Metalimnetic chlorophyll maxima in Lake Kinneret - Chlorobium revisited

1. A deep chlorophyll maxima (DCM) of the green sulfur bacterium Chlorobium phaeobacteroides was previously reported as a dense population in the oxygen devoid layers of Lake Kinneret, Israel. 2. In this study, we examined the vertical distribution and diversity of the DCM photosynthetic community and characterized it spectrally and genetically, over two consecutive years. 3. Pigment composition, together with 16S rDNA sequencing data unveil the presence of more than a single Chlorobium species as dominant members of the DCM community. Altogether five different Chlorobia genotypes were identified, four of which occurred in both of the studied years. Chlorobia genotypes composing the DCM appear at a similar relative rate in two consecutive years, despite the fact that timing and intensity of the DCM were different. Phylogenetic analysis places the dominant genotype in the same clade as C. phaeobacteroides, suggesting that it contributes the majority of the bacteriochlorophyll e found in the DCM of the lake.4. Hierarchical clustering analysis demonstrates that dissolved oxygen concentration is a strong predictor for the distribution of all Chlorobia genotypes found in Lake Kinneret. Furthermore, this analysis suggests that competition likely exists between the various Chlorobia genotypes and proposes that C. phaeobacteroides is better equipped to cope with the conditions prevailing in Lake Kinneret metalimnion.