Implementation of the β-hydroxyaspartate cycle increases growth performance of Pseudomonas putida on the PET monomer ethylene glycol

Ethylene glycol (EG) is a promising next generation feedstock for bioprocesses. It is a key component of the ubiquitous plastic polyethylene terephthalate (PET) and other polyester fibers and plastics, used in antifreeze formulations, and can also be generated by electrochemical conversion of syngas, which makes EG a key compound in a circular bioeconomy. The majority of biotechnologically relevant bacteria assimilate EG via the glycerate pathway, a wasteful metabolic route that releases CO2 and requires reducing equivalents as well as ATP. In contrast, the recently characterized β-hydroxyaspartate cycle (BHAC) provides a more efficient, carbon-conserving route for C2 assimilation. Here we aimed at overcoming the natural limitations of EG metabolism in the industrially relevant strain Pseudomonas putida KT2440 by replacing the native glycerate pathway with the BHAC. We first prototyped the core reaction sequence of the BHAC in Escherichia coli before establishing the complete four-enzyme BHAC in Pseudomonas putida. Directed evolution on EG resulted in an improved strain that exhibits 35% faster growth and 20% increased biomass yield compared to a recently reported P. putida strain that was evolved to grow on EG via the glycerate pathway. Genome sequencing and proteomics highlight plastic adaptations of the genetic and metabolic networks in response to the introduction of the BHAC into P. putida and identify key mutations for its further integration during evolution. Taken together, our study shows that the BHAC can be utilized as 'plug-and-play' module for the metabolic engineering of two important microbial platform organisms, paving the way for multiple applications for a more efficient and carbon-conserving upcycling of EG in the future.Microbial Biotechnolog

Evidence of a landlocked reproducing population of the marine pejerrey Odontesthes argentinensis (Actinopterygii; Atherinopsidae)

In South America, the order Atheriniformes includes the monophyletic genus<em>Odontesthes</em> with 20 species that inhabit freshwater, estuarine and coastal environments. Pejerrey Odontesthes argentinensis is widely distributed in coastal and estuarineareas of the Atlantic Ocean and is known to foray into estuaries of river systems, particularly in conditions of elevated salinity. However, to our knowledge, a landlockedself-sustaining population has never been recorded. In this study, we examined the pejerrey population of Salada de Pedro Luro Lake (south-east of BuenosAires Province, Argentina) to clarify its taxonomic identity. An integrative taxonomic analysis based on traditional meristic, landmark-based morphometrics and genetictechniques suggests that the Salada de Pedro Luro pejerrey population represents a novel case of physiological and morphological adaptation of a marine pejerrey speciesto a landlocked environment and emphasises the environmental plasticity of this group of fishe

Reconstruction of Oligocene and Neogene freshwater fish faunas - an actualistic study on cypriniform otoliths

Fossil utricular otoliths (= lapilli) from cypriniform fishes have long been recorded from European Oligocene and Neogene freshwater and oligohaline sediments. Until now, their determination was limited to the family level owing to the lack of morphological investigations on lapilli of Recent cypriniforms. The present study introduces a terminology for the lapillus morphology that is based on the lapilli of 134 specimens of 20 cyprinid and one balitorid species. It is demonstrated that the lapillus has valuable characters for taxonomic classification. As a result, fossil lapilli from Oligocene and Miocene continental deposits from the western Mediterranean, the Swiss and the South German Molasse Basin, the Mainz Basin, and additionally from Anatolia could be determined. Nine species were identified: aff. Abramis sp. vel aff. Alburnus sp., aff. Alburnoides sp., aff. Barbus sp., cf. Leuciscussp., Palaeoleuciscus sp., Palaeotinca moeddeni sp. nov., Palaeotinca sp. 1, aff. Phoxinus sp., and aff. Rutilus sp. vel aff. Scardinius sp. Our study includes the oldest record of a Phoxinus−related and a Palaeotinca species from Europe. Additionally, aff. Abramis sp. vel aff. Alburnus sp. and aff. Alburnoides have been identified as fossils for the first time. The determination of the fossil lapilli has been supported by means of pharyngeal teeth, with the exception of aff. Abramis sp. vel aff. Alburnus sp., whose lapilli were found together with pharyngeal teeth of Palaeocarassius sp. It is suggested that these so−called Palaeocarassius pharyngeal teeth do not belong to an ancestor of the Carassiuslineage, but to a forerunner of the Abramis or Alburnuslineage. Our results support the previously described turnover in the Paratethys freshwater fish fauna about 17–18 Ma ago, when Palaeotinca spp. became extinct and the first appearance of Palaeoleuciscussp. and Palaeocarassiussp. (= aff. Abramissp. vel aff. Alburnus sp.) occurred. The Oligocene and Miocene cypriniform fishes did not evolve any provincialism from southern France throughout the Molasse Basin to the Mainz Basin

