Biology subjects

Lopez, N. I.

Publications and source records attributed to Lopez, N. I..

4 recordsLinked to original sources

bioRxiv2024

Unraveling the effects of polyhydroxyalkanoates accumulation in Pseudomonas extremaustralis growth and survival under different pH conditions

Polyhydroxyalkanoates (PHAs) are intracellular polymers that enhance bacterial fitness against various environmental stressors. Pseudomonas extremaustralis 14-3b is an Antarctic bacterium capable of accumulating, short-chain-length PHAs (sclPHAs), composed of C3-C5 monomers, as well as medium-chain-length PHAs (mclPHAs) containing [≥]C6 monomers. Since pH changes are pivotal in bacterial physiology, influencing microbial growth and metabolic processes, we propose that accumulated PHA increases P. extremaustralis fitness to cope with pH changes. To test this, we analyzed the production of sclPHA and mclPHA at different pH levels and its effect on bacterial survival against pH stress. P. extremaustralis was able to grow and accumulate PHA when the culture media pH ranged from 6.0 to 9.5, showing a marked loss of viability outside this range. Additionally, based on the analysis of different PHA-deficient mutants, we found that when exposed to both acidic and alkaline conditions, sclPHA and mclPHA conferred different protection against pH stress, with sclPHA making the main contribution. These results highlight the importance of PHA in supporting survival in pH-stressful environments.

microbiology↗

bioRxiv2024

BEYOND UNIFORMITY: Pyomelanin,s structural complexity impacts on UV shielding in Pseudomonas species with different lifestyles.

Melanin, a polymeric pigment synthesized by various organisms, confers advantageous traits, including heightened resistance to stress agents. In Pseudomonas, disruption of the tyrosine degradation pathway leads to pyomelanin production. Despite a shared synthetic pathway, the chemical structure of pyomelanin remains elusive due to its heterogeneous polymeric nature, suggesting composition variations even among closely related species. Our objective was to analyze pyomelanin structural features across Pseudomonas strains: CRISPR/nCas9-engineered hmgA mutants of PAO1 and PA14, reference strains of the human opportunist pathogen P. aeruginosa; a natural melanogenic mutant (PAM) from a patient; and a Tn5 mutant of the extremophile bacterium P. extremaustralis (PexM). Structural analysis revealed strain-specific differences. UV spectra exhibited dual peaks for PAO1 and PA14 mutants, while PAM and PexM displayed a single peak. FTIR indicated changes in the alcohol content ratio, with PAO1 and PA14 hmgA mutants having a near 1:1 ratio, PexM a dominant phenol band, and PAM a predominance of the alcohol band. Complex NMR spectra suggested non-linear polymers composed by substituted phenolic rings, carboxylic acids, and alkyl chains, highlighting inter-pigment disparities. UVC (254 nm) susceptibility assessment showed increased survival with pyomelanin addition, correlating with the attenuation of the incoming radiation due to absorption in the culture medium. Moreover, survival to UVC of P. extremaustralis was different depending on the melanin source being the most protective pyomelanin obtained from PAO1. These findings reveal distinct pyomelanin subgroups based on structure among strains, elucidating varied physiological effects.

microbiology↗

bioRxiv2023

Nitrosative stress under microaerobic conditions triggers inositol metabolism in Pseudomonas extremaustralis

Bacteria are exposed to reactive oxygen and nitrogen species that provoke oxidative and nitrosative stress which can lead to macromolecule damage. Coping with stress conditions involves the adjustment of cellular responses, which helps address metabolic challenges. In this study, we performed a global transcriptomic analysis of the response of Pseudomonas extremaustralis to nitrosative stress, induced by S-nitrosoglutathione (GSNO), a nitric oxide donor, under microaerobic conditions. The analysis revealed the upregulation of genes associated with inositol catabolism; a compound widely distributed in nature whose metabolism in bacteria has aroused interest. The RNA-seq data also showed heightened expression of genes involved in essential cellular processes like transcription, translation, amino acid transport and biosynthesis, as well as in stress resistance including iron-dependent superoxide dismutase, alkyl hydroperoxide reductase, thioredoxin, and glutathione S-transferase in response to GSNO. Furthermore, GSNO exposure differentially affected the expression of genes encoding nitrosylation target proteins, encompassing metalloproteins and proteins with free cysteine and /or tyrosine residues. Notably, genes associated with iron metabolism, such as pyoverdine synthesis and iron transporter genes, showed activation in the presence of GSNO, likely as response to enhanced protein turnover. Physiological assays demonstrated that P. extremaustralis can utilize inositol proficiently under both aerobic and microaerobic conditions, achieving growth comparable to glucose-supplemented cultures. Moreover, supplementing the culture medium with inositol enhances the stress tolerance of P. extremaustralis against combined oxidative-nitrosative stress. Concordant with the heightened expression of pyoverdine genes under nitrosative stress, elevated pyoverdine production was observed when myo-inositol was added to the culture medium. These findings highlight the influence of nitrosative stress on proteins susceptible to nitrosylation and iron metabolism. Furthermore, the activation of myo-inositol catabolism emerges as a protective mechanism against nitrosative stress, shedding light on this pathway in bacterial systems, and holding significance in the adaptation to unfavorable conditions.

microbiology↗

bioRxiv2022

Guanine crystals discovered in bacteria

Guanine crystals are organic biogenic crystals found in many organisms. Due to their exceptionally high refractive index, they contribute to structural color and are responsible for the reflective effect in the skin and visual organs in animals such as fish, reptiles and spiders. Occurrence of these crystals in animals has been known for many years, and they have also been observed in eukaryotic microorganisms, but not in prokaryotes. In this work we report the discovery of extracellular crystals in bacteria, and reveal that they are composed of guanine, and particularly the unusual monohydrate form. We demonstrate the occurrence of these crystals in Aeromonas and other bacteria, and investigate the metabolic traits related to their synthesis. In all cases studied the presence of the guanine crystals in bacteria correlate with the absence of guanine deaminase, which could lead to guanine accumulation providing the substrate for crystal formation. Our finding of the hitherto unknown guanine crystal occurrence in prokaryotes extends the range of guanine crystal producing organisms to a new domain of life. Bacteria constitute a new and more accessible model to study the process of guanine crystal formation and assembly. This discovery opens countless chemical and biological questions, including those about the functional and adaptive significance of their production in these microorganisms. It also paves the road for the development of simple and convenient processes to obtain biogenic guanine crystals for diverse applications. SignificanceGuanine crystal formation is well known in animals such as fish, reptiles and arthropods (among other eukaryotic organisms), but its occurrence has never been reported in prokaryotes. This manuscript describes the discovery of extracellular guanine crystals in bacteria, and reveals that they are composed of the unusual monohydrate form of guanine. Knowledge of guanine crystal biosynthesis in bacteria could lead to a better understanding of their synthesis in other organisms. It also paves the road for the development of simple and convenient processes to obtain biogenic guanine crystals for diverse applications. Our finding extends the range of guanine crystal producing organisms to a new domain of life.

microbiology↗