Polyhydroxyalkanoates (PHAs), the intracellular polymers produced by various microorganisms as carbon and energy storage, are of great technological potential as biodegradable versions of common plastics. PHA-producing microbes are therefore in great demand and a plethora of different environments, especially extreme habitats, have been probed for the presence of PHA-accumulators. However, the polar region has been neglected in this regard, probably due to the low accessibility of the sampling material and unusual cultivation regime. Here, we present the results of a screening procedure involving 200 bacterial strains isolated from 25 habitats of both polar regions. Agar-based tests, microscopy, and genetic methods were conducted to elucidate the biodiversity and potential of polar-region PHA-accumulators. Microscopic observation of Nile Red stained cells proved to be the most reliable screening method as it allowed to confirm the characteristic bright orange glow of the Nile Red–PHA complex as well as the typical morphology of the PHA inclusions. Psychrophilic PHA-producers belonged mostly to the Comamonadaceae family (Betaproteobacteria) although actinobacterial PHA synthesizers of the families, Microbacteriaceae and Micrococcaceae also featured prominently. Glacial and postglacial habitats as well as developed polar region soils, were evaluated as promising for PHA-producer bioprospection. This study highlights the importance of psychrophiles as biodiverse and potent polyhydroxyalkanoate sources for scientific and application-aimed research.

In recent years, extremophilic microorganisms have been employed as producers of the microbial bioplastics polyhydroxyalkanoates (PHA), which are of great biotechnological value. Nevertheless, cold-loving or psychrophilic (cryophilic) bacteria have been neglected in this regard. Here, we present an investigation of the Arctic glacier-derived PHA producerAcidovoraxsp. A1169. Biolog GEN III Microplates were used as a screening tool to identify the most suitable carbon substrate concerning PHA synthesis. The strain produced homopolymer poly(3-hydroxybutyrate) (PHB) most efficiently (2 g/L) at a temperature of 15 °C when supplied with fructose or mannitol as carbon sources with a substantial decrease of PHB biosynthesis at 17.5 °C. The PHB yield did not increase considerably or even decreased when carbon source concentration exceeded 10 g/L hinting that the strain is oligotrophic in nature. The strain was also capable of introducing 3-hydroxyvalerate (3HV) into the polymer structure, which is known to improve PHA thermoplastic properties. This is the first investigation providing insight into a PHA biosynthesis process by means of a true psychrophile, offering guidelines on polar-region bacteria cultivation, production of PHA and also on the methodology for genetic engineering of psychrophiles.

Vectors based on adeno-associated viruses (AAVs) are widely used as a delivery system in gene therapy. However, preexisting immunity against AAV remains a major limitation. This study examines the prevalence of AAV genomes and anti-AAV2 immunity in a Polish cohort of adult patients undergoing planned surgical interventions, which serves as a random sample of the general Polish population. The presence of AAV capsid sequences was analyzed in tissue samples using PCR and endogenous AAVs were detected in 33.95% of samples. Anti-AAV2 IgG antibodies were measured by a single point ELISA and were present in 80.93% of patients. Neutralizing activity was evaluated using an AAV2 transduction inhibition assay in HEK293T cells, revealing a 60% reduction in functional activity by patients’ sera. Tissue AAV PCR-positivity was associated with stronger neutralizing activity although the correlation with seropositivity was not as strong. These results suggest that pre-existing humoral immunity against AAV is common in the Polish adult population, indicating frequent exposure to naturally occurring AAVs. The findings provide important data on pre-existing anti-AAV immunity—a key factor considered in clinical trials and gene therapy development. Furthermore, the identification of naturally occurring AAV variants in human tissues points to the potential use of new sources of capsids with potentially distinct biological properties, which could contribute to the advancement of gene therapies.