Distributions of bacteriohopanepolyols in lakes and coastal lagoons of the Azores Archipelago
Abstract. Bacteriohopanepolyols (BHPs) are a diverse class of lipids produced by bacteria across a wide range of environments. In this study, we aim to further identify BHPs related to ecological niches and/or specific bacteria by characterizing the distribution of BHPs in suspended particulate matter (SPM) of the water column and in sediments in a range of lakes and coastal lagoons from the Azores Archipelago, as well as in a co-culture enriched for methanotrophs. Sediment samples from Azorean lakes with low oxygen conditions during the summer months (i.e., Azul, Verde, Funda, and Negra) contain relatively high abundances of BHPs that are typically associated with methane-oxidizing (methanotrophic) bacteria (i.e., aminotetrol, aminopentol, and methylcarbamate-aminopentol), as well as the ethenolamine-BHPs (i.e., ethenolamine-BHpentol and ethenolamine-BHhexol) and the formylated aminoBHPs. Both ethenolamine-BHPs and formylated aminoBHPs were also detected in a co-culture enriched for methanotrophs obtained from a lake. In the SPM of all water columns, bacteriohopanetetrol (BHT), BHT-cyclitol ether, and aminotriol are the dominant BHPs. In SPM from Lake Funda, nucleoside BHPs (i.e., Me-adenosylhopaneHG-diMe, N1-methylinosylhopane, 2Me-N1-inosylhopane, and Me-N1-inosylhopane) are present in low abundance or absent under oxic conditions but increase in concentration near the chemocline, suggesting potential in situ production of these nucleoside BHPs rather than an allochthonous origin. In contrast, sediments from shallow, well-mixed lakes (i.e., Empadadas, São Jorge, and Lomba) contain higher abundances of adenosylhopane and N1-methylinosylhopane, which likely originate from bacteria living in nearby soils. In the coastal lagoons, Cubres East and West, methoxylated-BHTs were detected, and higher abundances of ethenolamine-BHT were observed. This study highlights the diversity of BHPs in lakes and coastal lagoons and their potential as taxonomic markers for bacteria associated with certain ecological niches, which can be preserved in sedimentary records.
Nora Richter et al.
Status: open (until 31 Mar 2023)
- RC1: 'Comment on bg-2023-29', Anonymous Referee #1, 23 Mar 2023 reply
- RC2: 'Comment on bg-2023-29', Juliana Drozd, 23 Mar 2023 reply
Nora Richter et al.
Nora Richter et al.
Viewed (geographical distribution)
The study by Richter et al. describes distributions of BHPs in lacustrine and coastal environments of the Azores. In addition to the environmental samples, an enrichment culture enriched for methanotrophs was also studied. Using LCMS, the authors identified several novel BHPs and report detailed information of their mass spectral identification. The BHP distributions are then discussed in combination with geochemical parameters and the potential as taxonomic markers for different ecological niches is evaluated.
I like the manuscript and think it is well written and structured. The type of figures and the selected statistical methods are chosen well. The detailed identification of the new compounds seems sound and the reported mass spectra in the appendix will be very useful for further research. I am very much looking forward to the final version where the raw data are also accessible. Besides the analytical part, the discussion of the findings in context of previous studies is well balanced and adds important conclusions. Overall, not much should be changed before final publication.
It would be great if the authors could also make the inclusion lists for the analytical method available (see also minor comment). This would help “jump-start” implementation of the LCMS method in other labs.
The appendix is great in explaining in detail how the fragment spectra of the BHPs are used for identification. The main text then only contains a brief mentioning (according to line 212) – this is true for all novel compounds except the formylated-aminoBHPs where lines 262-278 are very similar to section B6 in the appendix. I suggest to shorten the main text version so that it is similar to the summary of findings of the other compounds and keep the details in the appendix B6.
Since there are so many compounds in the NMDS plot of Fig. 4, I wonder if it is possible to use colored font for the compounds clustering together in Fig. 4. For example color A for cluster of amino-containing compounds (referenced in line 323), color B for the nucleoside compounds (line 338) and so on (e.g. in line 466). This should then be indicated in the text (section lines 314-349) and in the caption of Fig. 4.
Section 3.5 (implications for the Rsoil proxy) is not reflected in the abstract and conclusions and should be added.
Minor comments and technical corrections
L67: replace “nor “ with “or”
L154: specify MS model?
L159: resolution does not have unit “ppm”
L159-160: why three separate inclusion lists? Can these lists be provided as supplemental material, other research would benefit a lot from this
L169: how was the normalization between sample runs done? Please explain.
L256: Fig 3e? I might have missed it, but Fig. 3e is not referenced?
L303-305: “Using ANOSIM we find a significant difference…”
Fig. 4: colors are not easy to distinguish (two shades of green, two of blue), choose additional other colors
L311: delete “there is”: “we find no significant difference”
L327: “was previously described”
Fig. 6 caption: RU should be “response units”, not “relative units”
Fig. 9 caption: indicate that structures are tentative structures
L478: instead of “an NMDS” use “the NMDS analysis”. This also reads a bit odd, the NMDS analysis shows many compounds. Do you mean that these compounds, the amino BHP cluster, is close to the sites mentioned in line 482?
L493: suggestion – “observe … in all sediment samples except Cubres East and West (Fig. 2)…”, move outside of parentheses
L538: “BHP distribution”
L603: perhaps “… appear to be produced in the water column…”
Appendix B1 second paragraph last sentence: typo – “…attribute this to a potential co-eluting…are unable to distinguish.”
Appendix B114: m/z 191 was searched in fragment spectra: “…in fragment spectra revealed two…”
Appendix B120: “..is not located in the ring system.”