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. 2021 Nov 29;9(12):2466.
doi: 10.3390/microorganisms9122466.

Low-Field Nuclear Magnetic Resonance Characteristics of Biofilm Development Process

Yajun Zhang  1   2 , Yusheng Lin  1   2 , Xin Lv  1   2 , Aoshu Xu  1   2 , Caihui Feng  1   2 , Jun Lin  1   2
Affiliations

Low-Field Nuclear Magnetic Resonance Characteristics of Biofilm Development Process

Yajun Zhang et al. Microorganisms. .

Abstract

To in situ and noninvasively monitor the biofilm development process by low-field nuclear magnetic resonance (NMR), experiments should be made to determine the mechanisms responsible for the T2 signals of biofilm growth. In this paper, biofilms were cultivated in both fluid media and saturated porous media. T2 relaxation for each sample was measured to investigate the contribution of the related processes to T2 relaxation signals. In addition, OD values of bacterial cell suspensions were measured to provide the relative number of bacterial cells. We also obtained SEM photos of the biofilms after vacuum freeze-drying the pure sand and the sand with biofilm formation to confirm the space within the biofilm matrix and identify the existence of biofilm formation. The T2 relaxation distribution is strongly dependent on the density of the bacterial cells suspended in the fluid and the stage of biofilm development. The peak time and the peak percentage can be used as indicators of the biofilm growth states.

Keywords: T2 relaxation; bacterial cell; biofilm growth; low-field NMR; porous media.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic of (a) bacterial samples for the four experiments and (b) NMR measurement and data analysis unit.
Figure 2
Figure 2
Growth curve of bacterial cells suspended in liquid media: (a) OD value vs. culture time; (c) the corresponding peak time of T2 relaxation distribution. The first points in (a,c) are measurements for the sterile liquid media before inoculation at room temperature. T2 relaxation distribution of the cell suspensions sampled at 0 h, 4 h, 8 h, 12 h, and 22 h for sample 1 (b) and sample 2 (d).
Figure 3
Figure 3
(a) T2 relaxation distributions of sample 3 (b3) at day 1, day 6, day 12, day 38, day 95, day 109, and a contrast sample. (b) Photos of sample 3, which were taken at day 6, day 38, and day 95 from a vertical insight (the row at left) and the bottom of the sample (the row at right). The peak times (c) and the corresponding peak percentage (d) of the T2 relaxation distributions for peak 1 of each sample (b1, b2, and b3) vs. culture time.
Figure 4
Figure 4
(a) T2 distribution of biofilm, which was obtained from the bottom of the cultured biofilm. (b,c) SEM images of biofilm corresponding to T2 in (a). (d) T2 distribution of biofilm, which was obtained from the upper layer of the cultured biofilm. (e,f) SEM images of biofilm corresponding to T2 in (d).
Figure 5
Figure 5
(a) The T2 relaxation distributions for the inoculated sample at day 1, day 55, and day 156 and the contrast sample. The peak percentage (b) and the peak time (c) of the T2 relaxation distribution for the biofouling sample.
Figure 6
Figure 6
Scanning Electron Microscope (SEM) images of (a) the clean sands and (b) sand coated by EPS and bacterial cells.
See this image and copyright information in PMC

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