Cell adhesion, multicellular morphology, and magnetosome distribution in the multicellular magnetotactic prokaryote Candidatus Magnetoglobus multicellularis.

Candidatus Magnetoglobus multicellularis is an uncultured magnetotactic multicellular prokaryote composed of 17-40 Gram-negative cells that are capable of synthesizing organelles known as magnetosomes. The magnetosomes of Ca. M. multicellularis are composed of greigite and are organized in chains that are responsible for the microorganism's orientation along magnetic field lines. The characteristics of the microorganism, including its multicellular life cycle, magnetic field orientation, and swimming behavior, and the lack of viability of individual cells detached from the whole assembly, are considered strong evidence for the existence of a unique multicellular life cycle among prokaryotes. It has been proposed that the position of each cell within the aggregate is fundamental for the maintenance of its distinctive morphology and magnetic field orientation. However, the cellular organization of the whole organism has never been studied in detail. Here, we investigated the magnetosome organization within a cell, its distribution within the microorganism, and the intercellular relationships that might be responsible for maintaining the cells in the proper position within the microorganism, which is essential for determining the magnetic properties of Ca. M. multicellularis during its life cycle. The results indicate that cellular interactions are essential for the determination of individual cell shape and the magnetic properties of the organism and are likely directly associated with the morphological changes that occur during the multicellular life cycle of this species.

Occurrence and diversity of viruses associated with cyanobacterial communities in a Brazilian freshwater reservoir.

As part of the phytoplankton of marine and freshwater environments around the world, cyanobacteria interact with viruses (cyanophages) that affect their abundance and diversity. Investigations focusing on cyanophages co-occurring with freshwater cyanobacteria are scarce, particularly in Brazil. The aim of this study was to assess the diversity of cyanophages associated with a Microcystis-dominated cyanobacterial bloom in a tropical reservoir. Samples were processed as viral fractions of water and cellular fractions, and temporal fluctuations in the abundance of Ma-LMM01-type cyanophages and their Microcystis hosts were determined by qPCR. We applied shotgun metagenomics to obtain a wider characterization of the cyanophage community. During the study period, Microcystis gene copies were quantified in all cellular fractions, and the copy number of the Ma-LMM01 phage gene tended to increase with host abundance. Metagenomic analysis demonstrated that Caudovirales was the major viral order associated with the cyanophage families Myoviridae (34-88%), Podoviridae (3-42%), and Siphoviridae (6-23%). The metagenomic analysis results confirmed the presence of Microcystis cyanophages in both viral and cellular fractions and demonstrated a high relative abundance of picocyanobacteria-related viruses and Prochlorococcus (36-52%) and Synechococcus (37-50%) phages. For other main cyanobacterial genera, no related cyanophages were identified, which was probably due to the scarce representation of cyanophage sequences in databanks. Thus, the studied reservoir hosted a diverse cyanophage community with a remarkable contribution of phages related to picoplanktonic cyanobacteria. These results provide insights that motivate future sequencing efforts to assess cyanophage diversity and recover complete genomes.

The reductive glycine pathway allows autotrophic growth of Desulfovibrio desulfuricans.

Six CO2 fixation pathways are known to operate in photoautotrophic and chemoautotrophic microorganisms. Here, we describe chemolithoautotrophic growth of the sulphate-reducing bacterium Desulfovibrio desulfuricans (strain G11) with hydrogen and sulphate as energy substrates. Genomic, transcriptomic, proteomic and metabolomic analyses reveal that D. desulfuricans assimilates CO2 via the reductive glycine pathway, a seventh CO2 fixation pathway. In this pathway, CO2 is first reduced to formate, which is reduced and condensed with a second CO2 to generate glycine. Glycine is further reduced in D. desulfuricans by glycine reductase to acetyl-P, and then to acetyl-CoA, which is condensed with another CO2 to form pyruvate. Ammonia is involved in the operation of the pathway, which is reflected in the dependence of the autotrophic growth rate on the ammonia concentration. Our study demonstrates microbial autotrophic growth fully supported by this highly ATP-efficient CO2 fixation pathway.

Intraspecific variability in response to phosphorus depleted conditions in the cyanobacteria Microcystis aeruginosa and Raphidiopsis raciborskii.

