Insights into the Development of Phototrophic Biofilms in a Bioreactor by a Combination of X-ray Microtomography and Optical Coherence Tomography

Abstract

As productive biofilms are increasingly gaining interest in research, the quantitative monitoring of biofilm formation on- or offline for the process remains a challenge. Optical coherence tomography (OCT) is a fast and often used method for scanning biofilms, but it has difficulty scanning through more dense optical materials. X-ray microtomography (μCT) can measure biofilms in most geometries but is very time-consuming. By combining both methods for the first time, the weaknesses of both methods could be compensated. The phototrophic cyanobacterium Tolypothrix distorta was cultured in a moving bed photobioreactor inside a biocarrier with a semi-enclosed geometry. An automated workflow was developed to process µCT scans of the biocarriers. This allowed quantification of biomass volume and biofilm-coverage on the biocarrier, both globally and spatially resolved. At the beginning of the cultivation, a growth limitation was detected in the outer region of the carrier, presumably due to shear stress. In the later phase, light limitations could be found inside the biocarrier. µCT data and biofilm thicknesses measured by OCT displayed good correlation. The latter could therefore be used to rapidly measure the biofilm formation in a process. The methods presented here can help gain a deeper understanding of biofilms inside a process and detect any limitations.

Passively immobilized cyanobacteria Nostoc species BB 92.2 in a moving bed photobioreactor (MBPBR): Design, cultivation, and characterization

“…It thus can be assumed that less light reaches the inner areas of the carrier and therefore the biofilm grows less well here. However, as we have already shown for T. distorta , it even grows better there at the start, presumably because of lower shear forces (Schaefer et al, 2021). Thus, apparently enough light was able to penetrate the carriers to allow growth to occur.…”

“…They were able to show that these genes were responsible for a small heat-stable substance which was released into the culture supernatant and hindered biofilm growth. Agostoni T. distorta in the same system, we found evidence that nutrient deficiency can also induce increased biofilm formation (Schaefer et al, 2021). According to our knowledge, a correlation between CO 2 concentration and the biofilm formation of cyanobacteria has previously not been described yet.…”

“…PCC6803 and thus with biofilm formation. For T. distorta in the same system, we found evidence that nutrient deficiency can also induce increased biofilm formation (Schaefer et al, 2021). According to our knowledge, a correlation between CO 2 concentration and the biofilm formation of cyanobacteria has previously not been described yet.…”

“…However, the values obtained did not correlate well with the biomasses (data not shown). Using a combination of optical coherence tomography and a x-ray microtomography, we were able to measure the development of a biofilm of Tolypothrix distorta with spatial and temporal resolution inside the carrier in the psMBPBR (Schaefer et al, 2021). It can be assumed that the results can basically be transferred to N. sp.…”

Influence of wettability and surface design on the adhesion of terrestrial cyanobacteria to additive manufactured biocarriers

“…Regarding different biocarrier structures, the highest growth of heterotrophic and phototrophic biofilms has often been observed in the protected internal structures and cavities when used in fluidized beds [36,43,44]. As the cyanobacteria tended to adhere to the grooves of the lateral area on the cultivated biocarriers (Fig.…”