Despite the surge of microbial genome data, experimental testing is important to confirm inferences about the cell biology, ecological roles and evolution of microorganisms. As the majority of ...archaeal and bacterial diversity remains uncultured and poorly characterized, culturing is a priority. The growing interest in and need for efficient cultivation strategies has led to many rapid methodological and technological advances. In this Review, we discuss common barriers that can hamper the isolation and culturing of novel microorganisms and review emerging, innovative methods for targeted or high-throughput cultivation. We also highlight recent examples of successful cultivation of novel archaea and bacteria, and suggest key microorganisms for future cultivation attempts.
Co-aggregation of anaerobic microorganisms into suspended microbial biofilms (aggregates) serves ecological and biotechnological functions. Tightly packed aggregates of metabolically interdependent ...bacteria and archaea play key roles in cycling of carbon and nitrogen. Additionally, in biotechnological applications, such as wastewater treatment, microbial aggregates provide a complete metabolic network to convert complex organic material. Currently, experimental data explaining the mechanisms behind microbial co-aggregation in anoxic environments is scarce and scattered across the literature. To what extent does this process resemble co-aggregation in aerobic environments? Does the limited availability of terminal electron acceptors drive mutualistic microbial relationships, contrary to the commensal relationships observed in oxygen-rich environments? And do co-aggregating bacteria and archaea, which depend on each other to harvest the bare minimum Gibbs energy from energy-poor substrates, use similar cellular mechanisms as those used by pathogenic bacteria that form biofilms? Here, we provide an overview of the current understanding of why and how mixed anaerobic microbial communities co-aggregate and discuss potential future scientific advancements that could improve the study of anaerobic suspended aggregates.
Key points
• Metabolic dependency promotes aggregation of anaerobic bacteria and archaea
• Flagella, pili, and adhesins play a role in the formation of anaerobic aggregates
• Cyclic di-GMP/AMP signaling may trigger the polysaccharides production in anaerobes
Carboxydotrophic bacteria (CTB) have received attention due to their ability to synthesize commodity chemicals from producer gas and synthesis gas (syngas). CTB have an important advantage of a high ...product selectivity compared to chemical catalysts. However, the product spectrum of wild-type CTB is narrow. Our objective was to investigate whether a strategy of combining two wild-type bacterial strains into a single, continuously fed bioprocessing step would be promising to broaden the product spectrum. Here, we have operated a syngas-fermentation process with
and
with in-line product extraction through gas stripping and product condensing within the syngas recirculation line. The main products from
fermentation at a pH of 6.0 were ethanol and acetate at net volumetric production rates of 65.5 and 431 mmol C·L
·d
, respectively. An estimated 2/3 of total ethanol produced was utilized by
to chain elongate with the reverse β-oxidation pathway, resulting in
-butyrate and
-caproate at net rates of 129 and 70 mmol C·L
·d
, respectively.
likely reduced the produced carboxylates to their corresponding alcohols with the reductive power from syngas. This resulted in the longer-chain alcohols
-butanol,
-hexanol, and
-octanol at net volumetric production rates of 39.2, 31.7, and 0.045 mmol C·L
·d
, respectively. The continuous production of the longer-chain alcohols occurred only within a narrow pH spectrum of 5.7-6.4 due to the pH discrepancy between the two strains. Regardless whether other wild-type strains could overcome this pH discrepancy, the specificity (mol carbon in product per mol carbon in all other liquid products) for each longer-chain alcohol may never be high in a single bioprocessing step. This, because two bioprocesses compete for intermediates (i.e., carboxylates): (1) chain elongation; and (2) biological reduction. This innate competition resulted in a mixture of
-butanol and
-hexanol with traces of
-octanol.
Carbon monoxide can act as a substrate for different modes of fermentative anaerobic metabolism. The trait of utilizing CO is spread among a diverse group of microorganisms, including members of ...bacteria as well as archaea. Over the last decade this metabolism has gained interest due to the potential of converting CO-rich gas, such as synthesis gas, into bio-based products. Three main types of fermentative CO metabolism can be distinguished: hydrogenogenesis, methanogenesis, and acetogenesis, generating hydrogen, methane and acetate, respectively. Here, we review the current knowledge on these three variants of microbial CO metabolism with an emphasis on the potential enzymatic routes and bio-energetics involved.
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•Synthetic microbial co-cultures are potential robust and resilient catalysts for bio-based processes.•Tailor-made microbial co-cultures increase the possibilities to convert complex ...substrates to specific products.•Thermodynamic-based microbial interactions are promising to increase product yield and steer metabolism.•Combination of genetic and synthetic-culture engineering can result in superior bioprocesses for applications in biotechnology.
