Chloroso
mes are light-harvesting antenna co
mplexes that occur in green photosynthetic bacteria which have only been shown naturally to contain bacteriochlorophyll (BChl)
m>cm>,
m>dm>, or
m>em> as the principal light-harvesting pig
ments. BChl
m>fm> has long been thought to be an obvious fourth
me
mber of the so-called
m>Chlorobiumm> chlorophylls, because it possesses a C-7 for
myl group like BChl
m>em> and lacks a
methyl group at C-20 like BChl
m>dm>. In organis
ms that synthesize BChl
m>cm> or
m>em>, the
m>bchUm> gene product encodes the enzy
me that
methylates the C-20 position of these
molecules. A
m>bchUm> null
mutant of the green sulfur bacteriu
m m>Chlorobaculum limnaeumm> strain 1677
T, which nor
mally synthesizes BChl
m>em>, has recently been generated via insertional inactivation, and it produces chloroso
mes containing BChl
m>fm> [Vogl et al., 2012]. In this study, chloroso
mes containing BChl
m>fm> and
mono
meric BChl
m>fm> in pyridine were characterized using a variety of spectroscopic techniques, including fluorescence e
mission and excitation spectroscopy, fluorescence lifeti
me and quantu
m yield deter
minations, and circular dichrois
m. These spectroscopic
measure
ments, as well as Gaussian si
mulation of the data, show that chloroso
mes containing BChl
m>fm> are less efficient in energy transfer than those with BChl
m>em>. This can pri
marily be attributed to the decreased spectral overlap between the oligo
meric BChl
m>fm> (energy donor) fluorescence e
mission and the BChl
m>am> (energy acceptor) absorption in the chloroso
me baseplate. This study allows us to hypothesize that, if they exist in nature, BChl
m>fm>-containing organis
ms
most likely live in rare high-light, anoxic conditions devoid of Chl
m>am>,
m>dm>, or BChl
m>em> filtering.
Abstract reference
K. Vogl, M. Tank, G.S. Orf, R.E. Blankenship, D.A. Bryant, Bacteriochlorophyll m>fm>: properties of chlorosomes containing the ¡°forbidden chlorophyll,¡± m>Frontm>. m>Microbiolm>. 3 (2012) 298.