Abstract
Bacteria are now generally believed to adopt two main lifestyles: planktonic individuals, or surface-attached biofilms. However, in recent years medical microbiologists started to stress that suspended bacterial aggregates are a major form of bacterial communities in chronic infection sites. Despite sharing many similarities with surface-attached biofilms and are thus generally defined as biofilm-like aggregates, these non-attached clumps of cells in vivo show much smaller sizes and different formation mechanisms. Furthermore, ex vivo clinical isolates were frequently reported to be less attached to abiotic surfaces when compared to standard type strains. While this third lifestyle is starting to draw heavy attention in clinical studies, it has a long history in natural and environmental sciences. For example, marine gel particles formed by bacteria attachment to phytoplankton exopolymers have been well documented in oceans; large river and lake snows loaded with bacterial aggregates are frequently found in freshwater systems; multispecies bacterial “flocs” have long been used in wastewater treatment. This review focuses on non-attached aggregates found in a variety of natural and clinical settings, as well as some recent technical developments facilitating aggregate research. The aim is to summarise the characteristics of different types of bacterial aggregates, bridging the knowledge gap, provoking new perspectives for researchers from different fields, and highlighting the importance of more research input in this third lifestyle of bacteria closely relevant to our daily life.
Highlights
The past 150 years have witnessed numerous breakthroughs in understanding the biology, biochemistry and ecology of free-swimming single celled planktonic bacteria following Louis Pasteur and Robert Koch’s seminal contributions
Recognition of the ubiquitous nature of the aggregate lifestyle is raising a number of fundamental questions: How are these non-attached bacterial aggregates formed? What are their functions both in nature and our bodies? Are there any fundamental similarities shared among aggregates formed in very different environments? Can we learn something from nature to help fight chronic diseases? Just as the pioneering marine work on biofilms led to the later clinical discoveries, the aggregates in marine, freshwater, wastewater and medical settings are summarised here, which may bring in inspirations on new directions of mechanistic studies, as well as more effective treatment strategies
The existence of non-surface attached bacterial aggregates discovered from ocean, fresh water, wastewater treatment systems, as well as chronic infection sites were collectively presented, providing new perspectives and questions based on some fundamental similarities or differences
Summary
The past 150 years have witnessed numerous breakthroughs in understanding the biology, biochemistry and ecology of free-swimming single celled planktonic bacteria following Louis Pasteur and Robert Koch’s seminal contributions. Extensive studies on marine gel particles (MGP) and associated bacterial communities in sea surface waters, as well as the formation and fate of these aggregates during their sedimentation to the deep ocean were conducted by different groups (Zhou et al, 1998; Passow et al, 2001; Passow, 2002b; Engel, 2004; Cunliffe and Murrell, 2009; Cunliffe et al, 2009a,b; Ortega-Retuerta et al, 2009a; Galgani and Engel, 2013; Taylor et al, 2014; Busch et al, 2017; Engel et al, 2017; Mari et al, 2017; Zäncker et al, 2019).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
