Effect of biofilm on fluorescence measurements derived from fast repetition rate fluorometers

Abstract

This study evaluates, for the first time, the influence of biofilms on single and double optical window (SOW and DOW, respectively) fast repetition rate fluorometer (FRRF) measurements of microalgal photosystem-II initial fluorescence (F₀), maximum fluorescence (F_m), variable fluorescence (F_v = F_m – F₀), quantum yield (F_v/F_m) and functional absorption cross section (σ_PSII)]. Biofilms with chlorophyll > 0.1 μg cm⁻² and > 0.3 μgcm⁻² on SOW and DOW, respectively, produced a substantial increase in fluorescence. However, the relative magnitude of biofouling effects depended on sample chlorophyll concentrations, being more critical at concentrations < 1 mg m⁻³. In DOW-FRRF, biofilms affected F₀ (increased) and F_v/F_m (decreased) but not F_v and σ_PSII, whereas in SOW-FRRF, biofilms increased fluorescence and showed a variable effect on F_v/F_m and σ_PSII, because only biofilms on SOW attained actual F_m. As a result, the biofilm effect was substantial on SOW-FRRF measurements. On the other hand, the neutral-density filters (representing non-chlorophyll containing biofilms) with different transmission levels reduced the fluorescence signal. Correction procedures for the above photosystem-II parameters are proposed here.

Keywords:

• fast repetition rate fluorometer
• optical windows
• biofilms
• chlorophyll
• transmission

Acknowledgements

The first author, JSP, gratefully acknowledges the Japanese Government Scholarship (Monbukagakusho) provided by Ministry of Education, Science, Sports and Culture, Government of Japan and the Government of India for nominating him for the scholarship. The authors thank the Director, CSIR-National Institute of Oceanography (CSIR-NIO) and Dr A.C. Anil CSIR-NIO, Goa, India for support and encouragement. They also thank Dr S.S. Sawant for his constructive suggestions and two anonymous reviewers for their important comments which improved the manuscript. This paper is a NIO contribution no. 5766.

Disclosure statement

No potential conflict of interest was reported by the authors.