7th joint conference "Joint Microbiology & Infection Conference 2024" of the DGHM and VAAM

Chair

Prof. Dr.

Cell shape modification as novel buoyancy control mechanism of marine Roseobacter bacteria

Environmental Microbiology & Processes

The Roseobacter group (class Alphaproteobacteria)- accounts for up to 25% of the bacterial community in marine habitats. Members of this group are physiologically versatile, which can be regarded as prerequisite for an adaptation to different ecological niches. In a constantly changing environment, they can exploit transient nutrient pulses and thereby successfully compete against microorganisms inhabiting the same habitat. Morphological heterogeneity is another common trait in the Roseobacter group. Morphotypes range from rod- shaped single cells of variable length to multicellular rosettes and filaments. For Dinoroseobacter shibae it has been shown that cell elongation is regulated by quorum sensing[1].Here, we present evidence that for Phaeobacter inhibens DSM 17395, a common model organism of the Roseobacter group and successful colonizer of marine surfaces, there are triggers for cell elongation- decoupled from studied quorum sensing mechanisms. Using time-lapse microscopy experiments and quantitative image analysis we show that P. inhibens undergoes morphological changes in response to the presence of yeast and algal extracts. We demonstrate that the longitudinal cell elongation increases the buoyancy of the bacterial cells. The phenotype was still observed for a P. inhibens mutant strains devoid of the cell cycle ranscriptional regulator gene ctrA. Removing the eukaryotic trigger by medium exchange results in an immediate reinitiation of cell division and reversal of the elongated cell morphotype back to rod- shaped single cells and rosettes. We hypothesize that P. inhibens uses cell shape modifications to control buoyancy in a nutrient-rich zone and to enlargen the surface are for attachment.[1] D. Patzelt, H. Wang, I. Buchholz, M. Rohde, L. Gröbe, S. Pradella, A. Neumann, S. Schulz, S. Heyber, K. Münch, R. Münch, D. Jahn, I. Wagner-Döbler, J. Tomasch, You are what you talk: quorum sensing induces individual morphologies and cell division modes in Dinoroseobacter shibae, The ISME Journal, 7 (2013) 2274-2286.

Oral Presentation

(Pan)genomic analysis of two Rhodococcus isolates and their role in phenolic compound degradation

Introduction: Members of the genus Rhodococcus are known for their ability to degrade a wide range of aromatic compounds such as phenolic exudates from plants. They have a high potential to adapt to different habitats due to their linear plasmids and large genome size.Goals and Methods: We used comparative genomics to investigate the genomic properties of two newly described Rhodococcus strains (R. pseudokoreensis R79T and R. koreensis R85) isolated from apple rhizosphere and compared their traits to other members of the genus. Of particular interest was their ability to degrade phenolic substances as part of a multidisciplinary approach to mitigate apple replant disease (ARD).Results: The pan-genome of 109 high-quality Rhodococcus genomes was open with a small core (1.3 %), consisting of genes responsible for basic cell functions. The range of genome sizes was immense (3.7 Mbp to 10.9 Mbp). Genomes of strains associated with hosts were generally smaller than those of environmental isolates, that displayed exceptionally large genome sizes. Due to the large genomic differences, we support taxonomic reclassification of certain rhodococci to new genera. Furthermore, we found several strains to be taxonomically incorrectly assigned or being probably undescribed species. Taxonomic affiliation was the most important factor in predicting the genetic content and clustering of the genomes. In addition, we found genes that differentiated between strains based on habitat. This could potentially be used for targeted isolation and screening for desired traits. All members of the genus Rhodococcus had at least one gene involved in benzoate degradation, whereas biphenyl degradation was mainly restricted to strains closely phylogenetically related to our isolates.Summary: The genomic features displayed by our isolates suggest a potential application in the reduction of phenolic exudates of plants in soil. The approximately 40% of genes that remain unclassified in larger Rhodococcus genomes, particularly those from environmental isolates, require further investigation to explore the metabolic potential of this genus.

Professor

Elucidating the upper pathway in anaerobic phenanthrene degradation

Polycyclic aromatic hydrocarbons (PAHs) threaten human lives since they are carcinogenic. They are widely distributed in the environment and oil. However, oxygen is rapidly depleted in water-saturated sediments containing PAHs, making anaerobic microorganisms responsible for biodegradation. So far, only the anaerobic degradation pathway of naphthalene as a model compound has been studied in more detail but the anaerobic degradation of larger PAHs such as phenanthrene is still unknown.The anaerobic degradation of phenanthrene starts with the activation of the compound via carboxylation yielding 2-phenanthroic acid. An aryl-CoA ligase was confirmed to be responsible of the subsequent conversion of the produced 2-phenanthroic acid to 2-phenanthroyl-CoA.Here, we studied putative following reduction reactions targeting the aromatic rings of phenanthrene to overcome the high resonance energy. We elucidated the function of four newly identified type III aryl-CoA reductases from the TRIP1 enrichment culture involved in anaerobic phenanthrene degradation. The corresponding genes were heterologously expressed in Escherichia coli, the enzymes purified, and their catalytic activity toward 2-phenanthroyl-CoA was confirmed by Liquid Chromatography–Mass Spectrometry and UV-vis spectroscopy. The oxygen-sensitive, ATP-independent enzymes reduced 2-phenanthroyl-CoA to decahydro-2-phenanthroyl-CoA with dithionite-reduced methyl viologen as electron donor. The reactions occurred in consecutive two-electron reduction steps each catalyzed by one enzyme. The four enzymes together could also reduce the last benzyl-ring of the former phenantroyl-CoA, which is thermodynamically very challenging. The four enzymes belong to the old yellow enzyme family, which contain the flavin cofactors flavin mononucleotide and flavin adenine dinucleotide. Iron content analysis and structural homology modeling confirmed that the four enzymes contain an iron-sulfur cluster which mediates electron transfer. In conclusion, we demonstrated that the ATP-independent NADH-Flavin oxidoreductases are responsible for phenanthrene ring reduction and belong to the recently discovered type III aryl-CoA reductases.

