Impact of metabolite accumulation on the structure, viability and development of succinic acid–producing biofilms of Actinobacillus succinogenes

Abstract

Biofilms of Actinobacillus succinogenes have demonstrated exceptional capabilities as biocatalysts for high productivity, titre, and yield production of succinic acid (SA). The paper presents a microscopic analysis of A. succinogenes biofilms developed under varied fermenter conditions. The concentration of excretion metabolites is controlled by operating the fermenter in a continuous mode where the liquid throughput is adjusted. It is clearly illustrated how the accumulation of excreted metabolites (concomitant with the sodium build-up due to base dosing) have a severe effect on the biofilm structure and physiology. Under high accumulation (HA) conditions some cells exhibit severe elongation while maintaining a cross sectional diameter like the rod/cocci shape cells predominantly found in low accumulation (LA) conditions. The elongated cells formed at high accumulation conditions were found to be more viable than the clusters of rod/cocci shaped cells and appear to form connections between the clusters. The global microscopic structure of the HA biofilms also differed significantly from the LA biofilms. Although both exhibited shedding after 4 days of growth, the LA biofilms were more homogenous (less patchy), thicker and with high viability throughout the biofilm depth. Viability of the HA biofilms were threefold lower than the corresponding LA biofilms towards the end of the fermentation. Visual observations were supported by quantitative analysis of multiple biofilm samples and strengthened the main observations. The work presents valuable insights on the effect of metabolite accumulation on biofilm structure and growth.

Immobilization of Cd Using Mixed Enterobacter and Comamonas Bacterial Reagents in Pot Experiments with Brassica rapa L.

“…In addition, the in vitro addition of SA promoted the formation of H 2 S and biofilms in cocultured strains. Mokwatlo et al showed that SA contributed to the formation of biofilms, and stable biofilms in turn promoted the production of more SA by bacteria . In addition, the formation of cell wall biosynthesis also contributes to biofilm biosynthesis .…”

“…Mokwatlo et al showed that SA contributed to the formation of biofilms, and stable biofilms in turn promoted the production of more SA by bacteria. 45 In addition, the formation of cell wall biosynthesis also contributes to biofilm biosynthesis. 46 Similarly, in our study, the cell wall biosynthesis metabolic pathway in the A11 strain was upregulated in the coculture conditions.…”

Well Knowledge of the Physiology of Actinobacillus succinogenes to Improve Succinic Acid Production

“…In fact, succinate had an important inhibitory effect on cell growth as well as on SA production; to our knowledge, this observation was not widely reported. Cells growth was suitable for inhibition detection caused by SA production [72]. The results obtained from inhibition tests carried out on different Petri dishes showed negative growth starting from 0.4 mol L −1 of SA concentration.…”

Effect of shear on morphology, viability and metabolic activity of succinic acid-producing Actinobacillus succinogenes biofilms

“…Two types of bioreactors were used in the study. The first bioreactor (bioreactor A) was custom developed by this research group for the purpose of microscopic visualisation of biofilm development; the details of this reactor was presented in Mokwatlo et al [16]. The visualisation and analysis of the microscopic biofilm development was facilitated by the extraction of multiple asynchronous sterile samples of biofilm coupons from the bioreactor volume.…”

“…Various studies on biofilms have shown that hydrodynamic shear conditions and the specific growth rate of biofilms, among other factors, greatly influence the formation of biofilms, particularly their structure, stability, and the activity of cells embedded in them [13][14][15]. A previous study, by this research group, investigated the influence of acid accumulation on the development, structure, and viability of A. succinogenes biofilms [16]. This study found that high acid conditions (above 10 g L −1 SA) impeded biofilm growth and resulted in patchy biofilms with significant cell death, whereas low acid conditions (below 10 g L −1 SA) favoured biofilm growth with relatively higher cell viability within biofilms.…”