Do bacteria of different species absorb different wavelengths of light? How different?
Most of my searching has lead to topics about Optical Dispertion which seems to be species independent as opposed to single species.
Yes they do, as demonstrated by the fact that bacteria have different colors ! Moreover, some bacteria are photosynthetic and others aren't; the photosynthetic bacteria have a very specific mechanism for absorbing light that the others don't so it stands to reason they won't absorb the same wavelengths.
This page talks about it very nicely, with a list of different colors and bacteria that have them:
Money quote :
Bacteria are pigmented or colored. Pigmented bacteria are also known as chromobacteria. Bacterial pigments are water soluble or insoluble; water soluble pigments are diffused in the growth medium. Chemically, bacterial pigments are pyrrole, phenazine, carotenoid, xanthophylls and quinine or quinone derivatives. The pigment molecules are synthesized in cell wall or periplasmic space. We can visualize pigmentation in bacteria in specific growth medium or my staining bacterial cells with a dye to observe under microscope. It has been proved that only aerobic and facultatively aerobic bacteria are pigmented because, molecular oxygen is essential for pigmentation. Therefore, anaerobic bacteria are nonpigmented. Pigment synthesis is also dependent on light, pH, temperature and media constituents like indicator dyes. They display all the colors from rainbow including light or dark tinges and unual colors like black, white, brown, golden, silver and fluorescent green, yellow or blue.
And the list:
Purple: Spirillum rubrum
Violet: Chromobacterium violacein
Indigo: Janthinobacterium lividum
Blue: Streptomyces coelicolor
Green: Chlorobium tepium
Yellow: Xanthomonas campestris
Orange: Sarcina aurentiaca
Red: Serratia marcenscens
Brown: Rhizobium etli
Black: Prevotela melaninogenica
Golden: Staphylococcus aureus
Silver: Actinomyces sp.
White: Staphylococcus epidermidis
Cream: Proteus vulgaris
Pink: Micrococcus roseus
Maroon: Rugamonas rubra
Fluorescent blue/green: Pseudomonas aeruginosa
Fluorescent yellow: Pseudomonas fluorescens
It appears some purposes of producing pigments, aside from photosynthesis, are to absorb UV light (i.e. absorbing a specific wavelength is the entire point) or mopping up free radicals.
An additional note, from the Wikipedia page for Rhodospirillum rubrum, the first bacterium in that list (which Wikipedia describes as "pink" but close enough):
The photosynthesis of R. rubrum differs from that of plants as it possesses not chlorophyll a, but bacteriochlorophylls. While bacteriochlorophyll an absorbs light having a maximum wavelength of 800 to 925 nm, chlorophyll absorbs light having a maximum wavelength of 660 to 680 nm.
And while that paragraph describes "chlorophyll a" as being a feature of plants, other bacteria do use it such as Chlorobium tepidum, so there you can see some wavelengths that are absorbed by one and not the other.
Yes, they do, just as Rozenn Keribin has explained in her answer. In addition to the answer above, there is a 1954 research paper written by Shibata, Bensen and Calvin freely available from the Berkeley Lab of the University of California which should give you the theoretical background, experimental methodology as well as some data on the absoprtion spectra of different micro-organisms including bacteria: