Global Concerns of Ship’s Ballast Water Mediated Translocation of Bacteria

Abstract

Shipping facilitates transportation of over 90 % of the world’s commodities and eventually transfers ~10 billion tons of ballast water which is routinely taken aboard vessels to maintain their stability. The ballast water contains different nonindigenous species (NIS) that include bacteria, microscopic algae, virus, invertebrates, vertebrates, plants, etc. The movements of cargo ships between the continents and along the coastlines have facilitated the spread of these marine species to new localities where they have established themselves mostly in the ports and the coastal niches. Thus, ballast water is recognized as a potent vector of invasive coastal marine species that has threatened the biodiversity. The introduction of such alien organisms into the ecosystem is termed as “bioinvasion” and is among one of the greatest threats to the ocean health.

Microorganisms unlike many other organisms can be introduced into alien environments in bigger numbers as they are highly abundant, are capable of forming resting stages, and can withstand adverse environmental conditions. In ships, microorganisms are found either in ballast water, residual sediments, or biofilms formed on the interior tank surfaces and are also associated with the plankton which serves as microhabitat for bacteria. It is now well established that one of the primary vectors for the transport of vegetative and resting stages of aquatic microbes including disease-causing potentially pathogenic bacteria globally is the ballast water. The introduction of such pathogens has direct impact on the human health and thus has societal relevance. Thus, understanding microbiology of ballast water is of environmental importance as the discharged ballast water may contain infectious pathogens. The ballast water performance standards for different size classes of organisms are provided by the International Convention for the Control and Management of Ship’s Ballast Water and Sediments (IMO 2004). As per these standards (D2 regulation of the convention), the planktonic forms need to be substantially reduced before discharge. In view of this, technologists are considering various options while designing the treatment technologies. The primary reason is the alteration in the microbial population as planktonic organisms are associated with the bacteria, and these bacteria are released in large numbers, while large planktonic organisms are destroyed.

The routine methods used for bacteriological assessment of seawater quality are lengthy. Recently, many scientists working in diverse fields have used flow cytometry (FCM), a technique that allows rapid and accurate counting of bacteria. A matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) using mass spectral libraries of different bacterial species has been also used to characterize different bacteria in ballast water. This method is cost-efficient, quicker, and reliable. However, most (~99 %) of prokaryotes in the environment cannot be cultured in the laboratory. The hurdle of exploring this segment of the microbiome has recently been solved by the development of different molecular tools which can accurately identify the unculturable microbiome and classify them further to species level, thereby overcoming taxonomic ambiguity. An overview of the ecology of microbes in ballast water and different analytical techniques that are used for monitoring bacteria in ballast water other than conventional methods is addressed.