A simple technique to mitigate microplastic pollution and its mobility (via ballast water) in the global ocean.

Ballast water transport is considered as one of the major vectors for dispersal of microplastics around the global oceans. In this commentary, a simple, inexpensive solution has been proposed to reduce microplastic pollution and its mobility via ballast water. A screening chamber (with stainless steel three layered mesh) is proposed to be attached to the existing Ballast Water Treatment Systems (BWTSs) in cargo ships to filter back-flushed sea water from BWTSs. The three layered screens (500, 300 and 100 µm) will not only avoid clogging and easy separation of different size groups of microplastic particles but also help in smooth discharge of water to the sea. This technique is expected to remove a large number of microplastic particles (ranging from 0.0015 to 1020 million) from a single voyage. The proposed chamber may help to collect 0.0003-204 metric tons of particles/day, depending upon the geographical location of ballast intake in the global ocean. These estimations were made by considering a daily turnover of 0.033 billion tonnes of ballast water globally. This proposed screening chamber attached to the existing BWTSs in cargo ships, along with other region-specific ocean cleaning initiatives, will help in mitigating microplastic pollution in the global ocean.

The response of Prorocentrum sigmoides and its associated culturable bacteria to metals and organic pollutants.

This study investigates the effect of metals (cadmium, lead, mercury, and tellurium) and organic pollutants (benzene, diesel, lindane, and xylene) on a dinoflagellate-Prorocentrum sigmoides Böhm-and its associated culturable bacteria. Two bacterial cultures (Bacillus subtilis strain PD005 and B. xiamensis strain PD006) were isolated from P. sigmoides and characterized by scanning electron microscopy, 16S ribosomal RNA sequencing, biochemical analyses, and growth curve studies. This study points to a mutualistic relationship between P. sigmoides and its associated Bacillus isolates. P. sigmoides enhanced the growth of its associated Bacillus spp., through the secretion of extracellular exudates. In return, both Bacillus isolates contributed to the resistance of P. sigmoides to metals and organic pollutants. P. sigmoides and both Bacillus isolates exhibited concentration-dependent responses to metals and organic pollutants. An intriguing feature was the similar response of P. sigmoides and its associated Bacillus isolates to mercury and cadmium, indicating a co-selection of mercury and cadmium resistance. This provides support to the "dinoflagellate host-phycosphere bacteria" behaving as a single functional unit. However, the sensitivity profiles of P. sigmoides and its associated Bacillus isolates are different with respect to metals versus organic pollutants. These aspects need to be addressed in future studies to unravel the effect of metal and organic pollutants on dinoflagellates, an important component of the phytoplankton community, and to discern the influence of associated "phycosphere" bacteria on the response of dinoflagellates to pollutants.

The effect of bacteria on diatom community structure--the 'antibiotics' approach.

To investigate the effect of bacteria on diatoms at the community level, sediment samples from an intertidal tropical environment were treated with penicillin (a ß-lactam antibiotic that can affect diatoms only through bacteria). Streptomycin (an aminoglycoside) and chloramphenicol, antibiotics that can potentially affect protein synthesis in diatom organelles and photosynthesis, were also used for comparison. The changes in diatom community structure and the resistant and tolerant bacterial fractions were analyzed through microscopy, culture techniques and denaturing gradient gel electrophoresis. The reduction in bacterial abundance when treated with penicillin resulted in suppression of Amphora coffeaeformis, a dominant diatom in the study area. The bacterial community preferred the 'tolerance' strategy over 'resistance' in response to treatment with penicillin; these changes in bacterial dynamics were probably linked to concurrent changes in diatom community structure. The observations with penicillin differed from those with streptomycin that did not seem to significantly affect diatoms, and chloramphenicol, which consistently inhibited diatoms. Overall, the results of this study highlight the significance of bacteria in structuring benthic diatom communities and call for the inclusion of the 'antibiotics' approach in studies addressing diatom-bacterial interactions at the community level.