Harnessing the potential of microbes: Identification and implementation of a new Pseudomonas strain for use in the field of industrial precious metal recycling

The challenges posed by climate change and the scarcity of resources call for new, sustainable production processes. In the field of precious metal recovery, research into the use of cyanogenic microorganisms has been ongoing for decades, however, without reaching sufficient technical maturity. At BRAIN Biotech, we have isolated a novel Pseudomonas strain (Pseudomonas metallosolvens) that exhibits particularly high metal tolerance, robustness and productivity in biocyanide synthesis, while being BSL-1 classified. This allows it to be used in industrial processes for the extraction of precious metals. Employing design of experiment (DOE) approaches, both the cultivation and extraction conditions for precious metals were optimized and a storage-stable formulation of the cells was developed for use as industrial starter cultures in dedicated recycling processes. Targeted bioprocess development has made it possible to scale up biocyanidation from laboratory scale to pilot scale (2 x 750 L) and to implement processing of gold-bearing ashes with promising results. Various influencing variables were taken into account, ranging from composition and physico-chemical accessibility of precious metals in different material classes to biologically relevant parameters such as oxygen transfer rate, pH, temperature and the effect of shear forces. Thanks to the interdisciplinary collaboration between chemists, microbiologists and process engineers, it was possible to scale up this complex process of biocyanidation to a relevant scale and to set up a mobile pilot demonstrator for further process development.

Bioleaching of nickel and cobalt from laterite ores in Brazil: A reactor-based approach

Laterite ore deposits in Brazil and other tropical countries house substantial nickel and cobalt resources, as well as other vital raw materials. Traditional methods for extracting nickel and cobalt, such as pyrometallurgy or high-pressure acid leaching, come with significant downsides, including high energy usage, reagent expenses, and the necessity for costly equipment. To tackle these challenges, the German-Brazilian project BioProLat aims for an integrated, low-energy, and environmentally friendly biohydrometallurgical process for extracting metals from Brazilian laterite ores.The process involves harnessing acidophilic bacteria that use sulfur as an electron donor, linking sulfur oxidation to the reduction of ferric iron. This transformative mechanism converts insoluble metal compounds into water-soluble forms. Consequently, sulfuric acid is produced, creating the essential acidic conditions to maintain the solubility of iron and other metals. Laboratory-scale bioreactor experiments were done with varying parameters such as pH, temperature, and the selection of a suitable bacterial consortium for optimal bioleaching of nickel and cobalt. Notably, aerobic bioleaching of laterite with a consortium of Acidithiobacillus thiooxidans strains achieved a maximal extraction of 85% cobalt and 85 % nickel from a laterite ore sample. Comprehensive mineralogical and geochemical analyses were conducted to identify mineral phases susceptible to bioleaching and estimate the proportions of cobalt and nickel released from various mineral phases. The overarching objective is to upscale the optimized process, transforming untapped ores and limonite stockpiles into valuable resources while unlocking new reserves of raw materials through enhanced metal recovery from existing mines, including economic and environmental evaluation.

Prof.Dr.

Use of microorganisms in peat-free and peat-reduced substrates.

Conventional horticultural practices often rely on the use of peat as a primary component in growing media. However, due to the environmental repercussions associated with peat extraction and its limited availability, a critical need has been prompted to explore sustainable alternatives. This study, a part of the ToPGa research project "Development and evaluation of peat-reduced production systems in horticulture", focuses on addressing challenges related to nitrogen (N) immobilization, substrate compaction and optimizing plant growth in cultivation systems that minimize or eliminate peat usage by using microorganisms. A comprehensive understanding of microorganisms and their influence on substrate quality could transform horticultural practices, presenting a more environmentally conscious approach while concurrently improving plant health and productivity. First, the impact of various substrates on plant growth was examined. Eight distinct substrate mixtures, comprising peat, green compost, wood fiber, nettle fiber, digestate, loess/loam, and perlite were used. Both sterile and unsterile treatments were applied to all substrates. Petunia hybrida cv. 'Mitchell' and Ocimum basilicum were chosen as the plant species. The plants' phenotypic characteristics were observed, and the substrates were analyzed for their chemical properties at the experiment's commencement and conclusion. After six weeks, both plant species exhibited superior growth in a sterile, peat-free substrate composed of 50% green compost and 35% wood fiber, as well as in a substrate mixture of 50% peat, 25% green compost, and 25% digestate, irrespective of sterility. In the subsequent phase, diverse microorganisms will be introduced to different substrate mixtures to augment substrate quality and assess their effects on plant growth development. Various plant growth-promoting rhizobacteria (PGPR), Schizophyllum commune, arbuscular mycorrhizal fungi (AMF) and Dark Septate Endophytes (DSEs) will be employed, leveraging their unique qualities for counteracting N-immobilization and substrate compaction. This aims to establish and enhance microbial consortia designs for future studies.

Oral Session
Environmental Microbiology & Processes 2

Appointment

Chair

Topic

Programme

Oral SessionEnvironmental Microbiology & Processes 2

Appointment

Chair

Topic

Programme

Oral Session
Environmental Microbiology & Processes 2