Some tropical cyanobacteria have spread to temperate freshwaters during the last decades. To evaluate their further development in temperate lakes, we studied the temperature- and light-dependent growth of three invasive (Cylindrospermopsis raciborskii, Anabaena bergii and Aphanizomenon aphanizomenoides) and three native (Aphanizomenon gracile, Aphanizomenon flos-aquae and Anabaena macrospora) cyanobacterial species (Nostocales) from German lakes. We also included one potentially invasive (Aphanizomenon ovalisporum) Nostocales species. We conducted semi-continuous culture experiments and a microcosm experiment along a natural light gradient. Temperature data were used to design a model to simulate the development of selected species according to three temperature scenarios (past, present and future). Native species had significantly higher growth rates than invasive species and the potential invader A. ovalisporum at low temperatures (≤10°C), while the opposite was true at high temperatures (≥35°C). Maximum growth rates of A. ovalisporum, A. aphanizomenoides and C. raciborskii were clearly higher than those of A. bergii and the native species. Regarding light-dependent growth, significant differences were found between single species but not between all native and invasive species. The model simulation demonstrates a shift in dominance from the native A. gracile in the historic scenario to C. raciborskii populations in the future scenario, in which also the potential invader A. ovalisporum is able to establish populations in temperate lakes. Our findings suggest that any further temperature increase would promote the growth and development of Nostocales species in general, and that of the invasive species in particular, and would enable a more northward expansion of A. ovalisporum.

Biological methane (CH₄) mitigation combined with biopolymer (PHA-polyhydroxyalkaonate/PHB-polyhydroxybutyrate) production is a viable option in this fossil fuel-constrained era. Methantrophs are bacteria that can re-route CH₄ into PHA/PHB under nutrient-starved conditions. However, most studies (up to 90%) investigated pure cultures to demonstrate capacity for PHA/PHB accumulation, which on an industrial scale is unlikely to be serviceable. Furthermore, commercialization is handicapped as there are still a number of unresolved issues which affect productivities, such as optimized process variables, characterization of robust consortia, and optimized reactor design. This review will summarize existing knowledge and highlight research needs to fast track methanotrophic PHA/PHB production from CH₄.

Cyanotoxins are secondary metabolites produced by cyanobacteria, of varied chemical nature and toxic effects. Although cyanobacteria thrive in all kinds of ecosystems on Earth even under very harsh conditions, current knowledge on cyanotoxin distribution is almost restricted to freshwaters from temperate latitudes. In this review, we bring to the forefront the presence of cyanotoxins in extreme environments. Cyanotoxins have been reported especially in polar deserts (both from the Arctic and Antarctica) and alkaline lakes, but also in hot deserts, hypersaline environments, and hot springs. Cyanotoxins detected in these ecosystems include neurotoxins—anatoxin-a, anatoxin-a (S), paralytic shellfish toxins, β-methylaminopropionic acid, N-(2-aminoethyl) glycine and 2,4-diaminobutyric acid- and hepatotoxins –cylindrospermopsins, microcystins and nodularins—with microcystins being the most frequently reported. Toxin production there has been linked to at least eleven cyanobacterial genera yet only three of these (Arthrospira, Synechococcus and Oscillatoria) have been confirmed as producers in culture. Beyond a comprehensive analysis of cyanotoxin presence in each of the extreme environments, this review also identifies the main knowledge gaps to overcome (e.g., scarcity of isolates and –omics data, among others) toward an initial assessment of ecological and human health risks in these amazing ecosystems developing at the very edge of life.