Phosphorus loading plays an important role in the occurrence of cyanobacterial blooms and understanding how this nutrient affects the physiology of cyanobacteria is imperative to manage these phenomena. Microcystis aeruginosa and Raphidiopsis raciborskii are cyanobacterial species that form potentially toxic blooms in freshwater ecosystems worldwide. Blooms comprise numerous strains with high trait variability, which can contribute to the widespread distribution of these species. Here, we explored the intraspecific variability in response to phosphorus depleted conditions (P-) testing five strains of each species. Strains could be differentiated by cell volume or genetic profiles except for those of the same species, sampling location and date, though these presented differences in their response to (P-). Although differently affected by (P-) over 10 days, all strains were able to grow and maintain photosynthetic activity. For most M. aeruginosa and R. raciborskii strains growth rates were not significantly different comparing (P+) and (P-) conditions. After ten days in (P-), only one M. aeruginosa strain and two R. raciborskii strains showed reduction in biovolume yield as compared to (P+) but in most strains chlorophyll-a concentrations were lower in (P-) than in (P+). Reduced photosystem II efficiency was found for only one R. raciborskii strain while all M. aeruginosa strains were affected. Only two M. aeruginosa and one R. raciborskii strain increased alkaline phosphatase activity under (P-) as compared to (P+). Variation in P-uptake was also observed but comparison among strains yielded homogeneous groups comprised of representatives of both species. Comparing the response of each species as a whole, the (P-) condition affected growth rate, biovolume yield and chlorophyll yield. However, these parameters revealed variation among strains of the same species to the extent that differences between M. aeruginosa and R. raciborskii were not significant. Taken together, these results do not support the idea that R. raciborskii, as a species, can withstand phosphorus limitation better than M. aeruginosa and also point that the level of intraspecific variation may preclude generalizations based on studies that use only one or few strains.

Draft Genome Sequences of Two Brazilian Cyanobacterial Strains of Cylindrospermopsis raciborskii: Differences in Membrane Transporters, Saxitoxin Production, and Antioxidant Activities.

We report here the draft genome sequences of two Brazilian strains of Cylindrospermopsis raciborskii, a saxitoxin-producer (CYRF) and a non-saxitoxin producer (CYLP), with each strain comprising one assembled scaffold. We revealed differences in the compositions of gene members coding for membrane transporters and antioxidant activities between the strains.

Chitosan as coagulant on cyanobacteria in lake restoration management may cause rapid cell lysis.

Combining coagulant and ballast to remove cyanobacteria from the water column is a promising restoration technique to mitigate cyanobacterial nuisance in surface waters. The organic, biodegradable polymer chitosan has been promoted as a coagulant and is viewed as non-toxic. In this study, we show that chitosan may rapidly compromise membrane integrity and kill certain cyanobacteria leading to release of cell contents in the water. A strain of Cylindrospermopsis raciborskii and one strain of Planktothrix agardhii were most sensitive. A 1.3 h exposure to a low dose of 0.5 mg l-1 chitosan already almost completely killed these cultures resulting in release of cell contents. After 24 h, reductions in PSII efficiencies of all cyanobacteria tested were observed. EC50 values varied from around 0.5 mg l-1 chitosan for the two sensitive strains, via about 5 mg l-1 chitosan for an Aphanizomenon flos-aquae strain, a toxic P. agardhii strain and two Anabaena cylindrica cultures, to more than 8 mg l-1 chitosan for a Microcystis aeruginosa strain and another A. flos-aquae strain. Differences in sensitivity to chitosan might be related to polymeric substances that surround cyanobacteria. Rapid lysis of toxic strains is likely and when chitosan flocking and sinking of cyanobacteria is considered in lake restoration, flocculation efficacy studies should be complemented with investigation on the effects of chitosan on the cyanobacteria assemblage being targeted.

Lipase production and Penicillium simplicissimum morphology in solid-state and submerged fermentations.

A comparative study of Penicillium simplicissimum morphology and lipase production was performed using solid-state (SSF) and submerged (SmF) fermentation. SSF was carried out on babassu cake as culture medium and SmF on a semi-synthetic medium and a medium based on suspended babassu cake grains. Yield of product on biomass, specific activity and conidia production were 3.3-, 1.3- and 2-fold higher in SSF. In SmF, the type of fungus growth differed according to the medium. Using the semi-synthetic medium, the fungus formed densely interwoven mycelial masses without conidia production, whereas using the babassu-based medium the fungus formed free mycelia and adhered to the surfaces of the grains, producing conidia. The results show that babassu cake induces conidiation in SmF. In SSF, the fungus not only grew on the surface of the grains, producing conidia abundantly, but also effectively colonized and penetrated the babassu particles. The high conidia production and lipase productivity in SSF may be related to the low availability of nutrients or to other stimuli associated with this type of fermentation. Thus, the high production of the thermostable P. simplicissimum lipase, using a non-supplemented, low-cost agro-industrial residue as the culture medium, demonstrates the biotechnological potential of SSF for the production of industrial enzymes.