close to the substratum surface, pillars were characterised by having defined borders with a network of channels ranging from 40 – 200 m in width separating them. However, towards the middle of the biofilm depth some of the pillars coalesced. For this reason low cross sectional area coverage of biofilm consistently occurred at the bottom portion of the biofilm whilst the highest coverage was in the middle portion of the biofilm. Regarding cell morphology, very large differences were observed. Planktonic cells were rod-shaped, whereas sessile cells expressed an elongated rod morphology and thus were much longer and thinner compared with planktonic cells. Planktonic cells were 1 – 2 m thick and 4 – 5 m long, while sessile cells were 0.5 – 1 m thick and 5 – 100 m long. Long sessile cells resulted in extensive tangling in microcolony pillars, which may have contributed to the structural stability of the pillars. Fibre-like connections of constant diameter were observed between cells, and between the cells and surface. The diameter of these connections was approximately 20 – 30 nm. Viability stains showed that in the bottom portion (from 0 - 20 m above the substratum surface) of the biofilm, most of the cells were dead. However, the portion of covered area attributed to living cells increased past the middle of the biofilm towards the top part of the biofilm. A high percentage of living cells was thus found towards the top part of the biofilm. Overall, 65% (with 2% standard deviation) of the entire biofilm was composed of dead cells. In this way, the results show that operation at high acid conditions comes at a cost of low overall biomass productivity due to decreased active biomass. en_ZA
dc.description.availability Unrestricted en
dc.description.degree MEng en
dc.description.department Chemical Engineering en
dc.identifier.citation Mokwatlo, SC 2017, Microscopic visualisation of succinate producing biofilms of Actinobacillus succinogenes, MEng Dissertation, University of Pretoria, Pretoria, viewed yymmdd <http://hdl.handle.net/2263/62782> en
dc.identifier.other S2017 en
dc.identifier.uri http://hdl.handle.net/2263/62782
dc.publisher University of Pretoria en
dc.rights © 2017 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. en
dc.subject Actinobacillus succinogenes en
dc.subject Biofilm structure en
dc.subject Scanning electron microscopy en
dc.subject Confocal scanning laser microscopy en
dc.subject UCTD en
dc.title Microscopic visualisation of succinate producing biofilms of Actinobacillus succinogenes en_ZA
dc.type Dissertation en


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