Abstract
Groundwork on cyanobacterial external layers is crucial for an improved understanding of the persistent dominance of cyanobacteria in freshwaters. In this study, the role of two morphotypes of external layers in Microcystis and Nostoc in mass transfer and instantaneous temperature shock were explored by noninvasive microtest technology (NMT) after a series of pretreatments, to obtain the external layers retained or stripped samples. The results showed no statistical influence on photosynthetic activity between retained and stripped samples in both Microcystis and Nostoc. External-layer-retaining strains had higher net O2 effluxes than stripped strains. Moreover, the net NH4+ influx was significantly higher for the sheath retaining Nostoc than for the stripped sample, indicating that external layers might be an important feature driving mass transfer in cyanobacteria. However, the role of slime in NH4+ absorption was limited compared with that of sheath. In addition, external-layer-retaining strains exhibited a longer response time to instantaneous temperature shock, greater net O2 effluxes at a 4 °C shock and lower net O2 influx at a 35 °C shock, which were interpreted as reflecting a tolerance to temperature fluctuation over short time scales via a buffer function of external layers to stabilize cell activity, ameliorating the efficiency of photosynthesis and respiration. These results advance current knowledge regarding the external layers, especially the dense sheath, involved in the mass transfer in cyanobacteria, and provide new clues concerning the adaptive strategies of cyanobacteria under global climate changes.
Highlights
Surface coats are widespread, surrounding microorganisms as well as some plant and animal cells
Our findings suggest that external layers, especially the dense sheath, may have an ameliorating impact on the efficiency of photosynthesis and photosynthesis-coupled respiration in cyanobacteria when sufferingMiscrhooorgratn-itsemrsm202t0e, 8m, xpFeOrRaPtEuErReRflEuVIcEtWuation
Through noninvasive microtest technology (NMT) analysis, we show that external-layer-retaining strains have higher net O2 effluxes than stripped strains, while the role of slime in NH4+ absorption is limited compared with that of sheath
Summary
Surface coats are widespread, surrounding microorganisms as well as some plant and animal cells. By comparing the surface coats of a variety of cell types, Bennett [1] proposed a generalized terminology of “glycocalyx” for this biochemical structure. This structure has received increasing attention; yet, the terminology is often confused and not strictly followed. It was referred to as the sheath and/or capsule based on morphological aspects in microorganisms [2,3]. Regardless of the differences in the definitions above, we tend to use a more generalized term, “external layers”, focusing on the surface coats that perform specific eco-physiological functions to support cyanobacteria in the natural environment
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