Nitrogen fixation in a non-heterocystous cyanobacterial mat from a mountain river

Abstract

In situ nitrogen fixation was investigated in a cyanobacterial mat growing on the bed of rocks of the Muga River, Spain. The filamentous non-heterocystous cyanobacterium Schizothrix dominated the mat, showing nitrogenase activity in the light at similar rates to those found in nearby heterocystous Rivularia colonies. N2 fixation in the light was significantly increased by an inhibitor of PSII and oxygen evolution, DCMU (3-[3,4-dichlorophenyl]-1,1-dimethylurea), and anaerobic conditions. However, no nitrogenase activity was found in the dark. Addition of fructose as a respiratory substrate induced nitrogenase activity in samples incubated under aerobic conditions in the dark but not in anaerobic conditions. Microelectrode oxygen profiles showed internal microaerobic microzones where nitrogen fixation might concentrate. Analyses of the 16S rRNA gene revealed only the presence of sequences belonging to filamentous non-heterocystous cyanobacteria. nifH gene diversity showed that the major phylotypes also belonged to this group. One of the three strains isolated from the Schizothrix mat was capable of fixing N2 and growing in the absence of combined N. This was consistent with the nifH gene analysis. These results suggest a relevant contribution of non-heterocystous cyanobacteria to nitrogen fixation in these mats.

Wet season cyanobacterial N enrichment highly correlated with species richness and <i>Nostoc</i> in the northern Australian savannah

“…On the other hand, the significant increase in bioavailable N in May appeared to be related to late season rains (in April) indicative of the investment in the storage of N in cyanophycin (granules) and EPS. Other records of seasonal influence on both C and N fixation have been previously demonstrated; however, the synchrony between these events on a monthly and bimonthly basis shows how well balanced the cyanobacterial biophysical and chemical functions were, dictated by rainfall and consequently soil moisture (Büdel et al, 2009;Castillo-Monroy et al, 2010).…”

“…It is now understood that there is a broad range of N-rich metabolites that are continually released and consumed by Microcoleus (Baran et al, 2015). It has also been demonstrated that N enrichment was associated with Gloeocapsa (Wyatt and Silvey, 1969), Porphyrosiphon (Prasanna et al, 2000) and Schizothrix (Berrendero et al, 2016). Indeed, many cyanobacteria obtain N by scavenging from mutually shared EPS (Rossi et al, 2017) or have multiple mechanisms for N fixation either in the dark (Lüttge, 1997), through O 2 inhibition (Stal, 1995), in anaerobic circumstances (Murukesan et al, 2016) or aquatic cyanobacterial mats when submerged under water (Berrendero et al, 2016;Stewart, 1980).…”

“…Cyanobacterial diversity characteristically provides a range of biochemical and physical attributes that promote resilience to microhabitat variability and climatic extremes (Rossi and De Philippis, 2015). As the biophysical structural form of the community develops, diversity of macroand microorganisms increases (Büdel et al, 2009). As phototrophic organisms, cyanobacteria are, in mass, valuable as ecosystem engineers facilitating soil fertility on several levels (Jones et al, 1994;Eldridge et al, 2010).…”

Cyano-assassins: Widespread cyanogenic production from cyanobacteria

“…The ability of strains to fix nitrogen and produce cyanide seems to be not strictly related with heterocyte formation, as nifH gene fragment was also present in non-heterocytous cyanobacteria strains that produce nitrogen. Non-heterocytous cyanobacteria can fix nitrogen either in dark (Bergman et al, 2006) or in light combined with mechanisms for protecting the O 2 -labile nitrogenase (Berrendero et al, 2016). HCN can inhibit a wide range of metabolic processes (Knowles and Bunch, 1986), but the most pertinent effect in photosynthetic micro-organisms seems to be the inhibition of the reduced form of nitrate reductase (Lorimer et al, 1974).…”

How environment selects: Resilience and survival of microbial mat community within intermittent karst spring Krčić (Croatia)

“…In nutrient‐depleted environments, cyanobacteria are generally also considered as the principal diazotrophs. However, the magnitude and importance of this fixation in lotic ecosystems are poorly understood (Berrendero et al, ).…”