Leucine-to-carbon empirical conversion factor experiments: does bacterial community structure have an influence?

Area of Science:

• Marine microbiology
• Bacteriology
• Biogeochemical cycling

Background:

• Empirical conversion factors (eCFs) are used to estimate bacterial biomass production.
• The accuracy of eCFs is questionable in seawater cultures due to dominance by non-native phylotypes.
• Drivers of eCF variability, such as community composition versus environmental factors, are not well understood.

Purpose of the Study:

• To investigate the relationship between bacterial community structure and eCFs in seawater cultures over a year.
• To determine if changes in eCFs are driven by bacterial community composition or in situ environmental conditions.

Main Methods:

• Year-long seawater cultures were maintained.
• Bacterial community structure was analyzed using catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH).
• Correlations between eCFs and the abundance of major bacterial phylogenetic groups were assessed.

Main Results:

• Gammaproteobacteria dominated cultures, increasing with nutrient enrichment.
• Flavobacteria abundance increased in winter cultures with high chlorophyll a.
• Weak but significant correlations were found between eCFs and broad phylogenetic groups (Gamma-, Alpha-, Flavobacteria).
• Specific groups (Alteromonadaceae, Rhodobacteraceae) showed no significant correlation with eCFs.

Conclusions:

• The rapid growth of Alteromonadaceae in cultures does not strongly influence eCF variations.
• Environmental conditions and the growth of specific bacterial phylotypes interact to shape eCFs.
• eCFs in seawater cultures are influenced by a complex interplay of environmental factors and microbial community dynamics.