Anabaena sp. PCC7120 is a filamentous nitrogen-fixing cyanobacterium whose cells are surrounded by an inner cytoplasmic membrane and an outer membrane. Eight outer membrane proteins were previously identified in our laboratory, and preliminary studies indicated that two such proteins, namely, Alr2269 and All3983, may be involved in calcium uptake and/or utilization. In this study, I present clear results to show that at least Alr2269 is required for the growth of Anabaena PCC7120 under low-calcium conditions.
The main researches and results are described in three parts:
1. Comparison of Anabaena sp. PCC 7120 with mutant alr2269::C.CE2 or all3983::C.CE2 showed that All3983 was up-regulated in mutant alr2269::C.CE2, while no significant difference was found between the all3983::C.CE2 mutant and the wide type.
2. Reporter genes luxAB were used to analyze the transcription of all3983. The expression of all3983 in mutant alr2269::C.CE2 was induced upon calcium depletion. The transcription of all3983 in alr2269::C.CE2 was at a higher level than in the wide type, which was consistent with the 2-DE analysis at protein level.
3. The growth of the wide type and mutants on different calcium concentration was compared. The growth rate of alr2269::C.CE2 in BG111/50ca was significantly reduced in comparison to that of the wide type and restored to the wide type level after complementation with the wide type alr2269. In BG111/1000ca, mutant all3983::C.CE2 grew at a slightly lower rate than the wide type, but the complementation was not successful.
Based on these results, it is hypothesized that Alr2269 is involved in calcium uptake and/or utilization.