Microbial predation accelerates granulation and modulates microbial community composition

BMC Microbiology

article

Chan, Siew Herng¹  Ismail, Muhammad Hafiz¹  Tan, Chuan Hao¹  Rice, Scott A.¹  McDougald, Diane¹ 

[1] Singapore Centre for Environmental Life Sciences Engineering, Nanyang Technological University;Interdisciplinary Graduate School, Nanyang Technological University;School of Biological Sciences, Nanyang Technological University;School of Materials Science and Engineering, Nanyang Technological University;The iThree Institute, University of Technology Sydney

关键词: Granulation;    Protozoa;    Bacteriophage;    Metagenomics;    Activated sludge;    Microbial predation;   

DOI  :  10.1186/s12866-021-02156-8

学科分类：放射科、核医学、医学影像

来源: BioMed Central

【 摘 要 】

Bacterial communities are responsible for biological nutrient removal and flocculation in engineered systems such as activated floccular sludge. Predators such as bacteriophage and protozoa exert significant predation pressure and cause bacterial mortality within these communities. However, the roles of bacteriophage and protozoan predation in impacting granulation process remain limited. Recent studies hypothesised that protozoa, particularly sessile ciliates, could have an important role in granulation as these ciliates were often observed in high abundance on surfaces of granules. Bacteriophages were hypothesized to contribute to granular stability through bacteriophage-mediated extracellular DNA release by lysing bacterial cells. This current study investigated the bacteriophage and protozoan communities throughout the granulation process. In addition, the importance of protozoan predation during granulation was also determined through chemical killing of protozoa in the floccular sludge. Four independent bioreactors seeded with activated floccular sludge were operated for aerobic granulation for 11 weeks. Changes in the phage, protozoa and bacterial communities were characterized throughout the granulation process. The filamentous phage, Inoviridae, increased in abundance at the initiation phase of granulation. However, the abundance shifted towards lytic phages during the maturation phase. In contrast, the abundance and diversity of protozoa decreased initially, possibly due to the reduction in settling time and subsequent washout. Upon the formation of granules, ciliated protozoa from the class Oligohymenophorea were the dominant group of protozoa based on metacommunity analysis. These protozoa had a strong, positive-correlation with the initial formation of compact aggregates prior to granule development. Furthermore, chemical inhibition of these ciliates in the floccular sludge delayed the initiation of granule formation. Analysis of the bacterial communities in the thiram treated sludge demonstrated that the recovery of ‘Candidatus Accumulibacter’ was positively correlated with the formation of compact aggregates and granules. Predation by bacteriophage and protozoa were positively correlated with the formation of aerobic granules. Increases in Inoviridae abundance suggested that filamentous phages may promote the structural formation of granules. Initiation of granules formation was delayed due to an absence of protozoa after chemical treatment. The presence of ‘Candidatus Accumulibacter’ was necessary for the formation of granules in the absence of protozoa.

【 授权许可】

CC BY|CC0