The genusLimnohabitans(Comamonadaceae,Betaproteobacteria) is a common and a highly active component of freshwater bacterioplanktonic communities. To date, the genus has been considered to contain only heterotrophic species. In this study, we detected the photosynthesis genespufLMandbchYin 28 of 46 strains from threeLimnohabitanslineages. ThepufMsequences obtained are very closely related to environmentalpufMsequences detected in various freshwater habitats, indicating the ubiquity and potential importance of photoheterotrophicLimnohabitansin nature. Additionally, we sequenced and analyzed the genomes of 5 potentially photoheterotrophicLimnohabitansstrains, to gain further insights into their phototrophic capacity. The structure of the photosynthesis gene cluster turned out to be highly conserved within the genusLimnohabitansand also among all potentially photosyntheticBetaproteobacteriastrains. The expression of photosynthetic complexes was detected in a culture ofLimnohabitans planktonicusII-D5Tusing spectroscopic and pigment analyses. This was further verified by a novel combination of infrared microscopy and fluorescentin situhybridization.IMPORTANCEThe data presented document that the capacity to perform anoxygenic photosynthesis is common among the members of the genusLimnohabitans, indicating that they may have a novel role in freshwater habitats.
We investigated changes in quality and quantity of extracellular and biomass-derived organic matter (OM) from three axenic algae (genera Rhodomonas, Chlamydomonas, Coelastrum) during growth of Limnohabitans parvus, Limnohabitans planktonicus and Polynucleobacter acidiphobus representing important clusters of freshwater planktonic Betaproteobacteria. Total extracellular and biomass-derived OM concentrations from each alga were approximately 20 mg l-1and 1 mg l-1respectively, from which up to 9% could be identified as free carbohydrates, polyamines, or free and combined amino acids. Carbohydrates represented 54%-61% of identified compounds of the extracellular OM from each alga. In biomass-derived OM of Rhodomonas and Chlamydomonas 71%-77% were amino acids and polyamines, while in that of Coelastrum 85% were carbohydrates. All bacteria grew on alga-derived OM of Coelastrum, whereas only Limnohabitans strains grew on OM from Rhodomonas and Chlamydomonas. Bacteria consumed 24%-76% and 38%-82% of all identified extracellular and biomass-derived OM compounds respectively, and their consumption was proportional to the concentration of each OM compound in the different treatments. The bacterial biomass yield was higher than the total identifiable OM consumption indicating that bacteria also utilized other unidentified alga-derived OM compounds. Bacteria, however, also produced specific OM compounds suggesting enzymatic polymer degradation or de novo exudation.
- MeSH
- aminokyseliny analýza metabolismus MeSH
- biomasa MeSH
- Burkholderiaceae klasifikace růst a vývoj metabolismus MeSH
- Chlorophyta metabolismus MeSH
- Comamonadaceae klasifikace růst a vývoj metabolismus MeSH
- Cryptophyta metabolismus MeSH
- metabolismus sacharidů fyziologie MeSH
- plankton metabolismus mikrobiologie MeSH
- polyaminy analýza metabolismus MeSH
- sacharidy analýza MeSH
- sladká voda mikrobiologie MeSH
- Publikační typ
- časopisecké články MeSH
We examined the effect of light on the heterotrophic activity of the filamentous cyanobacterium Planktothrix rubescens and on its relationship with the accompanying bacteria. In situ leucine uptake by bacteria and cyanobacteria was determined in a subalpine mesotrophic lake, and natural assemblages from the zone of maximal P. rubescens abundances were incubated for 2 days at contrasting light regimes (ambient, 100× increased, dark). Planktothrix rubescens from the photic zone of the lake incorporated substantially more leucine, but some heterotrophic activity was maintained in filaments from the hypolimnion. Exposure of cyanobacteria to increased irradiance or darkness resulted in significantly lower leucine incorporation than at ambient light conditions. Highest abundances and leucine uptake of Betaproteobacteria from the genus Limnohabitans were found in the accompanying microflora at suboptimal irradiance levels for P. rubescens or in dark incubations. Therefore, two Limnohabitans strains (representing different species) were co-cultured with axenic P. rubescens at different light conditions. The abundances and leucine incorporation rates of both strains most strongly increased at elevated irradiance levels, in parallel to a decrease of photosynthetic pigment fluorescence and the fragmentation of cyanobacterial filaments. Our results suggest that Limnohabitans spp. in lakes might profit from the presence of physiologically stressed P. rubescens.
- MeSH
- Comamonadaceae metabolismus fyziologie MeSH
- fotosyntéza fyziologie MeSH
- heterotrofní procesy MeSH
- jezera mikrobiologie MeSH
- leucin metabolismus MeSH
- mikrobiologie vody MeSH
- sinice metabolismus fyziologie MeSH
- světlo MeSH
- tma MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