Are hybridization and polyploidization phenomena detectable in the fossil record? - A case study on otoliths of a natural hybrid, Poecilia formosa (Teleostei: Poeciliidae).

Hybridization and polyploidization phenomena play an important role for speciation processes. In the fossil record, however, evidences of such phenomena are difficult to identify. We Studied whether effects of hybridization and polyploidization are visible in the morphology of fish otoliths. Otoliths are massive calcium carbonate concretions positioned in the inner ear of teleost fishes. Thus, otoliths possess a high preservation potential and often provide the sole fossil remains of teleost fishes since Cretaceous times. As an extant model, we chose the natural hybrid Poecilia formosa and the parental species P latipinna and P mexicana. We analyzed otolith contours (N = 170) using Fourier shape analysis. In addition, the height to length ratio was Calculated. Otoliths of P. formosa were found to be clearly distinct from P. latipinna and P. mexicana, and their otolith contours were intermediate to those of the two parental species. However, otolith Contours of P. formosa were slightly more similar to those of P. mexicana, which represents the "maternal part" of the hybridization event. In part, the otolith contour and the height to length ratio revealed distinct differences between populations (two diploid, one triploid Population) of P.formosa. We suggest that these differences may be a result of geographic differentiation and to a minor degree due to differences at the ploidy level. Our study shows that it may be possible to trace hybridization in the fossil fish record based on otolith morphology

Hearing in Cavefishes

Caves and associated subterranean habitats represent some of the harshest environments on Earth, yet many organisms, including fishes, have colonized and thrive in these habitats despite the complete absence of light, and other abiotic and biotic constraints. Over 170 species of fishes are considered obligate subterranean inhabitants (stygobionts) that exhibit some degree of troglomorphy, including degeneration of eyes and reduction in pigmentation. To compensate for lack of vision, many species have evolved constructive changes to non-visual sensory modalities. In this chapter we review hearing in cavefishes, with particular emphasize on our own studies on amblyopsid cavefishes. Hearing in cavefishes has not been well studied to date, as hearing ability has only been examined in four species. Two species show no differences in hearing ability relative to their surface relatives, while the other two species (family Amblyopsidae) exhibit regression in the form of reduced hearing range and reduction in hair cell densities on sensory epithelia. In addition to reviewing our current knowledge on cavefish hearing, we offer suggestions for future avenues of research on cavefish hearing and discuss the influence of Popper and Fay on the field of cavefish bioacoustics

On the flexibility of the cellular amination network in E. coli

Ammonium (NH4+) is essential to generate the nitrogenous building blocks of life. It gets assimilated via the canonical biosynthetic routes to glutamate and is further distributed throughout metabolism via a network of transaminases. To study the flexibility of this network, we constructed an Escherichia coli glutamate auxotrophic strain. This strain allowed us to systematically study which amino acids serve as amine sources. We found that several amino acids complemented the auxotrophy either by producing glutamate via transamination reactions or by their conversion to glutamate. In this network, we identified aspartate transaminase AspC as a major connector between many amino acids and glutamate. Additionally, we extended the transaminase network by the amino acids β-alanine, alanine, glycine, and serine as new amine sources and identified d-amino acid dehydrogenase (DadA) as an intracellular amino acid sink removing substrates from transaminase reactions. Finally, ammonium assimilation routes producing aspartate or leucine were introduced. Our study reveals the high flexibility of the cellular amination network, both in terms of transaminase promiscuity and adaptability to new connections and ammonium entry points.Microbial Biotechnolog