Research Article Diagnosis of the Diatom Community upon Biofilm Development on Stainless Steels in Natural Freshwater Caroline Richard, 1 Smita Mitbavkar, 2 and Jessem Landoulsi 3,4 1 Laboratoire de M´ ecanique et Rh´ eologie (LMR), EA 2640, Polytech’Tours, Universit´ e Franc ¸ois Rabelais de Tours, 37200 Tours, France 2 CSIR-National Institute of Oceanography, Dona Paula, Goa 403 004, India 3 Sorbonne Universit´ es, UPMC Univ Paris 06, 75005 Paris, France 4 CNRS, UMR 7197, Laboratoire de R´ eactivit´ e de Surface, 75005 Paris, France Correspondence should be addressed to Caroline Richard; caroline.richard@univ-tours.fr and Jessem Landoulsi; jessem.landoulsi@upmc.fr Received 26 January 2017; Accepted 13 April 2017; Published 25 May 2017 Academic Editor: David Alsteens Copyright © 2017 Caroline Richard et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tis paper reports the development of bioflms on stainless steels (SS) upon exposure in a natural freshwater ecosystem for about six months and focuses on the composition of diatom populations. By using environmental scanning electron microscopy (ESEM) technique, we provide a detailed description regarding diatom identifcation at species level as well as their main characteristics, including type, morphology, ability to form colony, and motility. Results reveal the presence of both prostrate (initial colonizers) and stalked (late colonizers) forms. Pennate diatoms, Cocconeis placentula and Amphora cofeaeformis, and a centric diatom, Melosira varians, are shown to be the abundant forms regardless of the SS type. Pennate diatoms dominate the community and are directly attached to the substratum, whereas the centric form is entangled in the bioflm matrix in a signifcant number. Te dominance of adnate forms suggests that these cells are sturdy and successfully maintaining their population. In situ monitoring of the electrochemical response of immersed materials showed ennoblement of the open circuit potential, which seems to be due to the biogenic production of H 2 O 2 , detected in a signifcant amount within the bioflms. Te substantial enrichment of bioflms with diatoms potentially suggests the implication of these microorganisms in the process of ennoblement. A mechanism is proposed in this paper describing the possible interactions of diatom community with SS in the studied ecosystem. 1. Introduction Diatoms are microscopic, unicellular, autotrophic algae which are members of the heterokontic group of cells and are responsible for a major portion of the primary productivity, thus forming the base of the food chain in aquatic ecosystems. Based on their morphology, two types of diatoms are identifed, centric with a radial symmetry and pennate with a bilateral symmetry. In general, the centric types are abundant in the water column, whereas the pennate ones are found in bioflms formed on natural or artifcial surfaces. Tis is due to their ability to attach to substrata via extracellular polymeric substances (EPS) which are secreted through a structure known as a raphe [1]. Depending on the positioning and number of raphes, pennate diatoms are classifed as monoraphid (one raphe), biraphid (two raphes, both present on one valve or one on each valve), and araphid (no raphe). Some diatom species attach to substrata with the help of structures such as stalks or pads [2]. Both centric and pennate types are ofen observed in each other’s habitats. As centric types do not possess raphes, they are found entangled within the bioflm community. Both forms occur as single cells or as colonies in various shapes (flaments, ribbons, fans, zigzags, or even stellate). Within the bioflms, these diatoms play a similar role as their counterparts in the water column forming the base of the benthic food webs. Although the role of diatoms as primary producers in aquatic environments is of major importance, their presence on artifcial man-made structures is a serious issue. Diatom fouling may, indeed, greatly afect the performance of metallic Hindawi Scanning Volume 2017, Article ID 5052646, 13 pages https://doi.org/10.1155/2017/5052646