Fig. 1

Characterization of the OA signal and spectra of phototrophic bacteria injected into tumors. a–e OA signal of phototrophic bacteria Rba. capsulatus SB1003 (SB1003), mutant ΔcrtJ (ΔcrtJ), and Rba. sphaeroides (Rba. sp.) injected into 4T1 and CT26.WT tumors. For each strain, data are shown from three mice before injection (green), immediately after injection (red) and at several timepoints after injection (black); dotted line represents the average (n = 3). The signal was calculated as the sum of the signal intensities at the maximum wavelength of all unmixed pixels in the region of interest summed over all slices. Target spectra for unmixing were the 860-nm absorption peaks of all strains. Data from PBS-injected mice used as a control. f–j Change of the OA spectra of the same mice shown in a-e over time. Shown are the average spectra of all three mice per strain and timepoint. Data from before injection are shown in green; immediately after in red and at increasing timepoints as shades of gray (24, 48, 72/96, 168/192 h). The spectrometrically determined absorption spectrum of the injected agent is shown for comparison as a dotted line. k MSOT slice of the mid-section of a 4T1 tumor-bearing mouse at 24 h after injection with Rba. capsulatus ΔcrtJ and illuminated at 720 nm. l Cryosection of 4T1 tumor-bearing mouse at terminal timepoint (168 h) after injection with Rba. capsulatus SB1003. Excitation 740/40 nm bandpass, emission 850 nm longpass, exposure 10 s, gain 40. The analyzed region of interest (i.e., tumor) is indicated as a dotted line in both images (k, l). Scale bar: 2 mm