Short-term effects of temperature on the abundance and diversity of magnetotactic cocci

Renaissance for magnetotactic bacteria in astrobiology

Capable of forming magnetofossils similar to some magnetite nanocrystals observed in the Martian meteorite ALH84001, magnetotactic bacteria (MTB) once occupied a special position in the field of astrobiology during the 1990s and 2000s. This flourish of interest in putative Martian magnetofossils faded from all but the experts studying magnetosome formation, based on claims that abiotic processes could produce magnetosome-like magnetite crystals. Recently, the rapid growth in our knowledge of the extreme environments in which MTB thrive and their phylogenic heritage, leads us to advocate for a renaissance of MTB in astrobiology. In recent decades, magnetotactic members have been discovered alive in natural extreme environments with wide ranges of salinity (up to 90 g L-1), pH (1-10), and temperature (0-70 °C). Additionally, some MTB populations are found to be able to survive irradiated, desiccated, metal-rich, hypomagnetic, or microgravity conditions, and are capable of utilizing simple inorganic compounds such as sulfate and nitrate. Moreover, MTB likely emerged quite early in Earth's history, coinciding with a period when the Martian surface was covered with liquid water as well as a strong magnetic field. MTB are commonly discovered in suboxic or oxic-anoxic interfaces in aquatic environments or sediments similar to ancient crater lakes on Mars, such as Gale crater and Jezero crater. Taken together, MTB can be exemplary model microorganisms in astrobiology research, and putative ancient Martian life, if it ever occurred, could plausibly have included magnetotactic microorganisms. Furthermore, we summarize multiple typical biosignatures that can be applied for the detection of ancient MTB on Earth and extraterrestrial MTB-like life. We suggest transporting MTB to space stations and simulation chambers to further investigate their tolerance potential and distinctive biosignatures to aid in understanding the evolutionary history of MTB and the potential of magnetofossils as an extraterrestrial biomarker.

Patterns of Structural and Functional Bacterioplankton Metacommunity along a River under Anthropogenic Pressure

Bacteria, an integral part of aquatic ecosystems, are responsible for the circulation of matter and flow of energy. Since bacterioplankton rapidly responds to any natural and human-induced disturbances in the environment, it can serve as a bioindicator of these changes. Knowing factors that shape the microbial community structure may help the sustainable management of the water environment. However, the identification of environmental signals affecting the structure and function of bacterioplankton is still a challenge. The study analyses the impact of environmental variables on basic microbial parameters, which determines the effectiveness of ecological processes in rivers. Measurements of bacterioplankton abundance (BA) and extracellular enzyme activity (EEA) were based on fluorescent markers. The bacterial community structure was determined by 16S rRNA gene amplicon sequencing (Illumina). The results indicate spatial variation in bacterioplankton abundance. Temporal variation was not significant. Lipase and aminopeptidase had the highest level of activity. EEA was not correlated with bacterial abundance but was significantly correlated with temperature. Moreover, differences in lipase, α-glucosidase and β-glucosidase activity levels between spring and summer were noted. At the same time, the location of sampling site had a significant influence on aminopeptidase activity. The taxonomic analysis of bacterioplankton communities in the Brda River indicated that, although different numbers of OTUs were recorded in the studied river sections, bacterioplankton biodiversity did not change significantly along the river with distance downstream. Anthropogenically modified river sections were characterized by the dominance of Flavobacterium (Bacterioidetes) and hgcl clade (Actinobacteria) taxa, known for their ability to produce extracellular enzymes. PCoA analysis revealed that the sites located in the lower river course (urban area) had the most similar bacterial community structure (β-diversity). The study provides new insight into the changes in microbial communities along the river and emphasizes the potential impact of anthropogenization on these processes.

Yield cultivation of magnetotactic bacteria and magnetosomes: A review

Magnetotactic bacteria (MTB) have started to be employed for the biosynthesis of magnetic nanoparticles, due to the rapidly increasing demand for nanoparticles in biomedical, biotechnology and environmental protection. MBT are the group of prokaryotes that have the ability to produce bio-magnetic minerals or bio-magnetic crystals of either magnetite (Fe₃ O₄ ) or greigite (Fe₃ S₄ ) in numerous shapes and size ranges, known as magnetosomes (MS). MS compel MTB to respond to the applied external magnetic field. However, it is extremely difficult to grow MTB and produce high yield of MS under artificial environmental conditions, thus creating a major hurdle to relocate MTB technology from laboratory scale to industrial or commercial level. Therefore, to best of our knowledge this review is the first attempt to highlight existing research developments about the laboratory scale and mass production of MS by MTB. Moreover, the optimum culture media and environmental conditions used for the cultivation of MTB were also considered. Finally, future research is encouraged for the improvement of MS yield which will result in the development of advanced nanotechnology/magnetotechnology.

