Abstract
Our understanding on the importance of viral lysis in the functioning of tropical estuarine ecosystem is limited. This study examines viral infection of prokaryotes and subsequent lysis of cells belonging to different morphotypes across a salinity gradient in monsoon driven estuarine ecosystem (Cochin estuary, India). High standing stock of viruses and prokaryotes accompanied by lytic infection rates in the euryhaline/mesohaline region of the estuary suggests salinity to have an influential role in driving interactions between prokaryotes and viruses. High prokaryotic mortality rates, up to 42% of prokaryote population in the pre-monsoon season is further substantiated by a high virus to prokaryote ratio (VPR), suggesting that maintenance of a high number of viruses is dependent on the most active fraction of bacterioplankton. Although myoviruses were the dominant viral morphotype (mean = 43%) throughout the study period, there was significant variation among prokaryotic morphotypes susceptible to viral infection. Among them, the viral infected short rod prokaryote morphotype with lower burst estimates (mean = 18 viruses prokaryote-1) was dominant (35%) in the dry seasons whereas a substantial increase in cocci forms (30%) infected by viruses with high burst size (mean = 31 viruses prokaryote-1) was evident during the monsoon season. Such preferential infections of prokaryotic morphopopulations with respect to seasons can have a strong and variable impact on the carbon and energy flow in this tropical ecosystem.
Highlights
Viruses are ubiquitous biological entities that occur in a wide variety of aquatic ecosystems infecting both prokaryotes and eukaryotes [1, 2]
The present study is one among the few conducted in a monsoon impacted tropical estuarine system (Cochin Estuary) which documents the standing stock of viruses and their lytic infection in relation to environmental parameters across three distinct seasons
Spatio-temporal patterns were evident in viral abundance and in their infection rates of prokaryote morphopopulations between the wet and dry seasons which were related to primary and secondary production
Summary
Viruses are ubiquitous biological entities that occur in a wide variety of aquatic ecosystems infecting both prokaryotes and eukaryotes [1, 2]. Viral infected prokaryotic cell morphotypes were subjectively recorded as elongated thin rod, short rod, fat rod, filamentous and cocci (i.e. prokaryotic morphopopulations) based on observations during TEM examination.
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