Synechocystis sp PCC 6803 strains lacking photosystem I and phycobilisome function.

Abstract

The Jacob Blaustein lnstitute for Desert Research, Ben-Gurion University of the Negev, Sede-Boker 84990, ISiaelTo design an in vivo system allowing detailed analysis of photosystem II (PSII) complexes without significant interference from other pigment complexes, part of the psaAB operon coding for the core proteins of photosystem I (PSI) and part of the apcE gene coding for the anchor protein linking the phycobilisome to the thylakoid membrane were deleted from the genome of the cyanobacterium Synechocystis sp strain PCC 6803. Upon transformation and segregation at low light intensity (5 pE m+ sec-l), a PSI deletion strain was obtained that is light tolerant and grows reasonably well under photoheterotrophic conditions at 5 pE m-2 sec-l (doubling time -28 hr). Subsequent inactivation of apcE by an erythromycin resistance marker led to reduction of the phycobilin-to-chlorophyll ratio and to a further decrease in light sensitivity. The resulting PSI-IesslapcE-strain grew photoheterotrophically at normal light intensity (50 pE m-2 se&) with a doubling time of 18 hr. Deletion of apcE in the wild type resulted in slow photoautotrophic growth. The remaining phycobilins in apcE-strains were inactive in transferring light energy to PSII. Cells of both the PSI-less and PSI-IesslapcE-strains had an approximately sixfold enrichment of PSll on a chlorophyll basis and were as active in oxygen evolution (on a per PSll basis) as the wild type at saturating light intensity. Both PSI-less strains described here are highly appropriate both for detailed PSll studies and as background strains to analyze site-and region-directed PSll mutants in vivo.

Light-dependent chlorophyll a biosynthesis upon chlL deletion in wild-type and photosystem I-less strains of the cyanobacterium Synechocystis sp. PCC 6803

“…After 144 h of growth in 5 #E m -2 s -~ light, the Chl level in the chlL-mutant was more than 4 times higher than that in the PS I-less/chlL-strain. This is close to the final ratio of 5 in the Chl amount on a per-cell basis in the wild type vs. in the PS I-less strain [37]. Figure 4A also shows that no significant difference existed in the rate of Chl biosynthesis in the chlL-mutant at high (50/~E m -2 s-1) and low (5 #E m -2 s -1 ) light intensity.…”

“…The pFQ22 plasmid was used to transform the Synechocystis 6803 wild-type strain and a PS l-less strain carrying a deletion in psaAB [37]. Details regarding the transformation of Synechocystis 6803 have been published [44,46].…”

“…The strain can grow in darkness provided that a brief period of illumination is given every day (light-activated heterotrophic growth, LAHG) [ 3 ]. Synechocystis 6803 strains that lack PS I have been developed by genetic deletion of the PS I core complex upon transformation with a plasmid in which part of the psaAB operon (coding for the PS I core complex) was deleted and replaced with an antibioticresistance cassette [37,40]. The PS I-less (psaAB deletion) strains do not survive under light conditions routinely used for wild-type cultures (continuous light at 50/~E m -2 s-~) but can grow under LAHG conditions [40] as well as in continuous light at 5/~E m -2 s -1 [37].…”

Functional phycobilisome core structures in a phycocyanin-less mutant of cyanobacterium Synechococcus sp. PCC 7942

“…PCC 7002 (Bryant et al 1990) and more recently in Synechocystis sp. PCC 6803 (Shen et al 1994), and in both the cases the resulting mutants were capable of photoautotrophic growth. In contrast, attempts to inactivate the 75 kDa large core linker have indicated that this linker is essential for survival in Synechococcus sp.…”

Function and organization of Photosystem I polypeptides

“…Although these mutant strains required light-activated photoheterotrophic conditions for growth, other groups have generated PsaA-or PsaB-less cyanobacterial mutants in Synechocystis sp. PCC 6803 (Shen et al 1993), Anabaena variabilis (Toelge et al 1991;Nyhus et al 1993), or Synechococcus sp. PCC 7002 (D.A.…”