浑球红假单胞菌(Rhodopseudomonas sphaeroides)色素基因的突变对生长速率及光合固氮的影响

浑球红假单胞菌Rps.sphaeroides 6128经甲基磺酸乙酯诱变处理,分离获得23株色素突变种。不具有细菌叶绿素a和类胡萝卜素的无色突变株不能光养生长,蓝绿突变株305不含带色的类胡萝卜素,但能光养生长,其世代时间比亲本株长5倍左右,而且,没有还原乙炔和放氢的固氮酶活性。绿色突变株309缺失球形烯和球形烯酮。当光照强度从3000lx增加到4000lx时,绿色突变株与亲本株生长速率之差由5.3小时缩短为0.3小时,其光合固氮和光合放氢的活性分别为亲本株的30％和45％。各菌株ATP的含量因所含色素成份不同而异。在指数生长期,蓝绿突变株305的ATP含量只有亲本株的8％,绿色突变株309的ATP含量为亲本株的32％,各色素变种的固氮能力与它们菌体ATP的含量相关。类胡萝卜素在为光合固氮提供能源中起着重要的作用。

EFFECT OF PIGMENT GENE MUTATION ON GROWTH RATE AND PHOTOSYNTHETICAL NITROGEN FIXATION IN RHODOPSEUDOMONAS SPHAEROIDES

Twenty three mutants, which differ from the parental strain in the nature of their pigment system, were isolated from Rps. sphaeroides 6128 after mutagenesis with ethylmethane sulfonate (EMS). The colorless mutant 320 without bacteriochlorophyll a and carotenoide could not grow photosynthetically. The blue-green mutant 305 was devoid of carotenoides but capable of photosynthetical growth. The doubling time of this mutant was longer than that of parental strain by about 5 times. Furthermore, the mutant had no nitrogenase activity as measured by acetylene reduction and hydrogen production. The green mutant 309 lacked spheroidene and spheroidenone. With the increase of light intensity from 3000 lx to 4000 lx, the difference in doubling time between mutant 309 and parent 6128 decreasedfrom 5.3 h to 0.3 h. In comparison with parental strain, the mutant had 30% of photosynthetic nitrogen-fixing activity and 45% of photosynthetic hydrogenevolution activity. The difference of ATP content between various mutants and parental strain was correlated with their photopigment. ATP contents of blue-green mutant and green mutant in the exponential phase of photosynthetic growth were 8% and 32% of that of parent respectively. It is well demonstrated that the ATP content of the various mutants is related to their nitrogen-fixing ability. Carotenoid plays an important role in providing sufficient energy for photosynthetic nitrogen fixation.