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Bacteria can switch between planktonic forms (single cells) and biofilms, i.e., bacterial communities growing on solid surfaces and embedded in a matrix of extracellular polymeric substance. Biofilm formation by pathogenic bacteria often results in lower susceptibility to antibiotic treatments and in the development of chronic infections; thus, biofilm formation can be considered an important virulence factor. In recent years, much attention has been directed towards understanding the biology of biofilms and towards searching for inhibitors of biofilm development and of biofilm-related cellular processes. In this report, we review selected examples of target-based screening for anti-biofilm agents: We focus on inhibitors of quorum sensing, possibly the most characterized target for molecules with anti-biofilm activity, and on compounds interfering with the metabolism of the signal molecule cyclic di-GMP metabolism and on inhibitors of DNA and nucleotide biosynthesis, which represent a novel and promising class of biofilm inhibitors. Finally, we discuss the activation of biofilm dispersal as a novel mode of action for anti-biofilm compounds.

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Photosynthetic microorganisms play crucial roles in aquatic ecosystems and are the major primary producers in global marine ecosystems. The discovery of new bacteria and microalgae that play key roles in CO 2 fixation is hampered by the lack of methods to identify hitherto-unculturable microorganisms. To overcome this problem we studied single microbial cells using stable-isotope probing (SIP) together with resonance Raman (RR) microspectroscopy of carotenoids, the lightabsorbing pigments present in most photosynthetic microorganisms. We show that fixation of 13 CO 2 into carotenoids produces a red shift in single-cell RR (SCRR) spectra and that this SCRR-SIP technique is sufficiently sensitive to detect as little as 10% of 13 C incorporation. Mass spectrometry (MS) analysis of labelled cellular proteins verifies that the red shift in carotenoid SCRR spectra acts as a reporter of the 13 C content of single cells. Millisecond Raman imaging of cells in mixed cultures and natural seawater samples was used to identify cells actively fixing CO 2 , demonstrating that the SCRR-SIP is a noninvasive method for the rapid and quantitative detection of CO 2 fixation at the single cell level in a microbial community. The SCRR-SIP technique may provide a direct method for screening environmental samples, and could help to reveal the ecophysiology of hitherto-unculturable microorganisms, linking microbial species to their ecological function in the natural environment.