This paper reports a non-invasive method for in situ biofilm quantification based on the use of hyperspectral imaging to analyze a chromatically and texturally heterogeneous substrate as granite colonized by green algae and cyanobacteria. Biofilm-forming microorganisms were inoculated on granite blocks and incubated under laboratory conditions for 21 days. The intensity of the green stains formed on the granite surfaces differed depending on the initial concentration of microorganisms used. A biofilm quantification (BQ) index was computed to determine the level of colonization on the surfaces. The index was obtained by comparing the quotient of the reflectance of the green (G) and red (R) bands of each pixel of the hyperimage against a threshold value, fth. The optimal value of the threshold was determined by examining the linear correlation between the BQ index and the chlorophyll a extracted. The BQ results were then compared with the F0 and ΔE*ab parameters yielded by colour spectrophotometry and PAM fluorometry techniques and used as reference methodologies to quantify greening on stone surfaces. The BQ index showed a high level of consistency with all of the other parameters; it was linearly correlated with the chlorophyll a concentration, F0 andΔE*ab, with high coefficients of determination (r2 > 0.92) for the range from 1.87 to 5.69 μg chl a.cm-2. The strength of the BQ index lies in its double use as a biomarker of quantity and percentage cover, as well as its good performance under different conditions, ranging from initial phototrophic colonization and thin (young) biofilms covering 21.19% of the surface to profuse biological colonization covering 67.36% of the surface. Moreover, the proposed BQ index may be able to be used with other types of rock with less heterogeneous surfaces than granite.

中文翻译：

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使用高光谱成像量化花岗岩上的光养生物膜

本文报告了一种非侵入性的原位生物膜量化方法，该方法基于使用高光谱成像来分析颜色和纹理异质基底，如绿藻和蓝藻定植的花岗岩。将形成生物膜的微生物接种在花岗岩块上并在实验室条件下培养 21 天。在花岗岩表面形成的绿色污渍的强度因所用微生物的初始浓度而异。计算生物膜量化 (BQ) 指数以确定表面上的定植水平。该指数是通过将超图像的每个像素的绿色 (G) 和红色 (R) 波段的反射率的商与阈值 fth 进行比较来获得的。通过检查 BQ 指数与提取的叶绿素 a 之间的线性相关性来确定阈值的最佳值。然后将 BQ 结果与通过彩色分光光度法和 PAM 荧光测定技术得出的 F0 和 ΔE*ab 参数进行比较，并用作量化石材表面绿化的参考方法。BQ 指数显示出与所有其他参数的高度一致性；它与叶绿素 a 浓度 F0 和ΔE*ab 呈线性相关，在 1.87 至 5.69 μg chl a.cm-2 范围内具有高决定系数 (r2 > 0.92)。BQ 指数的优势在于它作为数量和覆盖百分比的生物标志物的双重用途，以及它在不同条件下的良好性能，从最初的光养定植到覆盖 21 的薄（年轻）生物膜。19% 的表面有大量的生物定植覆盖了 67.36% 的表面。此外，提议的 BQ 指数可能能够用于具有比花岗岩更少异质表面的其他类型的岩石。