Are globetrotting bacteria just hitching a ride or are they helpful?

The skin of any marine animal provides a unique interface between it and the environment.  Microbial communities found on the skin are known to cause disease in many fish and marine mammals, but could they also be an indicator of good health?

A team from Woods Hole has analysed skin samples from 56 Humpback whales, Megaptera novaeangliae.  This species is of particular interest as they are found in all of the worlds oceans, they also have huge annual migrations which will undoubtedly lead to changes in their environment, with temperatures varying between 6-25°C.  Using using 454 pyrosequencing of SSU rRNA genes, 23 major taxonomic groups were found to be associated with the skin of the humpback whales.  The majority of the bacteria found belonged to the Bacteroidetes and Gammaproteobacteria classes, and many skin samples also contained bacteria belonging to the Firmicutes and Alphaproteobacteria classes.  Two genera, Tenacibaculum (Bacteroidetes) and Psychrobacter (Gammaproteobacteria) were found to be abundant within the majority (97%) of whale skin samples, and collectively made up a large portion, 55–75%, of the skin-bacterial community.  Further analysis showed that differences in abundance of the Tenacibaculum and Psychrobacter spp. were linked to the geographic areas from which the samples were taken.   The same two species also significantly differed in abundance between samples taken from whales that were not actively feeding, in the Pacific Ocean and those who were feeding, in the Bering sea and Atlantic ocean. 

The sequences of the Tenacibaculum and Psychrobacter spp. appear to be specific to Humpback whales although they are closely related to sequences from bacteria taken from dolphins.  Although Tenacibaculum spp. have been associated with disease in fish, it is unlikely that this is the case with this particular species due to the abundance in which it is found on the whale skin.  It has been shown in other studies that Tenacibaculum spp. could actually act as a predator species and could have an antifouling effect, actually helping to keep the whales skin clear and healthy.

Of the two bacterial species, Psychrobacter spp. is globally more widespread and is known to be tolerant of a number of different environmental conditions including temperature and salinity.  Other Psychrobacter spp. are known to be able to produce cold shock proteins and it is therefore likely that the species associated with these whales can also manufacture such proteins to protect themselves against the extreme cold conditions experienced during migration. 

Further investigation is required to determine if the feeding state of the whales which cause them to change to catabolic metabolism while in oligotrophic tropical waters can affect the composition of the associated microbial communities.  While in this state there is a decrease in repair of skin cells, and immune response, which could be linked to decrease in wound healing leaving the animals prone to infection.  So could any of the associated bacteria be producing antibiotics that could aid any healing, or could they be predatory and therefore preventing harmful bacteria from taking hold?  It is important to understand how these bacterial species may be beneficial for humpback whales and also to determine if they are could these properties be exploited for human health or anti fouling products?

Apprill, A., Robbins, J., Eren, A. M., Pack, A. A., Reveillaud, J., Mattila, D., ... & Mincer, T. J. (2014). Humpback whale populations share a core skin bacterial community: towards a health index for marine mammals?. PloS one, 9(3), e90785.