The Impact of Glass Material on Growth and Biocatalytic Performance of Mixed-Species Biofilms in Capillary Reactors for Continuous Cyclohexanol Production.

Ingeborg Heuschkel,Katja Bühler,Rohan Karande,Rakesh Dagini

doi:10.3389/fbioe.2020.588729

Ingeborg Heuschkel, Katja Bühler + Show 2 more

Open Access

https://doi.org/10.3389/fbioe.2020.588729

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Abstract

In this study, the growth and catalytic performance of mixed-species biofilms consisting of photoautotrophic Synechocystis sp. PCC 6803 and chemoheterotrophic Pseudomonas sp. VLB120 was investigated. Both strains contained a cytochrome P450 monooxygenase enzyme system catalyzing the oxyfunctionalization of cyclohexane to cyclohexanol. Biofilm cultivation was performed in capillary glass reactors made of either, borosilicate glass (Duran) or quartz glass, in different flow regimes. Consequently, four phases could be distinguished for mixed-species biofilm growth and development in the glass-capillaries. The first phase represents the limited growth of mixed-species biofilm in the single-phase flow condition. The second phase includes a rapid increase in biofilm spatial coverage after the start of air-segments. The third phase starts with the sloughing of large biofilm patches from well-grown biofilms, and the final stage consists of biofilm regrowth and the expansion of the spatial coverage. The catalytic performance of the mixed-species biofilm after the detachment process was compared to a well-grown biofilm. With an increase in the biofilm surface coverage, the cyclohexanol production rate improved from 1.75 to 6.4 g m–2 d–1, resulting in comparable production rates to the well-grown biofilms. In summary, high productivities can be reached for biofilms cultivated in glass capillaries, but stable product formation was disturbed by sloughing events.

Highlights

The ability of the microbial photosynthetic machinery to convert solar radiation into chemical energy for fixing carbon dioxide into value-added chemicals has attracted academic and industrial attention for several decades (Böhmer et al, 2017; Mellor et al, 2017)
The objectives of the current work were (i) to evaluate mixed-species biofilm growth in glass capillaries under single-phase flow and segmented flow conditions (ii) to assess mixed-species biofilm stability based on the detachment process and (iii) to investigate the influence of detachment on the catalytic performance
The impact of the capillary material on the mixed-species biofilm development was evaluated by inoculating quartz and borosilicate glass capillaries with a mixed culture of Synechocystis sp

Summary

Introduction

The ability of the microbial photosynthetic machinery to convert solar radiation into chemical energy for fixing carbon dioxide into value-added chemicals has attracted academic and industrial attention for several decades (Böhmer et al, 2017; Mellor et al, 2017). Product titers and volumetric productivities obtained in these proof of concept studies have been very low compared to processes based on heterotrophic hosts such as E. coli or Pseudomonas (Liang et al, 2018; Santos-Merino et al, 2019) Some of these challenges could be circumvented by the cultivation of phototrophic organisms in a biofilm format, where cells are naturally immobilized in a self-produced extracellular polymeric matrix. In comparison to suspended cells, allow long retention times for slow-growing phototrophic organisms (Elenter et al, 2007), high tolerance toward toxic chemicals (Rosche et al, 2009; Halan et al, 2016), and generate high cell density (Chang et al, 2014; Hoschek et al, 2019a), resulting in a compact reactor design and continuous operation with high volumetric productivities. It was successfully used for converting cyclohexane to the corresponding alcohol and resulted in 98% substrate conversion and a stable product flux of 3.76 g m−2 d−1 for one month

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