Coolled pe2

Illumination sources tested were mercury light (HBO100 watts), metal halide (Olympus), Sola (Lumencor), CoolLED PE2 with 425 & 535/615 LAMs, Sola 2 (Lumencor, CoolLED PE4000) [8 ,9 ]. The Sola and Sola 2 produce LED-based white light continuous spectrum from 380 to 680 nm; by contrast the PE2 and the PE4000 produce selected wave lengths between 365nm and 770nm [8 ,9 ]. The PE2 unit can drive up to 4 LED wavelengths from 2 LAMs (LED Array modules) while the PE4000 has 16 selectable LED wavelengths which can be activated singly or in groups up to 4 [10 ]. The PE4000 can also be used as a source of white light but this was not tested here. Both companies provide alternative systems that were not tested. All excitation was done with the light source at full power unless specified.

For image acquisition, a Nikon Eclipse Ti-E inverted microscope was used, with Nikon CFI Plan Apo Lambda DM 100X Oil objective, CoolLED pE-2 or Lumencor Aura illumination system (470 or 485 nm LED, respectively, for excitation of GFP) and Andor iXon 897 EM-CCD camera. The following filters were employed: excitation filter bandpass 470/40 nm, dichroic mirror 495 nm and emission filter 525/50 nm (AHF Analysentechnik F46-470). Focus was maintained by Nikon’s PFS3 system. Acquisition was started within 10 min (generally ~7 min) after the bacteria had been introduced in the microfluidic system and every 10 min phase contrast images and GFP signal (200 ms exposure time) were acquired at multiple positions. The microscope was controlled by NIS Elements v4.51 software.