Bacteria from the “Saline di Tarquinia” marine salterns reveal very atypical growth profiles with regards to salinity and temperature

Abstract

Several thousand bacterial colonies were isolated from “Saline di Tarquinia” (Italy) marine salterns; after dereplication, thirty-one strains were obtained, confirming the low culturable bacterial diversity attributed to similar hypersaline environments. Strains were identified by 16S ribosomal DNA sequencing and phylogenetic analysis; most strains belonged to the class Gammaproteobacteria, with minorities from Actinobacteria, Bacilli and Alphaproteobacteria. Halomonas and Salinivibrio were predominant genera. To profile growth preferences, strains were cultivated at different salinities and temperatures. Non-metric multi-dimensional scaling (nMDS) analysis on growth data at different salinities identified four groups that were significantly correlated with the ecological categories conventionally used to describe halophiles. The majority were moderate halophiles with optimal growth at 40-80‰ salinity. Some were markedly euryhaline and grew from 40-80‰ to 240-280‰.Very uncommon behaviour was observed for some strains, with a clear optimum growth in the slight to moderate halophilic range, but also the ability to grow without salt. These bacteria could barely be included in the mentioned traditional definitions and we suggest to consider them as “norm-tolerant halophilic”, being somehow in-between the slight halophiles and the halotolerants. As for temperature, nMDS groups were less defined and uncorrelated to ecological categories. Most strains were mesophilic-psychrotolerant or mesophilic, and some psychrotolerants were also recorded. Generally, diffused eurythermism was observed and various strains displayed unusual “flat growth profiles” that showed a broad range of thermal optima. Overall, the majority of strains appeared to be well adapted to the “Saline di Tarquinia” environment and showed great temperature and salinity variations compared to species observed in other salterns.

Spatio-Temporal Variation of the Bacterial Communities along a Salinity Gradient within a Thalassohaline Environment (Saline di Tarquinia Salterns, Italy)

“…Marine salterns (MS) are transition areas subject to very intense daily and seasonal variations of environmental parameters, particularly water temperature and salinity. Few other extreme environments undergo fluctuations of water availability and temperature as extreme as MS [ 1 , 2 , 3 ], which expose organisms to high environmental stress. Thus MS, besides being excellent models to study microbial diversity and ecology at different salt concentrations, are also suitable models to investigate phenomena such as scarce water availability and desiccation linked to currently ongoing global change [ 3 , 4 ].…”

“…In particular, the levees between the various ponds were eroded, allowing mixing of waters with different salinity. However, ST can still be considered an extreme environment with broad and sudden variations of environmental parameters (in particular salinity and water temperature) in the majority of the ponds [ 3 ].…”

“…Only a preliminary investigation, carried out both by culture-dependent and culture-independent methods (DGGE), provided a first characterisation of the bacterial community found in some ponds [ 7 ]. Subsequently, a more detailed characterisation of the cultivable fraction was performed, analysing the ability of various strains to cope with temperature and salinity variations [ 3 ]. In addition, a recent survey regarding the Vibrio community in different ponds of the salterns was carried out [ 51 ].…”

Vibrio communities along a salinity gradient within a marine saltern hypersaline environment (Saline di Tarquinia, Italy)

“…Over time, the entire ST structure was heavily altered; in particular, the levees between the various ponds were eroded, allowing the mixing of waters with different salinity. However, ST can still be considered as an extreme environment with extensive and abrupt variations of the environmental parameters (in particular salinity and temperature) in the majority of the ponds (Barghini et al ., 2018a). The ST saltpan consists of a series of approximately 100 shallow interconnected ponds; in addition, there is a bigger pool (~1 ha, 2–3 m depth) used in the past as a brine storage basin (BSB).…”

“…Only a preliminary investigation, performed by DGGE, focused on the characterization of the whole bacterial community of some ponds (Barghini et al ., 2014). A more detailed characterization of the cultivable fraction was then carried out to delineate the adaptation ability of various strains to temperature and salinity variations (Barghini et al ., 2018a). No in‐depth studies regarding the whole prokaryotic community and/or specific bacterial groups of this unique environment are available yet.…”