215 - Respiratory protection of nitrogenase in Azotobacter vinelandii

This study is pretty similar to 214, on how oxygen levels influence the respiratory chain of Azotobacter vinelandii.

What They Saw
They grew cells in batch at low aeration, and then increased the aeration to expose cells to excess oxygen.

The results were similar to 214: when aeration increased, cells stopped growing until respiration had ramped up and leveled off. Despite the large increase in respiration, cellular ATP levels dropped 40%. P/O ratios decreased as respiration increased to accommodate the increased oxygen, at least for NADH dehydrogenase.

They tried adding chloramphenicol again, since last time it didn't affect the growth lag, but this time observed that it lessened the increase in respiration about half, and prevented cytochrome a₂ and other dehydrogenase increases.

What This Means
The M/N ratio, meaning maintenance M (moles ATP consumed per weight of cells over time) over phosphorylating efficiency N (P/O ratio x 2), explains doubling of respiratory activity upon increase in oxygen only if M increases or N decreases. It doesn't seem like M does increase, so N seems to be decreasing, because respiration uncouples from phosphorylation.

A. vinelandii seems to have different branches in its respiratory chain, which allows it to tolerate different and suddenly changing levels of oxygen.

Reference:

Jones, C. W., Brice, J. M., Wright, V. & Ackrell, B. A. C. Respiratory protection of nitrogenase in Azotobacter vinelandii. FEBS Letters 29, 77–81 (1973).

214 - The Respiratory System of Azotobacter vinelandii 2. Oxygen Effects

This study looks at how oxygen levels influence the respiratory chain in Azotobacter vinelandii.

What They Saw
They grew cells with high or low aeration (based on volume of culture in the same size flask), then isolated respiratory membranes and measured P/O ratios.

The cells grew and quickly used up all the dissolved oxygen. With high aeration, they grew much faster and leveled off once the oxygen was gone, and with low aeration the growth was slower (not even really logarithmic) but continued long after the oxygen was gone. Respiratory activities were 2-5x higher when cells were growing logarithmically with excess oxygen than when oxygen was limited.

If they suddenly increased the aeration when oxygen had run out, respiratory activity increased back up to high levels (1000 μl/h/mg dry weight). Cells didn't start growing again until it had leveled off. This lag was the same when chloramphenicol (which inhibits protein synthesis) was present, suggesting that it wasn't due to the synthesis of new enzymes for respiration.

When oxygen was being consumed, cytochrome and oxidase levels were pretty constant (except cyt o oxidase, which increased), but when oxygen ran out, levels of c₄, c₅, and b₁ increased quickly and a₂ more slowly. Cytochrome o oxidase and a₂ oxidase also increased a lot, a₁ less so. The increase of o was fastest and greatest.

P/O ratios were similar to those seen before at maximum, but they didn't reach this maximum until oxygen was mostly used up late in the logarithmic growth phase, at least for NADH dehydrogenase.

With low aeration, cytochrome levels were pretty constant (since oxygen ran out almost immediately), increasing just a little, except for cyt a₂ oxidase which went up pretty constantly. P/O ratios were pretty level too, and fairly high, similar to when oxygen ran out in high aeration.

What This Means
This kind of pattern fits in well with those seen in other obligate aerobes. Cytochromes probably increase during oxygen limitation to try to compensate for the limitation. But the low P/O ratios at high oxygen makes sense in light of respiratory protection; respiration is uncoupled from energy generation.

Reference:

Ackrell, B. A. C. & Jones, C. W. The Respiratory System of Azotobacter vinelandii 2. Oxygen Effects. Eur. J. Biochem. 20, 29–35 (1971).

352 - The Respiratory System of Azotobacter vinelandii: 1. Properties of Phosphorylating Respiratory Membranes

Similar to 161, this study looks at elements of Azotobacter vinelandii's respiratory chain and P/O ratios thereof.

What They Saw
They isolated respiratory membranes (basically pieces of cell with the respiratory chain intact but not much else, I think) and looked at oxygen reduction with different electron donors.

They saw P/O levels up to 1.1 with NADH and about 0.7 with malate, higher than in 161.

Reference:

Ackrell, B. A. C. & Jones, C. W. The Respiratory System of Azotobacter vinelandii: 1. Properties of Phosphorylating Respiratory Membranes. Eur. J. Biochem. 20, 22–28 (1971).