固氮蓝藻高光放氢突变种的筛选和放氢特点

作者以前报道过几种快速生长的固氮蓝藻在某种条件下能好气光放氢,其速度可以达到光合放氧速度的10—15%,但这种活性只有在不积累氢气的流动气相下或在短时间内发生。本文报道用亚硝基胍诱变所得到的Anabaena spp。Strain CA的高光放氢突变种——N9A和18A——的筛选和氢代谢特点。在达生长饱和光照以后,野生型的光放氢活性与光照强度的增加成正相关,而其吸氢活性则与之成负相关,显示高光照强度可能抑制吸氢酶的活性。无论在什么光强下,均测不到两个突变种的吸氢活性,暗示在突变种中,吸氢酶或有关系统受损伤。把细胞固相化在琼脂上,在密闭系统中,高光强下培养50个小时,两个突变种光释放和积累的氢分别为野生型的2倍(N9A)和6倍(18A),后者等于氢占气相(1%CO_2的空气)的1.8%。两个突变种在生长速度、叶绿素含量、乙炔还原活性以及光合放氧方面与野生型无明显不同。当以含50—100nM的镍离子的培养基培养时,野生型的好气净产氢活性完全丢失,其吸氢活性却增加约10倍。培养基中镍离子的存在,对两个突变种的高光放氢活性则毫无影响,而且在此情况下,仍测不出其吸氢活性。实验结果表明,这两个突变种系吸氢酶缺陷型突变种。

THE PHENOTYPIC HUP-MUTANTS OF THE NITROGENFIXING BLUE-GREEN ALGA (CYANOBACTERIUM), ANABAENA SPP. STRAIN CA

We have previously reported that a significant rate, 10tq 15% as that of photosynthetic oxygen evolution, of aerobic hydrogen production had been observed in several rapidly-growing nitrogen-fixing strains of blue-algae (Cyanobacteria) under flow system. The contineously high aerobic hydrogen photoproduction mutants (Designated N9A and 18A, meaning the mutagenesis being performed on Nov.9 and 18, at Am. 1982) of Anabaena spp. Strain CA was induced by using mutagen N-methyl-N-nitro-N-nitrosoguanidine (NTG) in ASP-2 medium containing 100 nM Ni~( ), 1% water-washed agar and minus nitrogen source. The mutants were incubated in closed flack for 50 hs with the cells immobilized in agar During the incubation, the mutants aceumulated H_2 at a quantity of 2 times (mutant N9A) and 6 times (mutant 18A) as much as that of the wildtype, and for mutant 18A, it was equal to 1.8% H_2 in the gas phase (1% CO_2 in air). Under the saturated light intensity of growing, the capacity of net aerobic hydrogen production for the wildtype was found to increase with the increasing light intensity, the reason was that H_2 uptake was reduced as growth light intensity increased. However, there was no detectable H_2 uptake in the mutants even they were grown under low light intensity. It suggests that the high light intensity may inhibit the activity of uptake hydrogenase, and this enzyme or the relevant electron transport may have been lost or damaged in the mutants.The mutants are not significantly different from the wildtype in growth rate in liquid medium, in chlorophyll a concentration and in the rates of C_2H_2 reduction and photosynthetic oxygen evolution. In wildtype, the addition of 50 to 100 nM Ni~( 2) to growth medium abolished net H_2 photoproduction and increased the rate of dark H_2 uptake to about 10 times, while in both mutants, H_2 evolution was independent of Ni~( 2) in growth medium.The results suggest that these mutants, N9A and 18A, are the phenotypic Hup~- mutants of nitrogen-fixing Cyanobacterium, Anabaena spp. strain CA.