Cocultivated bacteria can increase or decrease the culture lifetime of Chlorella vulgaris

Exchange or Eliminate: The Secrets of Algal-Bacterial Relationships

Algae and bacteria have co-occurred and coevolved in common habitats for hundreds of millions of years, fostering specific associations and interactions such as mutualism or antagonism. These interactions are shaped through exchanges of primary and secondary metabolites provided by one of the partners. Metabolites, such as N-sources or vitamins, can be beneficial to the partner and they may be assimilated through chemotaxis towards the partner producing these metabolites. Other metabolites, especially many natural products synthesized by bacteria, can act as toxins and damage or kill the partner. For instance, the green microalga Chlamydomonas reinhardtii establishes a mutualistic partnership with a Methylobacterium, in stark contrast to its antagonistic relationship with the toxin producing Pseudomonas protegens. In other cases, as with a coccolithophore haptophyte alga and a Phaeobacter bacterium, the same alga and bacterium can even be subject to both processes, depending on the secreted bacterial and algal metabolites. Some bacteria also influence algal morphology by producing specific metabolites and micronutrients, as is observed in some macroalgae. This review focuses on algal-bacterial interactions with micro- and macroalgal models from marine, freshwater, and terrestrial environments and summarizes the advances in the field. It also highlights the effects of temperature on these interactions as it is presently known.

Different co-occurring bacteria enhance or decrease the growth of the microalga Nannochloropsis sp. CCAP211/78

Marine photosynthetic microalgae are ubiquitously associated with bacteria in nature. However, the influence of these bacteria on algal cultures in bioreactors is still largely unknown. In this study, eighteen different bacterial strains were isolated from cultures of Nannochloropsis sp. CCAP211/78 in two outdoor pilot-scale tubular photobioreactors. The majority of isolates was affiliated with the classes Alphaproteobacteria and Flavobacteriia. To assess the impact of the eighteen strains on the growth of Nannochloropsis sp. CCAP211/78, 24-well plates coupled with custom-made LED boxes were used to simultaneously compare replicate axenic microalgal cultures with addition of individual bacterial isolates. Co-culturing of Nannochloropsis sp. CCAP211/78 with these strains demonstrated distinct responses, which shows that the technique we developed is an efficient method for screening the influence of harmful/beneficial bacteria. Two of the tested strains, namely a strain of Maritalea porphyrae (DMSP31) and a Labrenzia aggregata strain (YP26), significantly enhanced microalgal growth with a 14% and 12% increase of the chlorophyll concentration, respectively, whereas flavobacterial strain YP206 greatly inhibited the growth of the microalga with 28% reduction of the chlorophyll concentration. Our study suggests that algal production systems represent a 'natural' source to isolate and study microorganisms that can either benefit or harm algal cultures.

Identification and comparison of the 3 early stages of resynthesis for the lichen Cladonia rangiferina

A lichen is an association between a biotrophic fungal partner and a green algal and (or) cyanobacterial partner, which may be considered a "controlled" parasitic interaction. While controlled parasitism implies benefit to both interacting partners, a parasitism that is not controlled implies that one partner benefits to the detriment of the other partner. The objective of this study was to compare morphological development of the interaction between Cladonia rangiferina with its compatible algal partner (Asterochloris glomerata/irregularis) and incompatible algae (Coccomyxa peltigerae and Chloroidium ellipsoideum) at 3 early resynthesis stages. The fungus was co-inoculated with each alga separately and the stages of development were compared using quantitative measures. The first 3 stages of development of the lichen thallus were identified in the compatible interaction as the "pre-contact" stage (1 day post co-inoculation (PCI)), "contact" stage (8 days PCI), and "growth together" stage (21 days PCI). Compatible interactions showed significantly shorter internode length, significantly more new lateral hyphal branches, significantly greater appressorial frequency, and no reduction in cell diameter of the algal cells, compared with incompatible interactions. At 21 days PCI, a parasitic interaction was observed between Cladonia rangiferina and Chloroidium ellipsoideum. These findings support the importance of recognition between compatible partners for successful lichenization. This study also revealed a strategy that may explain the success of this species in northern habitats. Identification of the resynthesis stages of Cladonia rangiferina is required before expression of the proteins involved in recognition and defense can be understood.

Brevifollis gellanilyticus gen. nov., sp. nov., a gellan-gum-degrading bacterium of the phylum Verrucomicrobia

The taxonomic properties of strain DC2c-G4T, a Gram-staining-negative, ovoid, gellan-gum-degrading bacterial isolate, were examined. Phylogenetic analysis based on 16S rRNA gene sequences identified this isolate as a member of the phylum Verrucomicrobia and closest to the genus Prosthecobacter . The 16S rRNA gene sequence similarities between this isolate and any of the type strains of species of the genus Prosthecobacter were less than 95 %. In addition, the absence of a single prostheca and the predominant menaquinone MK-7(H2) supported the differentiation of this isolate from the genus Prosthecobacter . Here, we propose Brevifollis gellanilyticus gen. nov., sp. nov. to accommodate the isolate. The type strain of the type species is DC2c-G4T ( = NBRC 108608T = CIP 110457T).

Roseimicrobium gellanilyticum gen. nov., sp. nov., a new member of the class Verrucomicrobiae

The taxonomic properties of strain DC2a-G7T, a Gram-negative, ovoid to rod-shaped, gellan gum-lysing bacterium, were examined. The 16S rRNA gene sequence similarity showed that DC2a-G7T is a member of the phylum Verrucomicrobia and the closest type strain of a species with a validly published name is Verrucomicrobium spinosum DSM 4136T, with a sequence similarity of 91.2 %. In addition to this similarity value lower than 95 %, the absence of prostheca, the orangey-red colony colour and the compositions of the major menaquinones and polar lipids also supported the differentiation of this bacterium from the genus Verrucomicrobium . Here, we propose the name Roseimicrobium gellanilyticum gen. nov., sp. nov. for the isolate. The type strain of Roseimicrobium gellanilyticum is DC2a-G7T ( = NBRC 108606T = DSM 25532T).

Identification and phylogenetic characterization of cobalamin biosynthetic genes of Ensifer adhaerens

Ensifer adhaerens CSBa was screened as a cobalamin producer. The draft genome sequence revealed that the strain possesses 22 cobalamin biosynthetic genes (cob genes). The cob gene arrangement on the genome of E. adhaerens CSBa was similar to that of other Ensifer species, and most similar to that of Pseudomonas denitrificans SC510. The cobN sequence phylogeny was generally congruent with that of the 16S rRNA gene, and it is suggeted that E. adhaerens CSBa might have inherited the cob genes from common ancestors of the Ensifer species. It was also suggested that the cob genes can be laterally transferred.