The described study investigates virus-bacteria and bacteria-chlorophyll a ratios as indicators for microbial food web structure for two shallow Kenyan soda-lakes which were intensively sampled from July 2008 to October 2009. For a cross-system analysis data from more than 17 other soda-lakes were used, based on data from own samplings as well as published sources. Furthermore, data from various aquatic systems (marine, freshwater, soda-lakes) from different climate zones were collected via a literature research.

The study provides interesting insight on important environmental parameters and their relation to indicators for the composition of the microbial community, identifying important differences between marine and inland waters.

Furthermore, the authors observe that the virus-bacteria ratio is strongly dependent on particulate matter concentration. The study links the indicators and observed trends to system specific environmental conditions, as well as food web composition (e.g. species poor communities and dominance of mesozooplankton in soda lakes which might lead to the proliferation of bacteria due to strong top-down control on microzooplankton). The authors furthermore suggest that the influence of particles on viral decay might be one critical factor in influencing the virus-bacteria ratio.

The study is very well written, it provides necessary details on the study sites, data collection and analysis.

Specifically, the cross-system-comparison provides important information on the relation of the two indicators with eutrophication and associated environmental factors. Thereby the findings raise new interesting questions and could guide future studies on the influence of particle type and concentration on virus-bacteria ratios. The found changes in the investigated ratios point to substantial changes in the composition of microbial communities influencing the relative importance of the microbial loop vs primary production on energy flow to higher trophic levels with eutrophication.