In nature, microorganisms live in multi-species communities allowing microbial interactions. These interactions are lost upon establishing a pure culture, increasing the metabolic burden and limiting the metabolic potential of the isolated microbe. In the past years, synthetic microbial co-cultivation, using well-defined consortia of two or more microbes, was increasingly explored for innovative applications in biotechnology. As such, interspecies interactions take place without the complexity of an open mixed culture, minimizing undesired side reactions. Ultimately, synthetic co-cultivation allows to take well-characterized microbes ‘off-the-shelf’ to create ecosystems with improved process capabilities. This review highlights some of the recent developments on co-cultivation, focusing on waste-to-chemicals conversions. It also addresses fundamental knowledge on microbial interactions deriving from these studies, which is important to further develop our ability to engineer functional co-cultures for bioproduction.
Harnessing the power of microbial autotrophy Claassens, Nico J; Sousa, Diana Z; Dos Santos, Vitor A P Martins ...
Nature reviews. Microbiology,
11/2016, Volume:
14, Issue:
11
Journal Article
Peer reviewed
Autotrophic microorganisms convert CO
into biomass by deriving energy from light or inorganic electron donors. These CO
-fixing microorganisms have a large, but so far only partially realized, ...potential for the sustainable production of chemicals and biofuels. Productivities have been improved in autotrophic hosts through the introduction of production pathways and the modification of autotrophic systems by genetic engineering. In addition, approaches are emerging in which CO
fixation pathways and energy-harvesting systems are transplanted into heterotrophic model microorganisms. Alternative promising concepts are hybrid production systems of autotrophs and heterotrophs, and bio-inorganic hybrids of autotrophic microorganisms with electrocatalysts or light-harvesting semiconductor materials. In this Review, we discuss recent advances and bottlenecks for engineering microbial autotrophy and explore novel strategies that will pave the way towards improved microbial autotrophic production platforms.
The performances of two FAU-type zeolites with different SiO2/Al2O3 ratios were evaluated for the removal of antibiotics of three different classes, namely azithromycin, ofloxacin, and ...sulfamethoxazole, from aqueous solutions. Commercial zeolites were used, without any previous treatment. Use of a small adsorbent dosage resulted in fast antibiotic adsorption that followed pseudo-second order kinetics. The removals of azithromycin and sulfamethoxazole were highly pH-dependent, with low removal percentages observed under acid (pH 2.5–4.5) and basic (pH 8.5–10.5) conditions, respectively. The Freundlich isotherm model provided the best fits to the adsorption data. The adsorption mechanisms appeared to involve both electrostatic and H-bonding interactions. Using an antibiotics mixture, percentage removals of azithromycin and ofloxacin onto the zeolites of up to 79% were obtained. Both materials presented good adsorption (>50%) of azithromycin and ofloxacin from a real sample of effluent wastewater. The results showed that zeolites with FAU structure can be used as effective adsorbents for the removal of antibiotics with different physicochemical properties, including molecules with large volumes, such as azithromycin.
•Fast and effective removal of antibiotics in aqueous media by FAU zeolite.•PH-dependent adsorption of azithromycin and ofloxacin by FAU zeolite.•Low competitive effect on adsorption efficiency of mixed antibiotics onto FAU zeolite.•Good adsorption of antibiotics from a wastewater sample onto FAU zeolite.
Six CO
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 CO
via the reductive glycine pathway, a seventh CO
fixation pathway. In this pathway, CO
is first reduced to formate, which is reduced and condensed with a second CO
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 CO
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 CO
fixation pathway.
Cerebral Venous Thrombosis: an Update Ferro, José M.; Aguiar de Sousa, Diana
Current neurology and neuroscience reports,
10/2019, Volume:
19, Issue:
10
Journal Article
Peer reviewed
Purpose of Review
The purpose of this update is to summarize the recent advances on the management of cerebral venous thrombosis (CVT).
Recent Findings
There is a trend in declining frequency of CVT ...patients presenting with focal deficits or coma and a decrease in mortality over time. Anemia and obesity were identified as risk factors for CVT. During pregnancy and puerperium, the higher risk of CVT occurs in the first months post-delivery. With appropriate management, 1/3 of comatose CVT patients can have a full recovery.
Summary
The management of CVT patients includes treatment of associated conditions, anticoagulation with parenteral heparin, prevention of recurrent seizures, and decompressive neurosurgery in patients with large venous infarcts/hemorrhages with impending herniation. After the acute phase, patients should be anticoagulated for 3–12 months. Results of recently completed randomized controlled trials on endovascular treatment and comparing dabigatran with warfarin will improve the treatment of CVT.
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