Concerning the role of cell lysis-cryptic growth in anaerobic side-stream reactors: the single-cell analysis of viable, dead and lysed bacteria.
In the Anaerobic Side-Stream Reactor (ASSR), part of the return sludge undergoes alternating aerobic and anaerobic conditions with the aim of reducing sludge production. In this paper, viability, enzymatic activity, death and lysis of bacterial cells exposed to aerobic and anaerobic conditions for 16 d were investigated at single-cell level by flow cytometry, with the objective of contributing to the understanding of the mechanisms of sludge reduction in the ASSR systems. Results indicated that total and viable bacteria did not decrease during the anaerobic phase, indicating that anaerobiosis at ambient temperature does not produce a significant cell lysis. Bacteria decay and lysis occurred principally under aerobic conditions. The aerobic decay rate of total bacteria (bTB) was considered as the rate of generation of lysed bacteria. Values of bTB of 0.07-0.11 d(-1) were measured in anaerobic + aerobic sequence. The enzymatic activity was not particularly affected by the transition from anaerobiosis to aerobiosis. Large solubilisation of COD and NH4(+) was observed only under anaerobic conditions, as a consequence of hydrolysis of organic matter, but not due to cell lysis. The observations supported the proposal of two independent mechanisms contributing equally to sludge reduction: (1) under anaerobic conditions: sludge hydrolysis of non-bacterial material, (2) under aerobic conditions: bacterial cell lysis and oxidation of released biodegradable compounds.
Department of Civil, Environmental and Mechanical Engineering, University of Trento, Via Mesiano, 77, 38123 Trento, TN, Italy. Electronic address: paola.foladori@ing.unitn.it.
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Foladori
Federal University of Santa Catarina, Trindade, Florianópolis, Brazil.
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Velho
Federal University of Santa Catarina, Trindade, Florianópolis, Brazil.
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Costa
Agenzia per la Depurazione, Autonomous Province of Trento, Via S. Giovanni 36, 38122 Trento, Italy.
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Bruni
Department of Industrial Engineering, University of Trento, Via Sommarive 9, 38123 Trento, Italy.
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Quaranta
Department of Civil, Environmental and Mechanical Engineering, University of Trento, Via Mesiano, 77, 38123 Trento, TN, Italy.
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Andreottola
D000332:Aerobiosis; D000693:Anaerobiosis; D001419:Bacteria / Q000201:enzymology / Q000254:growth & development*; D057919:Biological Oxygen Demand Analysis; D019149:Bioreactors / Q000382:microbiology*; D009584:Nitrogen / Q000378:metabolism; D010084:Oxidation-Reduction; D012722:Sewage / Q000737:chemistry / Q000382:microbiology*; D059010:Single-Cell Analysis; D014865:Waste Disposal, Fluid / Q000379:methods*
D012722:Sewage; D009584:Nitrogen
Anaerobic side-stream reactor; Cell lysis; Cryptic growth; Flow cytometry; Sludge reduction