Dear authors, when submitting the final version please address the following remarks by the referee:

The revised version of the manuscript is much improved.
Since the author insist on the title unchanged (“Molecular insights into the microbial formation of marine dissolved organic matter: recalcitrant or labile?”). The following points need to be addressed.

1. There are no molecular insights into the following key processes: the microbial transformation and chemical compositions of the used algal exudate, the used inoculated seawater that had been stored for 5 months, and the produced “non-labile DOC”.
2. The observation "Nitrate, nitrite and phosphate remained almost constant in all treatments" needed to be interpreted.
3. Compared to glucose, algal exude may be more likely to be structural materials for bacteria. (The analyses based on the saturated and reduced states also proved that). Glucose is the main or core material in TCA cycle, it could be either energy source or sub-material for synthesis of many other compounds that are essential for bacterial growth and metabolism. In addition, extra nutrient was introduced in the Exude incubation, the lower C/N ratio might influence the microbial activities including carbon uptake. The steady nutrient concentration (especially ammonium concentration) in the Exude incubation gave some clues for that.
4. The above are all related to the observation "BGE was comparable in the treatments which contained glucose (0.1) and substantially higher in the [exud] treatments (0.6)". Does this also mean labile DOC stimulates microbial respiration more strongly? Or that the added labile DOM lacks proper N content?