Isolation and characterization of Magnetospirillum from saline lagoon

Magnetotactic bacteria (MTB) are aquatic prokaryotes that orient themselves to earth's magnetic field with the help of intracellular organelle magnetosomes. Although many species of MTB have been identified, the isolation of MTB is a challenging task due to the lack of systematic isolation procedure and/or commercial media. In this study, we are reporting the isolation of magnetotactic spirillum from the Pulicat lagoon, India using a systematic and selective procedure. Sampling site was chosen on the basis of physicochemical properties of the ecosystem and the catalysed reporter deposition fluorescence in situ hybridization (CARD-FISH) analysis of sediment samples. In the current study, a combination of techniques including 'capillary racetrack' Purification and gradient cultivation resulted in the isolation of magnetotactic spirilla from aquatic sediments. Based on the 16S rRNA gene sequence analysis, the strain was identified as Magnetospirillum and was designated as Magnetospirillum sp. VITRJS1. The genes responsible for magnetosome formation (mamA, B, E, F, K, M, O, P, Q, T) were successfully detected using PCR amplification. The presence of cbbM gene confirmed that the isolate is chemolithoautotroph and utilises reduced sulphur as an electron source. Furthermore, magnetosomes extracted from VITRJS1 found to be cubo-octahedral in shape and 45 nm in size. Our results indicate that the systematic procedure using sediment analysis, CARD-FISH, and a combination of isolation methods enables the selective and rapid isolation of MTB from aquatic sediment sample.

Integrating niche-based process and spatial process in biogeography of magnetotactic bacteria

Microorganisms play key roles in biogeochemical and nutrient cycling in all ecosystems on Earth, yet little is known about the processes controlling their biogeographic distributions. Here we report an investigation of magnetotactic bacteria (MTB) designed to evaluate the roles of niche-based process and spatial process in explaining variation in bacterial communities across large spatial scales. Our results show that both environmental heterogeneity and geographic distance play significant roles in shaping dominant populations of MTB community composition. At the spatial scale in this study, the biogeography of MTB is relatively more influenced by environmental factors than geographic distance, suggesting that local conditions override the effects of dispersal history on structuring MTB community. Of note, we found that the strength of geomagnetic field may influence the biogeography of MTB. We argue that MTB have the potential to serve as a model group to uncover the underlying processes that influence microbial biogeography.

Paleomagnetic and paleoenvironmental implications of magnetofossil occurrences in late Miocene marine sediments from the Guadalquivir Basin, SW Spain

Although recent studies have revealed more widespread occurrences of magnetofossils in pre-Quaternary sediments than have been previously reported, their significance for paleomagnetic and paleoenvironmental studies is not fully understood. We present a paleo- and rock-magnetic study of late Miocene marine sediments recovered from the Guadalquivir Basin (SW Spain). Well-defined paleomagnetic directions provide a robust magnetostratigraphic chronology for the two studied sediment cores. Rock magnetic results indicate the dominance of intact magnetosome chains throughout the studied sediments. These results provide a link between the highest-quality paleomagnetic directions and higher magnetofossil abundances. We interpret that bacterial magnetite formed in the surface sediment mixed layer and that these magnetic particles gave rise to a paleomagnetic signal in the same way as detrital grains. They, therefore, carry a magnetization that is essentially identical to a post-depositional remanent magnetization, which we term a bio-depositional remanent magnetization. Some studied polarity reversals record paleomagnetic directions with an apparent 60–70 kyr recording delay. Magnetofossils in these cases are interpreted to carry a biogeochemical remanent magnetization that is locked in at greater depth in the sediment column. A sharp decrease in magnetofossil abundance toward the middle of the studied boreholes coincides broadly with a major rise in sediment accumulation rates near the onset of the Messinian salinity crisis (MSC), an event caused by interruption of the connection between the Mediterranean Sea and the Atlantic Ocean. This correlation appears to have resulted from dilution of magnetofossils by enhanced terrigenous inputs that were driven, in turn, by sedimentary changes triggered in the basin at the onset of the MSC. Our results highlight the importance of magnetofossils as carriers of high-quality paleomagnetic and paleoenvironmental signals even in dominantly terrigenous sediments.

Life with compass: diversity and biogeography of magnetotactic bacteria

Magnetotactic bacteria (MTB) are unique in their ability to synthesize intracellular nano-sized minerals of magnetite and/or greigite magnetosomes for magnetic orientation. Thus, they provide an excellent model system to investigate mechanisms of biomineralization. MTB play important roles in bulk sedimentary magnetism and have numerous versatile applications in paleoenvironmental reconstructions, and biotechnological and biomedical fields. Significant progress has been made in recent years in describing the composition of MTB communities and distribution through innovative cultivation-dependent and -independent techniques. In this review, the most recent contributions to the field of diversity and biogeography of MTB are summarized and reviewed. Emphasis is on the novel insights into various factors/processes potentially affecting MTB community distribution. An understanding of the present-day biogeography of MTB, and the ruling parameters of their spatial distribution, will eventually help us predict MTB community shifts with environmental changes and assess their roles in global iron cycling.